A new study has found that mercury levels are rising in many parts of the ocean. The study analysed liver samples from 738 harbour porpoises that stranded along UK coastlines between 1990 and 2021. It found that mercury levels increased over time, and animals with higher levels are more likely to die from infectious disease. Human activities such as the burning of fossil fuels have already tripled mercury in shallower ocean waters (less than 1,000 metres in depth) since the Industrial Revolution. Warmer seas and shifting food webs are exacerbating the problem by increasing the rate of accumulation in the marine food chain.