Abstract
Many of the methods for microplastics quantification in the environment are criticised creating problems with data validity. Quantification of microplastics in the surface microlayer of aquatic environments using glass plate dipping holds promise as a simple field method, but its efficiency has yet to be validated. We tested a standard glass plate dipping method to assess recovery of four common polymer microfibres and two common natural fibres, under three different salinities (freshwater, brackish water, saltwater). Overall recovery rates were low (26.8 ± 1.54%) but higher recoveries were observed under saltwater treatments (36.5 ± 3.01%) than brackish water (24.5 ± 1.92%) or freshwater (19.3 ± 1.92%). The fibre types showed different recovery rates, with acrylic yielding significantly higher recovery rates (37.0 ± 2.71%) than other fibres across treatments. No clear relationship between the density of the fibres and the recovery efficiency was seen. We suggest that, where this method is used for monitoring microplastics, the results will typically underestimate the total amount present, but that recovery is sufficiently consistent to allow comparison of differences between sampling locations. When comparing data across river-estuarine or similar transects salinity should be monitored to account for salinity-induced differences in sampling recovery.
Highlights
As with most environmental microplastic sampling, there is no standard method of sampling the SML
In salt water more PP, acrylic, wool and rayon microfibres were recovered than polyethylene terephthalate (PET) (p = 0.000; p = 0.000; p = 0.0.004; p = 0.004, Tukey’s tests), more PP fibres were recovered than cotton (p = 0.003, Tukey’s test) and more acrylic than cotton (p = 0.003, Tukey’s test)
Acrylic had the highest recovery rates across treatments with a mean of 37.0% (± 2.71 SE). This was higher than PET (17.33% ± 2.38 SE; p = 0.000, Dunn’s test), cotton (22.67% ± 3.04; p = 0.002, Dunn’s test), PP (28.67% ± 5.61; p = 0.009, Dunn’s test) and wool (25.67% ± 3.45 SE; p = 0.013, Dunn’s test) but similar to the recovery rate of rayon (29.33% ± 3.08 SE)
Summary
As with most environmental microplastic sampling, there is no standard method of sampling the SML. The density ranges of different polymers, as well as buoyancy of particles and their degree of weathering and aggregation, likely affects both concentration of microplastics in the SML and their recovery. Surface microlayers exist in freshwater and brackish water e nvironments[15], where the less saline water has a lower (or variable) density; this may affect microplastic concentration and recovery. We propose that this is the first study to (a) assess recovery rates of an SML sampling method for microplastics, and (b) to consider the effects of salinity on these recovery rates
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