Plastic fish: assessing the scale, chemical properties and biological effects of petrochemical plastics and bioplastics on aquaculture fish

Disposable plastics are an everyday part of our lives but we do not fully understand their impacts on animal welfare. Biobased plastics, termed bioplastics, are marketed as a more envrionmentally friendly alternative to traditional petrochemical plastics. We need to be sure, however, that these bioplastics and their breakdown products are safe when consumed. This interdisciplinary project between three university departments (Cardiff University, Schools of Biosciences, Chemistry and Engineering), driven by industry-led questions, will assess the chemical properties and biological impacts of petrochemical and bioplastics on farmed fish.

The combined mass of environmental plastic exceeds the mass of all fish on the planet. This is concerning on multiple levels; fish comprise the most abundant vertebrate species, they are a major source of protein for humans and aquaculture is the fastest growing food sector globally. If practiced sustainably, fish culturing can provide the lowest carbon source of animal protein for human populations. A key factor that threatens the welfare of managed fish stocks and their future sustainability is pollution. The scale of plastic pollution within managed fish stocks is largely unknown and this must be addressed now. Plastic particles have been detected in fish and human tissues demonstrating that plastics are part of the human food chain, so we must assess how this pervasive pollutant is impacting fish welfare. Our pilot data has shown that plastics without chemical additives impact fish welfare by reducing disease resistance and prolonging infections. However, this may just be 'the tip of the iceberg', as most plastics also have chemical additives, such as plasticisers and thermal stabilisers, and plastics can act as sponges for environmental toxins potentially causing more damage when consumed.
An emerging strategy in addressing plastic pollution is the development of bioplastics. While bioplastics currently only constitute 1% share of annual plastic production, they are widely marketed as an alternative to petrochemical plastics. Bioplastics are openly advertised as eco-friendly and biodegradable, yet research on their environmental suitability is extremely limited and previous degradation studies (conducted under unrealistic scenarios) show minimal degradation. But even if bioplastics do degrade faster than petrochemical plastics, they might paradoxically generate higher rates of persistent micro and nanoplastics. Furthermore, bioplastics contain the same chemical additives as petrochemical plastics, so we must assess how efficient they are at releasing these chemicals and adsorbing other chemical pollutants within aquatic environments. Likewise, we must understand the functional impacts of bioplastics, and the associated additives, when they are consumed by animals.

This project has three key objectives, which directly align with BBSRC strategic priorities on animal health, specifically welfare of managed animals, data driven biology and research that can inform public policy. Firstly, we will assess the scale of plastic pollution within aquaculture fish stocks across the UK. Secondly, in association with prevalent additives and environmental toxins that petrochemical plastics contain, we will assess the chemical properties of these plastics as well as their biological impacts on farmed fish with an emphasis on growth, metabolism, and disease resistance. Then, recognising the urgency to assess alternative plastic solutions, we will test the chemical properties and biological effects of bioplastics, when exposure and consumption occurs. In delivering this project, we will directly inform government agencies and aquaculture about the scale and associated effects of plastic pollution in fish stocks to support policies on plastic use and waste mitigation. By assessing the environmental suitability of bioplastics, future public outreach programmes can help prevent potential greenwashing.

Plastics are the dominant synthetic pollutant facing fish stocks globally and their combined mass now exceeds the biomass of all fish. Yet, we know very little about the functional impacts of plastic pollution on animal welfare. Bioplastics, which are poised as a potential solution to plastic pollution, remain largely unassessed for their environmental suitability. The utilitarian value of plastics is dependent on their chemical versatility, making them effective at bonding with chemical additives and environmental toxins, thereby acting as vehicles for multiple pollutants. With fish constituting a key protein source for humans, understanding the impacts of petrochemical plastic and bioplastic pollutants on fish must be addressed now. Concerningly, our pilot data reveals that even pristine microplastic exposure is detrimental to fish health, reducing their disease resistance and causing high mortalities. The molecular mechanisms underpinning these effects and the levels of plastics within managed fish stocks, however, are largely unknown.

The three objectives for this project support the UN's 2030 Sustainable Development Goals 6, 12 and 14. Firstly, we will assess the scale and types of plastic pollution within managed UK fish stocks. Secondly, we will investigate the physical chemistry and biological effects of petrochemical plastics in association with their chemical additives and environmental toxins on fish welfare (growth, metabolism, disease resistance, including molecular mechanisms, and mortality). Lastly, the chemical properties of bioplastics will be assessed, specifically their degradation, adsorption, and desorption capacity as well as welfare effects on fish when exposure occurs. Thus, this project assesses the scale and effects of plastic pollutants on aquaculture fish while also helping prevent potential greenwashing by providing empirical evidence for the environmental suitability of bioplastics.