Mussels exposed to polyester microfibres in seawater grow at a slower rate than unexposed mussels. This study examines whether cotton microfibres could have same impact

Microfibres of plastic and cotton are ubiquitous in the sea worldwide, and are known to be readily ingested by a range of marine organisms. As much as 12.7 million tonnes of plastic enters the oceans every year¹, with microplastics (MP) found in differing concentrations at different locations, and in various forms: fragments, films, beads and fibres. However, microfibres are the most prevalent form of both plastic (polypropylene, polyester), and non-plastic (cotton, rayon) marine micro-pollutants.

Bivalve shellfish, such as scallops and mussels, Mytilus spp., readily ingest MP, more so than some other marine species. As many as 88 items of MP per litre of seawater have recently been observed, raising concern over potential impacts on marine biota that can ingest them. Most cotton and plastic microfibres in aquatic environments are believed to derive from textile abrasion of man-made fabrics, during washing of clothing, for example, or from abrasion of ropes and nets.

The European Union is committed to reducing plastic waste in the environment and has a number of current and proposed strategies and regulations to achieve this. In 2022 the EU published the EU strategy for Sustainable and Circular textiles, focusing on the release of microplastic fibres from textiles. At present natural fibres such as cotton are not regulated, however, an expansion of the Eco-design directive is currently underway, which will include rules on the eco-design of sustainable products. Information on the impacts of non-synthetic microfibres, such as cotton, on marine animals is valuable to policymakers when considering regulatory changes.

This study was designed to tackle several knowledge gaps, firstly by using environmentally relevant concentrations of microfibres, and secondly by comparing the impact on mussels of natural cotton microfibres with synthetic polyester ones. The authors of the study are also the first to investigate the long-term exposure of shellfish to man-made plastic microfibres at environmentally relevant levels, to identify any chronic health effects. By studying juvenile mussels, which are likely to be less resilient to environmental pollutant exposure than adult mussels, the study could also detect impacts only discernible at this life stage of rapid growth.

The researchers exposed juvenile mussels to either red polyester or yellow cotton microfibres for 94 days. They tested two differing concentrations of polyester fibres on mussels – eight fibres per litre (representing current environmental samples), and 80 fibres per litre (representing future projected concentrations) – whereas cotton fibres were tested only at a concentration level of 80 fibres per litre. A control group of mussels was not exposed to microfibres of either material. Prior to the experiment the mussels were kept in filtered seawater for a week, to remove MP particles.

Mussels exposed to either cotton, or plastic microfibres, grew at a slower rate than unexposed mussels. At the higher concentration of 80 microfibres per litre, mussels grew 36% less over the three-month study period. According to the researchers, these findings show that polyester microfibres can, in realistic projected marine environmental concentrations, adversely affect mussel growth. Mussels are important prey for many marine species, whilst also providing carbon sequestration and a biofiltration service; hence a reduction in size could have wider ecosystem effects. Mussels are also an important farmed seafood: in 2018, 17.7 million tonnes were produced by aquaculture for consumption. Hence, a slower growth rate may affect the speed at which mussels reach harvestable size, and so impact the commercial viability of harvests.

Although not statistically significant, cotton microfibres also reduced mussel growth rate by 19% over the three-month study period, highlighting that other man-made particles should be investigated for their impact on marine life. The sublethal negative impact of microfibres on mussels shown by this experiment, when combined with additional multiple stressors from climate change, pollution, and overfishing, could have large-scale effects on marine ecosystems. Global bivalve populations are already declining, with many species already listed as endangered and some classed as extinct. Microfibres may expedite this pattern of decline.

According to the researchers, greater priority should be given to future research on the impacts of ingestion of natural microfibre particles, such as cotton, as well as plastic microfibres, on marine biota. Understanding the impacts of microplastics, and other man-made particulate pollution, can aid policymakers in identifying priority materials and products for regulatory attention.

Further Information

Horizon Europe, the EU’s funding programme for research and innovation, is supporting several projects which analyse the impact of the release of microplastics in the environment. For example,

Removal of microplastics from the environment using autochthonous wastewater-derived microbial consortia;

Photochemistry at the Ocean's Surface: Effects and Interactions of Dissolved Organic Matter with Microplastics.

Footnote:

1. Jambeck, J. R., Geyer, R., Wilcox, C., Siegler, T. R., Perryman, M., Andrady, A., Narayan, R., and Law, K. L. (2015). Plastic waste inputs from land into the Ocean. Science, 347(6223): 768–771.

Source:

Walkinshaw, C., Tolhurst, T.J., Lindeque, P.K., Thompson, R.C., and Cole, R. (2023) Impact of polyester and cotton microfibers on growth and sublethal biomarkers in juvenile mussels. Microplastics and Nanoplastics, 3: 5 (2023).

To cite this article/service:

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.