Potential increase of neurotoxic mercury risk in global blue carbon nature-based solutions

Blue carbon strategies are now being proposed as a promising, nature-based solution for achieving multiple benefits. Here we provide field evidence on the co-accumulation of organic carbon and neurotoxic mercury (Hg) in coastal environments. We estimate the global Hg stock in the top metre of sediment of blue carbon ecosystems to be 21,306 to 125,018 Mg (mean = 73,162 Mg), highlighting that Blue Hg stock is an important, dynamic, reactive, but overlooked Hg pool in global Hg cycle and health risk. Preserving and expanding blue carbon ecosystems have been hailed as a climate-friendly nature-based solution to store carbon. However, this can cause co-accumulation of neurotoxic mercury, highlighting the need for holistic climate solutions.