Risk assessment for heavy metals in community gardens of the city of Teresina, Brazil

Urban agriculture (UA) contributes actively to food security in cities worldwide. Urban crops can be polluted by heavy metals (HMs) emitted by several sources, therefore to assess the health risk linked to HMs contamination is a crucial priority. The present study assessed the HMs contamination risk in five community gardens within the city of Teresina, Brazil, three within the city, one in peri-urban fringes and one from the nearby rural area. In each garden soil and vegetables (lettuce, coriander and chives) were sampled and total HMs concentration determined. HMs contamination risk was assessed for both soil and vegetables, using respectively the geoaccumulation index (Igeo) and the health risk index (HRI). Moreover, the effect of two cropping systems (traditional soil versus simplified soilless system) on HMs pollution was investigated. The study shows that pollutants uptake by plants was not related to the total HMs concentration in topsoil, and more information on the bioavailable fraction are needed. Therefore, strategies aimed at the reduction of bioavailability of the pollutants in soil can be useful in urban agriculture (i.e., simplified soilless systems). Overall, the health risk index demonstrates that the vegetables grown in the city of Teresina can be considered safe for children’s consumption.