A cell culture model to study the impacts of plastic additives on marine mammal stress response

Abstract

Plastic pollution is an urgent and growing global crisis, with over 360 million tons of plastic produced annually and approximately 8 million tons entering our oceans each year. Plastics contain chemical additives that improve their function, but these chemicals are not chemically bound to the polymer and can migrate out of the plastic and into the environment. Many of these additives are lipophilic, putting marine mammals at particular risk of bioaccumulation of these contaminants due to their large lipid deposits and long lifespans. While previous research has demonstrated impacts of plastic additives on cellular, endocrine, immune, and reproductive systems in marine mammals, their effects on stress-response pathways remain underexplored. If additives exacerbate stress response at the molecular level, they may negatively impact marine mammals’ ability to forage or reproduce. This study investigated whether plastic additives influence the glucocorticoid receptor (GR) pathway, a key regulator of stress response. A literature review identified 26 plastic-derived chemical additives present across 29 cetacean species, with diethyl phthalate (DEP) and di-2-ethylhexyl phthalate (DEHP) among the most prevalent. Fibroblast cell lines from four marine mammal species — humpback whale (Megaptera novaeangliae), goose-beaked whale (Ziphius cavirostris), Atlantic bottlenose dolphin (Tursiops truncatus), and Tamanend’s bottlenose dolphin (Tursiops erebennus) — were exposed to varying concentrations of DEP and DEHP for 24 hours. The expression of three GR-related genes (ANGPTL4, ICAM1, and PTGS2) was quantified using reverse-transcription quantitative PCR (RT-qPCR). Results showed no consistent dose-dependent changes in gene expression for either chemical. Although DEP exposure was associated with significantly increased ANGPTL4 expression, overall expression levels were low, variability across samples was high, and standard curves were inconsistent, indicating a need for additional validation of this finding. This study suggests that diethyl phthalate (DEP) and di-2-ethylhexyl phthalate (DEHP), two widely detected plastic chemical contaminants in marine mammals, do not strongly induce a GR-mediated stress response as observed by expression of ANGPTL4, ICAM1, or PTGS2 genes. The potential for effects induced within alternative pathways or outside the sampled time frame, however, cannot be ruled out. Continued research on these plastic additives and the identification of thresholds of adverse biological effects are essential for supporting science-based regulatory strategies aimed at mitigating the long-term impacts of plastic additives on marine mammals.