Arsenic distribution in soils and rye plants of a cropland located in an abandoned mining area.

A mining impacted cropland was studied in order to assess its As pollution level and the derived environmental and health risks. Profile soil samples (0-50 cm) and rye plant samples were collected at different distances (0-150 m) from the near mine dump and analyzed for their As content and distribution. These cropland soils were sandy, acidic and poor in organic matter and Fe/Al oxides. The soil total As concentrations (38-177 mg kg(-1)) and, especially, the soil soluble As concentrations (0.48-4.1 mg kg(-1)) importantly exceeded their safe limits for agricultural use of soils. Moreover, the soil As contents more prone to be mobilized could rise up to 25-69% of total As levels as determined using (NH4)2SO4, NH4H2PO4 and (NH4)2C2O4·H2O as sequential extractants. Arsenic in rye plants was primarily distributed in roots (3.4-18.8 mg kg(-1)), with restricted translocation to shoots (TF=0.05-0.26) and grains (TF=<0.02-0.14). The mechanism for this excluder behavior should be likely related to arsenate reduction to arsenite in roots, followed by its complexation with thiols, as suggested by the high arsenite level in rye roots (up to 95% of the total As content) and the negative correlation between thiol concentrations in rye roots and As concentrations in rye shoots (|R|=0.770; p<0.01). Accordingly, in spite of the high mobile and mobilizable As contents in soils, As concentrations in rye above-ground tissues comply with the European regulation on undesirable substances in animal feed. Likewise, rye grain As concentrations were below its maximum tolerable concentration in cereals established by international legislation.