Influence of environmental changes on the biogeochemistry of arsenic in a soil polluted by the destruction of chemical weapons: A mesocosm study

Abstract

Thermal destruction of chemical munitions from World War I led to the formation of a heavily contaminated residue that contains an unexpected mineral association in which a microbial As transformation has been observed. A mesocosm study was conducted to assess the impact of water saturation episodes and input of bioavailable organic matter (OM) on pollutant behavior in relation to biogeochemical parameters. Over a period of about eight (8) months, the contaminated soil was subjected to cycles of dry and wet periods corresponding to water table level variations. After the first four (4) months, fragmented litter from the nearby forest was placed on top of the soil. The mesocosm solid phase was sampled by three rounds of coring: at the beginning of the experiment, after four (4) months (before the addition of OM), and at the end of the experiment. Scanning electron microscopy coupled to energy dispersive X-ray spectroscopy observations showed that an amorphous phase, which was the primary carrier of As, Zn, and Cu, was unstable under water-saturated conditions and released a portion of the contaminants in solution. Precipitation of a lead arsenate chloride mineral, mimetite, in soils within the water saturated level caused the immobilization of As and Pb. Mimetite is a durable trap because of its large stability domain; however, this precipitation was limited by a low Pb concentration inducing that high amounts of As remained in solution. The addition of forest litter modified the quantities and qualities of soil OM. Microbial As transformation was affected by the addition of OM, which increased the concentration of both As(III)-oxidizing and As(V)-reducing microorganisms. The addition of OM negatively impacted the As(III) oxidizing rate, however As(III) oxidation was still the dominant reaction in accordance with the formation of arsenate-bearing minerals.

Microbial community response to environmental changes in a technosol historically contaminated by the burning of chemical ammunitions

“…Each core was separated into four samples, H1 0-12.5 cm, H2 12.5-6 28 cm, H3 28-42 cm, and H4 42-75 cm. Sub-samples were dried and dedicated to soil characterization presented in Thouin et al (2018) and 2 g were immediately placed in sterile tubes, and stored at -20 °C until DNA extraction.…”

“…To evaluate a possible relationship between environmental parameters and bacterial composition during the experiment, bath data sets were analyzed by co-inertia analysis (COIA: Dray et al, 2003). Environmental parameter data are from Thouin et al (2017Thouin et al ( , 2018 and only the 15 dominant bacterial OTUs present in the overall samples were used in alaysis.The RV-coefficient, representing the strength of the co-variation, was calculated and statistically tested using the Monte Carlo randomization test with 999 random permutations.…”

“…In previous work, we showed that intrinsic organic matter (OM), mainly composed of charcoal from the contaminated material, is very high (≈ 25 %) (Thouin et al, 2016). This OM is characterized by high C/N (≈ 35) and low hydrogen index/oxygen index (HI/OI ≈ 0.1) and is therefore recalcitrant in nature (Thouin et al, 2018).…”

“…This previous study provided results on the processes that affect the fate of As and metals that were published in Thouin et al (2017Thouin et al ( , 2018. Adding litter contributed to the growth of As transforming microorganisms; soil saturation enhanced arsenate-reducing activity (Thouin et al, 2018) resulting in the increase of arsenite concentration in soil solution. However, only global microbial parameters (carbon mineralization, enumeration and activity tests for As-transforming microorganisms) were considered at this stage.…”

“…However, only global microbial parameters (carbon mineralization, enumeration and activity tests for As-transforming microorganisms) were considered at this stage. Here, we investigated the 5 structure of the microbial communities in the samples from this mesocosm experiment (Thouin et al 2017(Thouin et al , 2018 with the heavily contaminated technosol of the Place-à-Gaz, giving insight, for the first time, into the microbial diversity of polluted sites that are part of the complex legacy of chemical shell destruction. In a second time, the effects of two environmental parameters (namely water saturation events and natural organic matter input) on this diversity were evaluated through analyzes of the bacterial, archaeal and fungal communities in samples from the mesocosm experiment.…”