Destruction of chemical munitions from World War I has caused extensive local top soil contamination by arsenic and heavy metals. The biogeochemical behavior of toxic elements is poorly documented in this type of environment. Four soils were sampled presenting different levels of contamination. The range of As concentrations in the samples was 1937-72,820mg/kg. Concentrations of Zn, Cu and Pb reached 90,190mg/kg, 9113mg/kg and 5777mg/kg, respectively. The high clay content of the subsoil and large amounts of charcoal from the use of firewood during the burning process constitute an ample reservoir of metals and As-binding materials. However, SEM-EDS observations showed different forms of association for metals and As. In metal-rich grains, several phases were identified: crystalline phases, where arsenate secondary minerals were detected, and an amorphous phase rich in Fe, Zn, Cu, and As. The secondary arsenate minerals, identified by XRD, were adamite and olivenite (zinc and copper arsenates, respectively) and two pharmacosiderites. The amorphous material was the principal carrier of As and metals in the central part of the site. This singular mineral assemblage probably resulted from the heat treatment of arsenic-containing shells. Microbial characterization included total cell counts, respiration, and determination of As(III)-oxidizing activities. Results showed the presence of microorganisms actively contributing to metabolism of carbon and arsenic, even in the most polluted soil, thereby influencing the fate of bioavailable As on the site. However, the mobility of As correlated mainly with the availability of iron sinks.

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The battlefield of Verdun has seen some of the heaviest shelling in the history of mankind. This site as well as clean-up facilities in Germany may constitute contamination hot-spots and point-sources with leaking to groundwater. This study collected existing toxicological and ecotoxicological data on mustard gas degradation products, together with physicalchemical properties of listed compounds. It also provides quantities of these products measured in the groundwater of France, Germany and the pore water of the Baltic Sea. We indicate a deficiency of information on the toxicity of 1-oxa-4,5-dithiepane and 1,2,5trithiepane. In the groundwater of the German city of Munster 1-oxa-4,5-dithiepane was measured up to 250 µg/L, thus exceeding safe levels. Ecotoxicological studies classify this compound as toxic to aquatic organisms. 1,2,5-trithiepane is not a persistent compound. It was measured, however, in the groundwater at 1 µg/L level. This suggests that it could be formed from an active source of mustard gas. Considering the lack of toxicological data and the uncertainty about the amount of munition deposits, we suggest that research into the toxicity and exposure of, 1-oxa-4,5-dithiepane and 1,2,5trithiepane is needed for sites of concern.

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