Assessing the chemical interactions and biological effects of a petrochemical and bio-based plastic with a common plastic flame retardant and solvent

Microplastic pollution remains a persistent environmental challenge for aquatic environments. Yet, health impact assessments of microplastics focus largely on the polymers themselves. It is important to understand the chemical behaviour and biological effects of both plastics and chemicals associated with their production, such as additives and solvents. Here, the individual and interactive chemical behaviour and biological impacts of two microplastics and two associated chemicals are assessed: polyvinyl chloride (PVC), a traditional petroleum-based plastic; polyhydroxyalkanoate (PHA) a novel bio-based plastic; triphenyl phosphate (TPhP), a common plastic flame retardant; and a widely use solvent dimethyl sulfoxide (DMSO). Thermogravimetric analysis and Nuclear Magnetic Resonance revealed no significant polymer chemical adsorption and desorption of TPhP or DMSO nor any evidence of reaction products between TPhP and DMSO. Biological assays on a freshwater fish host-parasite system, assessed fish growth, feeding, disease resistance and parasite survival. Both microplastics, the TPhP and solvent DMSO individually and interactively had no significant impact on fish growth. However, PVC alone and PHA + TPhP + DMSO significantly inhibited feeding behaviour of fish and increased mortality. Fish exposed to the solvent DMSO alone experienced the highest disease burdens. Interestingly, off-host survival of parasitic worms exposed to DMSO or TPhP + DMSO was higher than unexposed control worms. This study highlights the complex effects of microplastics and plastic associated chemicals on biological systems, and that novel bio-based plastics are not necessarily 'better' especially when associated with the same chemicals. Industry must be required to declare which chemicals are used in the manufacture of plastic products.