Abstract
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.
Highlights
The upper chamber is unscrewed and rinsed; recovering particles attached to the inner walls that would be lost using other filtration approaches
polyvinyl chloride (PVC) contamination occurred during the extraction of 20 samples, with indicative grey shavings found in both negative controls and field samples
Without continuously closing and opening the ball valve, contamination caused by the resulting friction is substantially reduced
Summary
As part of method validation work for future microplastic sampling campaigns, a pilot study of extraction efficiency and contamination potential of a Sediment Microplastic Isolation (SMI) unit designed by Coppock et al [1] was performed using estuarine sediments collected in the United Kingdom (UK). A sub-set (N = 20) was processed using an SMI unit (Fig. 1; Image a) with zinc chloride (ZnCl2; 1.5 g cmÀ3) solution as per the original Coppock et al [1] protocol. Striations were evidenced on the ball valve after 20 extractions (Fig.; Image b) that were not originally documented (Fig. 1; Image c) suggesting a risk of polyvinyl chloride (PVC) contamination of the samples. This was confirmed by analysing blank samples, which contained grey fragments/shavings (Fig.; Image d) further. Contamination occurring within the processing time of 20 samples suggests that long-term use of this unit may lead to overestimation of PVC polymers in field samples. As a result of this contamination, a modification to the operation of the SMI unit was proposed which is presented
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