Impact of Micro-plastics on Microbial Activity in Soil

Abstract

Particulate plastics (i.e., ‘micro-plastics’ or ‘nano-plastics) are synthetic polymer particles measuring less than 5 mm in diameter. These particles have extensively been used worldwide as primary constituents (i.e., in cosmetics) and secondary constituents (i.e., breakdown of plastic mulch). Therefore, particulate plastics are widely found in aquatic and terrestrial environments and also identified as causing severe pollution. Because their impact on microbial functions in terrestrial environment remains largely unclear, an incubation study was conducted to examine the impact of particulate plastic contamination on microbial activity in soil. In this study soil samples were mixed with particulate plastics at the ratio of 6.4% (w/w) in soil. Two types of contaminants, perfluorooctane sulfonate (PFOS) at 1000 μg kg−1 soil and copper (Cu) at 500 mg kg−1 soil, were also used. After two weeks of the incubation period, soil respiration, microbial biomass carbon (MBC), dehydrogenase activity (DHA) and bioavailable Cu were measured. Results indicated low basal respiration, DHA and MBC in contaminated soil treatments. Although Cu toxicity caused a 30% decrease in DHA in soil, the toxicity caused by both Cu and PFOS was more profound. The microbial activities in the contaminated soils were higher in the presence than absence of particulate plastic addition. Our experimental evidence suggests that the particulate plastics interact with organic and inorganic contaminants and modulate their toxicity to soil microbial activities.