Ingestion and Inhalation of Metal(loid)s through Preschool Gardening: An Exposure and Risk Assessment in Legacy Mining Communities

Children residing in legacy mining towns are potentially disproportionately exposed to metal(loid)s via ingestion (of food, water, and incidental soil), and dust inhalation, thus, increasing their risk of exposure when engaging in school or home gardening or playing outside in non-garden, playground soil. The purpose of this citizen-science study was to assess preschool children’s potential metal(loid) exposure through these routes. Parents and teachers were trained to properly collect water, soil, and vegetable samples from their preschools throughout Nevada County, California. Arsenic (As), cadmium (Cd), and lead (Pb) concentrations in garden irrigation sources did not exceed the U.S. EPA Safe Drinking Water Act and Lead and Copper Rule’s maximum contaminant and action levels. In general, As and Pb concentration from garden and playground soil samples exceeded the U.S. EPA Regional Screening Level (RSL), CalEPA’s California Human Health Screening Level (CHHSL) and California Department of Toxic Substances Control Screening Level (DTSC-SL). In contrast, all Cd concentrations were below these recommended screening levels. Dust samples (< 10 μm diameter) were generated from surface garden and playground soil collected at the preschools. Soil and dust samples were then analyzed by in-vitro bioaccessibility assays using synthetic lung and gastric fluids to estimate the bioaccessible fraction of As, Cd, and Pb in the body. Metal(loid) exposure via homegrown produce revealed that lettuce, carrot, and cabbage grown in the preschool gardens accumulated a higher concentration of metal(loid) than those store-bought nation-wide (U.S. FDA Total Diet Study, 2006-2013). None of the vegetables exceeded the respective recommendation maximum levels for Cd and Pb set by the World Health Organization Codex Alimentarius Commission. Lastly, a dietary assessment consisting of a 24-hour recall and food frequency questionnaire was administered to determine ingestion rates of foods shown to accumulate these contaminants. The results of this study suggest that consumption of preschool-grown foods and incidental soil ingestion were major contributors to preschool-aged children’s exposure to As, Cd, and Pb. This comprehensive environmental monitoring and exposure assessment that includes child-specific dietary data and the average daily doses of contaminants through ingestion of soil, water, and vegetable and inhalation of dust informs future risk assessment and public health interventions related to childhood exposure to these metal(loid)s