Urban forests near municipal solid waste incinerators do not show elevated trace metal or rare earth element concentrations across three cities in the northeast USA.

With the World Bank estimating global municipal solid waste MSW to increase to 3.4 billion tonnes by 2050, municipal solid waste incineration (MSWI) needs to be considered as part of sustainable waste management. In spite of major advancements in air pollution control systems and emission regulations, emissions of trace metals (TMs) (As, Cd, Cu, Ga, Mn, Ni, Pb, V, W, Zn) and rare earth elements (REEs) (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb) may occur. Here, leaves, wood, forest floor, and A horizons in urban forests were assessed to determine if TM and REE concentrations show enrichment near MSWI relative to other urban areas for three cities in the northeastern USA. Vegetation and soil concentrations measured were generally comparable to concentrations observed in previous studies in non-urban sites. Overall, higher TM and REE in forest floor, A horizons, leaves, and wood were not observed consistently for MSWI sites when compared to city sites. Although pooled forest floor Ni and V and A horizon La and Nd concentrations were significantly different, they were not consistent but driven by a large difference at one of the three cities. This indirect study suggests air pollution control systems have prevented or have reduced TM and REE emissions to local urban forests to negligible amounts. Further studies are needed to evaluate potential interferences from other urban air pollution sources, and conduct direct emission measurements to validate MSWIs are not emitting TMs and REEs.