The toxicology of potassium and sodium iodates

TOXICOLOGY

1,

87-96

(1959)

The Toxicology

of Potassium

II.

of

Subacute STEWART

National

Toxicity

H.

Potassium

WEBSTER,

MARY

AND

EDWARD

and Sodium

lodate

E. F.

in

RICE,

Mice BENJAMIN

and

lodates Guinea

Pigs

HIGHMAN,

STOHLMAN

Institute of Arthritis and Metabolic Diseases, National Institutes of Health, United States Public Health Service, Department of Health, Education, and Welfare, Bethesda, Maryland Received

September

17, 1958

Use of potassium or sodium iodate in salt, as a prophylactic agent for endemic goiter, has been praposed by Johnson and Herrington (1927) and more recently by Scrimshaw et al. (1953), Mendez et al. (1953), Murray (19.53)) and by the Endemic Goitre Study Group of the World Health Organization (1953). Acute animal-toxicity studies, carried out from 1865 to 1916 [for bibliography, see Macciotta ( 19 16) 1, furnish little information about the effects of prolonged ingestion of iodates. However, Murray (1953) cited a few subacute tests on rabbits made by Perry and also reported experiments in which NaI03 was administered orally to fourteen rabbits for four to fourteen months without producing any significant pathologic changes. Work on Swiss mice by Webster et al. (1957) has shown that food in the stomach greatly decreased the acute toxic effects of orally administered iodate. The absence of significant changes in most of the animals which were allowed 2 weeks to recover after sublethal doses, made a study of subacute toxicity desirable. EXPERIMENTS

WITH

MICE

Methods Subacute toxic effects of KIOa were determined by administering the iodate to comparable groups of mice in their drinking water in the following concentrations: O.OSs, O.lO%, 0.2570, 0..50%, and 0.75%. A 0.65% KI solution, equivalent in iodine content to 0.84% KIO.?, served 87

88

STEWART

H. WEBSTER,

ET AL.

for comparison, and two control groups received water. All solutions were prepared from distilled water and analytical-grade chemicals. Seventy-six weanling female white Swiss mice, consisting of nineteen sets of four littermates each, were separated into four lots. The first lot of twenty mice, drawn from five litters, was divided among the O.OS%, O.lO%, and 0.25% KIOS groups, and their control group. The mice in each group were housed in separate glass jars, each containing a littermate from the five different litters. Consequently, the littermate composition of each jar was alike. A second lot of twenty mice was similarly divided and housed in four additional jars to increase the number in each group to ten. Two additional lots of mice, drawn from the remaining nine sets in the same manner, were used for the 0.50% and 0.75% KIOa groups, the 0.65% KI group, and their corresponding control groups. Four jars had only four mice each. The animals were bedded on sawdust and were allowed free access to dry Purina Laboratory Chow and drinking water. Water was supplied from inverted glass bottles having glass tubes so designed as to minimize contamination and loss from evaporation and leakage. The bottles were weighed twice weekly to determine liquid consumption and refilled with fresh solutions. The mice were weighed individually at the same time. Three animals in the 0.75% KI03 group died during the first week. The remaining 73 mice survived the experimental period of 15-16 weeks. After 12-13 weeks hematologic studies were made on all mice. During the fifteenth week about half of the animals of each group were given an oral challenge dose of KIOj at about the LDb0 level to assay any increased tolerance or susceptibility. Similar studies were made on an additional group of twenty mice, half of which were kept on drinking water containing 0.25% KIOa for 6 weeks preceding the oral challenge dose of iodate. The remainder received the challenge dose only. Survivors were killed with ether at the end of the experiment for .pathologic study. Autopsies were performed also on all animals that died during the experiment. Tissues saved for microscopic study were fixed in 10% aqueous buffered formalin (pH, 7.0). Results and Conclusions Weight increases for the various groups during the experiment and the calculated intakes of water and iodate are given in Table 1. Although the range in concentration of the iodate solutions was 15: 1, the cor-

body

(1 Calculated

Total KIO, (mg/mouse)

for

day

(g)

of KIO,

104 days

on 104th

as amount

intake

KIO, intake (w/kg/day)

day

Av.

on 3rd

KIO, intake (mg/kg/day)

day

day

Av.

(g)

liquid intake from 1st to 104th day (ml/mouse/day)

on 104th

weight

Av.

weight

WEIGHT

weight gain on 104th (as “/o gain of control)

Av.

of mice

IX

Av.

initial

body

Av.

Number

GAIN

equivalent

-

-

-

3.6

22.5

11.5

10

TABLE

amount

1

196

72

144

of iodine

3.8

358

122

277

3.4

104

22.6

98

11.2

11.3

10

0.10

BY

WHITE

831

292

540

3.2

87

21.6

-

-

-

3.5

22.9

9 11.6

10

used (%)

12.0

73

H,,O only

Solution 0.25

OR IODIDE

KI”,

IODATE.

22.1

10

0.05

OF WATER.

Hz0 only

CONSUMPTION

containing

AND

1292

387

795

2.5

90

21.4

11.2

9

0.50

FEMALE

K'%

MICE

1653

685

756

2.1

88

2 1.3

11.4

6

0.75

KI

2558a

1029a

1944”

3.3

94

22.0

11.4

9

0.65

90

STEWART

H.

WEBSTER,

ET AL.

responding range in total consumption of iodate per mouse was about 8: 1, due to the lower liquid intake of the higher-concentration groups. At the beginning of the experiment the 0.75% KIOa group drank only about 25% as much as the controls, but later the consumption increased to between 60% and 70% of the control group. However, controls and mice given lower concentrations of iodate drank less liquid as they grew larger. As indicated by the iodide mice (Table 1)) a relatively high salt concentration in the drinking water does not greatly influence liquid intake or gain in weight. This was further shown by other mice which received normal saline in their drinking water for 11 weeks and drank as much liquid as those on water and suffered no decrease in growth rate. Accordingly, it seems reasonable to conclude that the restriction of liquid by the mice given the higher iodate concentrations may be due to the bad taste and/or toxic effects of the drinking water. It is likely that the reduced consumption of liquid is accompanied by a decrease in the amount of food ingested or vice versa, which would result in a decreased growth rate. TABLE SUMMARY

OF BLOOD

2

EXAMINATIONS Average

RBC

Grour,

(X

H,O control 0.05% KIO, O.lOo/, KIO, 0.25% KIO, H,O

control KIO, 0.75% KIO, 0.65% KI

0.50%

a These

Hemoglobin

10B/cm)

(ail00 ml)

for: Hematocrit (% packed cells)

WBC (X

lW/cm)

9.87 & 1.06

16.0 f

0.8

50.5 rk 6.1

9.82 f

9.86 -c 1.48 9.28 k 1.34

15.5 iI 2.1 14.9 -+ 1.7

49.5 -c 6.4 47.8 -c 3.1

14.6 e

46.1 k 4.9

9.25 -+ 0.69 8.39 C 0.5Sa

16.6 ? 0.6 16.7 k 1.5

51.2 & 1.6 51.7 2 3.3

19.8 -c 5.7

8.26 t

15.7 2 1.1 16.5 2 0.9

47.4 -c 4.7 51.8 t 4.8

22.7 & 8.0 21.0 -c 5.6

1.34

0.81a

9.28 +- 0.98

values

FOR 73 MICE values

are significantly

lower

than

1.3a

in the corresponding

control

16.4 C 4.5 19.4 IfI 7.8 14.3 2 5.1 16.8 k 7.6

23.1 f

6.9

group.

Statistical tests carried out on the hematologic data (Table 2)) using Student’s t-test (Snedecor, 1946), indicate significantly lower values for the red blood cells or hemoglobin in three of the groups which received the higher concentrations of iodate. Mortality among the 62 mice given an oral challenge dose at approximately the LDc,, value ( 1120 mg/kg KIOS) was about 33% for both

SUBACUTE

TOXICITY

OF POTASSIUM

IODATE

91

control and iodate animals. A slightly lower mortality among the 0.50% and 0.75% KIOa groups suggested that high dosages may slightly increase tolerance toward iodate. No evidence of increased susceptibility to this compound was observed. In the 0.75% KIOa group, the three mice dying within the first week showed weight loss and emaciation, presumably due to severe voluntary water restriction. In addition, the mice killed by the challenge dose of iodate exhibited the usual gross and microscopic changes accompanying acute oral intoxication (Webster et al., 1957). However, at the end of the experimental period the mice which received iodate only in the drinking water appeared to be in excellent physical condition and no gross abnormalities attributable to iodate were found at autopsy. In only three of twenty-four iodate animals was the pH of the stomach contents increased above 4, and none showed histologic alterations in the gastric mucosa. Microscopic studies showed hemosiderin deposits in the renal convoluted tubules in nearly all mice which received 0.507, KIOa for 16 weeks. Similar changes were seen in only a few mice which received distilled water, iodide, or lower concentrations of iodate. The deposition of hemosiderin, in addition to the reduced blood values (Table 2) is strong evidence of increased hemolysis due to the iodate. No other significant changes were found. Our studies show that mice can tolerate much larger amounts of iodate if it is administered in the drinking water than if it is given in one large dose by stomach tube. In the earlier study (Webster et al., 1957), the oral LDso value for a single dose of iodate administered by stomach tube was found to be 531 mg/kg for mice fasted on screens and 1177 mg/kg for nonfasted mice. In the present study, the 0.10% KIOa group consumed a maximal amount of 277 mg/kg per day, and the 0.25% KIOs group reached a maximal amount of 540 mgjkg per day during the first few days of the experiment. However, the maximal 24-hour consumption of KIO:<, 23.8 mg or 1256 mg/kg per day, was reached in the 0.75% KIOa group by two animals on the thirty-first day of the experiment. During a 2-week period, their average consumption was 1231 mg/kg per day. These results show that iodate can be consumed by mice at extremely high dosage levels for several months with only minimal toxic effects, provided that this compound is ingested in small doses with food in the stomach.

92

STEWART

EXPERIMENTS

H.

WEBSTER,

WITH

ET AL.

GUINEA

PIGS

Methods In another similar study on the subacute toxicity of KIOa, young, colored guinea pigs of the Beltsville strain were divided into three groups. No littermates were available, but each group was nearly equal in total weight and included six males and six females. One group was given 0.05% KIOa in the drinking water, a second 0.50% KIOa, and a third, the control group, was given distilled water. Each animal was housed in a separate cage and fed dry Purina Rabbit Chow ad libitum supplemented by kale six times a week. Consumption of liquid and weight of animals were determined as described above. Because the 0.50% KI03 group drank so little, the iodate concentration was reduced to 0.25% after the fourteenth day. Blood samples were taken from two males and two females in each group 5-6 days before the end of the 4-week experimental period and red cell count, hematocrit, hemoglobin, white cell count, and differential counts were determined. The animals were killed with ether and given a postmortem examination. The eyes of each one were examined microscopically, while other organs were studied in only a few animals in each group. Results and C,onclusions As shown in Table 3, marked water restriction and smaller gain in weight took place in the 0.507&0.25~ KIOs group. Unlike the mice, the consumption of liquid by the guinea pigs, particularly by the controls, increased as the animals became larger. Although the guinea pigs were over twenty times as heavy as the mice, the control groups of each species consumed nearly the same amount of water per kilogram, averaging about 180 ml/kg per day. In addition, however, the guinea pigs received a large supplement of water from the kale. Due to the relatively greater voluntary restriction of liquid by the guinea pigs, the 0.05% KI03 group consumed less iodate, expressed in milligrams per kilogram, than the 0.05% KIOa mice in the previous experiment. However, the 0..507&-0.25% KIOs guinea pigs consumed approximately the same amount of iodate per kilogram as the 0.10% KIOa mice. The blood examinations failed to show any striking changes attributable to the iodate. All animals remained in good physical condition during

SUBACUTE

TOXICITY

OF POTASSIUM

93

IODATE

the 4-week period. No gross changes were observed on postmortem examination and no retinal degeneration (Highman et aE., 19.55) or other significant histologic changes were noted. The pH of the stomach contents of the animals given iodate only in the drinking water varied between 2 and 4 and averaged 2.3. The controls had the same limits and averaged 3.0. TABLE GAIN

IN WEIGHT

AND CONSUMPTION

3

OF WATER

AND IODATE Solution KIO, (0.05%)

Es,0 anly

Number

of animals

Sex Av. Av. Av.

initial

body

weight

final

weight

(kg)

weight gain on 28th (as 70 gain of control)

(kg)

BY 36 GUINEA

PIGS

used KIO, (OSO-0.25%)

6

6

6

6

6

8 0.23

0

0 0.20

6

0

0.22

6 0.24

6

0.25

0.23

0.45

0.39

0.45

0.37

0.37

0.35

day

-

95

100

55

71

30

44

24

14

12

72

52

41

22

20

-

81

78

30

32

-

82

56

292

261

-

59

56

143

145

-

662

540

1708

1525

-

Av.

initial liquid intake (ml/day) 39 Av. final liquid intake 77 (ml/day) Av. total liquid intake in 28 days (as % intake of controls) Av.

initial

KIO,

b&g/day) Av. final KIO, h-@Wday) Total KIO, (mg/animal)

intake intake

intake

for

28 days

In the 0.05% KIOa group, the maximal daily consumption of iodate was about 120 mg/kg, much less than for the 0.05% KIOa group of mice. In the O.SO%-0.25% KIOa group, however, maximal values of guinea pigs as high as 485 mg/kg per day were attained during a S-day period. Exact determinations of the oral LD.50 value for this species have not been made, but it is known (Webster, 1954, unpublished) to be less than 400 mg/kg for fasted animals. It is evident, therefore, that with guinea pigs as well as with mice, divided doses of iodate allow the animals to consume relatively large amounts of the drug without producing toxic symptoms.

94

STEWART

GENERAL

H.

WEBSTER,

ET AL.

DISCUSSION

The use of dilute solutions of KI03 for drinking water is a convenient way of administering the drug to rodents. Since animals were observed to eat and drink frequently, good mixing of food and water is insured. Presumably more iodate solution would have been consumed by the guinea pigs if the kale had been replaced by ascorbic acid. However, the danger of the iodate (an oxidizing agent) reacting with ascorbic acid (a strong reducing agent) made this plan undesirable. Previous work (Webster et al., 1957 ; Webster, 1954, unpublished) has shown that the pH of the gastric contents of mice and guinea pigs is frequently increased from 2-4 to 5-7 in animals showing toxic symptoms after oral administration of iodate. Maintenance of normal pH values and absence of changes in gastric mucosa in the experimental animals indicate their ability to tolerate the drug at the dosage levels used. Oral LD50 values for fasted mice have been determined earlier with sodium and potassium iodates (Webster et al., 1957). When expressed as millimoles per kilogram, the values for the two compounds are nearly identical. Since there was no reason to believe that a difference in behavior would be shown by the two iodates in the present study, only the potassium compound was used. The rabbits used in Murray’s work (1953) received doses of NaI03 twice weekly which averaged 0.286 mg/kg per day, or 0.309 mg/kg per day if calculated at KI03. Our dosages for guinea pigs were 150 to 1500 times greater. With our mice, dosages up to 900 times that used by Murray were without demonstrable toxic effects over a four-month period. During this time these mice received from 60 to 160 times the 1.5 mg/kg iodine dosage recommended as the daily nutrient allowance for mice (Albritton, 1954). To receive the same dosage as that given to mice, a 70-kg human being would have to ingest S-20 g of KI03 in a day. These amounts are 14,000 to 56,000 times as much as the daily requirement of iodine for man (Curtis, 1951). The magnitude of the oral LDsO value for KI03 (1177 mg/kg for nonfasted white Swiss mice) is less important as a criterion of safety than the size of each individual dose. The mouse and guinea pig are able to handle considerably greater quantities of iodate when the drug is ingested in small quantities in the drinking water with food in the stomach. In a similar manner, man would be expected to consume only small amounts of iodate at any one time, and this would undoubtedly be

SUBACUTE

TOXICITY

OF POTASSIUM

95

IODATE

mixed with food. Accordingly, this marked reduction in toxicity or increase in toleration of KI03, produced by ingestion of small repeated doses, bears on the proposed use of iodate in salt for human consumption. SUMMARY Each of six groups of nine or ten white Swiss mice received as drinking water one of the following solutions for 15-16 weeks: 0.05%, 0.1070, O.2S%, O.SO%, and 0.75% KIO,, and 0.65% KI. Two similar control groups received water. During the fifteenth week an oral challenge dose of KIO,, at approximately the LD,, value, was given by stomach tube to about half of the animals. Mortality data showed no significant change in iodate tolerance. Except for three mice in the 0.75% KIO, group that died during the first week, all mice that had received iodate only in the drinking water appeared healthy and showed no toxic symptoms at the end of the experiment. However, hematologic and pathologic studies indicated increased hemolysis among the 0.25% KIO, and higher concentration groups. No significant pathologic changes were found except for some hemosiderin deposition, attributable to hemolysis by iodate, in the renal convoluted tubules of a few in the 0.25% KIO, group and in nearly all mice in the 0.50% and 0.75% KIO., groups. The KI mice showed no significant changes attributable to this compound. Similar subacute toxicity experiments were carried out for 4 weeks on 36 guinea pigs. One group received 0.05% KIO, in the drinking water, a second received 0.50%-0.25% KIO,, and a third received only water. Both iodate groups remained in apparent good health and showed no significant alterations in the blood picture and no gross or microscopic changes attributable to iodate. The daily consumption of KIO, in the drinking water by some mice and guinea pigs at times exceeded the estimated oral LD,o values for single doses of iodate given by stomach tube. This indicates a marked increase in toleration of iodate when given in divided, small doses with food in the stomach and bears on the proposed use of KIO,, in iodating salt for culinary purposes. REFERENCES E. C., Ed. Saunders, Philadelphia. CURTIS, G. M. (1951).

ALBRITTON,

40,

(1954). Iodine

Standard in the

Values atomic

in Nutrition age.

J. Am.

and Pharm.

p, 69.

Metabolism, Assoc.,

Sci.

Ed.

479-487.

ENDEMIC

Study-group 293-309.

GOITRE STUDY on endemic

GROUP OF THE WORLD HEALTH goitre-Final report. Bull. World

ORGANIZATION (1953). Health Organization 9,

B., WEBSTER, S. H., and RICE, M. E. (1955). Degeneration of retina and gastric parietal cells and other pathologic changes following administration of iodates. Federation Proc. 14, 572. JOHNSON, A. H., and HERRINGTON, B. L. (1927). Factors influencing the loss of iodine from iodized salt. J. Agr. Research 35, 167-183.

HIGHMAN,

96

STEWART

H. WEBSTER,

ET AL.

C. (1916). Ricerche intorno al comportamento nell’organismo animale degli iodati alcalini ed alle loro azione tossiche. Arch. jarmacol. sper. 22, 3-38. MENDEZ, J., CABFZAS,A., CASTILLO, F., and SCRIMSHAW, N. S. (1953). Effect of administration of potassium iodate, potassium iodide and placebo tablets on endemic goiter and protein bound nitrogen levels in school children. Federation Proc. 12, 423-424. MURRAY, M. M. (1953). The effects of administration of sodium iodate to man and animals. Bull. World Health Organization 9, 211-216. SCRIMSHAW, N. S., CABEZAS, A., CASTILLO, F., and MENDEZ, J. (1953). Effect of potassium iodate on endemic goitre and protein-bound iodine levels in school children. Lancet 266, 166-168. SNEDECOR, G. W. (1946). Statistical Methods Applied to Experiments in Agriczrlture and Biology, 4th ed., pp. 62-68. Iowa State College Press, Ames, Iowa. WEBSTER,S. H., RICE, M. E., HIGHMAN, B., and VON OETTINGEN,W. F. (1957). The toxicology of potassium and sodium iodates: Acute toxicity in mice. 1. Phaumacol. MAC~IOTTA,

Ezptl.

Thevap.

120, 171-178.