title: Kinetics of Dimethylated Thioarsenicals and the Formation of Highly Toxic Dimethylmonothioarsinic Acid in Environment.
abstract: Dimethylmonothioarsinic acid (DMMTAV) is a highly toxic, thiolated analogue of dimethylarsinic acid (DMAV). In comparison, a further thiolated analogue, dimethyldithioarsinic acid (DMDTAV), and DMAVboth exhibit lower toxicity. To understand the environmental conditions responsible for forming DMMTAV, the kinetics of DMAVthiolation are examined. The thiolation of DMAVis pH-dependent and consists of two consecutive first-order reactions under excess sulfide conditions. The first thiolation of DMAVto form DMMTAVis faster than the second one to DMDTAV. DMMTAVis therefore an intermediate. The first reaction is first-order in H2S at pH 6.0 and 20 °C; therefore, the overall reaction is second-order and the rate coefficient in this condition is 0.0780 M-1s-1. The rate coefficient significantly decreases at pH 8.0, indicating that H2S(aq) triggers the thiolation of DMAV. The second reaction rate is significantly decreased at pH 2.5; therefore, reaction under strongly acidic conditions leads to accumulation of highly toxic DMMTAVin the early stages of thiolation. The transformation of DMDTAVto DMMTAVis catalyzed in the presence of ferric iron. Formation of DMMTAVshould be considered when assessing risk posed by arsenic under sulfidic or sulfate reducing conditions.
authors.affiliation: Department of Earth System Sciences, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea.|Natural Science Research Institute, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea.
authors.forename: Youn-Tae
authors.initials: YT
authors.lastname: Kim
authors.affiliation: Seoul Center, Korea Basic Science Institute , 6-7 Inchon-ro 22-gil, Seongbuk-gu, Seoul 02855, Republic of Korea.
authors.forename: Hosub
authors.initials: H
authors.lastname: Lee
authors.affiliation: Seoul Center, Korea Basic Science Institute , 6-7 Inchon-ro 22-gil, Seongbuk-gu, Seoul 02855, Republic of Korea.
authors.forename: Hye-On
authors.initials: HO
authors.lastname: Yoon
authors.affiliation: Department of Earth System Sciences, Yonsei University , 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea.
authors.forename: Nam C
authors.initials: NC
authors.lastname: Woo
mesh_terms: D001151:Arsenic; D001152:Arsenicals; D002101:Cacodylic Acid / Q000031:analogs & derivatives*; D004777:Environment; D007700:Kinetics
chemical_list: D001152:Arsenicals; D002101:Cacodylic Acid; D001151:Arsenic