Soil versus plant as indicators of agroecosystem pollution by potentially toxic elements

The major route of potentially toxic elements (PTEs) to humans is the intake through food. They enter the food chain principally by plants uptake from the soil and, to a less extent, through foliar deposition. The soil-to-plant transfer as part of the biogeochemical cycle of these elements is a complex and hardly predictable process. In this study, we investigated the capability of soils and plants to indicate PTEs inputs in an intermingled urban-rural landscape of south Italy affected by legal and illegal waste disposal and dumping. For this aim, 172 agricultural soil and plant (edible part) samples were collected in pairs from 47 municipalities and analyzed for 12 PTEs (As, Be, Cd, Co, Cu, Cr, Ni, Pb, Se, Tl, V, Zn). Soil extractions with 1 M NH4NO3 and 0.05 M EDTA pH 7 were applied to assess PTEs bioavailability. Results were examined according to plant species and main soil chemical properties. For Pb and Cd, the soil-to-plant transfer factors (TF) and the corresponding soil benchmark concentrations were also investigated. Zinc, Cu, Cd, and Pb were the only PTEs of anthropic origin severely polluting from 10 to 16% of the soils, but only in a very few cases exceeded physiological or EU legal critical values in the edible part of the plants. An evaluation of human risk due to the ingestion of these elements was tried; no risk for consumers for Zn, Cu, and Pb, while for Cd three values slightly exceeded the tolerable daily intake. Therefore, we conclude that crops cultivated in the studied area could represent only a moderate risk for human health. No correlation was found between soil and plant data, which likely highlights different pollution inputs. A large variability characterized the Pb and Cd TF, making it difficult to establish a unique benchmark concentration for the studied agricultural soils.