209. Phosphoric acid, phosphates and polyphosphates (FAO Nutrition Meetings Report Series 48a)

FAO Nutrition Meetings
Report Series No. 48A
WHO/FOOD ADD/70.39

TOXICOLOGICAL EVALUATION OF SOME
EXTRACTION SOLVENTS AND CERTAIN
OTHER SUBSTANCES

The content of this document is the
result of the deliberations of the Joint
FAO/WHO Expert Committee on Food Additives
which met in Geneva, 24 June -2 July 1970¹

Food and Agriculture Organization of the United Nations
World Health Organization

¹ Fourteenth report of the Joint FAO/WHO Expert Committee on Food
Additives, FAO Nutrition Meetings Report Series in press; Wld Hlth
Org. techn. Rep. Ser., in press.

PHOSPHORIC ACID, PHOSPHATES AND POLYPHOSPHATES

This monograph contains a re-evaluation of the data on phosphoric
acid and phosphates. It includes the substances listed below for which
specifications for identity and purity have been issued as indicated:

Phosphoric acidi¹)
Monosodium monophosphate²)
Disodium monophosphate²)
Trisodium monophosphate²)
Monopotassium monophosphate²)
Dipotassium monophosphate²
Tripotassium monophosphate²)
Monocalcimn monophosphate³)
Dicalcium monophosphate⁴)
Tricalcium monophosphate⁴)
Monomagnesium monophosphate⁴)
Dimagnesium monophosphate⁴)
Trimagnesium monophosphate⁴)
Disodium diphosphate²
Tetrasodium diphosphate²)
Pentasodium triphosphate²)
Sodium polyphosphate²)

¹⁾Specifications for Identity and Purity of Food Additives, Vol. 1,
Rome FAO, 1962

²⁾FAO Nutrition Meetings Report Series, No. 35; Wld Hlth Org.
techn. Rep. Ser., 1964, 281

³⁾FAO Nutrition Meetings Report Series, No. 40; Wld Hlth Org.
techn. Rep.Ser., 1966, 339

⁴⁾FAO Nutrition Meetings Report Serin, No. 46B; WHO/Food Add./70.37

PHOSPHORIC ACID AND ITS SALTS

Biological Data

Biochemical aspects

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 determinations. Doses
of 2 to 4 g of phosphate act as weak saline 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 feed additives,
behave differently from the sodium salts and are therefore dealt with
together.

Acute toxicity

Compound Animal Route Minimum lethal dose Reference
mg/kg body-weight

NaH₂PO₄ guinea-pig oral >2000 Eichler, 1950

Na₂HPO₄ rabbit i.v. 985 - 1075 Eichler, 1950
infusion

Short-term studies

Rat. There are many reports of short-term studies to determine
the effects of the addition of monophosphates to the diet of rats
(House and Hogan, 1955; Maynard et al., 1957; Selye and Bois, 1956;
MacKay and Oliver, 1935; Behrens and 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
and 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 and
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 - 0.51%P) (Lang, 1959; Hahn and Seifen,
1959; van Esch et al, 1957), the diet used by MacKay and 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 and 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 and 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
130 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
and Hogan, 1955; Hogan et al., 1950).

Man. Studies on 15 students, who drank 2000-4000 mg of
phosphoric acid in fruit juices every day far 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 5-7000 mg of NaH₂PO₄ (corresponding to 1000-1500 mg of P) did not
produce adverse effects (Lang, 1959). Similarly a daily intake of 6000
mg of NaH2PO4 2H2O as tolerated without difficulty (Lauersen, 1953).

Long-term studies

Rat. Three successive, generations of 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.

DISODIUM DIPHOSPHATE, TETRA SODIUM DIPHOSPHATE

Biological data

Biochemical aspects

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.

Acute toxicity

Animal Route Minimum lethal dose Reference
(mg/kg body weight)

Rabbit i.v. approx. 50 Behrens and Seelkopf,
1932

Rat oral LD₅₀ >4000 Datta et al., 1962
(Na₄P₂O₇)

Short-term studies

Rat. In a series of successive experiments (Hahn and 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 6 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.

Long-term studies

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 = 400-5000. 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).

PENTASODIUM TRIPHOSPHATE, SODIUM POLYPHOSPHATE (Graham's
Sodium polyphosphate)

Biological Data

Biochemical aspects

Several studies indicate that polyphosphates can be hydrolyzed
in vivo by enzymes with the formation of monophosphates. The
localisation of different polyphosphates in the nuclei of animal cells
has been demonstrated (Grossmann and Lang, 1962). Injected
hexameteaphosphate 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 (Gotte, 1953). When
administered parenterally a small part of these products may escape in
the urine as oligophosphates (Gosselin et al., 1952; Gotte, 1953). The
higher polyphosphates are probably not absorbed 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 (Gotte, 1953). With Graham's salt and
Kurrol's salt, 10-30% 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 and 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 and 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).

Acute toxicity

LD₅₀ Approx.LD₁₀₀
Animal Sustance Route (mg/kg body (mg/kg body Reference
weight) weight)

mouse hexametaphosphate oral > 100 Behrens and
(neutralized Na salt) Seelkopf,1932

rabbit " i.v. approx. 140 "

rat 1/3 Kurrol's salt and oral 4000 van Esch et
2/3 tetra- and i.v. 18 al. 1957
disodium diphosphates "
(water soluble,
neutral)

Short-term studies

Rat. Groups of 5 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 and 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 identifical 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 ware normal (Hahn and 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; Gotte, 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 5 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 4.0
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 be attributed to the treatment (Hodge, 1956).

Long-term studies

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 rate 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 57 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 2 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.

Comments

The main conclusion from the data on mono- and diphosphates is
that kidney damage is the most sensitive criterion of its toxic
action. This damage is of the general type of nephrocalcinosis. From a
consideration of the complete experimental evidence, it can be
estimated that diets containing 1% P or more may be nephrocalcinogenic
in rats. Phosphoric acid does not differ from any other acid used as
food additive in carrying any special hazard regarding caries
formation in teeth while its phosphate moiety contributes in a normal
way to the total dietary phosphate load.

At higher concentrations in the diet and in acute experiments, an
additional toxic action of diphosphate has been noted which is
probably mainly due to the hydrolysis and resulting acidification
occurring in the intestinal tract. This effect, however, is not
relevant to the evaluation of ADI's where the more sensitive criterion
of kidney damage is used. Undesirable acute effects from the
hydrolysis of diphosphate in the stomach are not likely to occur in
the concentrations that are at present used in food products, since
the resulting concentrations in the final product as consumed are much
below the concentration that produced such effects in the animal
experiments. Since the nephrotoxic action of diphosphate is no greater
than that of monophosphate, there is no basis for any estimate of
ADI's different from that for phosphoric acid or monophosphates.

Polyphosphates are not absorbed as such to any significant
extent, but only in the form of monophosphates to which they are
broken down in the intestine. The biological effects of ingested
polyphosphate are, therefore, determined by the amount of
monophosphate formed and absorbed. Since the extent of hydrolysis of
polyphosphates in the intestine is difficult to predict, the safest
course is to assume conversion to monophosphate is complete. Thus,
for the purposes of toxicological evaluation, polyphosphates may be
considered equivalent to monophosphates.

Since nearly every food normally contains phosphates, it is
impossible to indicate ADI's of these compounds as food additives
without regard to the phosphate intake from food itself. For this
reason, ADI's are given as total daily intakes both from food and from
food additives. Excessively high phosphorus levels in the total diet,
adverse alterations in the dietary numeral balance (i.e. Ca/P ratio),
or an appreciable increase in the total mineral content of the diet as
a whole should be avoided. There is ample evidence to support the
safety of the addition of small quantities of phosphates to food.
Recent investigations have shown that greater attention should be paid
to the contribution to the daily phosphate load from drinking water as
a result of the general rise in phosphate pollution of water
resources.

Evaluation

It appears rational to treat ingested phosphates from all natural
and food additive sources as a single entity. The dose levels
producing nephrocalcinosis were not consistent among the various rat
feeding studies.

The lowest dose levels that produce nephrocalcinosis overlap the
higher dose levels failing to do so. The usual calculation is probably
not suitable for food additives that are also nutrients. 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 2 800 calories, this gives a dose level of 6
600 mg P per day as the best estimate of the lowest level that might
conceivably cause nephrocalcinosis in man.

Level causing no significant toxicological effect in the rat

0.75% (= 7 500 ppm) in the diet equivalent to 375 mg/kg body weight of
P per day.

Estimate of acceptable total dietary Phosphorus intakes for man
(from phosphate additives and natural amounts in food)

mg/kg body weight P

Unconditional acceptance 0-30
Conditional acceptance* 30-70

Since acceptable levels of phosphate intake depend on the amount
of calcium in the diet, no uniform unconditional or conditional zones
of acceptance can be applied to countries having widely divergent
levels of dietary calcium. The unconditional acceptance zone may be
regarded as suitable for communities with a low calcium intake and the
conditional acceptance zone for those with a high calcium intake in
the normal diet.

REFERENCES

Anon (1968a) Lancet, 1, 1187

Anon (1968b) Brit. med. J., 1, 268

Behrens, B. & Seelkopf K. (1932) Arch. exp. Path., 169, 238

Bonting, S. L. & Jansen, B. C. (1956)Voeding, 17, 137

Buydens. M. R. (1957) Bull. Acad. Roy. Med. Bulg., 22, 293

Chapman, D. G. & Campbell, J. A. (1957) Brit. J. Nutr., 11, 127

Craig, J. M. (1957) Amer. J. Path., 33, 621

Datta, P. K. et al. (1962) J. Sci. Food Agric., 13, 556

Dymsza, H. A., Reussner, G. Jr. & Thiessen, R. Jr. (1959) J. Nutr.,
69, 419

Ebel, J. P. (1958) Ann. Nutr. Alim., 12, 57

Eichler, O. (1950) Handbuch der experimentellen Pharmakologie. Bd 10,
Berlin, 363

van Esch, G. J. et al. (1957) Arzneimittel-Forsch., 7, 172

FAO/WHO (1962) FAO Nutrition Meetings Report Series, No. 31; Wld
Hlth Org. techn. Rep. Ser., 228

FAO/WHO (1964) FAO Nutrition Meetings Report Series No. 35; techn.
Rep. Ser., 281

Fourman, J. (1959) Brit. J. exp. Path., 40, 464

van Genderen, H. (1958) in Kondensierte Phosphate in Lebensmitteln,
Berlin, Springer

van Genderen, H. (1961) Z. Ernahrungsw. Suppl. 1, 32

Gosselin, R. E. et al. (1952) J. Pharmacol. Ther., 106, 180

Gotte, H. (1953) Z. Naturforsch., 86, 173

Grossmann, D. & Lang K. (1962) Biochem. Z. 336, 351

Hahn, F., Jacobi, H. & Rummel, W. (1956) Naturwissenschaften, 43,
539

Hahn, F., Jacobi, H. & Seifen, E. (1958) Arzneimittel-Forsch., 8,
286

Hahn, F. & Seifen, E. (1959) Arzneimittel-Forsch., 9, 501

Hahn, F. (1961) Z. Ernahrungsw. Suppl. 1, 55

Haldi, J. et al. (1939) J. Nutr., 18, 399

Hodge, H. C. (1956) Short-term oral toxicity tests of condensed
phosphates in rats and dogs Unpublished report

Hodge, H. C. (1960a) Chronic oral toxicity studies in rats of sodium
tripolyphosphate Unpublished report

Hodge, H.C. (1960b) Chronic oral toxicity studies in rats of sodium
hexametaphosphate Unpublished report

Hogan, A.G., Regan, W. O. & House, W. B. (1950) J. Nutr., 41, 203

House, W.B. & Hogan, A. G. (1955) J. Nutr. 55 507

Lang, K. ef al. (1955) Biochem. Z., 327, 118

Lang, K. (1958) in: Kondensierte Phosphate in Lebensmitteln, Berlin,
Springer

Lang, K. (1959) Z. Lebensmitt-Untersuch. 110, 450

Lauersen, F. (1953) Z. Lebensmitt-Untersuch., 96, 418

Long, C. ed. (1961) Biochemists' Handbook, London E. & F. N. Spon
Ltd., 251

MacKay, E.M. & Oliver, J. (1935) J. exp Med., 11 319

Mattenheimer, H. (1958) in: Kondensierte Phosphate in Lebensmitteln,
Berlin, Springer

Maynard, L. A. et al. (1957) J. Nutr., 64, 85

McElroy, W. D. & Glass, B., eds. (1952) Phosphorus metabolism
symposium, Baltimore, John Hopkins Press, vol. 2

McFarlane, D. (1941) J. Path. Bact., 52, 17

Sanderson, P. H. (1959) Clin. Sci., 18, 67

Saxton, J. A. Jr. & Ellis, G. M. (1941) Amer. J. Path., 17, 590

Schreier, K. & Noller, H. G. (1955) Naunyn-Schmiedeberg's Arch. exp.
Path. Pharmak., 227, 199

Selye, H. & Bois, P. (1956) Amer. J. Physiol., 187, 41

Sherman, H. C. (1947) Calcium and phosphorus in food and nutrition,
New York, Columbia University Press

    See Also:
       Toxicological Abbreviations