Potassium bromate – inhalable fraction. Documentation of proposed values of occupational exposure limits (OELs)

Abstract

Potassium bromate (V), (KBrO3) exists as white crystals, crystalline powder or granules. It is highly soluble in water, tasteless and odourless. Potassium bromate is a strong oxidizing agent. In the past it has been used as food additive in flour milling, as an ingredient in fish-paste in Japan, in cheese making, in beer malting, as a component of cold hair wave liquid and an oxidizing compound. Moreover, bromate is formed as a by-product of water disinfection by ozonation and is frequently detected in tap and bottled water. In fact bromate is one of the most prevalent disinfection by-product of surface water. Occupational exposure to potassium bromate occurs mainly in production plants during packaging processes. In Poland, about 1 160 persons were exposed to this compound in 2016. Bromate caused many acute poisonings by accidental ingestion, mainly among children, and more often ingested for tentative suicide by young women, especially hairdressers. In the acute phase of poisoning, gastrointestinal disturbances, irreversible hearing loss, and acute renal failure were observed. Acute renal failure was associated with hemolytic uremic syndrome. There are no data on chronic intoxication of humans by potassium bromate and epidemiological studies on this subject. On the basis of the value of median lethal dose (LD50) per os in rat, potassium bromate has been classified as a compound belonging to the category „Toxic”. Major toxic signs and symptoms in animals after a single intragastric administration of potassium bromate were tachypnea, hypothermia, diarrhea, lacrimation, suppression of locomotor movement, ataxic gait, and animals lying in a prone position. At autopsy the major findings were strong hyperemia of glandular stomach mucosa and congestion of lungs. Microscopically, necrosis and degenerative changes of the proximal tubular epithelium and hearing cells of internal ear were found. It was stated that the compound is not irritating, corrosive or sensitizing. In subchronic and chronic exposure of rodents, potassium bromate led to liver and kidney dysfunction and tubular epithelial damage. Potassium bromate had mutagenic and clastogenic effects. It induced point mutations, structural chromosome aberrations, micronuclei in polychromatic erythrocytes in male mice, DNA oxidative damage by modification of deoxyguanosine to 8-hydroxydeoxyguanosine, and DNA double-strand breakage. Potassium bromate induced neoplasms in rodents and exerted promotion effect in comparison with well-known carcinogens. Besides from preneoplastic changes, expressed by high incidences of renal cell tumors and dysplastic foci, bromate induced solid neoplasms, such as adenomas and adenocarcinomas in a rat kidney and thyroid, and mesotheliomas of peritoneum and tunica vaginalis testis. The European Union classified potassium bromate as a substance that can cause cancer (Group 1.B), whereas IARC classified it as a presumably carcinogenic agent for human (Group 2.B). In principle, effects of bromate on reproduction and ontogenetic development of offspring were not observed. Animal studies suggest that a kidney is a critical organ in the exposure to potassium bromate. The results of subchronic exposure of male rats to potassium bromate administered with drinking water were used to calculate the value of MAC-NDS. The critical effects in kidney were: an increase of organ weight and dose-dependent histopathological alterations defined as epithelium urinary tract hypertrophy. The NOAEL value is 1.5 mg/kg b.w./day. For the calculation of the maximum allowable concentration (MAC) value, 5 uncertainty factors with total value of 24 were used. Based on this estimation it is proposed to accept the MAC-TWA value for potassium bromate at 0.44 mg/m3. The risks of kidney and thyroid cancer in condition of occupational exposure are 2.2 · 10-3 and 0.6 · 10-3, respectively. There is no reason to determine the value of short-term exposure limit (STEL) and the biological exposure index (BEI). „Carc.1.B” notation (carcinogenic substance) was proposed