Microplastic fibres: Generation from textiles, and potential to sorb aqueous metal(loid)s in wastewater
Creators: name: Frost, Harrison
Publisher: name: University of Surrey
Year: 2023

description: Microplastics are persistent, ubiquitous environmental contaminants of increasing concern. The laundering of synthetic textiles is an important source of microplastic fibres, with millions potentially being generated in a single wash. These fibres enter the wastewater treatment, where they are likely to coexist with elevated concentrations of potentially toxic metals and metalloids, so sorption may occur. During wastewater treatment, the vast majority of microplastics are retained in the solid sludge, which is often applied to agricultural soils. Microplastics may therefore act as vectors, transporting sorbed metal(loid)s into agricultural soils or organisms. Research on the sorption of metal(loid)s onto microplastics has largely ignored polyethylene terephthalate (PET), the most widely used synthetic fibre in the manufacturing of apparel textiles.<br>
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description: The influence of the recycled fibre content of several fabric types on their shedding propensity was investigated using accelerated laundering, followed by the quantification of shed fibres in the laundering solution. The recycled fibre content of cotton knit, polyester knit, and polycotton twill weave fabrics did not significantly change the number of fibres shed. Results indicated that any changes to the fabric properties due to recycling, had a minimal impact on their tendency to shed during accelerated laundering.<br>
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description: PET fibres with an average length of 174.1 ± 131.8 µm were generated for use in experiments, by grinding PET fabric in a cryogenic mill. Sorption experiments were conducted with a range of 12 metal(loid)s (Sb, As, Cd, Cr, Cu, Co, Pb, Hg, Mo, Ni, V and Zn. Sorption affinity varied greatly between metal(loid) types, and distribution coefficients were highest for Pb (939.4 mL g&lt;sup&gt;-1&lt;/sup&gt;), followed by Cd (897.9 mL g&lt;sup&gt;-1&lt;/sup&gt;), Cu (507.3 mL g&lt;sup&gt;-1&lt;/sup&gt;), and Hg (402.9 mL g&lt;sup&gt;-1&lt;/sup&gt;). Sorption was generally very low for oxyanions (As, Sb, V), suggesting electrostatic interactions may be involved in the sorption mechanism.&lt;br&gt;
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description: Kinetics experiments were performed with Cd and Hg to determine the rate of sorption equilibration between these metals and PET microplastic fibres. The kinetics experiments revealed that equilibrium was reached in under 6 hours. This is well within the timeframe of water retention during wastewater treatment, suggesting that microplastics exiting wastewater treatment systems are likely to be saturated with metals.<br>
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description: Langmuir sorption capacities for Cd and Hg ranged from 4.3 – 5.3 µg g<sup>-1</sup>, and 17.3 – 23.1 µg g<sup>-1</sup> respectively, and were significantly affected by the initial pH. Results are generally consistent with similar studies, and suggest metal-loaded microplastics are unlikely to directly increase the total metal concentrations in agricultural soils. Literature data vary greatly however, reflecting the complexity of the sorption process which is influenced by the physicochemical properties of the microplastics (particle size, surface area, polymer type), the chemical properties of the sorbent (ionic radius, charge), the solution chemistry (pH, ionic strength, presence of humic substances), and other experimental factors (contact time, sorbent concentration range). Future research should consider whether microplastics can increase the bioavailability of sorbed metals to organisms, or alter their toxicity through synergistic effects.<br>