Microplastic exposure interacts with habitat degradation to affect behaviour and survival of juvenile fish in the field.

Coral reefs are degrading globally due to increased environmental stressors including warming and elevated levels of pollutants. These stressors affect not only habitat-forming organisms, such as corals, but they may also directly affect the organisms that inhabit these ecosystems. Here, we explore how the dual threat of habitat degradation and microplastic exposure may affect the behaviour and survival of coral reef fish in the field. Fish were caught prior to settlement and pulse-fed polystyrene microplastics six times over 4 days, then placed in the field on live or dead-degraded coral patches. Exposure to microplastics or dead coral led fish to be bolder, more active and stray further from shelter compared to control fish. Effect sizes indicated that plastic exposure had a greater effect on behaviour than degraded habitat, and we found no evidence of synergistic effects. This pattern was also displayed in their survival in the field. Our results highlight that attaining low concentrations of microplastic in the environment will be a useful management strategy, since minimizing microplastic intake by fishes may work concurrently with reef restoration strategies to enhance the resilience of coral reef populations.

Plasticiser leaching from polyvinyl chloride microplastics and the implications for environmental risk assessment.

Microplastics in aquatic environments is a growing concern, particularly due to the leaching of chemical additives such as plasticisers. To develop comprehensive environmental risk assessments (ERAs) of high-concern polymers and plasticisers, an understanding of their leachability is required. This work investigated diethylhexyl phthalate (DEHP) and bisphenol A (BPA) leaching from polyvinyl chloride (PVC) microplastics (average diameter = 191 µm) under simulated marine conditions. Leaching behaviours were quantified using gel permeation chromatography (GPC) and thermal gravimetric analysis (TGA), and the polymer's physiochemical properties analysed using differential scanning calorimetry (DSC), Fourier Transform-Infrared Spectroscopy (FT-IR) and optical microscopy. Experimental data were fitted to a diffusion and boundary layer model, which found that BPA leaching was temperature-dependent (diffusion-limited), whereas DEHP leaching was controlled by surface rinsing. Model predictions also highlighted the importance of microplastic size on leaching dynamics. These data contribute towards greater accuracy in ERAs of microplastics, with implications for water quality and waste management, including decommissioning of plastic infrastructure.

Understanding plasticiser leaching from polystyrene microplastics.

Plastic pollution in our oceans is of growing concern particularly due to the presence of toxic additives, such as plasticisers. Therefore, this work aims to develop a comprehensive understanding of the leaching properties of plasticisers from microplastics. This work investigates the leaching of phthalate acid ester (dioctyl terephthalate (DEHT) and diethylhexyl phthalate (DEHP)) and diphenol (bisphenol A (BPA) and bisphenol S (BPS)) plasticisers from polystyrene (PS) microplastics (mean diameter = 136 µm to 1.4 mm) under controlled aqueous conditions (temperature, agitation, pH and salinity). The leaching behaviours of plasticised polymers were quantified using gel permeation chromatography, high performance liquid chromatography and thermal gravimetric analysis, and the particle's plasticisation characterised using differential scanning calorimetry. Leaching rates of phthalate acid ester and diphenol plasticisers were modelled using a diffusion and boundary layer model, whereby these behaviours varied depending on their plasticisation efficiency of PS, the size of the microplastic particle and the surrounding abiotic conditions. Leaching behaviours of DEHT and DEHP were strongly influenced by the microplastic-surface water boundary layer properties, thus wave action (i.e., water agitation) increased the leaching rate of these plasticiser up to 66 % over 21-days, whereas BPA and BPS plasticisers displayed temperature- and size-dependent leaching and were limited by molecular diffusion throughout the bulk polymer (i.e., the microplastic). This information will improve predictions of plasticiser concentration (both that remain in the plastic and released into the surrounding water) at specific time points during the lifetime of a plastic, ultimately ensuring greater accuracy in the assessment of toxicity responses and environmental water quality.