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Microplastics may act as a vector for potentially hazardous metals in rural soils in Xiamen, China
Summary
Researchers investigating rural soils in coastal Xiamen, China found microplastics at abundances up to 2,222 items/kg alongside eight potentially hazardous metals including arsenic, cadmium, and mercury, suggesting microplastics may act as vectors for metal transport across agricultural land. The co-occurrence of microplastics and toxic heavy metals in farmland soils amplifies human health risks, as both contaminants can be taken up by crops and enter the food supply simultaneously.
Soil represents a key reservoir for microplastics (MPs) in the terrestrial environment. Unfortunately, scientific endeavors on MP pollution in rural soils of coastal cities appear to be inadequate. The interconnection between rural soil MPs and potentially hazardous metals (PHMs) is underexplored. This work investigated the combined pollution of MPs and 8 PHMs (As, Cd, Cr, Cu, Zn, Pb, Hg, and Ni) in the rural soils of Xiamen, a typical coastal city in China. Sixteen sites were selected based on different administrative areas and representative land use types in Xiamen for surface soil sampling. MP selection and identification were performed using a stereo light microscope and Senterra II Compact Raman Microscope. MPs were analyzed for elemental composition using scanning electron microscopy with energy dispersive X-ray spectroscopy. Soil properties and PHMs concentrations were measured using the relevant industrial and national standards. The abundance of MPs ranged from 15 to 2222 items kg–1 with an average of 229 ± 523 items kg–1, suggesting that the rural soils have been widely disturbed by MP contamination. The dominant shape, color, and size of MPs were fragments (55.3%) and fibers (35.8%), transparent (59.3%) and white (17.7%), and < 1 mm (64.4%), respectively. Polypropylene (67.6%) was the main polymer type, followed by polystyrene (11.0%) and polyester (9.4%). The abundance of MPs (except for the most contaminated S13) was not highly associated with PHMs contents in rural soil. The energy dispersive X-ray spectra manifested irregular distribution of Zn and Pb on the MP surfaces at site S13. MP pollution was widespread in rural soils in Xiamen. MPs served as the potential vector that transmitted PHMs to soils at high levels of PHMs. The rural soil MPs in Xiamen may be originated from agricultural, industrial, and human activities. This study provides insights into combined contamination of MPs and PHMs in rural soils in Xiamen, which will help formulate effective pollution abatement measures.