Occurrence and size distribution of microplastics in mudflat sediments of the Cowichan-Koksilah Estuary, Canada : a baseline for plastic particles contamination in an anthropogenic-influenced estuary

Abstract

Globally, large plastics and microplastics are ubiquitous pollutants in marine environments and coastal areas (Bergmann et al., 2015; Jambeck et al., 2015; Lebreton et al., 2017), and have reached unprecedented levels in the oceans (Bergmann et al., 2017; Eriksen et al., 2014; Kane et al., 2020; Lebreton et al., 2018). Coastal and estuarine environments in particular often contain the highest levels of microplastics because of their proximity to human settlements, and estuaries experience conditions such as wave action that facilitates the breakdown of macroplastics into smaller microfragments, with the exception of microfibers which occur mostly as fibers. As our understanding of the prevalence of microplastics and their impacts on marine-coastal ecosystems and the species that inhabit them grows it is becoming increasingly important to document baseline levels in areas with unique hydrological processes to assess risks to local wildlife (Browne et al., 2007; Browne et al., 2010; Andrady, 2011; Ross and Morales-Caselles, 2015; Bergmann et al., 2015). Microplastics are defined as plastic particles that are < 5 mm (i.e., < 5000 μm) in size, and can be separated into two categories: 1) primary microplastics that are deliberately manufactured (e.g., microbeads in cosmetics, industrial cleaners or virgin resin pellets for manufacturing and nurdles); and 2) secondary microplastics that are by-products, or break-down products, of larger plastics (i.e., polymers > 5mm), such as clothing, ropes, bags and bottles (Moore, 2008, GESAMP, 2010, Browne et al., 2007, Andrady, 2011, Duis and Coors, 2016). Most microplastics originate from terrestrial sources (e.g., household and industrial waste and wastewater), although these pollutants can also be released from marine activities (e.g., fishing, shipping) (Browne et al., 2007, Duis and Coors, 2016).