Inter-storm variation in microplastic concentration and polymer type at stormwater outfalls and a bioretention basin.

Microplastics (MP) are a commonly reported pollutant in the freshwater, marine, and soil environment. Few studies to date have reported MP concentrations and polymer types observed in stormwater, particularly not for catchments with separate storm sewers. The objectives of this study were to determine the microplastic concentration, polymer fingerprints, and the inter-storm variation of MP in two stormwater outfalls and a bioretention basin. Composite stormwater samples were collected at each site across three rain events each in catchments with urban and suburban land use. Particles 250 to 2000 µm were collected, separated into two sizes classes, treated with a wet peroxide oxidation, density separated with NaCl, and buoyant particles (fragments, films, and spheres) were collected for analysis with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Significant differences were observed in the total polymer concentrations and profiles between the sampling sites, potentially due to differences in land use within the catchments sampled, but not between size classes. The highest MP concentrations were observed in samples from the bioretention basin compared to the stormwater outfalls sampled, indicating the potential for green infrastructure to capture MP in the size range studied here. A weak but significant negative correlation was observed between cumulative rainfall (1.5 to 4.5 cm) and MP concentrations but no correlation was observed between antecedent dry days and MP concentrations. These data represent a conservative measure of MP concentrations given that fibers, particles <250 µm, and non-buoyant particles (i.e., density > 1.2 g/mL) were not targeted, but all targeted particles were analyzed with ATR-FTIR. Overall, these results presented provide insight into the loading and character (size, morphology, polymer type) of buoyant MP particles in stormwater that may be useful in designing mitigation strategies.

Total coliform and Escherichia coli in microplastic biofilms grown in wastewater and inactivation by peracetic acid.

Microplastics (MP) have been proposed as a vector for pathogenic microorganisms in the freshwater environment. The objectives of this study were (a) to compare the fecal indicator growth in biofilms on MP and material control microparticles incubated in different wastewater fractions and (b) to compare MP biofilm, natural microparticle biofilm, and planktonic cell susceptibility to disinfection by peracetic acid (PAA). Biofilms were grown on high-density polyethylene, low-density polyethylene, polypropylene MP, or wood chips (as a material control) and incubated in either wastewater influent or pre-disinfection secondary effluent. Reactors were disinfected with PAA, biofilms were dislodged, and total coliform and Escherichia coli were cultivated. Fecal indicators were quantifiable in both MP and wood biofilms incubated in the wastewater influent but only on the wood biofilms incubated in secondary wastewater effluent. More total coliform grew in the wood biofilms than MP biofilms, and the biofilms grown on MP and woodchips were more resistant to disinfection than planktonic bacteria. Thus, it may be possible to refer to the disinfection literature for fecal indicators in biofilm on other particles to predict behavior on MP. Treatments that remove particles in general would help reduce the potential for fecal indicator bypass of disinfection. PRACTITIONER POINTS: MP biofilm had lower concentrations of fecal indicators than wood biofilm Biofilm on MP was not more resistant to disinfection than wood biofilm Biofilms, regardless of substrate, were more resistant to disinfection than planktonic organisms.