Organic amendments application effect on a contaminated soil with arsenic

Soil is a non-renewable natural resource essential for obtaining food. Anthropogenic activities threaten this resource by exposing it to different pollutants, such as metals and metalloids, which can alter its functionality and threaten human health through the intake of food contaminated with these elements. The aim of this study was to evaluate the effect of two organic amendments, compost (CP) and biochar (BC) in a phytoremediation process of a soil contaminated with arsenic (As) at a dose of 60 mg/kg. For this purpose, germination tests and a greenhouse assay were carried out applying two doses of each amendment, 5 and 10% to As-contaminated soil using Lactuca sativa L. as control plant. The application of CP showed a decrease in the As bioavailability in the soil (from 1.95 mg/kg in control soil to 1.77 in CP 5% and 1.45 in CP 10%), decreasing the translocation to the aerial part and enhancing the development of plants, being this effect dose-dependent. The treatments with BC caused an increase in As bioavailability in the soil, allowing its translocation to the aerial part of the plants and affecting its development. In soil, both amendments increased organic matter content observing the greatest increases with CP. Moreover, using CP, an increase in the nutrients analyzed (N, P, K, Ca, Mg, and Na) was observed, as well as an increase in the total As content at the 10% dose. The enzymatic activity of the soils treated with CP increased significantly, whereas inhibition of most of the evaluated activities was observed with BC treatments. The application of CP led to an As immobilizing effect, decreasing As availability and preventing its translocation to plants. At the same time, it contributed to soil remediation, improving its fertility. Finally, the used BC mobilized As, which negatively affected the development of the lettuce plants, as well as the biological activity of the soil.