Every year, coal-fired power plants and mining activities release 2,000 metric tons of mercury gas into the atmosphere. The harmful substance then takes on various chemical forms as it circulates through air, soil, and water in a complex cycle. Mercury is particularly dangerous in the sea, where it accumulates in fish in the form of highly toxic methylmercury. When this compound enters the human body, it can have an adverse effect on brain development in children and cause cardiovascular disease in adults.
“Human activities are estimated to have tripled the amount of mercury on the ocean surface since the beginning of industrialization, ” says biogeochemist Martin Jiskra from the Department of Environmental Sciences at the University of Basel. Previously, experts assumed that mercury entered the ocean primarily through rain. “However, those are only assumptions, as there are no precipitation collecting stations over the sea.”
Rain is not the main entry point
The researcher has participated in a study that has just been published in the journal Nature, which reveals that gas exchange is also a very important entry point for mercury into the oceans. The team analyzed seawater samples using a new method that allows the researchers to distinguish whether the mercury originates from precipitation or entered the sea through gas exchange. This technique, known as “fingerprints”, is based on the measurement of small differences in weight between natural mercury atoms, known as isotopes.
The samples were collected at depths of up to 1,400 meters off the coast of Marseille and additional data was obtained from samples collected by research vessels in the North Atlantic.
The analyzes revealed that, contrary to previous assumptions, only about half of the mercury in the sea originates from precipitation, while the other half enters the oceans due to the absorption of mercury gas. ” At present, the contribution due to rainfall may be overestimated, ” explains Jiskra. Instead, the researcher suspects that mercury uptake by plants causes more heavy metal to be deposited in the soil, where it is safely retained in the soil and poses less of a risk to humans.
Good news for reducing pollution
Jiskra adds that the new findings are also important for the implementation of the 2013 Minamata Convention, according to which 133 countries committed to reducing mercury emissions: “If less mercury enters the sea through rainfall, a reduction in emissions could cause a drop in mercury levels in seawater faster than expected ”, he concludes.
Referencia: Jiskra, M., Heimbürger-Boavida, LE., Desgranges, MM. et al. Mercury stable isotopes constrain atmospheric sources to the ocean. Nature 597, 678–682 (2021). https://doi.org/10.1038/s41586-021-03859-8
