2019, 56(2):276-287.
DOI: 10.11766/trxb201806070306
Abstract:
Chemical warfare agents containing organoarsenic compounds such as Clark I (diphenylcyanoarsine) and Clark II (diphenylchloroarsine) were widely produced and used during World Wars I and II. After the wars, remains of these agents were simply dumped into the sea or buried underground, thus inevitably polluting the soil-water environments of the sits where they were disposed with the arsenic contained in the chemical weapons. In the environment, these abandoned chemical agents are easily hydrolyzed and oxidized into diphenylarsinic acid (DPAA), rather stable in structure, and other organoarsenic compounds. So far, DPAA has been detected in quite a number of the areas where these chemical weapons were dumped. The detection has aroused extensive concerns because the presence of DPAA may bring about environmental and health risks. Scholars both at home and abroad have already begun doing some researches, trying to find ways to analyze DPAA in the soil and water environments, determine their status and behaviors and remedy the polluted environments. However, few have done any to summarize systematically progresses in the research. In this paper, a review is presented to introduce some high-effect inorganic and organic extractants and GC as well as LC analytical methods for DPAA in the soil, and sources and status of the pollutant in the soil-water environments. Generally speaking, the DPAA contaminated areas are located mainly in Northeast China, and South and Southeast Japan. Especially in the chemical weapons dumping sites, the concentration of total arsenic is far beyond the criteria for safety. At the same time, the paper also discusses how DPAA is adsorbed/desorbed, translocated and transformed in the soil-water environment, what are the factors affecting the processes and what are the mechanisms. Studies in the past reported that the adsorption/desorption of DPAA in soil was controlled by a variety of factors, including pH, inorganic ions, Fe/Al oxides, organic matter, redox potential (Eh), etc. and adsorption of the substance was completed via ligand exchange reactions between hydroxyl groups of Fe/Al oxides and arsenate of DPAA, rather than the hydrophilic effect of organic matter; the effective transformation of DPAA in the soil occurred under flooded anaerobic conditions, and under sulfate-reducing conditions, in particular; and iron reduction and sulfate reduction were the two key factors controlling desorption and transformation of DPAA. In the end, the paper elaborates the physical, chemical and biological technologies available for remediation of DPAA contaminated soil-water environments, and their remediation efficiency, controlling factors and mechanisms as well. In terms of physic-chemical remediation, application of activated carbon, Fenton and Fenton-like oxidation and photochemical degradation has been demonstrated to be able to effectively remove DPAA in soil-water environments. In terms of bioremediation, certain progresses have been made, like screening of highly efficient DPAA degrading bacteria, unfolding microbial remediation and combined microbial-phytoremediation and previewing directions of the future researches. The paper holds that all the relevant research findings will serve as theoretical reference for future in-depth studies on DPAA pollution of soil-water environments, remediation of DPAA polluted environments, and protection of environmental quality and human health from DPAA pollution. For further researches, emphases should be laid on the following aspects: (1) To perfect quality assurance and quality control system for DPAA analytical methods, with focus on development of standard alternatives, purgation of internal standards and markers; (2) To launch investigations on scope and extent of DPAA contamination, while taking into the consideration of geographical locations, soil types and land-use patterns of the chemical weapon burial sites; (3) To explore forms of DPAA bonding with soil colloids, clay minerals and oxides in the soil and molecular binding mechanisms, and elucidate the mechanisms responsible for adsorption/desorption, translocation and transformation of DPAA in multi-media environment and at microscopic interfaces; (4) To explore for develop new remediation materials, intensify researches on physic-chemical-phyto combined remediation and continue to screen out highly efficient DPAA degrading bacteria and probe mechanisms of their effectiveness at molecular as well as genetic levels, while integrating genetic engineering, molecular biology with phytoremediation technologies, so as to eventually establish a bioremediation technical system applicable to DPAA contaminated media different in type and condition.