Riccardo Liguori Global warming isn't just melting glaciers, it's also releasing an invisible threat: heavy metals. A study published in Nature reveals how mercury and other toxic contaminants are invading the oceans and the food chain, ending up straight on our plates
@Zitoun et al. 2024
Unfortunately, we already know about the strong influence of climate change on our acidifying and warming oceans. One of the lesser known but more insidious consequences, however, would have to do with heavy metals, whose concentration in marine waters is growing.
Mercury, lead, arsenic, and even silver-derived from both natural and human activities-are now courtesy of global warming working their way into the seas and threaten marine flora and fauna, and thus our food supply.
Multifaceted problem with various causes
The sources of these metals are many. Natural processes such as the erosion of rock and volcanic activity contribute heavy metals to the environment. However, human activities significantly worsen this situation mainly because of industry, intensive agriculture, traffic, and waste disposal. “Human activities have increased the flow of certain metals by an order of magnitude compared to pre-industrial levels,” a recent study published in Nature has stated-a study called “Climate change driven effects on transport, fate and biogeochemistry of trace element contaminants in coastal marine ecosystems.”.
“We looked at both anthropogenic and natural sources, trying to understand how dispersion of these metal traces was affected by climate change-a field in which very few studies have been conducted so far,” says Dr. Rebecca Zitoun, a marine chemist at the GEOMAR Helmholtz Centre for Ocean Research Kiel and one of the co-authors of the study.
Climate change as risk multiplier
Climate change works as a threat multiplier by raising the levels of heavy metals within the ocean through various methods. A simple example is the gigantic release of mercury from the melting of glaciers and permafrost, which previously worked as repositories.
Increased rainfall and river runoff carries more metals from soils to the oceans.
Extreme weather events, such as flooding and storms are projected to occur more frequently in a changing climate, which can also remobilize heavy metals from sediments. “Climate change worsens the situation in several ways, one of which is the altered hydrology and thus contaminant transport from continents to oceans,” said the authors of the study.
Ocean acidification
Added to that is ocean acidification as yet another face of climate change. It is caused by increased levels of carbon dioxide in the atmosphere, which makes seawater more acidic; thus, increasing the solubility of heavy metals and making them even more absorbable in large amounts by marine organisms. “Ocean acidification can alter metal speciation and therefore their bioavailability”, the study says.
Implications for ecosystems and human health
The consequences of this phenomenon are very worrying, given that heavy metals translate to increased accumulation in the food chain, thereby contaminating fish that would eventually find their ways onto our tables. Mercury in particular is a neurotoxin that can cause serious health problems to human beings, especially in coastal communities dependent much on fishing. “Exposure to mercury poses a threat to human health, particularly for Indigenous and coastal populations that rely heavily on fish as a food source,” said the authors of the study.
The study, however, reassures that more detailed research in this field will help gain a better understanding of the many interactions involved between climate change and heavy metal contamination. “Further research is needed in order to fully comprehend the effects of climate change on the mobilization, transport, bioavailability, and toxicity of contaminants in marine ecosystems,” the study concludes.
Understanding this complex interaction between climate change and contaminants is necessary when considering management strategies to protect the health of both the oceans and the communities that use them, say the authors.
