Ahead of the peer-review meeting later in July, and as part of the process to determine if these substances should be listed in the RoC, the NTP has released a draft monograph assessing the carcinogenic potential of 13 mono-, di-, or trihaloacetic acids found as water disinfection by-products. The RoC lists substances that are either known, or may reasonably be anticipated, to be human carcinogens and to which a significant number of people are exposed. A preliminary listing recommendation of “reasonably anticipated to be a human carcinogen” has been made for four of these substances:

  • dichloroacetic acid, on the basis of liver tumours in mice and male rats
  • dibromoacetic acid, on the basis of liver tumours in mice, lung tumours in male mice, malignant mesothelioma in male rats and leukaemia in female rats
  • bromochloroacetic acid, on the basis of liver tumours in mice, tumours of the large intestine in rats, malignant mesothelioma in male rats and mammary gland tumours in female rats
  • bromodichloroacetic acid, on the basis of liver tumours in mice, malignant mesothelioma and skin tumours in male rats, and mammary gland and Harderian gland tumours in female rats.

Two further substances, chlorodibromoacetic acid and tribromoacetic acid, were also recommended to be listed as “reasonably anticipated to be a human carcinogen”, on the basis that metabolism studies demonstrate a biotransformation to bromochloroacetic acid and dibromoacetic acid, respectively, and that the mechanisms of carcinogenicity are plausible in humans.

The evidence of carcinogenicity from studies on monochloroacetic acid, monoiodoacetic acid and trichloroacetic acid was insufficient to meet the criteria for listing in the RoC. No experimental cancer studies were identified on monobromoacetic acid, diiodoacetic acid, chloroiodoacetic acid, bromoiodoacetic acid, tribromoacetic acid or chlorodibromoacetic acid.

US National Toxicology Program (NTP). Draft Report on Carcinogens Monograph on Haloacetic Acids Found as Water Disinfection By-Products. https://ntp.niehs.nih.gov/ntp/about_ntp/monopeerrvw/2017/july/haadraftmonograph.pdf


The above items were taken from the July 2017 issue of Toxicology and Regulatory News which is sent automatically to members of bibra.

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