Heavy metal accumulation in vegetable production soils under organic and chemical-fertilised practices: influence of soil and other environmental factors.

Heavy metal contamination in crop fields is considered critical to food safety and human health. Therefore, we aimed to generate empirical evidence for the influence of soil and other environmental factors on heavy metal accumulation in crop fields. Estimates of heavy metal contents (iron, chromium, manganese, cobalt, nickel, copper, zinc, and lead) and calcium and magnesium over certified organic and chemical-fertilised vegetable fields in South India were compared at soil series levels. It revealed specific trends concerning the influence of soil type (soil order and soil series), agricultural practices, and physicochemical soil characteristics. Pollution indices and a Monte Carlo-simulated human health risk assessment for vegetable fields belonging to each soil type were also comparatively evaluated. Multivariate analyses of the heavy metal contents over the soil types indicated it as the primary factor influencing the distribution of heavy metals in the fields. Manurial or other anthropogenic practices remain a secondary source. Moreover, chemical-fertilised farming generally resulted in increased levels of trace metals in the fields, particularly nickel, cobalt, and manganese, as well as an overall higher pollution load. However, fields under organic farming were not free from contamination. The zinc and lead levels in organic fields suggested potential inputs from contaminated organic amendments. The human health risk assessment of the region indicated that children face considerable non-carcinogenic and carcinogenic risks from chromium and nickel contents. Despite certain limitations of the study, the conclusion is that generalised agricultural policies favouring site-specific decisions are essential to control heavy metal contamination in crop fields.