Diphenylarsinic acid (DPAA) is an organic arsenic compound used for the synthesis of chemical weapons. We previously found that the residents of Kamisu city in Ibaraki Prefecture, Japan, were exposed to DPAA through contaminated well water in 2003. Although mounting evidence strongly suggests that their neurological symptoms were caused by DPAA, the dynamics of DPAA distribution and metabolism after ingestion by humans remain to be elucidated. To accurately predict the distribution of DPAA in the human body, we administrated DPAA (1.0 mg/kg/day) to cynomolgus monkeys (n = 28) for 28 days. The whole tissues from these monkeys were collected at 5, 29, 170, and 339 days after the last administration. The concentration of DPAA in these tissues was measured by liquid chromatography–mass spectrometry. We found that DPAA accumulated in the central nervous system tissues for a longer period than in other tissues. This finding would extend our knowledge on the distribution dynamics and metabolism of DPAA in primates, including humans. Furthermore, it may be useful for developing a treatment strategy for patients who are exposed to DPAA.

Environmental context. Contamination of groundwater by arsenic compounds used in chemical warfare research is a recently discovered environmental problem in Japan. We report evidence that the arsenic compounds originally present in the groundwater are transforming to thio-arsenic compounds of currently unknown environmental fate.Abstract. During routine analyses of groundwater samples contaminated with diphenylarsinic acid (DPAA) at Kamisu, Ibaraki Prefecture, Japan, we obtained data indicating that unknown arsenic compounds accounted for up to 75 % of the total arsenic in some of the samples. Results from using liquid chromatography in combination with elemental mass spectrometry and tandem molecular mass spectrometry suggested that two of the main unknown peaks were diphenyldithioarsinic acid and methylphenyldithioarsinic acid. These assignments were later confirmed by comparison with chemically synthesised compounds. A potential transformation scheme for DPAA in the environment is proposed based on the derivatives identified in the environmental samples.

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