How many microplastic particles are present in Canadian biosolids?

Area of Science:

• Environmental Science
• Ecotoxicology
• Soil Science

Background:

• Treated sewage sludge (biosolids) application to farmlands is a known pathway for microplastic particles (MPs) into terrestrial ecosystems.
• Previous estimates of microplastic concentrations in Canadian biosolids were limited to samples from only four wastewater treatment plants (WWTPs).

Purpose of the Study:

• To quantify microplastic concentrations in biosolids across Canada, addressing a significant knowledge gap.
• To compare microplastic levels in biosolids from various geographical regions, WWTP types, and sludge treatment processes.

Main Methods:

• Collected and analyzed biosolids samples from 22 WWTPs across nine Canadian provinces.
• Quantified microplastic particles per gram dry weight in each sample.
• Identified and categorized microplastic types (fibers, fragments).

Main Results:

• All analyzed biosolids samples contained substantial microplastic concentrations (228–1353 particles/g dry weight; median 636 particles/g).
• Microplastic concentrations were orders of magnitude higher than previously reported for biosolids internationally.
• Fibers constituted the dominant MP type (median 86%), followed by fragments (median 13%).
• No significant differences in MP concentrations were found based on geographical region, WWTP type, or sludge treatment.

Conclusions:

• Canadian biosolids harbor significantly higher microplastic concentrations than previously understood, posing a considerable risk to terrestrial ecosystems.
• The variability in microplastic concentrations appears influenced by complex interactions of local sewershed characteristics, WWTP processes, and operational factors.
• These findings underscore the importance of considering biosolids as a major source of microplastic pollution in land-based environments and necessitate further research into management strategies.