Heavy Metal Contaminants in the Ocean Can Become More Toxic Over Time, Study Finds

A new study is warning that trace metals like lead, arsenic and mercury that are present in ocean water can become more toxic over time as factors like ocean warming and acidity can increase the bioavailability of these trace elements.

Although these elements can naturally occur in coastal areas, their concentrations have increased due to human activities like agriculture and industrial manufacturing. Now, scientists warn that problems such as ocean acidification and warming are further strengthening the toxicity and spread of trace elements, both from natural and human sources.

“Human activities have increased the global flow of toxic metals such as lead by tenfold and mercury by three to seven times compared to pre-industrial levels,” Sylvia Sander, professor of marine mineral resources at GEOMAR, said in a statement. “Toxic elements like silver are increasingly detectable in coastal waters, originating from coal combustion and the growing use of silver nanoparticles in antibacterial products.” 

The researchers found that the effects of rising sea levels, ocean warming, melting sea ice, drying river beds and ocean acidification could all play roles in the transport and accumulation of trace elements, particularly those that occur naturally. The researchers published their findings in the journal Communications Earth & Environment.

^{Illustration of natural and anthropogenic sources, sinks and transport pathways of trace substances in coastal ecosystems that may interact with climate impacts. Red arrows indicate expected directions of change due to climate change. Zitoun et al. 2024}

But trace elements from human sources are also contaminating the environment, with heavy metals coming into the oceans from fossil fuel and industry activities. Further, shipping and plastics can also introduce more trace elements into the oceans, especially because plastics can bind certain metals, including lead and copper.

As ocean temperatures rise, the bioavailability of trace elements increases, meaning it becomes easier for marine life to absorb the trace elements, the researchers explained. Trace elements, especially copper, also experience an increase in bioavailability and solubility in the presence of more acidic water. Copper can become extremely toxic to marine life in higher concentrations. 

In a recent report on planetary vital signs, a team of international scientists confirmed that ocean warming and acidification had reached record extremes in recent years.

The authors of the new report on trace elements noted that there are still significant research gaps on how the effects of climate change could also impact ocean contaminants. In response, the study authors are calling for expanding the research on new and under-studied contaminants, expanding geographical research coverage, and establishing laws and risk assessments on trace elements.

“To better understand the impacts on ecosystems and human health, we need to close knowledge gaps on the interactions between pollutants and climate change and develop standardized methods that provide globally comparable data,” said Rebecca Zitoun, co-lead author of the study and a marine chemist at GEOMAR Helmholtz Centre for Ocean Research Kiel.