Rosie Williams, a toxicologist who works alongside Deaville, found in a 2021 study that high levels of PCBs in blubber samples from 267 stranded harbour porpoises are associated with reduced testicle size in male harbour porpoises. These pollutants are having a direct impact on fertility and potentially affecting the future breeding success of the species. PCBs are also known to suppress the immune system so porpoises with higher contaminant levels are more likely to die from infectious disease.