The influence of microplastics for the transportation of E. coli using column model

Abstract

Microplastics (MPs) are widely present in soils and can influence the transport of bacteria in complicated manners, which might affect the safety of water resources and public health. In this study, the effects of MPs from one classic plastic polyethylene (PE) and one biodegradable plastic poly-lactic acid (PLA) on the transport behaviors of bacteria were determined. The transportation of E. coli in pure quartz sands and quartz sands amended with PE or PLA MPs of different concentration (10% and 20%, λ = 0.1 and 0.2) were compared at different ionic strength (IS). The transport behaviors of bacteria were then interpreted by thermodynamics, extended Derjaguin–Landau–Verwey–Overbeek (xDLVO) theory and two-site kinetic retention model. Elevating MPs concentration or background solution IS would discourage bacterial migration in all cases. The presence of 10% MPs at low IS increased the bacterial transport and the breakthrough curves (BTCs) changed from “blocking” to symmetrical profile may due to the absorption of MPs on quartz sands and subsequent deposition site competition, as well as the size exclusion caused by MPs. Whereas, with λ = 0.2, both MPs inhibited the transport of bacteria may due to the couple effect of physical entrapment (straining) and surface roughness of MPs. The bacterial transport rate declined to about 60% in presence of 20% PLA MP, regardless of the ionic strength. Two-site kinetic retention modelling results showed that the retention sites increased with MPs amendment, which demonstrated that MPs in the transport medium could change the property of the medium, alter the deposition and transport behavior of bacteria. Our findings allowed for better understanding of the influence of MPs on bacterial transport and thus to a better assessment of the potential risks of MPs.