UNITED NATIONS ENVIRONMENT PROGRAMME
INTERNATIONAL LABOUR ORGANISATION
WORLD HEALTH ORGANIZATION
INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 194
Aluminium
This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.
Environmental Health Criteria 194
First draft prepared by Dr H. Habs, Dr B. Simon and Professor K.U.
Thiedemann (Fraunhofer Institute, Hoanover, Germany) and Mr P. Howe
(Institute of Terrestrial Ecology, Monks Wood, United Kingdom)
Published under the joint sponsorship of the United Nations
Environment Programme, the International Labour Organisation, and the
World Health Organization, and produced within the framework of the
Inter-Organization Programme for the Sound Management of Chemicals.
World Health Organization
Geneva, 1997
The International Programme on Chemical Safety (IPCS) is a joint
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carried out by the IPCS include the development of know-how for coping
with chemical accidents, coordination of laboratory testing and
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of the biological action of chemicals.
WHO Library Cataloguing in Publication Data
Aluminium
(Environmental health criteria ; 194)
1.Aluminium - toxicity 2.Aluminium - adverse effects
3.Environmental exposure I.Series
ISBN 92 4 157194 2 (NLM Classification: QV 65)
ISSN 0250-863X
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR ALUMINIUM
1. SUMMARY AND CONCLUSIONS
1.1. Identity, physical and chemical properties
1.2. Analytical methods
1.3. Sources of human and environmental exposure
1.4. Environmental transport, distribution and transformation
1.5. Environmental levels and human exposure
1.6. Kinetics and metabolism
1.6.1. Humans
1.6.2. Animals
1.7. Effects on laboratory mammals and in vitro test systems
1.8. Effects on humans
1.9. Effects on other organisms in the laboratory and field
1.10. Conclusions
1.10.1. General population
1.10.2. Subpopulations at special risk
1.10.3. Occupationally exposed populations
1.10.4. Environmental effects
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
2.2. Physical and chemical properties
2.2.1. Aluminium metal
2.2.2. Aluminium compounds
2.3. Analytical methods
2.3.1. Sampling and sample preparation
2.3.2. Separation and concentration
2.3.3. Detection and measurement
2.3.4. Speciation analysis of aluminium in water
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1. Natural occurrence
3.2. Anthropogenic sources
3.2.1. Production levels and processes
3.2.2. Uses
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION
4.1. Transport and distribution between media
4.1.1. Air
4.1.2. Freshwater
4.1.2.1 Dissolved aluminium
4.1.2.2 Aluminium adsorbed on particles
4.1.2.3 Aluminium in acidified waters
4.1.3. Seawater
4.1.4. Soil
4.1.5. Vegetation and wildlife
4.2. Biotransformation
4.2.1. Biodegradation and abiotic degradation
4.2.2. Bioaccumulation
4.2.2.1 Plants
4.2.2.2 Invertebrates
4.2.2.3 Fish
4.2.2.4 Birds
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
5.1.1. Air
5.1.2. Precipitation
5.1.3. Water
5.1.3.1 Freshwater
5.1.3.2 Seawater
5.1.4. Soil and sediment
5.1.5. Terrestrial and aquatic organisms
5.2. Occupational exposure
5.3. General population exposures
5.3.1. Air
5.3.2. Food and beverages
5.3.3. Drinking-water
5.3.4. Miscellaneous exposures
5.3.5. Total human intake of aluminium from
all environmental pathways
5.3.6. Aluminium uptake
6. KINETICS AND METABOLISM IN LABORATORY ANIMALS
6.1. Absorption
6.1.1. Animal studies
6.1.1.1 Inhalation exposure
6.1.1.2 Oral administration
6.1.1.3 Dermal
6.1.2. Studies in humans
6.1.2.1 Inhalation exposures
6.1.2.2 Oral administration
6.1.2.3 Dermal exposure
6.2. Distribution
6.2.1. Animal studies
6.2.2. Human studies
6.2.2.1 Transport in blood
6.2.2.2 Plasma aluminium concentrations in humans
6.2.2.3 Tissue aluminium concentrations in humans
6.3. Elimination and excretion
6.3.1. Animal studies
6.3.2. Human studies
6.3.2.1 Urinary excretion
6.3.2.2 Biliary excretion
6.4. Biological indices of exposure, body burden and organ
concentration
7. EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS
7.1. Single exposure
7.2. Short- and long-term exposure
7.2.1. Oral administration
7.2.2. Inhalation exposure
7.2.3. Parenteral administration
7.3. Reproductive and developmental toxicity
7.3.1. Reproductive effects
7.3.2. Developmental effects
7.4. Mutagenicity and related end-points
7.4.1. Interactions with DNA
7.4.2. Mutations
7.4.3. Chromosomal effects
7.5. Carcinogenicity
7.6. Neurotoxicity
7.6.1. Impairments of cognitive and motor function
7.6.2. Alterations in electrophysiological properties
7.6.3. Metabolic effects in the nervous system
7.7. Effects on bone
7.7.1. Toxic effects of aluminium in the skeleton
7.7.2. Dose response
7.8. Effects on mineral metabolism
8. EFFECTS ON HUMANS
8.1. General population exposure
8.1.1. Acute toxicity
8.1.2. Effects of short-term exposure
8.1.3. Neurotoxic effects
8.1.3.1 Aluminium and Alzheimer's disease (AD)
8.1.3.2 Epidemiological studies on AD and
environmental aluminium levels
8.1.3.3 Epidemiological studies relating
aluminium concentrations in water to
cognitive dysfunction
8.1.3.4 Other neurological conditions in the
general population
8.1.3.5 Conclusions regarding neurological
effects of aluminium
8.1.4. Allergic effects
8.2. Occupational exposure
8.2.1. Respiratory tract effects
8.2.1.1 Restrictive pulmonary disease
8.2.1.2 Obstructive pulmonary disease
8.2.2. Central nervous system effects
8.3. Cancer
8.4. Genotoxicity
8.5. Reproductive toxicity
8.6. Subpopulations at special risk
8.6.1. Encephalopathy
8.6.2. Osteomalacia
8.6.3. Microcytic anaemia
9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD
9.1. Laboratory experiments
9.1.1. Microorganisms
9.1.1.1 Water
9.1.1.2 Soil
9.1.2. Aquatic organisms
9.1.2.1 Plants
9.1.2.2 Invertebrates
9.1.2.3 Fish
9.1.2.4 Amphibians
9.1.3. Terrestrial organisms
9.1.3.1 Plants
9.1.3.2 Invertebrates
9.1.3.3 Birds
9.2. Field observations
9.2.1. Microorganisms
9.2.2. Aquatic organisms
9.2.2.1 Plants
9.2.2.2 Invertebrates
9.2.2.3 Vertebrates
9.2.3. Terrestrial organisms
9.2.3.1 Plants
9.2.3.2 Invertebrates
9.2.3.3 Vertebrates
10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT
10.1. Health effects
10.1.1. Exposure assessment
10.1.2. Evaluation of animal data
10.1.3. Evaluation of human data
10.2. Evaluation of effects on the environment
10.2.1. Exposure
10.2.2. Effects
11. CONCLUSIONS AND RECOMMENDATIONS FOR PROTECTION OF HUMAN HEALTH
AND THE ENVIRONMENT
11.1. Conclusions
11.1.1. Healthy general population
11.1.2. Subpopulations at special risk
11.1.3. Occupationally exposed populations
11.1.4. Environmental risk
11.2. Recommendations
11.2.1. Public health protection
11.2.2. Recommendations for protection of the environment
12. FURTHER RESEARCH
12.1. Bioavailability and kinetics
12.2. Toxicological data
12.3. Research on the relationship between aluminium exposure and
Alzheimer's disease
12.4. Occupational exposure
13. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCE
RESUME ET CONCLUSIONS
RESUMEN Y CONCLUSIONES
NOTE TO READERS OF THE CRITERIA MONOGRAPHS
Every effort has been made to present information in the criteria
monographs as accurately as possible without unduly delaying their
publication. In the interest of all users of the Environmental Health
Criteria monographs, readers are requested to communicate any errors
that may have occurred to the Director of the International Programme
on Chemical Safety, World Health Organization, Geneva, Switzerland, in
order that they may be included in corrigenda.
* * *
A detailed data profile and a legal file can be obtained from the
International Register of Potentially Toxic Chemicals, Case postale
356, 1219 Châtelaine, Geneva, Switzerland (telephone no. + 41 22 -
9799111, fax no. + 41 22 - 7973460, E-mail irptc@unep.ch).
* * *
This publication was made possible by grant number 5 U01
ES02617-15 from the National Institute of Environmental Health
Sciences, National Institutes of Health, USA, and by financial support
from the European Commission.
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WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR ALUMINIUM
Members
Dr T.M. Florence, Centre for Environmental Health Sciences, Oyster
Bay, New South Wales, Australia
Dr M. Golub, California Regional Primate Research Center, University
of California, Davis, California, USA
Mr P. Howe, Institute of Terrestrial Ecology, Monks Wood, Abbots
Ripton, Huntingdon, Cambridgeshire, United Kingdom
( Co-Rapporteur)
Professor D.R. McLachlan ( Retired from: Centre for Research in
Neurogenerative Diseases, University of Toronto, Toronto,
Ontario, Canada
Dr M. Moore, National Health and Medical Research Council, National
Research Centre for Environmental Toxicology, Coopers Plains,
Brisbane, Australia ( Chairman)
Dr T.V. O'Donnell, University of Otago, Wellington South, New Zealand
( Vice-Chairman)
Professor B. Rosseland, Norwegian Institute of Water Research (NIVA),
Oslo, Norway
Dr B. Simon, Fraunhofer Institute, Hanover, Germany ( Co-Rapporteur)
Dr B. Sjogren, Department of Occupational Medicine, Swedish National
Institute for Working Life, Solna, Sweden
Dr L. Smith, Disease Control Service, Public Health Branch, Ontario
Ministry of Health, North York, Ontario, Canada
Dr E. Storey, Royal Melbourne Hospital, Department of Pathology,
University of Melbourne, Parkville, Victoria, Australia
Dr H. Temmink, Department of Toxicology, Agricultural University,
Wageningen, The Netherlands ( Vice-Chairman)
Dr M.K. Ward, Department of Renal Medicine, Royal Victoria Infirmary,
Newcastle-upon-Tyne, United Kingdom
Dr M. Wilhelm, Health Institute, University of Dusseldorf, Dusseldorf,
Germany
Professor H.M. Wisniewski, New York State Institute for Basic
Research in Developmental Disabilities, Staten Island, New York,
USA
Professor P. Yao, Chinese Academy of Preventive Medicine, Institute
of Occupational Medicine, Ministry of Health, Beijing, China
Observers
Dr K. Bentley, Environmental Health Assessment and Criteria, Human
Services and Health, Woden, Australia
Dr O.C. Bœckman, Norsk Hydro, Porsgrunn Research Centre, Porsgrunn,
Norway
Dr J. Borak, Occupational and Environmental Health, Jonathan Borak &
Co., New Haven, Connecticut, USA
Dr I. Calder, Occupational and Environmental Health, South Australian
Health Commission, Adelaide, Australia
Dr J.N. Fisher, ALCOA of Australia Ltd, Point Henry Works, Geelong,
Victoria, Australia
Mr D. Hughes, Environment, Mount Isa Mine Holdings, Brisbane,
Australia
Dr P. Imray, Environmental Health Branch, Queensland Health, Brisbane,
Australia
Ms M.E. Meek, Environmental Health Directorate, Health Canada,
Tunney's Pasture, Ottawa, Ontario, Canada
Dr N. Priest, AEA Technology, Harwell, Didcot, Oxfordshire, United
Kingdom
Dr D. Wilcox, Medical Section, Health Services, Sydney Water, Sydney,
Australia
Secretariat
Dr G.C. Becking, International Programme on Chemical Safety
Inter-regional Research Unit, World Health Organization, Research
Triangle Park, North Carolina, USA ( Secretary)
Dr D. Johns, DPIE, Coal and Mineral Division, Canberra, Australia
( Temporary Adviser)
Mr D. Wagner, Chemicals Safety Unit, Human Services and Health,
Canberra, Australia ( Temporary Adviser)
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR ALUMINIUM
A WHO Task Group on Environmental Health Criteria for Aluminium
met in Brisbane, Australia, from 24 to 28 April 1995. The meeting
was sponsored by a consortium of Australian Commonwealth and State
Governments through a national steering committee chaired by
Dr K. Bentley, Director, Health and Environmental Policy, Department
of Health and Family Services, Canberra. The meeting was hosted and
organized by the NHMRC National Research Centre for Environmental
Toxicology (NRCET), Dr M. Moore, Director, being responsible for
the arrangements. Dr D. Lange, Chief Health Officer, welcomed
participants on behalf of Queensland Health, and Professor L. Roy
Webb, Vice-chancellor, Griffith University, welcomed them on behalf of
NRCET. Dr G.C. Becking, IPCS, welcomed the participants on behalf of
Dr M. Mercier, Director of the IPCS and the three cooperating
organizations (UNEP/ILO/WHO). The Task Group reviewed and revised the
draft criteria monograph and made an evaluation of the risks to human
health and the environment from exposure to aluminium.
The first draft was prepared under the coordination of Dr G.
Rosner, Fraunhofer Institute of Toxicology and Aerosol Research,
Germany, and Mr P. Howe, Institute of Terrestrial Ecology, Monks Wood,
United Kingdom. The draft reviewed by the Task Group, incorporating
the comments received following review by the IPCS Contact Points, was
prepared through the cooperative effort of the Fraunhofer Institute,
Institute of Terrestrial Ecology and the Secretariat.
Dr G.C. Becking (IPCS Central Unit, Inter-regional Research Unit)
and Dr P.G. Jenkins (IPCS Central Unit, Geneva) were responsible for
the overall scientific content and technical editing, respectively, of
this monograph.
The efforts of all who helped in the preparation and finalization
of this publication are gratefully acknowledged.
ABBREVIATIONS
AD Alzheimer's disease
AIBD aluminium-induced bone disease
cAMP cyclic adenosine monophosphate
CI confidence interval
1,25-(OH)2-D3 1,25-dihydroxy-vitamin D3
DOC dissolved organic carbon
EDTA ethylenediaminetetraacetic acid
i.p. intraperitoneal
i.v. intravenous
LOAEL lowest-observed-adverse-effect level
LOEL lowest-observed-effect level
LTP long-term potentiation
NFT neurofibrillary tangle
NIOSH National Institute for Occupational Safety and
Health (USA)
NOEC no-observed-effect concentration
NOEL no-observed-effect level
NTA nitrilotriacetic acid
OR odds ratio
PHF paired helical filaments
Pt platinum unit (1 unit equals the colour produced by
lung chloroplatinate in 1 litre of water)
PTH parathyroid hormone
s.c. subcutaneous
WAIS Weschler Adult Intelligence Scale
1. SUMMARY AND CONCLUSIONS
1.1 Identity, physical and chemical properties
Aluminium is a silvery-white, ductile and malleable metal. It
belongs to group IIIA of the Periodic Table, and in compounds it is
usually found as AlIII. It forms about 8% of the earth's crust and is
one of the most reactive of the common metals. Exposure to water,
oxygen or other oxidants leads to the formation of a superficial
coating of aluminium oxide, which provides the metal with a high
resistance to corrosion. Aluminium oxide is soluble in mineral acids
and strong alkalis but insoluble in water, whereas aluminium chloride,
nitrate and sulfate are water soluble. Aluminium halogenides, hydride
and lower aluminium alkyls react violently with water.
Aluminium possesses high electrical and thermal conductivity, low
density and great resistance to corrosion. It is often alloyed with
other metals. Aluminium alloys are light, strong and readily machined
into shapes.
1.2 Analytical methods
Various analytical methods have been developed to determine
aluminium in biological and environmental samples. Graphite furnace
- atomic-absorption spectrometry (GF-AAS) and inductively coupled
plasma - atomic-emission spectrometry (ICP-AES) are the most
frequently used methods. Contamination of the samples with aluminium
from air, vessels or reagents during sampling and preparation is the
main source of analytical error. Depending on sample pretreatment,
separation and concentration procedures, detection limits are
1.9-4 µg/litre in biological fluids and 0.005-0.5 µg/g dry weight in
tissues using GF-AAS, and 5 µg/m3 in air and 3 µg/litre in water
using ICP-AES.
1.3 Sources of human and environmental exposure
Aluminium is released to the environment both by natural
processes and from anthropogenic sources. It is highly concentrated in
soil-derived dusts from such activities as mining and agriculture, and
in particulate matter from coal combustion. Aluminium silicates
(clays), a major component of soils, contribute to the aluminium
levels of dust. Natural processes far outweigh direct anthropogenic
contributions to the environment. Mobilization of aluminium through
human actions is mostly indirect and occurs as a result of emission of
acidifying substances. In general, decreasing pH results in an
increase in mobility and bioavailability for monomeric forms of
aluminium. The most important raw material for the production of
aluminium is bauxite, which contains up to 55% alumina (aluminium
oxide). World bauxite production was 106 million tonnes in 1992.
Aluminium metal has a vide variety of uses, including structural
materials in construction, automobiles and aircraft, and the
production of metal alloys. Aluminium compounds and materials also
have a wide variety of uses, including production of glass, ceramics,
rubber, wood preservatives, pharmaceuticals and waterproofing
textiles. Natural aluminium minerals, especially bentonite and
zeolite, are used in water purification, sugar refining, brewing and
paper industries.
1.4 Environmental transport, distribution and transformation
Aluminium occurs ubiquitously in the environment in the form of
silicates, oxides and hydroxides, combined with other elements such as
sodium and fluorine and as complexes with organic matter. It is not
found as a free metal because of its reactivity. It has only one
oxidation state (+3) in nature; therefore, its transport and
distribution in the environment depend only upon its coordination
chemistry and the chemical-physical characteristics of the local
environmental system. At pH values greater than 5.5, naturally
occurring aluminium compounds exist predominantly in an undissolved
form such as gibbsite (Al(OH)3) or as aluminosilicates, except in the
presence of high amounts of dissolved organic material, which binds
with aluminium and can lead to increased concentrations of dissolved
aluminium in streams and lakes. Several factors influence aluminium
mobility and subsequent transport within the environment. These
include chemical speciation, hydrological flow paths, soil-water
interactions, and the composition of the underlying geological
materials. The solubility of aluminium in equilibrium with solid phase
Al(OH)3 is highly dependent on pH and on complexing agents such as
fluoride, silicate, phosphate and organic matter. The chemistry of
inorganic aluminium in acid soil and stream water can be considered in
terms of mineral solubility, ion exchange and water mixing processes.
Upon acidification of soils, aluminium can be released into
solution for transport to streams. Mobilization of aluminium by acid
precipitation results in more aluminium being available for plant
uptake.
1.5 Environmental levels and human exposure
Aluminium is a major constituent of a number of atmospheric
components particularly in soil-derived dusts (both from natural
sources and human activity) and particulates from coal combustion. In
urban areas aluminium levels in street dust range from 3.7 to
11.6 µg/kg. Airborne aluminium levels vary from 0.5 ng/m3 over
Antarctica to more than 1000 ng/m3 in industrialized areas.
Surface freshwater and soil water aluminium concentrations can
vary substantially, being dependent on physico-chemical and geological
factors. Aluminium can be suspended or dissolved. It can be bound with
organic or inorganic ligands, or it can exist as a free aluminium ion.
In natural waters aluminium exists in both monomeric and polymeric
forms. Aluminium speciation is determined by pH and the concentrations
of dissolved organic carbon (DOC), fluoride, sulfate, phosphate and
suspended particulates. Dissolved aluminium concentrations for water
in the circumneutral pH range are usually quite low, ranging from
1.0 to 50 µg/litre. This rises to 500-1000 µg/litre in more acidic
water. At the extreme acidity of water affected by acid mine drainage,
dissolved aluminium concentrations of up to 90 mg/litre have been
measured.
Non-occupational human exposure to aluminium in the environment
is primarily through ingestion of food and water. Of these, food is
the principal contributor. The daily intake of aluminium from food and
beverages in adults ranges between 2.5 and 13 mg. This is between 90
and 95% of total intake. Drinking-water may contribute around 0.4 mg
daily at present international guideline values, but is more likely
to be around 0.2 mg/day. Pulmonary exposure may contribute up to
0.04 mg/day. In some circumstances, such as occupational exposure and
antacid use, the levels of exposure will be much greater. For example,
> 500 mg of aluminium may be consumed in two average-sized antacid
tablets. There are some difficulties in assessing uptake from these
exposures because of analytical and sampling difficulties. Isotopic
investigations with Al26 indicate that one of the most bioavailable
forms of aluminium is the citrate and that there could be as much as
1% absorption when aluminium is in this form. However, humans would
absorb only 3% of their total daily uptake of aluminium from drinking-
water, a relatively minor source compared to food.
1.6 Kinetics and metabolism
1.6.1 Humans
Aluminium and its compounds appear to be poorly absorbed in
humans, although the rate and extent of absorption have not been
adequately studied. Concentrations of aluminium in blood and urine
have been used as a readily available measure of aluminium uptake,
increased urine levels having been observed among aluminium welders
and aluminium flake-powder producers.
The mechanism of gastrointestinal absorption of aluminium has not
yet been fully elucidated. Variability results from the chemical
properties of the element and the formation of various chemical
species, which is dependent upon the pH, ionic strength, presence of
competing elements (silicon), and the presence of complexing agents
within the gastrointestinal tract (e.g., citrate).
The biological behaviour and gastrointestinal absorption of
aluminium in humans ingesting aluminium compounds has been studied by
using the radioactive isotope Al26. Significant intersubject
variability has been demonstrated. Measured fractional uptakes of 5 ×
10-3 for aluminium as citrate, 1.04 × 10-4 for aluminium hydroxide
and 1.36 × 10-3 for the hydroxide given with citrate were reported. A
study of the fractional uptake of aluminium from drinking-water showed
an uptake fraction of 2.35 × 10-3. It was concluded that members of
the general population consuming 1.5 litres/day of drinking-water
containing 100 µg aluminium/litre would absorb about 3% of their total
daily intake of aluminium from this source depending upon the levels
found in food and the frequency of antacid use.
The proportion of plasma Al3+ normally bound to protein in
humans may be as high as 70-90% in haemodialysis patients with
moderately increased plasma aluminium. The highest levels of aluminium
may be found in the lungs, where it may be present as inhaled
insoluble particles.
The urine is the most important route of aluminium excretion.
After peroral administration of a single dose of aluminium, 83% was
excreted in urine after 13 days and 1.8% in the faeces. The half-life
of urinary concentration among welders exposed for more than 10 years
was 6 months or longer. Among retired workers exposed to aluminium
flake powders, the calculated half-lives were between 0.7 and 8 years.
1.6.2 Animals
Absorption via the gastrointestinal tract is usually less than
1%. The main factors influencing absorption are solubility, pH and
chemical species. Organic complexing compounds, notably citrate,
increase absorption. The aluminium absorption may interact with
calcium and iron transport systems. Dermal and inhalation absorption
has not been studied in detail. Aluminium is distributed in most
organs within the body with accumulation occurring mainly in bone at
high dose levels. To a limited but as yet undetermined extent,
aluminium passes the blood-brain barrier and is also distributed to
the fetus. Aluminium is eliminated effectively by urine. Plasma half-
life is about 1 h in rodents.
1.7 Effects on laboratory mammals and in vitro test systems
The acute toxicity of metallic aluminium and aluminium compounds
is low, the reported oral LD50 values being in the range of several
hundred to 1000 mg aluminium/kg body weight per day. However, the
LC50 values for inhalation have not been identified.
In short-term studies in which an adequate range of end-points
was examined following exposure of rats, mice or dogs to various
aluminium compounds (sodium aluminium phosphate, aluminium hydroxide,
aluminium nitrate) in the diet or drinking-water, only minimal effects
(decreases in body weight gain generally associated with decreases in
food consumption or mild histopathological effects) have been observed
at the highest administered doses (70 to 300 mg aluminium/kg body
weight per day). Systemic effects following parenteral administration
also included kidney dysfunction.
Adequate inhalation studies were not identified. Following
intratracheal administration of aluminium oxide, particle-associated
fibrosis was observed, similar to that found in other studies on
silica and coal dust.
No overt fetotoxicity was noted, nor were general reproductive
parameters noted after gavage treatment of rats with 13, 26 or 52 mg
aluminium/kg body weight per day (as aluminium nitrate). However, a
dose-dependent delay in the growth of offspring was noted with females
administered 13 mg/kg and in male offspring at 26 mg/kg. The lowest-
observed-adverse-effect level (LOAEL) for developmental effects
(decreased ossification, increased incidence of vertebral and
sternebrae terata and reduced fetal weight) was 13 mg/kg (aluminium
nitrate). These effects were not observed at much higher doses of
aluminium hydroxide. There were reductions in postnatal growth at
13 mg/kg (aluminium nitrate), although maternal toxicity was not
examined. In studies on brain development, grip strength was impaired
in offspring of dams fed 100 mg aluminium/kg body weight as aluminium
lactate in the diet, in the absence of maternal toxicity.
There is no indication that aluminium is carcinogenic. It can
form complexes with DNA and cross-link chromosomal proteins and DNA,
but it has not been shown to be mutagenic in bacteria or induce
mutation or transformation in mammalian cells in vitro. Chromosomal
aberrations have been observed in bone marrow cells of exposed mice
and rats.
There is considerable evidence that aluminium is neurotoxic in
experimental animals, although there is considerable variation among
species. In susceptible species, toxicity following parenteral
administration is characterized by progressive neurological
impairment, resulting in death with status epilepticus (LD50 =
6 µg Al/g dry weight of brain). Morphologically, the progressive
encephalopathy is associated with neurofibrillary pathology in
large and medium size neurons predominantly in the spinal cord,
brainstem and selected areas of the hippocampus. These tangles are
morphologically and biochemically different from those that occur in
Alzheimer's disease (AD). Behavioural impairment has been observed in
the absence of overt encephalopathy or neurohistopathology in
experimental animals exposed to soluble aluminium salts (e.g.,
lactate, chloride) in the diet or drinking-water at doses of 50 mg
aluminium/kg body weight per day or more.
Osteomalacia, as it presents in man, is observed consistently in
larger species (e.g., dogs and pigs) exposed to aluminium; a similar
condition is observed in rodents. These effects appear to occur in all
species, including humans, at aluminium levels of 100 to 200 µg/g bone
ash.
1.8 Effects on humans
No acute pathogenic effects in the general population have been
described after exposure to aluminium.
In England, a population of about 20 000 individuals was exposed
for at least 5 days to increased levels of aluminium sulfate,
accidentally placed in a drinking-water facility. Case reports of
nausea, vomiting, diarrhoea, mouth ulcers, skin ulcers, skin rashes
and arthritic pain were noted. It was concluded that the symptoms were
mostly mild and short-lived. No lasting effects on health could be
attributed to the known exposures from aluminium in the drinking-
water.
It has been hypothesized that aluminium in the drinking-water is
a risk factor for the development or acceleration of AD as well as for
impaired cognitive function in the elderly. It has also been suggested
that stamped fine aluminium powder and fume may be risk factors for
impaired cognitive function and pulmonary disease in certain
occupations.
Some 20 epidemiological studies have been carried out to test the
hypothesis that aluminium in drinking-water is a risk factor for AD,
and two studies have evaluated the association between aluminiun in
drinking-water and impaired cognitive function. Study designs ranged
from ecological to case control. Eight studies in populations in
Norway, Canada, France, Switzerland and England were considered
of sufficiently high quality to meet the general criteria for
exposure and outcome assessment and the adjustment for at least
some confounding variables. Of the six studies that examined the
relationship between aluminium in drinking-water and dementia or AD,
three found a positive relationship but three did not. However, each
of the studies had some deficiencies in the study design (e.g.,
ecological exposure assessment, failure to consider aluminium exposure
from all sources and to control for important confounders such as
education, socioeconomic status and family history, the use of
surrogate outcome measures for AD, and selection bias). In general,
the relative rists determined were less than 2, with large confidence
intervals, when the total aluminium concentration in drinking-water
was 100 µg/litre or higher. Based on current knowledge on the
pathogenesis of AD and the totality of evidence from these
epidemiological studies, it was concluded that the present
epidemiological evidence does not support a causal association between
AD and aluminium in drinking-water.
In addition to the epidemiological studies that examined the
relationship between AD and aluminium in drinking-water, two studies
examined cognitive dysfunction and AD in elderly populations in
relation to the levels of aluminium in drinking-water. The results
were again conflicting. One study of 800 male octogenarians consuming
drinking-water with aluminium concentrations up to 98 µg/litre found
no relationship. The second study used "any evidence of mental
impairment" as an outcome measure and found a relative risk of 1.72 at
aluminium concentrations greater than 85 µg/litre in 250 males. Such
data are insufficient to show that aluminium is a cause of cognitive
impairment in the elderly.
Reports of impaired cognitive function related to aluminium
exposure are conflicting. Most studies are on small populations, and
the methodology used in these studies is open to question with respect
to magnitude of effect reported, exposure assessment and confounding
factors. In a comparative study of cognitive impairment in miners
exposed to a powder containing 85% finely ground aluminium and 15%
aluminium oxide (as prophylaxis against silica) and unexposed miners,
the cognitive test scores and the proportion impaired in at least one
test indicated a disadvantage for the exposed miners. A positive
exposure-related trend of increased risk was noted.
In all occupational studies reported, the magnitude of effects
found, presence of confounding factors, problems with exposure
assessment and the probability of mixed exposures all make the data
insufficient to conclude that aluminium is a cause of cognitive
impairment in workers exposed occupationally to aluminium.
Neurological syndromes including impairment of cognitive
function, motor dysfunction and peripheral neuropathy have been
reported in limited studies of workers exposed to aluminium fume. A
small population of aluminium welders who were compared with iron
welders were reported to show a small decrement in repetitive motor
function. When a questionnaire methodology was used in another study,
an increase in neuropsychiatric symptoms was reported.
Iatrogenic exposure in patients with chronic renal failure,
exposed to aluminium-containing dialysis fluids and pharmaceutical
products, may cause encephalopathy, vitamin-D-resistant osteomalacia
and microcytic anaemia. These clinical syndromes can be prevented by
reduction in exposure to aluminium.
Premature infants, even where kidney impairment is not severe
enough to cause raised blood creatinine levels, may develop increased
tissue loading of aluminium, particularly in bone, when exposed to
iatrogenic sources of aluminium. Where there is kidney failure,
seizures and encephalopathy may occur.
Although human exposure to aluminium is widespread, in only a few
cases has hypersensitivity been reported following exposure to some
aluminium compounds after dermal application or parenteral
administration.
Pulmonary fibrosis was reported in some workers exposed to very
fine stamped aluminium powder in the manufacture of explosives and
fireworks. Nearly all cases involved exposure to aluminium particles
coated with mineral oil. That process is no longer used. Other cases
of pulmonary fibrosis have related to mineral exposures to other
agents such as silica and asbestos and cannot be attributed solely to
aluminium.
Irritant-induced asthma has been associated with inhalation
of aluminium sulfate, aluminium fluoride, potassium aluminium
tetrafluoride and with the complex environment of the potrooms during
aluminium production.
There is insufficient information to allow for classification of
the cancer risk from human exposures to aluminium and its compounds.
Animal studies do not indicate that aluminium or aluminium compounds
are carcinogenic.
1.9 Effects on other organisms in the laboratory and field
Aquatic unicellular algae showed increased toxic effect at low
pH, where bioavailability of aluminium is increased. They are more
sensitive than other microorganisms, the majority of 19 lake species
showing complete growth inhibition at 200 µg/litre total aluminium
(pH 5.5). Selection of aluminium-tolerant strains is possible; green
algae capable of growing in the presence of 48 mg/litre at pH 4.6 have
been isolated.
For aquatic invertebrates, LC50 values range from 0.48 mg/litre
(polychaete) to 59.6 mg/litre (daphnid). For fish, 96-h LC50 values
range from 0.095 mg/litre (American flagfish) to 235 mg/litre
(mosquito fish). However, care must be taken when interpreting the
results because of the significant effects of pH on the availability
of aluminium. The wide range of LC50 values probably reflects
variable availability. The addition of chelating agents, such as NTA
and EDTA, reduces the acute toxicity of aluminium to fish.
Responses to aluminium by macroinvertebrates are variable. In the
normal pH range aluminium toxicity increases with decreasing pH;
however, in very acidic waters aluminium can reduce the effects of
acid stress. Some invertebrates are very resistant to acid stress and
can be very numerous in acidic waters. Increased drift rate of
invertebrates has been reported in streams suffering either pH or
pH/aluminium stress; this is a common response to a variety of
stressors. Lake invertebrates generally survived field exposure to
aluminium but suffered as a result of phosphate reduction in
oligotrophic conditions induced by precipitation with aluminium.
Short- and long-term toxicity tests on fish have been carried out
under a variety of conditions and, most importantly, at a range of pH
values. The data show that significant effects have been observed at
monomeric inorganic aluminium levels as low as 25 µg/litre. However,
the complex relationship between acidity and aluminium bioavailability
makes interpretation of the toxicity data more difficult. At very
low pH (not normally found in natural waters) the hydrogen ion
concentration appears to be the toxic factor, with the addition of
aluminium tending to reduce toxicity. In the pH range 4.5 to 6.0
aluminium in equilibrium exerts its maximum toxic effect. Toxicity has
also been shown to increase with increasing pH levels in the alkaline
pH region. The mechanism of aluminium toxicity to fish has been
attributed to the inability of fish to maintain their osmoregulatory
balance, as well as respiratory problems associated with precipitation
of aluminium on the gill mucus. The former effect is associated with
lower pH levels. These laboratory findings have been confirmed by
field studies especially in areas under acid stress.
Amphibian eggs and larvae are affected by acidity and aluminium,
with interaction between the two factors. Reduced hatching, delayed
hatching, delayed metamorphosis, metamorphosis at small size, and
mortality have been reported in various species and at aluminium
concentrations below 1 mg/litre.
Exposure of roots of terrestrial plants to aluminium can cause
diminished root growth, reduced uptake of plant nutrients and stunted
plant development. Tolerance to aluminium has been demonstrated both
in the laboratory and the field.
1.10 Conclusions
1.10.1 General population
Hazards to neurological development and brain function from
exposure to aluminium have been identified through animal studies.
However, aluminium has not been demonstrated to pose a health risk to
healthy, non-occupationally exposed humans.
There is no evidence to support a primary causative role of
aluminium in Alzheimer's disease (AD), and aluminium does not induce
AD pathology in vivo in any species, including humans.
The hypothesis that exposure of the elderly population in some
regions to elevated levels of aluminium in drinking-water may
exacerbate or accelerate AD lacks adequate supporting data.
The data in support of the hypothesis that particular exposures,
either occupational or via drinking-water, may be associated with non-
specific impaired cognitive function are also inadequate.
There is insufficient health-related evidence to justify
revisions to existing WHO Guidelines for aluminium exposure in
healthy, non-occupationally exposed humans. As an example, there is an
inadequate scientific basis for setting a health-based standard for
aluminium in drinking-water.
1.10.2 Subpopulations at special risk
In people of all ages with impaired renal function, aluminium
accumulation has been shown to cause the clinical syndrome of
encephalopathy, vitamin-D-resistant osteomalacia and microcytic
anaemia. The sources of aluminium are haemodialysis fluid and
aluminium-containing pharmaceutical agents (e.g., phosphate binders).
Intestinal absorption can be exacerbated by the use of citrate-
containing products. Patients with renal failure are thus at risk of
neurotoxicity from aluminium.
Iatrogenic aluminium exposure poses a hazard to patients with
chronic renal failure. Premature infants have higher body burdens of
aluminium than other infants. Every effort should be made to limit
such exposure in these groups.
1.10.3 Occupationally exposed populations
Workers having long-term, high-level exposure to fine aluminium
particulates may be at increased risk of adverse health effects.
However, there are insufficient data from which to develop with any
degree of certainty occupational exposure limits with regards to the
adverse effects of aluminium.
Exposure to stamped pyrotechnic aluminium powder most often
coated with mineral oil lubricants has caused pulmonary fibrosis
(aluminosis), whereas exposure to other forms of aluminium has not
been proven to cause pulmonary fibrosis. Most reported cases had
exposure to other potentially fibrogenic agents.
Irritant-induced asthma has been associated with inhalation of
aluminium sulfate, aluminium fluoride or potassium aluminium
tetrafluoride, and with the complex environment within the potrooms
during aluminium production.
1.10.4 Environmental effects
Aluminium-bearing solid phases in the environment are relatively
insoluble, particularly at circumneutral pH values, resulting in low
concentrations of dissolved aluminium in most natural water.
In acidic or poorly buffered environments subjected to strong
acidifying inputs, concentrations of aluminium can increase to levels
resulting in adverse effects on both aquatic organisms and terrestrial
plants. However, there exist large species, strain and life history
stage differences in sensitivity to this metal.
The detrimental biological effects from elevated concentrations
of inorganic monomeric aluminium can be mitigated in the presence of
organic acids, fluorides, silicate and high levels of calcium and
magnesium.
There is a substantial reduction in species richness associated
with the mobilization of the more toxic forms of aluminium in acid-
stressed waters. This loss of species diversity is observed at all
trophic levels.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
The element aluminium (Al) was first obtained in an impure form
by Oersted in 1825, and pure aluminium was prepared by Woehler two
years later. The name aluminium is derived from alum, which the
ancient Greeks used as an astringent in medicine (Lide, 1991).
Aluminium is the most abundant metallic element and constitutes
8.13% of the earth's crust. Owing to its high reactivity, it is always
found combined with other elements and does not occur in its pure
state. Combined with oxygen, silicon, the alkali and alkaline-earth
metals, and fluorine, and as hydroxides, sulfates and phosphates,
aluminium appears in a wide variety of minerals (Frank et al., 1985;
Hudson et al., 1985; Lide, 1991).
Some aluminium compounds, synonyms and molecular formulae are
listed in Table 1. The most abundant natural aluminium ores are shown
in Table 2.
2.1 Identity
Pure aluminium is a silvery-white, malleable, ductile metal with
the atomic number of 13 and the relative atomic mass of 26.98. With
few exceptions aluminium is found in chemical compounds as AlIII.
Aluminium occurs naturally as 27Al; eight radioactive isotopes are
known, of which 26Al is the most stable with a half-life of 7.4 ×
105 years (Frank et al., 1985).
2.2 Physical and chemical properties
2.2.1 Aluminium metal
Elemental aluminium possesses many desirable characteristics and
is therefore widely used in commerce (Sax & Lewis, 1987; Lide, 1991).
Aluminium crystallizes in a face-centered cubic lattice that is stable
from 4 K to melting point; the coordination number is 12, it is light
and malleable, and thus is easily formed into a variety of shapes
(Frank et al., 1985).
Owing to the high charge/radius ratio of Al3+ in aqueous
solutions, the ion proteolyses part of the water envelope and forms
hydroxo complexes. It can also complex with electron-rich species,
such as fluoride and chloride. The chemical properties of aluminium
resemble those of beryllium and silicon. Because of its amphoteric
character, it reacts with mineral acids and strong alkalis (Sax &
Lewis, 1987). Although aluminium is one of the most reactive of the
common metals used commercially, it has excellent resistance to
Table 1. Chemical names, synonyms and molecular formulae of elemental aluminium and aluminium compoundsa
Chemical name CAS registry number Synonyms Formula
Aluminium 7429-90-5 Aluminium, metana Al
Aluminium chloride 7446-70-0 Aluminium trichloride AlCl3
Aluminium chlorohydrate 1327-41-9 Aluminium chlorohydroxide, AlCl(OH)5
11097-68-0 aluminium chloride, basic,
84861-98-3 chlorhydrol, polyaluminium chlorideb Al2Cl(OH)52H2O
Aluminium fluoride 7784-18-1 Aluminium trifluoride AlF3
Aluminium lactate 18917-91-4 Aluctyl Al(C3H5O3)3
Aluminium oxidec 1302-74-5 alpha-Alumina, corundum Al2O3
Aluminium oxide hydroxidec 14457-84-2 Diaspore alpha-AlO(OH) or alpha-Al2O3H2O
Aluminium oxide hydroxidec 1318-23-6 Boehmite gamma-AlO(OH) or gamma-Al2O3H2O
Aluminium oxide, trihydratec 20257-20-9 Bayerite, alpha-aluminium trihydroxide alpha-Al(OH)3 or alpha-Al2O33H2O
Aluminium oxide, trihydratec 13840-05-6 Nordstrandite, ß-aluminium trihydroxide ß-Al(OH)3 or ß-Al2O33H2O
Aluminium oxide, trihydratec 14762-49-3 Gibbsite, hydrargillite, gamma-aluminium gamma-Al(OH)3 or gamma-Al2O33H2O
trihydroxide
Nitric acid, aluminium salt 13473-90-0 Aluminium trinitrate, aluminium nitrate Al(NO3)3
Table 1. (Con't)
Chemical name CAS registry number Synonyms Formula
Phosphoric acid,
aluminium salt 7784-30-7 Aluminium orthophosphate AlPO4
Sodium aluminate 1302-42-7 NaAlO2, Na2OAl2O3 or
Na2Al2O4
Sulfuric acid, aluminium salt 10043-01-3 Alum, aluminium trisulfate, cake alum Al2(SO4)3
Trimethylaluminiumb 75-24-1 Al(CH3)3
2-Propanol, aluminium saltb 555-31-7 Aluminium isopropoxide, aluminium Al(OCH(CH3)2)3
isopropylate
2-Butanol, aluminium saltb 2269-22-9 Aluminium sec-butoxide, aluminium Al(OC4H9)3
butylate
a adapted from ATSDR (1992)
b Zietz (1985)
c Hudson et al. (1985)
Table 2. CAS chemical names and registry numbers, synonyms, trade names, content and molecular formula of aluminium oresa
Chemical name CAS registry Synonyms and trade Composition Formula
number names
Aluminium magnesium - Magnesium aluminium 48.8% O MgAl2(SiO4)2
silicate silicate 21.4% Si
20.6% Al
9.3% Mg
Aluminium silicate, hydrate - Kaolinite 40% Al2O3b Al2Si2O5(OH)4 or
46% SiO2 Al2O3SiO2H2O
14% H2O
Aluminium silicofluoride - Topaz 71.2% F 2Al2O32Al(F,OH)33SiO2
17.6% Si
11.2% Al
Ammonium aluminium 7784-26-1 Ammonium alum, - NH4Al(SO4)212H2O or
sulfate, hydrate ammonium Al2O3(NH4)2O24HOH
aluminium sulfate
Bauxite 1318-16-7 - 30-75% Al2O3 -
3-25% Fe2O3
9-31% H2O
2-9% SiO2
1-3% TiO2
Table 2. (Con't)
Chemical name CAS registry Synonyms and trade Composition Formula
number names
Potassium aluminium 7784-24-9 Potash alum, potassium 37% Al2O3 K(AlO)3(SO4)212H2O or
sulfate, hydrate aluminium sulfate 11% K2O Al2(SO4)3K2SO424HOH
39% SO3
13% H2O
Sodium aluminium 15096-52-3 Cryolite, greenland - Na3AlF6 or 3NaFAlF3
fluoride spar, isestone
Sodium aluminium 7784-28-3 Sodium alum, sodium - NaAl(SO4)212H2O or
sulfate, hydrate aluminium sulfate Al2(SO4)2Na2SO424HOH
Sodium calcium - Anorthosite, soda-lime 26-35% Al2O3b Na2OAl2O36SiO2 &
silicoaluminate feldspar 46-59% SiO2 CaOAl2O32SiO2
8-18% CaO
1-7% Na2O
a From: Sax & Lewis (1987)
b US Bureau of Mines (1967)
corrosion. Exposed to oxygen, water or other oxidants, a continuous
film of aluminium oxide (Al2O3) grows rapidly on the nascent
aluminium surface, providing the metal with a high resistance to
corrosion. The oxide film dissolves in alkaline solutions with
evolution of hydrogen and formation of soluble alkali-metal aluminates
(Sax & Lewis, 1987).
The oxide film on the solid metal is resistant to some acids
(e.g., nitric acid), and prevents further chemical attack on the
metal. However, the protective oxide film dissolves in some acids
(e.g., hydrochloric or hot sulfuric acids) and also in alkaline
solutions, exposing the metal to further reactions. At elevated
temperatures, aluminium metal reacts with water (above 180°C),
producing Al(OH)3 and H2, and with many metal oxides producing
Al2O3 and the metal. This reaction is used to produce certain
metals, for example, manganese and alloys (e.g., ferro-titanium).
Finely divided aluminium dust can ignite and cause explosions
(Wade & Banister, 1973; Frank et al., 1985).
Many applications of aluminium and its alloys are based upon its
inherent properties of high electrical and thermal conductivity, low
density, and great resistance to corrosion. Pure aluminium is soft and
lacks strength, but it can be alloyed with small amounts of Cu, Mg,
Si, Mn and other elements to impart greater strength and a variety of
other useful properties. Aluminium alloys are light, strong and
readily worked into a variety of shapes (Frank et al., 1985; Lide,
1991).
2.2.2 Aluminium compounds
The aluminium compounds of the greatest industrial importance are
aluminium oxide, aluminium sulfate and aluminium silicate. Some
physical and chemical data of aluminium and selected aluminium
compounds are summarized in Table 3.
Aluminium oxide is a white powder that is found as balls or
lump of various mesh sizes. Owing to its amphoteric character, it is
soluble in mineral acids and strong alkali. Aluminium oxide is
found in different modifications. The hexagonally closest-packed
alpha-modification "corundum" (alpha-Al2O3) is the most stable
oxide. Emery is an abrasive containing corundum, and ruby and sapphire
are impure crystalline varieties of gem quality (Hudson et al., 1985).
Formation of aluminium oxide by dehydration of the hydroxides produces
a series of alumina types still containing a small proportion of
hydroxyl groups and retaining some chemical reactivity. All oxides
produced at low temperatures are collectively referred to as
transitional oxides. Those formed by dehydration below 600°C are known
Table 3. Physical and chemical properties of aluminium and some of its compoundsa
Chemical name Relative atomic/ Melting Boiling Relative density Crystalline Solubilityd
molecular mass point (°C) point (°C) (g/cm3)b form
Aluminium 26.98 660 2450c 2.708 silver-white cubic sol alkali, HCl, H2SO4;
insol H2O, HNO3e
alpha-Aluminium 77.99 300 (-H2O) 2.420 monoclinic, powder sol acid; insol H2O,
hydroxide (bayerite) alcohole
Aluminium nitrate 213.00 74 135 - rhombic delinq. sol H2O, alkali,
(decomposes) acetone, HNO3
Aluminium oxide 101.94 2072 2980 3.965 (25) hexagonal very sl sol benzene;
insol H2O
gamma-Aluminium oxide 59.99 - - 3.440 orthorhomic sol acid; sl sol
hydroxide (boehmite) alkali; insol H2O,
alcohole
Aluminium phosphate 121.95 1500 - 2.566 rhombic platelets sol acid, alkali; insol H2O
Aluminium sulfate, 342.14 700 - 2.710 powder sol H2O, dil acid; sl
anhydrate (decomposes) sol alkali
Aluminium sulfate, 666.41 87 - 1.690 (17) monoclinic sol H2O, dil. acid; sl
hydrate (decomposes) sol alkali
Aluminium 204.25 119 141 1.035 (20) crystals sol alcohol, benzene,
isopropoxidee chloroform
a Compiled from ATSDR (1992)
b Temperature is given in parentheses
c Sax & Lewis (1987)
d Sol = soluble; insol = insoluble; sl = slightly
e Lide (1991)
as gamma-aluminas or activated aluminas, while the aluminas formed by
dehydration at higher temperatures (900-1000°C), the rho-aluminas, are
nearly anhydrous Al2O3 (Wade & Banister, 1973). At 1400°C all
transitional alumina converts to alpha-alumina (Hudson et al., 1985).
The structural and compositional differences among various forms of
alumina are associated with differing particulate size, particulate
surface area, surface reactivity and catalytic activity.
Various forms of aluminium hydroxides are known. The best defined
forms are the trihydroxides (Al(OH)3) and the oxide-hydroxides
(AlO(OH)). Besides these well-defined crystalline forms, several other
hydroxides have been described in the literature (Wefers & Bell,
1972). The aluminium hydroxides found abundantly in nature are
gibbsite (Al(OH)3), diaspore œ-(AlO(OH)), and boehmite
alpha-(AlO(OH)). They all convert to aluminium oxide when heated
(Hudson et al., 1985).
Aluminium sulfate can exist with varying proportions of water,
the common form being Al2(SO4)3Ê18H2O. It is almost insoluble
in anhydrous alcohol, but readily soluble in water. Above 770°C
decomposition to aluminium oxide is observed. Aluminium sulfate is
mainly used in water treatment, dyeing, leather tanning and in the
production of other aluminium compounds. Alums are crystalline double
salts composed of aluminium, sulfate and a monovalent cation, such
as potassium, sodium or ammonium, and have the general formula
M+Al3+(SO4)2Ê12H2O. In aqueous solution, alums show all the
chemical properties that their components show separately (Helmboldt
et al., 1985).
Clays are aluminium silicates. They have cation-exchange capacity
and the amounts and types of clay minerals in a soil largely determine
its physical properties and suitability for agriculture (Wild, 1988).
Aluminium halogenides, hydrides and lower aluminium alkyls react
violently with molecular oxygen, and are spontaneously inflammable in
air and explosive with water. Industrially these compounds are used as
co-catalysts for organometallic and organic synthesis, and as
intermediates in various production processes (Stokinger, 1987;
Budavari, 1989).
Further compounds of industrial interest are aluminium antimonide
(AlSb) and selenide (AlSe), which are employed in the semiconductor
technology industry (Budavari, 1989). Aluminium phosphide (AlP) is
used as a rodenticide and pesticide, but it is not discussed in this
monograph since its biocidal activity is due to the phosphide moiety
and not to the aluminium.
2.3 Analytical methods
Various methods for sampling, sample preparation and
determination of aluminium in biological and environmental samples
have been developed and described. An overview of standard methods is
given in Table 4.
2.3.1 Sampling and sample preparation
Because of the ubiquitous distribution of aluminium in nature,
care must be taken during sampling and sample preparation to avoid
contamination. Most analytical errors are due to contamination of the
sample with aluminium from air, vessels and reagents during sampling
and preparation for analysis. To prevent aluminium contamination, the
use of aluminium-free polyethylene, polypropylene, teflon or quartz
materials is recommended. Containers and laboratory materials have to
be washed with warm, dilute nitric acid and subsequently rinsed with
de-ionized water prior to use (Andersen, 1987).
Air is sampled with high volume samplers using low-ash cellulose
or cellulose ester filters for particulate aluminium (NIOSH, 1984).
Biological samples need to be preserved by cooling, freezing or
lyophilization. Preservation with 10% formalin is not recommended
because of a high risk of aluminium contamination (Bouman et al.,
1986).
Homogeneity of the samples is an absolute prerequisite for
accurate analysis. To prepare samples for analysis, inorganic samples
are usually dissolved in nitric acid or extracted with water.
Solutions are filtered with a membrane filter and the particulate
residue is analysed separately (Dunemann & Schwedt, 1984).
Water (DIN, 1993) and urine should be acidified with HNO3 or HCl
to pH < 2 to prevent adsorption effects and the precipitation of
salts. This ensures that aluminium remains in solution. Water samples
for speciation analysis should be stored, without acidification, in
high-density polyethylene bottles (Berden et al., 1994; Fairman et
al., 1994). Prior to analysis biological tissues must be homogenized
and separated or extracted. Blood and urine samples may be separated
by centrifugation and diluted, or, if appropriate, analysed directly
without pretreatment.
Table 4. Analytical methods for aluminium and aluminium compoundsa
Medium Sample preparation Analytical method Detection limit Recovery Reference
Environmental
samples
Air Sample collection on cellulose FAAS 500 µg/m3 (100-litre n.g. NIOSH (1984)
filter, ashing with HNO3 sample)
Sample collection on cellulose ICP-AES 5 µg/m3 (500-litre n.g. NIOSH (1984)
filter, ashing with HNO3 sample)
Water Reaction with sulfonitrazo DAF Spectrophotometry 4 µg/litre n.g. Ermolenko &
Dedkov (1988)
Reaction with Chromazurol S Spectrophotometry 0.0005 µg/0.5 ml- n.g. Schwedt (1989)
sample
Reaction with alizarin S Spectrophotometry 10 µg/litre; 50 µg/litre n.g. DIN (1993)
(after digestion)
Digestion with HNO3 and ICP-AES 100 µg/litre n.g. DIN (1993)
H2O2
Filtration, digestion with HNO3, Spectrophotometry 6-13 µg/litre range 98-100% van Benschoten &
reaction with 8-hydroxyquinoline ICP-AES 3 µg/litre limit detection Edzwald (1990)
Soil Extraction with H2O, filtration, GF-AAS n.g. Gardinier et
high-performance size exclusion al. (1987)
chromatography
Soil Extraction with H2O, filtration, Spectrophotometry 0.005 µg (absolute) n.g. Dunemann &
gel chromatography, reaction Schwedt (1984)
with Chromazurol
Fly ash Vacuum dried NAA n.g. Fleming &
Lindstrom (1987)
Table 4. (Con't)
Medium Sample preparation Analytical method Detection limit Recovery Reference
Rock, soil, Dried, digestion with ICP-AES 1-5 µg/litre > 57% Que Hee &
paint, HNO3/HCl Boyle (1988)
citrus leaves
Biological
samples
Serum Centrifugation, dilution with GF-AAS 14.3-150 µg/litre 97-102% Bettinelli et
Mg(NO3)2 (analytical range) al. (1985)
Plasma, Centrifugation, dilution with GF-AAS 4 µg/litre 90-102% Gardinier et
serum water al. (1981)
Whole blood, Dilution with Triton X-100 GF-AAS 1.9 µg/litre (serum), n.g. van der Voet
plasma, serum 1.8 µg/litre (plasma), et al. (1985)
2.3 µg/litre (blood)
Biological Wet-digestion, complexation NAA 2.1 µg/litre (liver) n.g. Blotcky et
tissue, urine with Tiron, anion-exchange 0.18 µg/ml (urine) al. (1992)
chromatography
Urine, blood Dilution with water ICP-AES 6 µg/litre n.g. Sanz-Medel et
al. (1987)
Dilution with water ICP-AES 0.3 µg/litre n.g. Mauras &
Allain (1985)
Table 4. (Con't)
Medium Sample preparation Analytical method Detection limit Recovery Reference
Biological Freeze dry, grind NAA n.g. Yukawa et
tissues al. (1980)
Dried, digestion with HNO3, GF-AAS 0.5 µg/g dry tissue 80-117% Bouman et
dilution with water al. (1986)
Dried, digestion with HNO3, AMS 106 atoms 26Al n.g. Kobayashi et
cation-exchange al. (1990)
chromatography
Digestion, high-performance Spectrophotometry 7 µg/litre 87-94% Dean (1989)
ion-exchange chromatography,
reaction with Tiron
Hair Washed with 2-propanol, GF-AAS 0.65 µg/g dry weight 84-105% Chappuis et
digestion with HNO3 al. (1988)
Body fluids Dilution with HNO3/HCl ICP-AES 1-5 µg/litre > 57% Que Hee &
Boyle (1988)
Haemodialysis Dilution with HNO3 and GF-AAS 3 µg/litre 93-108% Andersen (1987)
concentrates Triton X-100 (Zeeman-corrected)
Haemodialysis Reaction with ferron in Phosphorimetry 5.4 µg/litre n.g. De La Campa
fluids CTAB et al. (1988)
a AMS = accelerator mass spectrometry; CTAB = cetyltriammonium bromide; EDTA = ethylenediaminetetraacetic acid; FAAS = flame
atomic-absorption spectrophotometry; ferron = 7-iodo-8-quinolinol-5-sulfonic acid; GF-AAS = graphite furnace - atomic-absorption
spectrophotometry; ICP-AES = inductively coupled plasma - atomic-emission spectrophotometry; NAA = neutron activation analysis;
n.g. = not given; Tiron = 4,5-dihydroxy-1,3-benzenedisulfonic acid
Free aluminium may be determined directly from the samples or the
sample extracts. To determine insoluble aluminium compounds and
organically bound species, the samples (organic matter, air-filters,
water, soil, etc.) need to be subjected to wet ashing (digestion) or
dry ashing. Wet ashing, i.e. heating with nitric acid under reflux, is
suitable for most organic and biological samples. The residues are
dissolved in acids before analysis (NIOSH, 1984; Kobayashi et al.,
1990; DIN, 1993). After digestion, differentiation between free metal
species and kinetically labile and stable complexes is not possible.
2.3.2 Separation and concentration
A fractionation procedure for aluminium species in water using an
0.22 µm size filter has been proposed by van Benschoten & Edzwald
(1990). Total reactive aluminium is determined in the unfiltered,
acidified sample. Dissolved monomeric aluminium is analysed in the
unfiltered sample without acidification. Analysis of total dissolved
aluminium is performed after filtration and acidification of the
sample. Dissolved organically bound aluminium is analysed after
separation of the filtered sample on a column of cation exchange
resin. The eluate is acidified and analysed colorimetrically. For the
determination of dissolved organic monomeric aluminium, samples are
passed through a cation exchange column and are analysed with no
acidification.
In order to carry out long-term characterization of the highly
acute toxicity during the initial phase of aluminium polymerization in
"mixing zones" (Rosseland et al., 1992), in situ fractionation
techniques such as ultrafiltration (Lydersen et al., 1987) are
recommended (see section 9.1.2.3).
For the extraction of aluminium bound to fulvic acids, soil
samples may be extracted with copper chloride solution (Gardinier et
al., 1987). The clean-up of aqueous extracts of soil samples can be
performed by gel chromatography (Dunemann & Schwedt, 1984) or by size
exclusion chromatography. These methods are very mild and thus
suitable for the determination of labile aluminium species (Gardinier
et al., 1987).
Water samples may be concentrated by careful evaporation (DIN,
1993). Macro quantities of aluminium can be separated from small
amounts of interfering elements by precipitation of aluminium as
its hydroxide or phosphate. Chelating agents, such as EDTA,
8-hydroxyquinoline, and 2,2'-dihydroxyazobenzene, can be used to
extract aluminium into an organic solvent (Alderman & Gitelman, 1980).
Biological materials contain a variety of compounds that
can severely interfere with aluminium determinations. Hence,
chromatographic methods are often employed for sample purification.
Biological tissue samples may be cleaned-up by cation-exchange
chromatography after acid digestion (Dean, 1989; Kobayashi et al.,
1990). Blotcky et al. (1992) proposed the chelating of aluminium prior
to anion-exchange chromatography. Precolumn derivatization coupled
with reversed-phase high performance liquid chromatography (RP-HPLC)
is an effective method for the separation of the chelates of
different interfering metal ions (Nagaosa et al., 1991). Solvent
extraction of aluminium chelate complexes, e.g., 2,4-pentanedione and
4-methyl-2-pentanone, has been described as a separation and pre-
concentration step in the analysis of body fluids (Buratti et al.,
1984).
2.3.3 Detection and measurement
Spectrophotometric methods for aluminium analysis are simple
and quick, and are most often used for the determination of aluminium
in water. Samples are treated with inorganic or organic reagents to
form coloured soluble complexes that can be measured by absorption
spectrometry. Disadvantages of these methods are the narrowness of
the pH range of the reaction, the instability of the complexes, the
low selectivity, and the low sensitivity (Bettinelli et al., 1985).
The working range for the aluminium determination with chromazurol C
is 25-1000 µg/litre (Schwedt, 1989), with alizarin S it is 10-500
µg/litre (DIN, 1993), and with Tiron it is 7-5000 µg/litre (Dean,
1989). Detection limits of 1 µg/litre can be achieved. Chromatographic
separation of chelates of interfering metals increases the selectivity
of spectrophotometric methods.
De La Campa et al. (1988) and García et al. (1991) reported a
room temperature phosphorimetric method for aluminium analysis.
Aluminium reacts with 7-iodo-8-quinolinol-5-sulfonic acid (ferron) in
cetyltrimethylammonium bromide micelles to form a highly
phosphorescent complex. The method is used to determine aluminium in
water and dialysis fluids. The given detection limits are 5.4 µg/litre
and 2 µg/litre, respectively.
Instrumental methods applied to the determination of aluminium
include neutron activation, X-ray fluorescence, flame atomic-
absorption spectrophotometry, inductively coupled plasma - atomic-
emission spectrophotometry (ICP-AES) and graphite furnace - atomic-
absorption spectrophotometry (GF-AAS). However, neither X-ray
fluorescence nor flame absorption methods are sensitive enough to
measure trace levels in biological samples (Bettinelli et al., 1985).
The NIOSH procedure for aluminium analysis in air is applicable over a
working range of 50-5000 µg per sample or 0.5-10 mg/m3 for a
100-litre sample (NIOSH, 1984).
Neutron activation analysis produces excellent results but the
methods are time consuming and the facilities are not always readily
available. The method is used for determining aluminium in fly ash
(Fleming & Lindstrom, 1987) and biological tissues (Yukawa et al.,
1980; Blotcky et al., 1992). After digestion and concentration of the
biological samples, a detection limit of 2.1 µg/g was found for bovine
liver (Blotcky et al. 1992).
GF-AAS is the most frequently used technique to determine
aluminium at low concentrations. Detection limits between 0.5 and 4
µg/litre or µg/g are achieved with the analysis of various
environmental and biological samples (Gardinier et al., 1981; van der
Voet et al., 1985; Bettinelli et al., 1985; Andersen, 1987). Most
liquid samples can be injected directly after dilution into GF-AAS.
Dilution is necessary because most biological fluids have high salt
contents (in the order of 30%) (Andersen, 1987). To prevent
precipitation of aluminium and the formation of carbon residues, EDTA
or Triton X can serve as diluents. Ammonia may be added to convert
aluminium to aluminate and thus avoid loss of aluminium as its
chloride (Gardinier et al., 1981). Triton X-100 is used to reduce the
viscosity of the samples, and MgNO3 is added as a matrix modifier to
improve the volatility of aluminium (Bettinelli et al., 1985).
ICP-AES is used for the determination of aluminium in various
biological and environmental samples, allowing the simultaneous
determination of different elements at low levels of interference
(Mauras & Allain, 1985; Sanz-Medel et al., 1987). The NIOSH method for
aluminium determination in air samples is recommended for a working
range of 5-2000 µg/m3 for a 500-litre sample (NIOSH, 1984). A
detection limit of 1 µg/litre in biological and environmental samples
has been reported by Que Hee & Boyle (1988). ICP can also be combined
with a mass spectrometer to further increase the sensitivity of the
method. As a multi-element detector for reversed-phase liquid
chromatography, ICP-MS offers the ability to measure isotope ratios on
eluting peaks and to remove troublesome matrices on-line (Thompson &
Houk, 1986).
For 26Al tracer experiments (Kobayashi et al. 1990), the
application of accelerator mass spectrometry (AMS) has been described.
The limit of detection is 106 atoms; thus the sensitivity of AMS is
105 times greater than that of gamma-ray counting techniques.
Aluminium concentrations in human brain can be investigated by
laser multipoint microprobe mass analysis (LAMMA) using focussed laser
ionization with time-of-flight mass spectrometry (Stern et al., 1986).
27Al nuclear magnetic resonance (NMR) may be used to ascertain the
coordination of aluminium in soil solutions (Schierl, 1985).
Aluminium in natural water samples has been determined using
reversed-phase liquid chromatography of the 8-quinolinol complex using
spectrophotometric detection. A detection limit of 2 µg/litre was
reported (Nagaose et al., 1991).
2.3.4 Speciation analysis of aluminium in water
Speciation analysis aims to distinguish and determine
quantitatively different groups of physico-chemical species present
in a water sample. All speciation methods, with the exception of
potentiometric techniques and direct spectroscopic methods (e.g.,
NMR), will alter the speciation of the sample during measurement. This
may not be a disadvantage, particularly if, as is usual, the
speciation analysis is being carried out in order to estimate the
toxicity of the sample to aquatic biota. Toxicity itself is a dynamic
process, and the interaction of aluminium species in water with a
biomembrane (e.g., a fish gill) will change the aluminium species
distribution in the solution close to the biomembrane. The best
speciation probe is one that reacts with aluminium in a water sample
to a similar extent and at a similar rate to the reaction of a
biomembrane with the aluminium in the samples.
Speciation analysis of aluminium in a water sample is usually
carried out after first filtering the sample through a 0.45 µm
membrane filter to remove particulate matter. The filtrate can then be
analysed for groups of species by several different techniques,
including kinetic spectrophotometry (Parker & Bertsch, 1992a,b), ion
exchange (Driscoll, 1984) and ion chromatography (Jones, 1991).
Combinations of methods such as sample acidification, kinetic
spectrophotometry and ion exchange are frequently used to determine a
variety of species (Driscoll, 1984; Courtijn et al., 1990; van
Benschoten & Edzwald, 1990). These speciation schemes provide
information on various speciation groups, including total dissolved
aluminium, acid-soluble aluminium, total monomeric aluminium, reactive
monomeric aluminium, non-reactive monomeric aluminium, aluminium
fluoride complexes, organic monomeric aluminium and inorganic
monomeric aluminium. The terms "reactive" and "labile", as applied to
aluminium species, are operationally defined and refer to species that
react rapidly with an analytical probe such as a cation exchange resin
or a chromogenic reagent.
The aluminium species that are most toxic to aquatic organisms
are believed to reside in the reactive monomeric inorganic aluminium
fraction and to consist principally of aluminium hydroxy complexes
(Helliwell et al., 1983; Fairman et al., 1994; Parent & Cambell,
1994). Although the fluoro complex is toxic, it is less so than the
aluminium hydroxy complexes (Helliwell et al., 1983).
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1 Natural occurrence
Aluminium is released to the environment both by natural
processes and from anthropogenic sources. Natural processes far
outweigh the contribution of anthropogenic sources because aluminium
is a major constituent of the earth's crust, making up about 8% of the
earth's surface (Lantzy & Mackenzie, 1979). Anthropogenic releases
are mostly indirect, for example, through emission of acidifying
substances such as sulfur dioxide and nitrogen oxides to the
atmosphere. These acidify rain and soil and contribute to dissolution
of aluminium from the soil. The largest anthropogenic impact on
aluminium movement in the environment is through enhanced wind and
water erosion from cultivated land, notably when fallow. Aluminium is
the third most abundant element. It does not occur naturally in the
metallic, elemental state, but is widely distributed in the earth's
crust in combination with oxygen, fluorine, silicon and other
constituents. Aluminium occurs ubiquitously in silicates such as
feldspars and micas, complexed with sodium and fluoride as cryolite,
and in bauxite rock, which is composed of hydrous aluminium oxides,
aluminium hydroxides and impurities such as free silica. In general,
decreasing pH as a result of acid rain or the release of acid mine
drainage results in increased mobility of the monomeric forms of
aluminium (ATSDR, 1992). Chemical speciation in soil and water
affecting the bioavailability of aluminium to organisms is discussed
in chapter 4.
3.2 Anthropogenic sources
Direct anthropogenic releases of aluminium compounds are
primarily to the atmosphere and are associated with industrial
processes such as smelting. However, the use of aluminium and
aluminium compounds in processing, packaging, storage of food products
and as flocculants in the treatment of drinking-water may contribute
to its presence in drinking-water and food stuffs (ATSDR, 1992).
3.2.1 Production levels and processes
The most important raw material for the production of aluminium
is bauxite, which contains up to 55% alumina (aluminium oxide). The
commercial deposits of bauxite are mainly gibbsite (Al2O3Ê3H2O) and
boehmite (Al2O3ÊH2O). The bauxite is extracted by open-cast mining
(Dinman, 1983).
The production of the metal comprises two basic steps: refining
and reduction. Refining involves the production of alumina from
bauxite by the Bayer process in which bauxite is digested at high
temperature and pressure in a strong solution of caustic soda. The
resultant hydrate is crystallized and calcined to the oxide. Reduction
involves the reduction of alumina to virgin aluminium metal by the
Hall-Heroult electrolytic process using carbon electrodes and a
cryolite flux (Dinman, 1983).
World bauxite production was 106 million tonnes in 1992. A
comparison of the quarterly average figures for 1993 and 1994 with
this figure shows that production in major producing countries is
remaining fairly constant (World Bureau of Metal Statistics, 1994).
The total primary aluminium production for 1992 is summarized in Table
5. The amount of aluminium recovered from purchased or tolled scrap in
1992 was 14% of the total primary production figure. The total alumina
production for 1992 is summarized in Table 6. The total alumina
production figure includes 30 million tonnes for metallurgical uses
and 3 million tonnes for non-metallurgical uses. The total figures for
primary aluminium and alumina production have not changed greatly
since 1988.
3.2.2 Uses
Aluminium metal has a wide variety of uses including structural
material for construction, automobiles and aircraft, and the
production of metal alloys. Other uses include die-cast motor parts,
cooking utensils, decorations, road signs, fencing, beverage cans,
food packaging, foil, corrosion-resistant chemical equipment, solid
fuel rocket propellents and explosives, dental crowns, and denture
materials. In the electrical industry aluminium is used for power
lines, electrical conductors, insulated cables and wiring (ATSDR,
1992).
Table 5. Primary aluminium production in 1992 (from: IPAI, 1993)
Geographical area Thousands of tonnes
Africa 617
North America 6016
Latin America 1949
East and South Asia 1379
Europe 3319
Oceania 1483
Total 14 763
Table 6. Alumina production in 1992 (from: IPAI, 1993)
Geographical area Thousands of tonnes
Africa 604
North America 5812
Latin America 7627
East and South Asia 2360
Europe 5565
Oceania 11 803
Total 33 771
Aluminium compounds and materials also have a wide variety of
uses, some of which are listed in Table 7. Aluminium powder is used in
paints, protective coatings and fireworks. Natural aluminium minerals
especially bentonite and zeolite are used in water purification, sugar
refining, brewing and paper industries. Aluminium sulfate is used for
water purification, as a mordant in dyeing, and in paper production.
Other aluminium compounds are used as tanning agents in the leather
industry, and as components of human and veterinary medicines, glues,
disinfectants, and in toothpaste, styptic pencils, deodorants,
antacids and food additives. Clays (aluminium silicates) are used as
industrial raw materials (e.g., production of ceramics), and
aluminates are constituents of cement. Alkyl aluminium products are
used as catalysts for the production of low pressure polyethylene
(ATSDR, 1992).
Table 7. Main uses of aluminium compoundsa
Aluminium compounds Uses
alums hardening agent and setting accelerator for gypsum
plaster, in tanning and dyeing, and (formerly) in styptic
pencils
aluminas in water treatment and as accelerator for concrete
solidification (high alumina cements)
alkoxides in varnishes, for textile impregnation, in cosmetics and
as an intermediate in pharmaceutical production
borate production of glass and ceramics
carbonate antacid
chlorides production of rubber, lubricants and wood preservatives,
and in cosmetics as an astringent; the anhydrous
product is used as a catalyst and raw material in the
chemical and petrochemical industries; active ingredient
in antiperspirants
hydroxide stomach antacid, other pharmaceuticals
isopropoxide used in the soap and paint industries; waterproofing
textiles
phosphate antacid
silicate component of dental cement; antacid, food additives
sulfate used in water purification as a flocculent, in paper
production, as a mordant in dyeing, and as a starting
material for the production of other aluminium
compounds
trioxide used as an absorbent, abrasive and refractory material
sodium aluminium food additives
phosphate
a From: Helmbolt et al. (1985); ATSDR (1992)
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION
4.1 Transport and distribution between media
Aluminium occurs ubiquitously in silicates such as feldspars and
micas, complexed with sodium and fluoride as cryolite, and in bauxite
rock composed of hydrous aluminium oxides, aluminium hydroxides, and
impurities such as free silica (ATSDR, 1992). Aluminium is not
found as a free metal because of its reactivity. It has only one
oxidation state (+3); therefore, its transport and distribution in
the environment depend upon its coordination chemistry and the
characteristics of the local environmental system. Aluminium
partitions between solid and liquid phases by reacting and complexing
with water molecules and electron-rich anions, such as chloride,
fluoride, sulfate, nitrate, phosphate and negatively charged
functional groups on humic materials and clay.
At a pH greater than 5.5, naturally occurring aluminium compounds
exist predominantly in an undissolved form such as gibbsite (Al(OH)3)
or as aluminosilicates, except in the presence of high amounts of
dissolved organic material such as fulvic acid, which binds with
aluminium and can cause an increase in dissolved aluminium
concentrations in streams and lakes (ATSDR, 1992). Several processes
influence aluminium mobility and its subsequent transport within the
environment; these include chemical speciation, hydrological flow
paths, other spatial and temporal factors related to soil-water
interactions, and the composition of the underlying geological
materials (Grant et al., 1990). Watersheds with shallow, acidic soils
and poorly buffered surface waters mobilize aluminium when exposed to
acidic deposition (Driscoll et al., 1988).
4.1.1 Air
Aluminium enters the atmosphere as a major constituent of a
number of atmospheric particulates, such as soil-derived dusts from
erosion and particulates from coal combustion (Grant et al., 1990).
Eisenreich (1980) studied the atmospheric loading of aluminium to Lake
Michigan, USA. It was found that aluminium was generally associated
with large particles (> 2 µm diameter) and that these were deposited
near the source. The total atmospheric loading of aluminium to the
lake was calculated to be 0.86 kg/ha per year. The more industrialized
area south of the lake contributes 75% of this total loading. Cambray
et al. (1975) calculated the dry deposition flux of aluminium to the
North Sea to be 51 000 tonnes/year. Ottley & Harrison (1993)
calculated the flux to be 7 300 tonnes/year; they suggest that the
lower estimate is due to more spatially appropriate and extensive air
monitoring since 1975. Rahn (1981) calculated the input of aluminium
from the atmosphere to the Arctic Ocean at 30 000 tonnes/year. The
input was significantly less than those of oceanic and riverine inputs
(140 000 and 110 000 tonnes/year, respectively).
Guieu et al. (1991) compared atmospheric inputs with river inputs
of aluminium for the Golfe du Lion, France. Atmospheric inputs were
found to be 11% of total inputs of aluminium. Rainwater was analysed
for aluminium and only 19% was found in the dissolved fraction
(< 0.4 µm). Losno et al. (1993) monitored rainwater and snow for
aluminium and found large variations in the solubility of aluminium.
The variations seem to be largely due to pH, lower pH values
increasing the solubility of aluminium. Thermodynamic calculations
reveal that, at pH values higher than 5, equilibrium with gibbsite or
an insoluble trivalent alkaline form of aluminium acts to limit
solubility, whereas, at lower pH values, aluminium could be in
equilibrium with a hydroxysulfate salt.
4.1.2 Freshwater
4.1.2.1 Dissolved aluminium
In groundwater or surface water systems an equilibrium is formed
that controls the extent to which aluminium dissolution can occur. The
solubility of aluminium in equilibrium with solid phase Al(OH)3 is
highly pH-dependent. Aquo complex Al(H2O)63+ predominates at low
pH values (e.g., pH < 4), but as the pH of the solution increases
(e.g., pH 4-6) and/or the temperature rises, the positive charge
of aluminium forces hydrolysis of a water ligand producing the
Al(OH)(H2O)52+ ion. The degree of hydrolysis increases as the
solution pH increases, resulting in a series of Al-OH complexes such
as Al(OH)2+, Al(OH)2+, Al(OH) 4 - (Schecher & Driscoll, 1987).
Fluoride ions, being similar in size to hydroxyl ions, will readily
substitute in these complexes. At pH < 5.5, molar concentrati