Arsenic in agricultural soils may represent a risk for crop quality and surrounding water resources. In the frame of AgriAs project, “Evaluation and management of Arsenic contamination in agricultural soil and water”, a former chemical weapons destruction site converted into agricultural land was characterized. The objective of this study was to identify possible links between arsenic concentration and speciation and bio-indicators informing about the bioavailability of the toxic element. Plants lipidic bio-indicator Omega-3 Index showed that toxicity of the soil was not directly correlated with arsenic concentration. Conversely, arsenic level in the soil samples seemed to influence the density of microbes transforming As species.