Simple yet effective modifications to the operation of the Sediment Isolation Microplastic unit to avoid polyvinyl chloride (PVC) contamination

Effective microplastic extraction from sediment and soil samples requires a density separation step, with the ability to remove >80 % of plastic particles without introducing substantial contamination. Additional benefits such as affordability and simplicity allow microplastic campaigns on limited budgets the ability to achieve high extraction efficacies. Coppock et al. (2017) designed the Sediment Microplastic Isolation (SMI) unit with these criteria in mind, warning that long-term use may lead to polyvinyl chloride (PVC) contamination. As part of the method validation work for a large-scale international project, collecting samples from more than 100 rivers globally, a pilot study of extraction efficiency and contamination potential of an SMI unit was performed. PVC contamination occurred during the extraction of 20 samples, with indicative grey shavings found in both negative controls and field samples. The original protocol was modified and artificially spiked sediments (positive blanks) were run to test extraction efficacy. The modification, requiring the PVC ball valve to remain open throughout the extraction. This modification eliminated contamination caused by wear and tear of the ball valve, while still maintaining recovery rates >80 %. Three points describing the change not the original: • The PVC ball valve is open while sample is agitated with a magnetic stirrer. • The PVC ball valve remains open while the solution is decanted. • The upper chamber is unscrewed and rinsed; recovering particles attached to the inner walls that would be lost using other filtration approaches.