Human Health Risk Assessment From Exposure to Toxic Metals in Soils and Leafy Vegetables in Smallholder Farms of Northeastern Brazil.

Abstract

This study assessed human health risks associated with exposure to potentially toxic metals (PTMs) in soils and leafy vegetables cultivated in smallholder agricultural systems in Northeastern Brazil. Soil and vegetable samples were collected from 18 agricultural areas and analyzed for cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), lead (Pb), and zinc (Zn). A harmonized human health risk assessment (HHRA) was conducted following US Environmental Protection Agency (USEPA) guidelines, considering soil ingestion, dermal contact, inhalation of resuspended particles, and dietary intake of vegetables for adults and children. Recalculated average daily doses indicated that soil ingestion and vegetable consumption were the dominant exposure pathways, whereas dermal and inhalation contributions were minor. Children consistently exhibited higher exposure doses and hazard quotients than adults due to lower body weight and higher intake rates. Noncarcinogenic risk estimates for adults remained below the threshold of concern in all areas. In contrast, localized exceedances of the hazard index (HI > 1) were identified for children, revealing spatially explicit risk hotspots rather than uniform risk across the study area. Lettuce and arugula contributed substantially to dietary exposure, particularly for Cd, Pb, and Cr. A conceptual sensitivity analysis incorporating hypothetical bioaccessibility fractions demonstrated that risk estimates near the regulatory threshold are sensitive to realistic reductions in bioaccessible metal fractions. At the same time, the highest risk hotspots remain robust under conservative assumptions. Overall, the findings represent conservative, screening-level estimates that underscore the importance of age-specific exposure scenarios, spatially explicit risk evaluation, and targeted risk management strategies in smallholder farming systems.