Assessment of municipal food waste as a feedstock for contaminants in New York City composts

Food waste is a common feedstock for municipal compost that may be a source of heavy metal contamination throughout the food chain. In this study, we used portable X-ray fluorescence (pXRF) analysis on two settings (soil, solid waste) to quantify the contribution of food waste to concentrations of Pb, As, Cr, Cu, Zn, and Ni in three New York City composts. Food waste was collected from eight drop-off sites (FSDOs) across three boroughs. Finished composts were collected from three sites that utilized small, medium, and large-scale composting methods. Metal concentrations in food waste fell within food safety limits for dry weight, though compliance varied with pXRF setting and applied standards. Samples from the Sunnyside FSDO had the highest concentrations for all tested metals and the highest level of Pb (~25 ppm). All compost samples were compliant with U.S. Composting Council (2025) standards for all metals and well below the 300 ppm standard for Pb, though one site (MD) had double the Pb concentration compared to other sites in this study (FK and SD) and there were significant differences between all three sites. Differences in concentrations between pXRF settings for certain metals were significant in both food waste and composts. Developing a certified reference material for food waste and verifying results with chemical analysis like ICP-MS would improve pXRF use for similar studies. Overall, food waste is a safe feedstock, but more studies are needed to understand underlying variation in contaminant concentrations in food.