Bromate

Health Effects

Toxicokinetics

Fujii et al.²⁹ studied the absorption, degradation and excretion of bromate given orally as potassium bromate. In a preliminary study, male Wistar rats were given an aqueous solution of potassium bromate (dose 50 mg/mL as bromate) by gavage. Urine and faeces were collected for 24 hours, and bromate and bromide were determined. The animals were then sacrificed, and bromate and bromide were determined in the plasma, red blood cells, spleen, kidney, pancreas, stomach and small intestine. No bromate was detected in any tissues, although substantial amounts were found in urine (detection limits 2.5 µg/mL in urine and plasma and 5.0 µg/g in tissues). Bromide was found in significant amounts, up to six times control values (p < 0.01), in treated rats in the urine, red blood cells, plasma, stomach, kidney, small intestine and pancreas (in descending order).

A single dose of aqueous potassium bromate (100 mg/kg) was administered orally to groups of four Wistar rats. Animals were sacrificed after 15 minutes, 30 minutes, one hour, two hours, four hours or eight hours, and bromate was measured in stomach, small intestine, plasma and urine in the bladder. Bromate disappeared gradually from the stomach and reached a peak in the small intestine after 30 minutes, then decreased rapidly, reaching an undetectable level within four hours. The plasma concentration was at a maximum after 15 minutes (approx. 4 µg/mL), decreasing rapidly until it was no longer detectable after two hours. Bromate was at a peak after one hour in urine and then decreased rapidly; no urinary excretion was detected after four hours.²⁹ Groups of four male Wistar rats were administered an aqueous solution of potassium bromate by oral gav-age at doses of 0, 0.625, 1.25, 2.5, 5, 10, 20, 40, 60, 80 or 100 mg/kg bw, and bromate and bromide were determined in the urine in the 24 hours following dosing. No bromate was detected in urine of rats who received 2.5 mg/kg bw or less. At higher dose levels, bromate excretion was observed in increasing amounts in proportion to the dose. The excretion of bromide parallelled that of controls up to the 5 mg/kg bw dose. The excretion of bromide also increased in rats that received potassium bromate at 10 mg/kg bw or more.²⁹ Bromate is therefore rapidly absorbed from the gastrointestinal tract, partially converted to bromide in the tissues and excreted rapidly. As unchanged bromate could be determined in urine at doses of 5 mg/kg bw and above, it must come into contact with renal tissues at this or higher dose levels.^1,29 To understand the transformation of bromate into bromide, various isolated tissues and organs (liver, kidney, spleen, stomach, small intestine, plasma, red blood cells, saliva and stomach tissues) were incubated with bromate (10 ppm). All tissues except saliva and plasma degraded bromate to bromide with >84% efficiency. SH compounds, including cysteine and glutathione (GSH), were shown to be responsible at least in part for the breakdown of potassium bromate and the simultaneous formation of bromide ion. GSH had the highest degradative action and plays a major role in the reduction of bromate.³⁰

Acute and Short-term Exposure

Bromate is a highly toxic substance that has caused irreversible renal failure,³¹ deafness^32-34 and death³³ subsequent to accidental poisoning. A case report indicated that a single oral dose of sodium bromate in adults (14 g/person) can cause vomiting, epigastralgia, watery diarrhoea and anuria within 30 minutes and deafness within 12 hours.³⁵ Bromate intoxication commonly occurs in hairdressers, as many permanent wave neutralizers still contain a 2% potassium bromate or a 10% sodium bromate solution. Serious poisoning in children has been reported subsequent to ingestion of 2-4 ounces of a 2% solution of potassium bromate (equal to 1.2-2.4 g of potassium bromate).³³ Oral lethal doses for adults are reported to be between 5 and 50 mg/kg bw.³⁶ Potassium bromate is more toxic than sodium bromate.³²

Mack³⁷ reviewed the reported cases of bromate poisoning and found that acute toxic effects usually manifest within one hour of ingestion with gastrointestinal symptoms, including nausea, vomiting, abdominal pain and diarrhoea. This is followed by central nervous system depression, varying from lethargy to coma. Both these conditions are reversible.

Potassium bromate administered orally and intraperitoneally to mice gave LD₅₀s (as bromate) of 289-471 and 177 mg/kg bw, respectively.³⁸ In another study, rats, mice and hamsters were administered potassium bromate by gavage, resulting in LD₅₀s of 400-495 mg/kg bw, 280-355 mg/kg bw and 388-460 mg/kg bw, respectively.¹ In a study in which potassium bromate doses of 250-4000 mg/L were administered in drinking water to male and female B6C3F₁ mice (10 per sex per dose) for a period of 10 weeks, no lethal or histopathological effects occurred at doses below 1000 mg/L that might be associated with the uptake of potassium bromate.¹ In a 13-week study, potassium bromate was administered to groups of F344 rats (10 per sex per group) in water at concentrations of 0, 150, 300, 600 or 1250 mg/L. Doses of 2500, 5000 and 10 000 mg/L were also attempted; however, they were unpalatable. All rats exposed to 1250 mg/L died within seven weeks, and the remaining animals survived for 13 weeks. Significant inhibition of body weight gain was seen in males dosed at 600 and 1250 mg/L. A significant increase in levels of glutamate oxaloacetate transaminase, glutamate pyruvate transami-nase, lactate dehydrogenase, alkaline phosphatase, blood urea nitrogen, serum sodium and cholinesterase was observed in both males and females given 600 mg/L. Droplets were observed in the cytoplasm of the proximal tubular epithelium in treated males (no doses were specified). Extensive regenerative changes were reported in the renal tubules. In another study in which groups of five male F344 rats were orally given potassium bromate at 600 mg/L for 12 weeks, the droplets in the renal tubules were found as early as four weeks after the start and decreased to control levels four weeks after treatment ended. From the morphological characteristics, they were identified as eosinophilic bodies rather than hyaline droplets. Full details of recovery were not provided.¹

Carcinogenicity

Groups of 53 male and 53 female F344 rats, 4-6 weeks old, were given drinking water containing potassium bromate at concentrations of 0, 250 or 500 mg/L (calculated by the authors as average potassium bromate doses of 0, 12.5 and 27.7 mg/kg bw per day for males and 0, 12.5 and 25.5 mg/kg bw per day for females) for a period of 110 weeks. Because the highest dose caused a significant reduction in body weight gain in males, the dose was lowered to 400 mg/L at week 60 for male rats. Mean survival time in male rats given 500 mg/L was shorter than that in controls. In females, the survival rates of treated and control rats were comparable. The incidence of renal cell tumours in the control group, low-dose group and high-dose group was determined to be 3/53 (6%), 32/53 (60%) and 46/52 (88%) for males and 0/47 (0%), 28/50 (56%) and 39/49 (80%) for females. Effects were statistically significant (p < 0.001) for all exposed groups. The renal cell tumours were observed in weeks 111, 77 and 14 in control, low-dose and high-dose males, respectively, and in weeks 89 and 85 in low-dose and high-dose females, respectively. Most renal cell tumours were microscopic in size, although some were visible as round, yellowish-white or greyish projections from the renal cortex. Histologically, these tumours were classified as adenocarcinomas and adenomas. The incidence of peritoneal mesotheliomas in males was 6/53 (11%) for the control group, 17/52 (33%) for the low-dose group (p < 0.05) and 28/46 (59%) for the high-dose group (p < 0.001). No peritoneal mesotheliomas were observed in female rats. Potassium bromate was found to be carcinogenic in both male and female rats.³⁹ In order to study carcinogenic effects at low concentrations, six-week-old male F344 rats (20-24 per group) were given potassium bromate in drinking water for a period of 104 weeks at concentrations of 0, 15, 30, 60, 125, 250 or 500 mg/L (average potassium bromate doses were 0, 0.9, 1.7, 3.3, 7.3, 16.0 and 43.4 mg/kg bw per day). Significant decreases in survival period (82.8 ± 11.7 weeks vs. 103.1 ± 3.3 weeks) and body weight gain (330.7 g vs. 398.8 g) were observed in the group administered 500 mg potassium bromate/L when compared with the control group. Statistically significant increases were observed in the incidence of renal cell tumours in rats treated with a dose of 125 mg/L or more ($7.3 mg/kg bw per day). The incidence of renal cell tumours increased significantly in a dose-related manner -- 5/24 (21%; p < 0. 05), 5/20 (25%; p < 0. 05) and 9/20 (45%; p < 0.001) -- in groups given 125, 250 and 500 mg potassium bromate/L, respectively. A significant increase in occurrence of dysplastic foci in kidneys was observed in animals receiving potassium bromate doses of 30 mg/L or more ($1.7 mg/kg bw per day). Follicular adenomas and adenocarcinomas of the thyroid were found in rats treated at 60, 250 and 500 mg/L (p < 0.05). Although peritoneal mesotheliomas were found in rats receiving doses of 30 mg/L or more, these were significant (p < 0.001) only in animals receiving the highest dose.^40,41

Groups of female B6C3F₁ mice (approximately 50 per group) were administered potassium bromate at concentrations of 0, 500 or 1000 mg/L in drinking water for 78 weeks (average dose of 0, 56.5 and 119.8 mg/kg bw per day) followed by tap water for 26 weeks and subsequently killed. No significant increase in the number of tumours was observed macroscopically or microscopically at any site. Body weight increase was markedly reduced in the high-dose group.³⁹ In a review article by Kurokawa et al.,¹ the authors discussed a 1987 study by Kurokawa et al.⁴² in which groups of 27 male mice of B6C3F₁, BDF₁ and CDF₁ strains were given potassium bromate at 750 mg/L in drinking water (intake was in the range of 60-90 mg/kg bw per day for all three strains) for 88 weeks and compared with groups of 15 controls given drinking water only. No significant differences were found in growth rate and survival time between experimental and control animals. The incidence of renal cell tumours, which were histologically identical to those seen in rats, was 3/26, 1/27 and 1/27 in B6C3F₁, BDF₁ and CDF₁ mice, respectively, compared with no incidence in controls (it is noted that the number of animals in the control group was low, and no statistical analysis was presented). Dysplastic foci were found in two of 26 B6C3F₁mice and four of 27 BDF₁ mice, but the incidence was not statistically significant, with dysplastic foci occurring in one of 15 mice in B6C3F₁ and BDF₁ control groups. The authors concluded that potassium bromate induced renal cell tumours in mice. This conclusion was supported by the fact that spontaneous induction of renal cell tumours is historically very low in mice (0.1% or 3/2543 in B6C3F₁ males and 0.08% or 2/2522 in B6C3F₁females) and that the renal tumours observed in mice were identical to those observed in rats. As well, significant increases in the occurrence of adenomas of the small intestine (14/21, p < 0.01) in CDF₁ mice and adenomas of the liver (7/26, p < 0.05) in B6C3F₁ mice were also observed.

Kurokawa et al.¹ discussed a study by Takamura et al.⁴³ that examined species differences in the carcinogenicity of potassium bromate. Groups of 20 male Syrian golden hamsters were administered potassium bromate in drinking water at 0, 125, 250, 500 or 2000 mg/L for a period of 89 weeks.⁴³ No difference was noted in survival times. The mean final body weights of animals treated with 2000 mg potassium bromate/L were significantly reduced, and the mean absolute and relative kidney weights were significantly higher in animals that received 2000 or 250 mg/L than in controls. Renal adenomas were developed in one, two and four hamsters in groups given 250, 500 and 2000 mg/L, respectively, and dysplastic foci were also seen. No renal cell tumours were found in control animals (no statistical analyses were presented). The structural and cellular morphological characteristics of renal cell tumours and dysplastic foci were quite similar to those observed in rats. The spontaneous development of renal cell tumours in hamsters was noted to be extremely low in historical controls from other laboratories, giving some limited support to the hypothesis that the observed lesions, although of low incidence, were induced by potassium bromate.¹ In order to better understand the mechanisms underlying the carcinogenicity and organ specificity of potassium bromate, the promoting effects of this compound were tested using N-ethyl-N-hydroxyethylnitrosamine (EHEN), a potent initiator. In this study, groups of seven-week-old male Fischer 344 rats were given drinking water as 1) distilled water alone for 26 weeks (group 1); 2) distilled water containing EHEN at 500 or 1000 mg/L for two weeks followed by distilled water for 24 weeks (groups 2 and 3); 3) distilled water containing EHEN at 500 or 1000 mg/L for two weeks followed by distilled water containing potassium bromate (99.5% pure) at 500 mg/L for 24 weeks (groups 4 and 5); or 4) distilled water for two weeks followed by distilled water containing potassium bromate at 500 mg/L for 24 weeks (group 6). All animals were killed at the end of 26 weeks. Significant increases in the number of renal tumours (p < 0.05) and dysplastic foci (p < 0.01) were found in animals administered potassium bromate following initiation with EHEN (groups 4 and 5), compared with the animals administered EHEN only (groups 2 and 3), potassium bromate only (group 6) or controls (group 1) (there were no tumours in the latter two). This demonstrates some promoting activity of potassium bromate on kidney lesion development. The incidences of renal cell tumours were as follows: group 1 (controls), 0/19; group 2, 9/22 (41%); group 3, 4/23 (17%); group 4, 9/19 (47%); group 5, 10/20 (50%); and group 6, 0/20. No tumours other than renal tumours were found in these animals.⁴⁴ Potassium bromate showed no initiating action in this test. A follow-up study to determine whether a threshold level of potassium bromate treatment exists for the enhancement of renal tumorigenesis was undertaken, still using EHEN as the initiator.⁴⁵ Groups of six-week-old F344 rats (15 per sex) were treated with 1) EHEN for the first two weeks and then potassium bromate (at concentrations of 15, 30, 60, 125, 250 or 500 mg/L) for the subsequent 24 weeks; 2) EHEN for the first two weeks and then distilled water for the subsequent 24 weeks; or 3) distilled water for the first two weeks and then potassium bromate (500 mg/L) for the subsequent 24 weeks. Results confirmed those found previously; no dysplastic foci or tumours were observed with controls (distilled water only) or potassium bromate only. A non-significant increase was seen in the EHEN group and in the EHEN plus 15 mg potassium bromate/L group. Significant increases were observed in all other groups (p < 0.05 at 30 mg potassium bromate/L; p < 0.01 at 60 mg/L or more). This appeared to indicate a threshold level between 15 and 30 mg/L for promotion of renal tumori-genesis under the conditions of this experiment.

In a more recent study,⁴⁶ levels of 8-hydroxydeoxy-guanosine (8-OH-dG) -- a substance formed following the damage of DNA by oxygen radical-forming compounds -- and cumulative replicating fractions (CRFs) were measured in the kidneys and livers of F344 rats receiving a single gavage dose of 100, 200 or 400 mg potassium bromate/kg bw. In addition, female rats were given 0.05% EHEN initiator followed by 500 mg potassium bromate/L for 30 weeks. Levels of 8-OH-dG in the kidneys were significantly increased at 200 and 400 mg/kg bw and correlated with increased in CRFs of proximal tubules. The study suggests that oxidative stress generated by potassium bromate exposure may be associated with induction of cell proliferation and associated promoting activity.

In a 104-week study in male F344 rats to test the initiating potential of potassium bromate, potassium bromate given by gavage as a single dose of 300 mg/kg bw (the maximum tolerated dose, which induced regenerative changes in kidney) was ineffective as a renal tumour initiator when followed from weeks 2 to 104 by a diet containing 4000 mg barbital sodium/L, a recognized rodent renal tumour promoter. Dysplastic foci of renal tubular cells (putative pre-neoplastic lesions) were observed in 16/27 (59%) animals given potassium bromate plus barbital sodium and in 16/23 (69%) animals given barbital sodium alone, compared with 3/27 (11%) given potassium bromate only and 1/23 (4%) in controls (significant differences between first two groups and last two groups at p < 0.001). No statistically significant increase in tubular cell adenomas or carcinomas was observed in any group, although a trend towards increased adenomas was evident in the two barbital sodium groups, with and without the initiating dose of potassium bromate. Nephropathy was significantly increased after 30 and 52 weeks in the same two groups. It was noted that the 300 mg/kg bw dose given here was lower than the 400 mg/kg bw dose given in a study by Kasai et al.⁴⁷ in which potassium bromate initiation by production of oxygen radicals was observed, thus suggesting that there may be a threshold dose at which oxygen radicals are produced, leading to initiation of carcinogenesis.⁴⁸ In a recent study,⁴⁹ the carcinogenicity and chronic toxicity of potassium bromate were studied in male B6C3F₁ mice and F344/N rats. Mice were treated with 0, 80, 400 or 800 mg potassium bromate/L (0, 9.1, 42.4 and 77.8 mg/kg bw per day) in drinking water for up to 100 weeks. Rats were provided with 0, 20, 100, 200 or 400 mg potassium bromate/L (0, 1.5, 7.9, 16.9 and 37.5 mg/kg bw per day). No significant differences were seen in survival times, body weight gain or feed consumption. However, a decrease in water consumption with increasing potassium bromate concentration was noted when compared with controls. The study confirmed that potassium bromate results in an increased incidence of renal tumours, thyroid follicular tumours and mesotheliomas in a dose-dependent fashion in male rats. Although rat renal cell tumours were seen at 100 mg/L (6/47), 200 mg/L (3/39) and 400 mg/L (12/32), they were statistically significant only at the highest dose. An increased incidence of renal cell tumours was also noted in mice and found to be treatment related. These kidney tumours were seen at all dose levels in male mice -- 800 mg/L (1/44), 80 mg/L (5/38) and 40 mg/L (3/41) -- but they were statistically significant only at the 80 mg/L dose (p < 0.05).

Although renal nephrosis was not associated with treatment in rats and mice, a treatment-related increase in the presence of eosinophilic droplets within the cytoplasm of proximal tubule epithelium was noted in rats in the same study.⁴⁹ The presence of these eosinophilic droplets was shown to be a result of oxidative damage. The transitional cells within the renal pelvis were markedly hyperplastic in rats at potassium bromate doses greater than 20 mg/L, but no urothelial hyperplasia was noted in the mouse renal pelvis. No hyperplastic response was seen in the urinary bladder, and no treatment-related hyperplasia of the urinary bladder was associated with urothelial hyperplasia of the renal pelvis. Mesothe-lioma originating from the tunica vaginalis testis was induced in the rat in a dose-dependent manner at all dose levels. The mesotheliomas spread to other sites by direct implantation or seeding from the primary tumour and were frequently found scattered throughout the peritoneal cavity on the serosal surfaces of many organs. The frequency of multiple sites for this tumour did not appear to be dose dependent. Thyroid follicular tumours were increased in rats in a treatment- and dose-related manner. An increased incidence of thyroid follicular proliferative lesions was noted at all doses; however, tumours were statistically increased only at doses of 200 and 400 mg/L. This study shows that potassium bromate is carcinogenic in the rat kidney, thyroid and mesothe-lium and in the kidney of the male mouse. Potassium bromate was carcinogenic in rodents in drinking water at concentrations as low as 20 mg/L (1.5 mg/kg bw per day).⁴⁹

Special Studies

Lipid peroxidation (LPO) in the kidney of male F344 rats was significantly increased (p < 0.01) after intravenous administration of potassium bromate at doses of 77, 96, 120 and 150 mg/kg bw. The increases were dose and time dependent. When an exogenous source of cysteine was provided by pre-treating with 400 mg/kg bw, LPO remained at the control level. Administration of diethylmaleate, a GSH depletor, prior to intravenous treatment with a potassium bromate dose as low as 20 mg/kg bw significantly increased LPO, and eosino-philic droplets were noted in the tubular epithelium of

the kidney. No equivalent increase in LPO was seen in kidneys of two strains of mice and hamsters treated intravenously with potassium bromate at 120 mg/kg bw, although LPO was slightly increased in a third strain of mouse. A possible relationship was suggested between LPO in the kidney and the differences in species susceptibility to tumour formation noted in a previous study.⁵⁰ A significant increase in 8-OH-dG was noted in kidney DNA of male F344 rats after a single intragastric dose of 400 mg potassium bromate/kg bw, and a positive significant correlation between formation of this substance within DNA and induction of renal cell tumours was also found. No increase was apparent in the liver.⁴⁷ After a single intravenous potassium bromate dose of 70 mg/kg bw was given to male F344 rats, LPO was significantly increased after six hours and continued to increase until a plateau was reached at 48-96 hours; 8-OH-dG rose sharply at 24 hours, then decreased somewhat, as did the relative kidney weight. This suggested that the LPO rise in the cell is closely related to, and precedes, the 8-OH-dG rise, which is indicative of DNA damage. A dose-response study at potassium bromate concentrations of 0, 20, 40 and 80 mg/kg bw indicated no effects on LPO or 8-OH-dG at 20 mg/kg bw, slight but significant effects at 40 mg/kg bw and marked effects at 80 mg/kg bw.⁵¹ A study by Chipman et al.⁵² confirms these findings; when combined with studies by Sai et al.,^51,53 it suggests that DNA oxidation is concomitant with LPO and toxicity at high doses and that there is a secondary mechanism for DNA oxidation in renal car-cinogenesis.

Induction of LPO and 8-OH-dG and increases in relative liver weight by an intraperitoneal dose of potassium bromate at 80 mg/kg bw were significantly inhibited by the antioxidants GSH or cysteine given intra-peritoneally at 2 × 800 and 2 × 400 mg/kg bw, respectively, pre- and post-injection. The antioxidant vitamin C also acted as an inhibitor at a daily intragastric dose of 200 mg/kg bw per day for five days prior to bromate dosing. Superoxide dismutase (18 000 U/kg) and vitamin E (100 mg/kg bw for five days), also antioxidants, were ineffective.⁵⁴ Micronucleus induction in peripheral blood reticulocytes by a potassium bromate dose of 60 mg/kg bw was similarly inhibited in male rats, in the same protocol as the preceding study.⁵⁵

Genotoxicity

Weakly positive results were obtained for the mutagenicity of potassium bromate in the Ames test using Salmonella typhimurium strain TA100 at a concentration of 3 mg/plate following metabolic activation.⁵⁶ However, negative results were found with other strains: TA98, TA1535, TA1537 and TA1538.^1,57 Negative results were also found in tests with Escherichia coli^56,58 and in Bacillus subtilis both with and without metabolic activation.⁵⁷ In a repeat of earlier Ames tests, potassium bromate again showed weak positive activity with TA100 with and without activation and with TA102 and TA104 with activation only. The latter two strains are known to be sensitive to chemicals that generate oxygen radicals.¹ Sodium bromate and silver bromate were also found to be negative in Ames tests with TA97, TA98, TA100 and TA102 strains in concentrations of 5 mg/plate and 25 µg/plate, respectively.¹ Potassium bromate induced chromosomal aberrations in cultured Chinese hamster fibroblast cells at concentrations of 0.0625-0.25 mg/mL in both the presence and absence of metabolic activation. The incidence of structural aberrations in cells was 100% after 24 hours at the maximum dose.⁵⁸ Chromatid breaks were also induced in CH DON-6 cells at a potassium bromate concentration of 0.084 mg/mL.¹ Positive results were also obtained in an in vivo study of the acute cytogenetic effects of potassium bromate on bone marrow cells in male Long-Evans rats following oral or intraperitoneal administration of 334.0 and 250.5 mg/kg bw, respectively (it is noted that these doses were close to the LD₅₀ values). In both cases, the number of aberrant cells increased progressively, reaching a maximum of 10.5% at 12 hours (intraperitoneal) and 10.8% at 18 hours (oral) after administration. Significant differences were observed at three, six and 12 hours following intraperitoneal administration and at 12 and 18 hours following oral administration.⁵⁹ Potassium bromate gave positive dose-dependent responses in mouse micronucleus tests with two strains of male mice (Ms/Ae and CD-1) using femoral bone marrow poly-chromatic erythrocytes following intraperitoneal or oral gavage administration of doses between 18.8 and 150 mg/kg bw (intraperitoneal) or between 37.5 and 300 mg/kg bw (oral).³⁸ Similar results were reported for male ddY mice at doses above 100 mg/kg bw for the oral route and above 25 mg/kg bw for the intraperitoneal route.⁶⁰ These results were also found using peripheral blood reticulocytes with intraperitoneal dosing at 18.8-212 mg/kg bw in male CD-1 mice.⁶¹

Reproductive Effects

No reproductive studies were found that tested bromate directly, via water or gavage. A study has been conducted⁶² on groups of rats given bread made from flour treated with potassium bromate; however, as bromate is changed to bromide during the baking process,² this study would not be relevant here.