Assessment of Biofilm Growth on Microplastics in Freshwaters Using a Passive Flow-Through System

Abstract

Biofilms that colonize on the surface of microplastics (MPs) in freshwaters may pose a potential health risk. This study examined factors that influence MP-associated biofilm growth, including polymer type, degree of weathering, and source water quality. Weathered MPs produced in-lab were employed in biofilm trials conducted on site using a passive flow-through system with raw water at drinking water treatment facility intakes. Adenosine triphosphate (ATP) was used to quantify biofilm abundance; biofilm composition was assessed via metagenomic sequencing. Biofilm growth was observed on all polymer types examined and most prevalent on polyvinyl chloride (PVC), where ATP levels were 6 to 12 times higher when compared to other polymers. Pathogen-containing species including Salmonella enterica and Escherichia coli were present on all polymers with relative abundance up to 13.7%. S. enterica was selectively enriched on weathered MPs in specific water matrices. These findings support the need to research the potential accumulation of pathogenic organisms on microplastic surfaces.

Keywords: ATP; HDPE; LDPE; PET; PP; PVC; biofilm; freshwater; metagenomics; weathering.

Figure 1

ATP associated with five virgin polymer types and four source waters. Vertical bars indicate maximum and minimum values, boxes indicate upper and lower quartiles, “×” indicates mean value, “−” indicates median. n = 6 for Otonabee River and n = 8 for all others.

Figure 2

Correlation between (virgin) PVC-associated ATP concentrations and source water as characterized by DOC, 8 samples collected over 16 weeks for Lake Ontario and Grand River (upstream and downstream), and 6 samples collected over 21 weeks for Otonabee River. Vertical bars represent ± one standard deviation (n = 2).

Figure 3

ATP concentrations associated with virgin and weathered polymers in three water matrices; “8 wk” or “16 wk” indicate exposure time in weeks, “V” = virgin, “W” = weathered; vertical bars indicate ± 1 standard deviation (Lake Ontario: DOC = 1.72–4.25 mg/L, temperature = 9.1–20.6 °C; Grand River (upstream): DOC = 5.31–13.15 mg/L, temperature = 5.9–28.1 °C; Grand River (downstream): DOC = 3.92–6.55 mg/L, temperature = 9.9–24.3 °C).

Figure 4

Phylum-level relative abundance within MP-associated biofilms. Selected polymer–source water combinations include 16- and 21-week virgin polymers and Otonabee River, and 8-week virgin and weathered polymers and Grand River (downstream).

Figure 5

PCoA plots of biofilm communities based on Bray–Curtis dissimilarity, ellipses created at 95% confidence based on (a) polymer type and (b) source water.