Toxicological evaluation of some food
additives including anticaking agents,
antimicrobials, antioxidants, emulsifiers
and thickening agents
WHO FOOD ADDITIVES SERIES NO. 5
The evaluations contained in this publication
were prepared by the Joint FAO/WHO Expert
Committee on Food Additives which met in Geneva,
25 June - 4 July 19731
World Health Organization
Geneva
1974
1 Seventeenth Report of the Joint FAO/WHO Expert Committee on
Food Additives, Wld Hlth Org. techn. Rep. Ser., 1974, No. 539;
FAO Nutrition Meetings Report Series, 1974, No. 53.
PHOSPHORIC ACID, POLYPHOSPHATES AND THEIR CALCIUM, MAGNESIUM,
POTASSIUM AND SODIUM SALTS
Explanation
These compounds have been evaluated for acceptable daily intake
by the Joint FAO/WHO Expert Committee on Food Additives (see Annex 1,
Refs Nos. 6, 7, 9, 13, 20 and 23) in 1961, 1963, 1964, 1965, 1969 and
1970.
Since the previous evaluation, additional data have become
available and are summarized and discussed in the following monograph.
The previously published monographs have been revised and are
reproduced in their entirety below.
BIOLOGICAL DATA
BIOCHEMICAL ASPECTS
(a) Phosphoric acid and its salts
Phosphoric acid is an essential constituent of the human
organism, not only in the bones and teeth, but also in many enzyme
systems. Phosphorus plays an important role in carbohydrate, fat and
protein metabolism. The level of inorganic phosphate in the blood
is stabilized by exchange with the mineral depot in the skeleton
through the action of parathyroid hormone. This hormone inhibits
tubular reabsorption of phosphates by the kidney and brings about
demineralization of bone tissue through the action of osteoclasts. The
amount of parathyroid hormone that enters the circulation is probably
regulated by the calcium level of the blood. Intestinal absorption
depends on requirements and is therefore limited. Excretion takes
place mainly in the faeces as calcium phosphate so that the continuous
use of excessive amounts of sodium phosphate and phosphoric acid may
cause a loss of calcium. As a result of physiological regulating
mechanisms, man and animals can tolerate large variations in phosphate
intake without the balance being upset.
Some investigators have considered that the formation in the
intestinal tract of insoluble salts of phosphate with calcium iron
and other metal ions might result in decreased absorption of such
minerals. From studies dealing with this aspect (Lang, 1959; van Esch
et al., 1957; Lauersen, 1953; van Genderen, 1961) it is concluded that
moderate dose levels of phosphates do not impair absorption as shown
by results from carcass analyses or haemoglobin cathartics.
Phosphate supplementation of the diet of rodents has been shown
to lead to reduction in the incidence of dental caries and different
phosphates have different powers in reducing the cariogenic potential
of the carbohydrates in a diet. Phosphate supplements seem to exert
their cariostatic effect on the tooth surface either directly during
eating or by excretion in the saliva (Anon., 1968a; Anon., 1968b).
Little specific toxicological information on potassium
monophosphates is available. There is no reason to consider that the
potassium salts, in the amounts that could be used as food additives,
behave differently from the sodium salts and are therefore dealt with
together.
(b) Disodium and tetrasodium diphosphate
In the animal body diphosphate is formed from adenosyl
triphosphate (ATP) in many enzymatic reactions. It is either utilized
by entering phosphorolytic reactions, or it is hydrolyzed by an
inorganic diphosphatase to monophosphate (Long, 1961). Ingested
diphosphate is readily converted to monophosphate (Fourman, 1959;
Mattenheimer, 1958); no diphosphate was found in faeces or urine of
rats treated with diets containing up to 5% tetrasodium diphosphate.
In these experiments diphosphate was almost completely absorbed by the
gut and excreted as monophosphate in the urine.
(c) Pentasodium triphosphate, sodium polyphosphate (Graham's sodium
polyphosphate)
Several studies indicate that polyphosphates can be hydrolyzed
in vivo by enzymes with the formation of monophosphates. The
localization of different polyphosphates in the nuclei of animal
cells has been demonstrated (Grossmann & Lang, 1962). Injected
hexametaphosphate is more slowly degraded than tripolyphosphate
(Gosselin et al., 1952), and the highly polymerized Tammann's salt
(KNa polyphosphate) is even more slowly eliminated from the blood
after i.v. injection than is Graham's salt (Götte, 1953). When
administered parenterally a small part of those products may escape in
the urine as oligophosphates (Gosselin et al., 1952; Götte, 1953). The
higher polyphosphates are probably not adsorbed as such in the
intestinal tract. After hydrolysis into smaller units absorption takes
place. The larger the molecule, the less the speed of hydrolysis and
absorption, as shown by studies using p32 labelled polyphosphate
(Ebel, 1958).
After giving hexametaphosphate to rats and rabbits by stomach
tube, no more than trace amounts of labile phosphate were found
in the urine (Gosselin et al., 1952). The oral administration of
radioactively-labelled Tammann's salt did not give rise to
radioactivity in the blood (Götte, 1953). With Graham's salt and
Kurrol's salt, 10 to 30% was absorbed as monophosphate and small
amounts of oligophosphates were found in the urine (Lang et al., 1955;
Lang, 1958). In experiments in rats with labelled tripolyphosphates
and Graham's salt these polymers were not absorbed as such, but were
taken up after hydrolysis into monophosphate and diphosphate. In a
period of 18 hours only 40% of the dose of Graham's salt was
hydrolyzed and absorbed. The bacterial flora of the intestinal tract
may contribute to the hydrolysis of the polyphosphates (Schreier &
Noller, 1955). In other experiments, radioactively-labelled Kurrol's
salt was given orally to rats. About half the radioactivity was
recovered from the faeces, mainly as polymeric phosphate, and only a
small percentage of the dose was found in the urine, in this case in
the form of monophosphate.
It is noted that, for practical reasons, in the studies cited
high dosages were given to the animals. The efficiency of hydrolysis
and absorption may be greater at lower dose levels, such as were used
in the short-term and long-term feeding experiments quoted. In some
of these (van Esch et al., 1957) the "monophosphate action", as
demonstrated by the production of nephrocalcinosis, was not much
smaller than when the same dose level was administered by the addition
of monophosphate to the food. In another study, this applied only to
tripolyphosphate, while Graham's salt had definitely less effect on
the kidney (Hahn et al., 1958).
The possibility of the intermediate formation of small amounts of
trimetaphosphate in the hydrolysis of polyphosphates has been
considered (Mattenheimer, 1958). At present, the only known method of
production of sodium polyphosphate is by the fusion process. In this
process metaphosphates are also formed in amounts up to 8% and their
presence is technically unavoidable. It is of interest to note
that these metaphosphates (sodium trimetaphosphate and sodium
tetrametaphosphate) have been tested in short-term experiments in rats
and dogs in conjunction with polyphosphates (Hodge, 1956). The
metaphosphates are also hydrolyzed to monophosphates. No specific
action of these metaphosphates different from that of the other
phosphates has been observed, and it is concluded that the presence of
these impurities does not present a hazard. It is also noted that the
preparation of sodium polyphosphates used in the toxicological studies
mentioned always contained metaphosphates in amounts up to 8%.
It has been considered by many authors that the ingestion of
polyphosphate in the food may result in a loss of minerals (Ca, Fe,
Cu, Mg) which are bound to the polyphosphate and are lost in the
faeces with unhydrolyzed polyphosphate. For this reason, in most of
the toxicological studies cited, particular attention has been paid to
the mineral composition of the carcass and to the possible development
of anaemia.
The experimental results available indicate that such an
action, if it occurs at all, is not significant. Anaemia is not a
characteristic feature of treatment with high dose levels of
polyphosphate and hexametaphosphate had no effect on iron utilization
by rats (Chapman & Campbell, 1957).
The use of polyphosphates for the prevention of scale formation
in lead pipe water systems may lead to excessive lead levels in
drinking-water (Boydens, 1957).
(d) Disodium and tetrasodium phosphate
In the animal body diphosphate is formed from adenosyl
triphosphate (ATP) in many enzymatic reactions. It is either utilized
by entering phosphorolytic reactions, or it is hydrolyzed by an
inorganic diphosphatase to monophosphate (Long, 1961). Ingested
diphosphate is readily converted to monophosphate (Schreier & Nöller,
1955; Mattenheimer, 1958); no diphosphate was found in faeces or urine
of rats treated with diets containing up to 5% tetrasodium
diphosphate. In these experiments diphosphate was almost completely
absorbed by the gut and excreted as monophosphate in the urine.
(e) Calcium and magnesium phosphate tribasic
Calcium phosphates are insoluble in water and constitute the
following series: calcium phosphate (menobasic) which is used as
acidulant and mineral supplement; calcium phosphate (dibasic) is used
as dietary supplement in doses of 1 g orally; calcium phosphate
(tribasic) is used as gastric antacid in doses of 1 g orally; and bone
phosphate. Metabolically they behave as sources of calcium and
phosphate ions. These compounds need not be considered separately from
other monophosphates from the toxicological point of view.
Magnesium phosphates are mostly insoluble in water and form the
following series: magnesium phosphate (monobasic); magnesium phosphate
(dibasic) which is used as laxative: magnesium phosphate (tribasic) is
used as antacid in doses of 1 g orally. Metabolically they behave as
sources of magnesium and phosphate ions. These compounds need not be
considered separately from other monophosphates from the toxicological
point of view.
TOXICOLOGICAL STUDIES
Acute toxicity
(a) Phosphoric acid and its salts
Minimum lethal
Compound Animal Route dose (mg/kg bw) Reference
NaH2PO4 guinea-pig oral > 2000 Eichler, 1950
Na2HPO4 rabbit i.v. infusion 985 - 1075 Eichler, 1950
(b) Disodium and tetrasodium diphosphate
Minimum lethal dose
Animal Route (mg/kg) References
Rabbit i.v. approx. 50 Behrens & Seelkopf, 1932
Rat oral LD50 > 4000 Datta et al., 1962
(Na4P2O7)
(c) Pentasodium triphosphate, sodium polyphosphate (Graham's
sodium polyphosphate)
Approx.
LD50 LD100
Animal Substance Route (mg/kg bw) (mg/kg bw) References
Mouse hexametaphosphate Behrens &
(neutralized Na oral 100 Seelkopf, 1932
salt)
approx. "
Rabbit " i.v. 140
Rat 1/3 Kurrol's salt van Esch et
and 2/3 oral 4000 al. 1957
tetra- and disodium
diphosphates (water i.v. 18 "
soluble, neutral)
(d) Disodium and tetrasodium phosphate
Minimum lethal dose
Animal Route (mg/kg) References
Rabbit i.v. About 50 Behrens & Seelkopf, 1932
Rat oral LD50 (Na4P2O7): > 4000 Datta et al., 1962
Short-term studies
(a) Phosphoric acid and its salts
Rat
There are many reports of short-term studies to determine the
effects of the addition of monophosphates to the diet of rats (House &
Hogan, 1955; Maynard et al., 1957; Selye & Bois, 1956; MacKay &
Oliver, 1935; Behrens & Seelkopf, 1932; McFarlane, 1941; van Esch et
al., 1957; Sanderson, 1959). Pathological effects in the parathyroids,
kidneys and bones have been observed in mature male rats fed a diet
containing an excessively high level (8%) of sodium orthophosphate for
seven months or until the animal succumbed (Saxton & Ellis, 1941).
Histological and histochemical changes in the kidneys have been found
in rats fed for 24 to 72 hours on a diet containing an excess of
inorganic phosphate (10% disodium acid phosphate) (Craig, 1957).
Three groups of 12 rats each were fed diets containing added
dibasic potassium phosphate so that the calcium and phosphorus
concentrations in the experimental diets were as follows:
Diet Calcium % Phosphorus %
Control 0.56 0.42
"normal orthophosphate" 0.47 0.43
"high orthophosphate" 0.50 1.30
The experiment was conducted in three stages, with experimental
observations made when animals had consumed the test diets for 50, 60
and 150 days. No adverse physiological effects were observed
clinically at autopsy or on histological examination. All the data
obtained from this study indicated that there was probably adequate
absorption and utilization of calcium, phosphorus and iron with both
high and normal levels of monophosphate (Dymsza et al., 1959).
Reports of short-term studies do not provide for a
differentiation between the action of the mono-, di- and trisodium or
potassium salts; several authors have used "neutral mixtures" e.g. of
mono- and disodium monophosphates. There is no reason to expect a
specific action on the part of one of these three monophosphates, the
relevant factor being the phosphate content and the acidity of the
food mixture as a whole. On high-dose levels, hypertrophy of the
parathyroid glands has been observed. A more important and more
sensitive criterion for the deleterious action of phosphate overdosage
is the appearance of metastatic calcification in soft tissues,
especially in the kidney, stomach and aorta. Kidney calcification may
be observed in a few weeks or months, depending on the dose level. The
pathology of calcification and necrosis of the tubular epithelium in
the kidneys (nephrocalcinosis) has been studied in detail (MacKay &
Oliver, 1935; McFarlane, 1941; Sanderson, 1959; Fourman, 1959).
It is difficult to indicate a border line between those levels
that do not produce nephrocalcinosis and those that produce early
signs of such changes, because: (1) even on diets to which no
phosphate has been added, rats, in apparently healthy condition, may
have a few isolated areas of renal calcification; (2) the composition
of the diet (amount of calcium, acid-base balance, vitamin D) has an
important influence on the appearance of renal calcification.
There are numerous reports of experimental phosphate-containing
diets that do not produce kidney damage by excessive calcification,
e.g. the Sherman diet (0.47 to 0.51%P) (Lang, 1959; Hahn & Seifen,
1959; van Esch et al., 1957), the diet used by MacKay & Oliver (1935)
(0.62% P) and the commercial "Purina A" diet (0.90% P) (Lang, 1959).
Early calcification has been observed in rats on a Sherman diet
to which 1% of a 2:3 mixture of NaH2PO4 and Na2PHO4 was added,
bringing the P-content to 0.71% (van Esch et al., 1957). Similar
effects were observed with the addition of a phosphate mixture
resulting in a P-content of 0.89% (Hahn & Seifen, 1959), and with
levels of phosphate in the diet corresponding to a P-content varying
from 1.25% to 2.85% (Lang, 1959; MacKay & Oliver, 1935; Eichler, 1950;
McFarlane, 1941; van Esch et al., 1957; Haldi et al., 1939).
In recent experiments (Dymsza et al., 1959), however, a diet to
which K2HPO4 had been added and containing 1.3% P and 0.5% Ca did
not produce nephrocalcinosis in a group of 12 mice within a period of
150 days, although the weight of the kidneys was increased. Also food
and protein efficiency was diminished as compared with animals on the
control diet. These effects may have resulted from the large amount of
salts added to the diet in these experiments.
Guinea-pig
Diets containing 0.9% P and 0.8% Ca or higher levels of phosphate
produced calcification in the soft tissues (House & Hogan, 1955; Hogan
et al., 1950).
(b) Disodium and tetrasodium diphosphate
Rat
In a series of successive experiments (Hahn & Seifen, 1959; Hahn
et al., 1958), Na4P2O7 was added in concentrations of 1.8%, 3% and
5% to a modified Sherman diet and fed to groups of 34-36 young rats
for six months. The studies also included control groups and groups
receiving the same levels of sodium monophosphate. With 3% and 5%
diphosphate diets growth was significantly decreased and at both these
concentrations nephrocalcinosis appeared as the main toxic effect. The
degree of damage to the kidneys was about the same as that observed in
the corresponding monophosphate groups.
With the 1.8% diphosphate and monophosphate diets, normal growth
occurred but a slight yet statistically significant increase in kidney
weight was noted. Microscopic examination revealed kidney
calcification in some of the animals, both in the diphosphate and
monophosphate groups. This was more extensive than the calcification
occasionally found in the control animals. In an additional
experiment, 1.1% of diphosphate and of monophosphate were used (Hahn,
1961). There was a slight growth retardation in the first part of the
experiment. After 39 weeks a slight degree of kidney calcification was
noted and this was the same for both phosphates (Hahn, 1961).
In a recent series of experiments (Datta et al., 1962), Sherman
diets containing 1%, 2.5% and 5% Na4P2O7 were fed for 16 weeks to
groups of 20 male and female rats weighing between 90 and 115 g; a
similar group received a diet containing 5% monophosphate. In the
sodium phosphate groups, growth was normal up to the 2.5% level;
kidney weight was increased at the 2.5% level (females) and above;
kidney function was (concentration test) decreased at the 2.5% level
(males) and above. Kidney damage (calcification, degeneration and
necrosis) was observed in a greater percentage of rats in the 1% group
than in the controls. At the higher concentration of sodium
diphosphate more severe kidney damage occurred and, in addition, some
of the animals had hypertrophy and haemorrhages of the stomach. The
latter abnormality was not found in rats in the 5% monophosphate
group.
(c) Pentasodium triphosphate, sodium polyphosphate (Graham's
sodium polyphosphate)
Rat
Groups of five male rats were fed for a period of one month on
diets containing 0.2%, 2% and 10% sodium hexametaphosphate or 0.2%, 2%
and 10% sodium tripolyphosphate. Control groups were given the
standard diet, or diets with the addition of 10% sodium chloride or 5%
disodium phosphate (Hodge, 1956).
With 10% of either of the polyphosphate preparations and also
with 10% sodium chloride in the diet, growth retardation occurred, but
none of the rats died. Increased kidney weights and tubular necrosis
were, however, observed. With 2% of polyphosphate in the diet, growth
was normal, but in the kidneys inflammatory changes were found which
were different from the tubular necrosis observed in the 10% groups.
With 0.2% of polyphosphate in the diet, normal kidneys were seen. In
another series of experiments (Hahn & Seifen, 1959; Hahn et al., 1958;
Hahn et al., 1956), 3% and 5% of sodium tripolyphosphate (pH 9.5 in 1%
solution) and 1.8%, 3% and 5% of Graham's salt (pH 5) were added to a
modified Sherman diet, which was then fed during 24 weeks to groups of
36 male and 36 female rats. Growth retardation was exhibited by the
rats in the 5% polyphosphate groups. With 3% of either preparation, a
temporary growth inhibition was observed, and with 1.8% of Graham's
salt (male animals) growth was normal. Nephrocalcinosis was observed
in the 3% and 5% groups. It was noted that the degree of damage with
Graham's salt was less than that in control groups treated with the
same concentrations of orthophosphate; with tripolyphosphate, however,
kidney damage was practically identical with that exhibited by the
animals in the orthophosphate group. In the animals on a diet
containing 1.8% Graham's salt, calcification in the kidneys was slight
or absent and the kidney weights were normal (Hahn & Seifen, 1959).
In a further group of experiments (van Esch et al., 1957; van
Genderen, 1958), Kurrol's salt was used in a commercial preparation
consisting of 1/3 Kurrol's salt and 2/3 of a mixture of disodium and
tetrasodium diphosphate (Na2H2P2O7 and Na4P2O7). Kurrol's
salt is practically insoluble in water, but the mixture with
diphosphate can be dissolved and a 1% solution had a pH of 7.6. Groups
of 10 male and 10 female rats were fed for a period of 12 weeks on a
Sherman diet to which 0.5%, 1%, 2.5% and 5% of the preparation had
been added. Normal growth was observed in the groups treated with the
0.5%, 1% and 2.5% concentrations of the polyphosphate mixture, but in
those receiving the 5% concentrations growth retardation was
exhibited. Kidney weights were normal in the 0.5% group, slightly
increased (males significantly) in the 1% group and further increased
in the 2.5% and 5% groups. The histopathological examination revealed
that in the kidneys of the animals of the 5% group definite
nephrocalcinosis had occurred, with extensive damage to the tubular
tissue. Calcification was also observed in other tissues. In the 2.5%
group a less extensive nephrocalcinosis was exhibited, and in the 5%
group isolated areas of calcification with lymphocyte infiltrations
were found. In the 0.5% group kidney structure was normal. The results
obtained with this polyphosphate preparation were practically
identical, qualitatively and quantitatively, with the results of a
similar experiment made with a neutral mixture of NaH2PO4 and
Na2HPO4 carried out at a later date in the same laboratory (Hahn et
al., 1958; Götte, 1953).
In other experiments, groups of 12 male rats were treated with
diets to which 0.9% and 3.5% sodium hexametaphosphate had been added
(corresponding to 0.46% and 1.20% P). Other groups received the
control diet alone (0.4% P and 0.5% Ca), or with addition of potassium
monophosphate. To the experimental diets different amounts of salts
were added to replace cornstarch in order to equalize the levels of
major minerals; this resulted in a rather high salt concentration. The
duration of treatment was up to 150 days. With 3.5% added
hexametaphosphate growth and food and protein efficiency were poorest.
The kidneys of the animals fed the high level of hexametaphosphate
were significantly heavier than those of the control rats. This was
perhaps a manifestation of the high salt load on the kidneys. No
histopathological abnormalities were observed in kidney sections from
animals taken from any of the groups (Dymsza et al., 1959).
Dog
Sodium tripolyphosphate (Na5P3O10) and sodium
hexametaphosphate were fed to one dog each in a dose of 0.1 g/kg per
day for one month; two other dogs received daily doses which increased
from 1.0 g/kg at the beginning to 4.0 g/kg at the end of a five-month
period.
The dog treated with the starting dose of 10 g/kg/day of
hexametaphosphate began to lose weight when the daily dose reached
2.5 g/kg, while the one receiving gradually increasing doses
of tripolyphosphate lost weight only when its diet contained
2.0 g/kg/ day. In other respects (urinalysis, haematology, organ
weights) the animals were normal, with the exception of an enlarged
heart, due to hypertrophy of the left ventricle, in the dog receiving
gradually increasing doses of sodium tripolyphosphate. In addition,
tubular damage to the kidneys was observed in both dogs on the higher
dose regime. In the tissues of the dogs fed 0.1 g/kg/day no changes
were found that could he attributed to the treatment (Hodge, 1956).
(d) Disodium and tetrasodium phosphate
Rat
In a series of successive experiments (Hahn et al., 1958; Hahn &
Seifen, 1959) tetrasodium diphosphate (Na4P2O7) was added in
concentrations of 1.8%, 3% and 5% to a modified Sherman diet and fed
to groups of 34 to 36 young rats for six months. The studies also
included control groups and groups receiving the same levels of
sodium monophosphate. With 3% and 5% diphosphate diets growth was
significantly decreased and at both these concentrations
nephrocalcinosis appeared as the main toxic effect. The degree of
damage to the kidneys was about the same as that observed in the
corresponding monophosphate groups.
With the 1.8% diphosphate and monophosphate diets, normal growth
occurred, but a slight yet statistically significant increase in
kidney weight was noted. Microscopic examination revealed kidney
calcification in some of the animals, both in the diphosphate and
monophosphate groups. This was more extensive than the calcification
occasionally found in the control animals. In an additional
experiment, 1.1% of diphosphate and of monophosphate were used. There
was a slight growth retardation in the first part of the experiment.
After 39 weeks, a slight degree of kidney calcification was noted and
this was the same for both phosphates (Hahn et al., 1958).
In a series of experiments Sherman diets containing 1%, 2.5% and
5% tetrasodium diphosphate (Na4P2O7) were fed for 16 weeks to
groups of 20 male and 20 female rats weighing between 90 and 115 g; a
similar group received a diet containing 5% monophosphate. In the
sodium diphosphate groups, growth was normal up to the 2.5% level;
kidney weight was increased at the 2.5% level (females) and above;
kidney function, as determined by a concentration test, decreased at
the 2.5% level (males) and above. Kidney damage (calcification,
degeneration and necrosis) was observed in a greater percentage of
rats in the 1% group than in the controls. At the higher
concentrations of sodium diphosphate more severe kidney damage
occurred and, in addition, some of the animals had hypertrophy and
haemorrhages of the stomach. The latter abnormality was not found in
rats in the 5% monophosphate group (Datta et al., 1962).
Long-term studies
(a) Phosphoric acid and its salts
Rat
Three successive generations o£ rats were fed diets containing
0.4% and 0.75% of phosphoric acid for 90 weeks. No harmful effects on
growth or reproduction could be observed. No significant differences
were noted in the blood picture in comparison with control rats and
there was no other pathological finding which was attributable to the
diets. There was no acidosis, nor any change in the calcium
metabolism. The dental attrition was somewhat more marked than that in
the control rats (Lang, 1959). No other long-term studies on
monophosphates have been found in the literature.
(b) Disodium and tetrasodium diphosphate
Rat
No specific studies with diphosphates have been made, but in one
series of experiments a mixed preparation was used which consisted of
2/3 Na2H2P2O7 and 1/3 Kurrol's salt (KPO3)n. H2O with n = 400 to
5000. Concentrations of 0.5%, 1% and 5% were added to a Sherman diet
and given to groups of 10 male and 10 female rats. From these animals
a second and third generation were produced, during which the
treatment with phosphates was continued. Growth and fertility and
average life span were normal and the life span was not significantly
reduced up to the 2.5% level. Nephrocalcinosis occurred at the 1%
level and above. At 0.5% no abnormalities were observed that were not
also present in control animals. At none of the concentrations did
tumours appear with higher frequency than in the controls (van Esch et
al., 1957).
(c) Pentasodium triphosphate, sodium polyphosphate (Graham's
sodium polyphosphate)
Rat
To a Sherman diet containing 0.47% P a mixture of 1/3 Kurrol's
salt and 2/3 diphosphate was added in concentrations of 0.5%, 1%, 2.5%
and 5% and fed to groups of 30 male and 10 female rats from weaning to
end of their life span (van Esch et al., 1957). Two successive
generations of offspring were produced on these diets. Significant
growth inhibition was observed in the 5% groups of both first and
second generations. In other groups growth was normal. Fertility was
normal in the 0.5%, 1% and 2.5% groups, but much decreased in the 5%
group. Haematology of the 0.5%, 1% and 2.5% groups showed a decreased
number of erythrocytes in the 2.5% group, second generation only. In
the 0.5% group no kidney damage attributable to the polyphosphate
treatment was observed, but in the groups having higher intakes renal
calcification occurred in a degree increasing with the dose level.
In another series of feeding tests (Hodge, 1960a), diets
containing 0.05%, 0.5% and 5% sodium tripolyphosphate were given for
two years to groups of 50 male and 50 female weanling rats. Only when
5% of polyphosphate was added to the diet was growth reduced; the
reduction was significant in males but slight and delayed in females.
A smaller number of rats survived in the 5% groups than in the other
groups. A low grade of anaemia was sometimes observed in the 5% groups
only. Increased kidney weights were noted in the 5% group;
pathological changes which could be ascribed to treatment were not
observed in the 0.5% and 0.05% groups. In the control group and the
0.5% tripolyphosphate group, reproduction studies were carried out
over three generations involving the production of two litters in each
generation. Reproduction was normal and no changes in the offspring
were observed.
A long-term study (Hodge, 1960b) of the same design was made with
sodium hexametaphosphate also at concentrations of 0.05%, 0.5% and 5%
in the diet. Growth retardation occurred only in the 5% groups.
Mortality was high in all groups but had no relation to the amount of
hexametaphosphate in the diet. Periodic blood examination gave normal
haematological values. Kidney weights were increased in the 5% group
and calcification was present. Rats given the 0.5% diet did not have
significant changes in the kidneys. Reproduction studies for three
generations in the 0.5% group revealed normal performance in every
respect.
(d) Disodium and tetrasodium phosphate
No specific long-term studies with diphosphates have been made,
but in one series of long-term experiments a mixed preparation was
used which consisted of 2/3 disodium and tetrasodium diphosphate
(Na2H2P2O7 and Na4P2O7) and 1/3 Kurrol's salt.* Concentrations
of 0.5%, 1%, 2.5% and 5% were added to a Sherman diet and given to
groups of 10 male and 10 female rats. From these animals a second and
third generation were produced, during which the treatment with
phosphates was continued. Growth and fertility and average life span
were normal and the life span was not significantly reduced up to the
2.5% level. Nephrocalcinosis occurred at the 1% level and above. At
0.5% no abnormalities were observed that were not also present in
control animals. At none of the concentrations did tumours appear with
a higher frequency than in the controls (van Esch et al., 1957).
OBSERVATIONS IN MAN
Studies on 15 students, who drank 2000 to 4000 mg of phosphoric
acid in fruit juices every day for 10 days, and on two males who
received 3900 mg of phosphoric acid every day for 14 days, revealed no
observable change in urine composition indicative of a disturbed
metabolism (Lauersen, 1953). The long-continued daily intake of 5 to
7000 mg of NaH2PO4 (corresponding to 1000 to 1500 mg of P) did not
produce adverse effects (Lang, 1959). Similarly a daily intake of
6000 mg of NaH2PO4 Ê 2H2O was tolerated without difficulty
(Lauersen, 1953).
Comments:
Ingested phosphates from natural sources should be considered
together with that from food additives sources. The usual calculation
for provision of a margin of safety is probably not suitable for food
additives that are also nutrients. The dose levels producing
nephrocalcinosis were not consistent, among the various rat feeding
studies. However, the rat is exquisitely susceptible to calcification
and hydronephrosis upon exposure to acids forming calcium chelates or
complexes. The lowest dose levels that produce nephrocalcinosis
overlap the higher dose levels failing to do so. The lowest level that
produced nephrocalcinosis in the rat (1% P in the diet) is used as the
basis for the evaluation and, by extrapolation based on the daily food
intake of 2800 calories, this gives a dose level of 6600 mg P per day
as the best estimate of the lowest level that might conceivably cause
nephrocalcinosis in man. Nutritional demands to balance Ca:P ratio do
not apply to calcium phosphate itself.
* Kurrol's salt is a polymer of high molecular weight obtained by
fusion of monopotassium monophosphate. The formula is (KPO3)n.H2O,
where n = 400 to 5000.
EVALUATION
Estimate of acceptable total dietary phosphorus load for man
0-70* mg/kg bw.
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