Abstract
Invasive zebra and quagga mussels (Dreissena spp.) in the Great Lakes of North America are biomonitors for chemical contaminants, but are also exposed to microplastics (<5 mm). Little research has examined in situ microplastic ingestion by dreissenid mussels, or the relationship between microplastics and chemical contaminants. We measured microplastics and chemical contaminants in mussel tissue from Milwaukee Harbor (Lake Michigan, United States) harvested from reference locations and sites influenced by wastewater effluent and urban river discharge. Mussels were deployed in cages in the summer of 2018, retrieved after 30 and 60 days, sorted by size class, and analyzed for microplastics and body burdens of three classes of contaminants: alkylphenols, polyaromatic hydrocarbons, and petroleum biomarkers. Microplastics in mussels were higher in the largest mussels at the wastewater-adjacent site after 30 days deployment. However, there was no distinction among sites for microplastics in smaller mussels, and no differences among sites after 60 days of deployment. Microplastics and chemical contaminants in mussels were not correlated. Microplastics have a diversity of intrinsic and extrinsic factors which influence their ingestion, retention, and egestion by mussels, and which vary relative to chemicals. While dreissenid mussels may not serve as plastic pollution biomonitors like they can for chemical contaminants, microplastics in dreissenid mussels are widespread, variable, and have unknown effects on physiology, mussel-mediated ecosystem processes, and lake food webs. These data will inform our understanding of the spatial distribution of microplastics in urban freshwaters, the role of dreissenid mussels in plastic budgets, and models for the fate of plastic pollution.
Highlights
Bivalves such as clams, oysters, and mussels, are commonly used to measure chemical contaminants in the environment as they are sessile, considered relatively tolerant to toxic compounds, and abundant in aquatic ecosystems globally (Sericano et al, 1995; Farrington et al, 2016)
There was no difference among sites in June when microplastic was quantified as No./g wet weight, dry mass, or ash-free dry mass (AFDM) (Figure 3A and Supplementary Figures 1A, 2A)
In August, there were no significant differences in microplastic abundance among sites (Figures 2C, 3C and Supplementary Figures 1C, 2C)
Summary
Oysters, and mussels, are commonly used to measure chemical contaminants in the environment as they are sessile, considered relatively tolerant to toxic compounds, and abundant in aquatic ecosystems globally (Sericano et al, 1995; Farrington et al, 2016). The Mussel Watch Program assesses mussel tissue for basic metrics (e.g., moisture, lipid content), as well as concentration of contaminants of emerging concern including alkylphenols, polycyclic aromatic hydrocarbons (PAHs), and petroleum biomarkers. Petroleum biomarkers (i.e., hopanoids, steranes, and triaromatic steroids; TAS) are assessed in mussel tissue to investigate the source and fate of petroleum hydrocarbons in the environment given their resistance to degradation (Wang and Stout, 2010). These classes of contaminants may co-occur with plastic contamination in aquatic organisms, but this has not yet been examined in mussel tissues for freshwater bivalves
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