ena-STUDY-BRGM-29-10-2018-15:15:16:564-470
Microbial community response to environmental changes in a technosol historically contaminated by the burning of chemical ammunitions.
The burning of chemical weapons in the 1926–1928 period produced polluted technosols with extremely elevated levels of arsenic, zinc, lead and copper. One such site in France, known as the “Place-à-Gaz”, has remained undisturbed since destruction of the shells. More than 200,000 shells were destroyed on this site by thermal treatment. The residues from this combustion formed a black layer containing slag, coal, ash and ammunitions residues. The layer is highly contaminated with As, Zn, Cu and Pb (which concentrations respectively reach 72.8 g.kg-1, 90.2 g.kg-1, 9.1 g.kg-1 and 5.8 g.kg-1) and with organic compounds. The response of microbial communities in samples of such a soil to controlled environmental changes, namely organic matter supply and water saturation, was studied in an eight month mesocosm experiment. The experimental soil cylinder was divided into four distinct layers, from H1 (surface), to H4 (bottom). After three months of stabilization, the soil was subjected to dry/wet cycles (over a period of about eight months). The dry periods were characterized by saturation of only the bottom H4 level of the mesocosm and by the addition of around 12 L of mineral water once a week. The wet periods were characterized by water saturation of the two deepest levels, H3 and H4, and by the addition of 6 L of water every two days. At the midpoint of the experiment (i.e. after four months), 24 kg of fragmented organic forest litter sampled at the Place-à-Gaz site were added to the top of the surface soil (level H1). Coring was performed in the mesocosm at the beginning of the experiment (T0), just prior to the addition of fragmented forest litter (4 months, T4), and at the end of the experiment (8 months, T8). Each core was separated into four samples, H1 0–12.5 cm, H2 12.5–28 cm, H3 28–42 cm, and H4 42–75 cm. The structure of the prokaryotic and eukaryotic community was assessed using sequencing of 16S rRNA and 18S rRNA on these samples. In spite of the high concentrations of toxic elements, microbial diversity was found to be close to that of non-polluted soils. The bacterial community was dominated by Proteobacteria, Acidobacteria and Bacteroidetes, while the fungal community was dominated by Ascomicota. Amongst the most abundant bacterial OTUs, including Sphingomonas as a major genus, some were common to soil environments in general whereas a few, such as organisms related to Leptospirillum and Acidiferrobacter, seemed to be more specific to the geochemical context. Evolution of the microbial abundance and community structures shed light on modifications induced by water saturation and the addition of forest litter to the soil surface.
The burning of chemical weapons in the 1926–1928 period produced polluted technosols with extremely elevated levels of arsenic, zinc, lead and copper. One such site in France, known as the “Place-à-Gaz”, has remained undisturbed since destruction of the shells. More than 200,000 shells were destroyed on this site by thermal treatment. The residues from this combustion formed a black layer containing slag, coal, ash and ammunitions residues. The layer is highly contaminated with As, Zn, Cu and Pb (which concentrations respectively reach 72.8 g.kg-1, 90.2 g.kg-1, 9.1 g.kg-1 and 5.8 g.kg-1) and with organic compounds. The response of microbial communities in samples of such a soil to controlled environmental changes, namely organic matter supply and water saturation, was studied in an eight month mesocosm experiment. The experimental soil cylinder was divided into four distinct layers, from H1 (surface), to H4 (bottom). After three months of stabilization, the soil was subjected to dry/wet cycles (over a period of about eight months). The dry periods were characterized by saturation of only the bottom H4 level of the mesocosm and by the addition of around 12 L of mineral water once a week. The wet periods were characterized by water saturation of the two deepest levels, H3 and H4, and by the addition of 6 L of water every two days. At the midpoint of the experiment (i.e. after four months), 24 kg of fragmented organic forest litter sampled at the Place-à-Gaz site were added to the top of the surface soil (level H1). Coring was performed in the mesocosm at the beginning of the experiment (T0), just prior to the addition of fragmented forest litter (4 months, T4), and at the end of the experiment (8 months, T8). Each core was separated into four samples, H1 0–12.5 cm, H2 12.5–28 cm, H3 28–42 cm, and H4 42–75 cm. The structure of the prokaryotic and eukaryotic community was assessed using sequencing of 16S rRNA and 18S rRNA on these samples. In spite of the high concentrations of toxic elements, microbial diversity was found to be close to that of non-polluted soils. The bacterial community was dominated by Proteobacteria, Acidobacteria and Bacteroidetes, while the fungal community was dominated by Ascomicota. Amongst the most abundant bacterial OTUs, including Sphingomonas as a major genus, some were common to soil environments in general whereas a few, such as organisms related to Leptospirillum and Acidiferrobacter, seemed to be more specific to the geochemical context. Evolution of the microbial abundance and community structures shed light on modifications induced by water saturation and the addition of forest litter to the soil surface.