Trace metals and metalloids in peri-urban soil and foliage across geologic materials, ecosystems, and development intensities in Southern California

Abstract

Purpose: Southern California is a mega-metropolitan area with abundant air pollution, complex geology, and diverse Mediterranean ecosystems. The objective of this study was to evaluate trace metal and metalloids (TMMs) (As, Cd, Co, Cr Cu, Ni, Pb, U, V, Zn) in soils and foliage of peri-urban areas and explore potential effects from human-development, ecosystems, and geologic material. Materials and methods: Foliage of dominant native vegetation, soil samples (0–20 cm), saprolite, and unweathered rock samples were collected across fifty-four sampling sites in foothills spanning coastal Los Angeles and Orange counties to inland San Bernardino and Riverside counties. Results and discussion: Soil As, Cd, Cu, and Pb concentrations were regionally elevated, but not as elevated as point-source polluted sites elsewhere. Soil Cd, Cr, Cu, Pb, and Zn concentrations were above EPA Ecological Soil Screening Levels. Further, enrichment factors (EF) normalized to Ti concentrations in bedrock suggest minor to moderate As, Cd, Cr, Cu, Pb, and V accumulation in soils. Our foliar TMM concentrations and bioaccumulation factors (BAF) (foliar and soil ratio) indicate no bioaccumulation and limited effects across geologic, development intensity, and ecosystems groups. Conclusions: Sedimentary-derived soils affected soil TMMs, but likely not through inheritance of TMMs but by promoting clay and organic matter availability. Proximity to higher development intensity resulted in As, Cd, Cr, Cu, and Pb accumulation in peri-urban soils. Foliar TMM concentrations and BAFs suggest geologic materials, human development, and ecosystem properties were not important factors and TMMs were likely controlled by plant uptake or ecophysiology.