Abstract
Microplastics pollution has been threatening the global environmental security, in which agricultural activities are considered as a main source of microplastics occurrence in soils. However, little is known about the occurrence characteristics of microplastics in agricultural soils with long-term plastic film mulching. Therefore, the abundance, distribution, and composition of microplastics were investigated by analyzing 225 soil samples collected from typical maize (Zea mays L.) planting zones with and without long-term (>20 years) plastic film mulching in northern China. Microplastics abundance in mulched soils (754 ± 477 items kg–1) was significantly higher than that in non-mulched soils (376 ± 149 items kg–1), which indicated that plastic film mulching contributed half of microplastics in soils. Moreover, microplastics abundance was significantly positively related to the length of time with film mulching applied. The percentage of microplastics <0.5 mm in mulched soils (50.9%) was significantly lower than that in non-mulched soils (62.2%). Microplastics abundance and size in mulched and non-mulched soils decreased with increased soil depth. Most microplastics were fragments of polypropylene, films of polyethylene, and fibers of polyester. The proportion of films in mulched soils was significantly higher than in non-mulched soils, whereas that of fibers was significantly higher in non-mulched soils. This study confirmed that long-term plastic film mulching increases microplastics pollution in agricultural soils, warranting further evaluation of the associated ecological risks of microplastics in soil ecosystems.
Highlights
Global plastic production has increased from 230 to 359 million tons between 2005 and 2018, and China accounted for 30% of that production (Statista, 2020)
This study confirmed the occurrence of microplastics in maize farmland soils with long-term plastic film mulching in northern China
Microplastics pollution characteristics was revealed in typical maize farmland soils with and without long-term plastic film mulching
Summary
Global plastic production has increased from 230 to 359 million tons between 2005 and 2018, and China accounted for 30% of that production (Statista, 2020). With recycling rates that are generally low, plastic waste is considered a global environmental pollution issue because of its low degradability (Barboza et al, 2018). Plastics can remain in the environment permanently, Microplastics in Maize Mulched Soil they decompose into increasingly smaller pieces of plastic debris under the actions of biological, physical, and chemical processes, such as decomposition by intestinal microorganisms and insects, agriculture cultivation, weathering, and oxidative degradation under ultraviolet irradiation (Sul and Costa, 2014; Rillig et al, 2017; Ahmed et al, 2018). Microplastics have received special attention and are listed as the second most important scientific issue in the ecology and environmental science (Farrell and Nelson, 2013; Horton et al, 2017). Soils are the major and direct sources of microplastics, much remains unknown regarding microplastics in terrestrial environments (Rillig, 2012; Horton et al, 2017)
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