Sinking of buoyant freshwater microplastics induced by biofilm growth

Session: Microplastics in Freshwater Systems: Advances in Chemistry, Biology and Physics (2)

Patricia Semcesen, University of Toronto, [email protected]
Roberta Fulthorpe, University of Toronto Scarborough, [email protected]
Mathew Wells, University of Toronto Scarborough, [email protected]

Abstract

Laboratory experiments tested the effects of microbial (biofilm) growth on the buoyancy of irregularly shaped microplastics in a freshwater environment. Biofilm-induced effects on the settling onset time, rise and settling velocities of fabricated polypropylene microplastics were quantified and compared to non-biofouled microplastics. Biofilm growth induced sinking of small microplastics (125-212 µm) beginning at 18 days, 6 days sooner than for large microplastics (1000-2000 µm). Hence, smaller microplastics can be expected to become deposited in sediments closer to their sources relative to larger particles. It can be estimated that microplastic particles are lost to sediments in 2-3 weeks given typical water current velocities on the order of 5 cm/s over distances comparable to the approximate widths of Lakes Michigan, Erie, and Ontario on the order of 50 km. Understanding the effects of biofilm growth on microplastics improves understanding of the potential distribution and accumulation of microplastics in the Great Lakes.