Aquaculture uses large amounts of plastic for infrastructure and equipment, which likely contributes to microplastic (MP; <5 mm) release to the environment. In addition to feed pipes and cage collars, pen nets are considered to be a potential source for MP release. In-situ net cleaning, typically using dedicated pressure washers, may exacerbate abrasion of nets and their coatings, leading to higher MP emissions during cleaning periods. As a result, fibres as well as synthetic particles from net coatings may be dispersed into the surrounding seawater.
A laboratory experiment simulating abrasion damage through net cleaning was performed to quantify and compare MP release from common and alternative net (Nylon, HDPE, Dyneema, ENTEX) and rope (polyolefins, HDPE, Dyneema) materials, both new and used. For the net material, samples with two coatings used to extend material lifetime were also included. The abrasion tests were conducted using a Buraschi abrasion simulator system (Figure 1). Particles released into the water were washed and filtered on 500 and 10 µm filters to isolate ’large’ and ’small’ MP fractions. The collected material was then quantified and physicochemically characterised using a combination of gravimetric measurements, microscope imaging and chemical fingerprinting by pyrolysis GC-MS.
Results indicate increased release from nylon nets compared to the HDPE, Dyneema and Entex nets. Coatings interacted differently with the various net materials, where there was no change in MP release from the coated Dyneema nets, but an increased particle release from the coated nylon nets. For ropes, we observed increased release from new Dyneema compared to new polyolefins and HDPE. For both nets and ropes, used materials released more MP than new ones.
The next step will be to conduct measurements in the field to validate the laboratory data. However, the outcomes of the laboratory study already indicate that the aquaculture industry may reduce current MP releases to the marine environment by selecting specific combi-nations of net and rope materials/polymers.