The presence of persistent organic pollutants (POPs) in all the world's oceans but one has been in steady decline since 2001, when 152 countries agreed on a comprehensive global ban. The exception has been the Arctic Ocean, which has seen a sharp rise in POPs in its frigid waters over the past several decades.
In a paper published in the journal Science Advances, Concordia assistant professor Xianming Zhang reported a study with an international team of researchers on the effectiveness of global regulatory efforts and legislative measures on persistent organic pollutants (POPs) in the planetary marine environments. This study highlighted the success of source control measures demonstrated by a general decreasing trend in POP concentrations across various maritime regions. However, the Arctic Ocean and its marginal seas have experienced a rise in POP levels. Their presence poses potential dangers to animals and people as they enter the fragile ecosystem's food web.
"Persistent organic pollutants are very stable, bioaccumulative and toxic, meaning they do not break down easily and can move through the global environment and accumulate up through the food chain, causing both environmental and health impacts" says Zhang, an assistant professor in the Department of Chemistry and Biochemistry and the co-director of Centre for Research in Molecular/Multiscale Modeling.
"Over the period when POPs were produced and reaching the environment, long-range atmospheric transport had been the main pathway through which POPs reached the Arctic. When source regulations are in place, ocean circulation plays a more important role in delivering historically emitted POPs to the Arctic. This is the rationale of this study," Zhang explains.
The region's cold waters extend the chemicals' already long half-lives by decades in some cases, and its ocean current patterns and natural restrictions like ice cover make them more likely to stay there - a process known as "cold trapping."
"Along with the health concerns they pose by entering the food web through animals like whales, seals and polar bears, POPs in the Arctic are also ethical issues as many of the chemicals are not produced or used in the Arctic but the Arctic population and ecosystems are exposed to higher levels of chemicals that are emitted from other parts of the world," Zhang says.
Xianming Zhang: "Persistent organic pollutants are very stable, bioaccumulative and toxic, meaning they do not break down easily and can move through the global environment and accumulate up through the food chain."
Long-lasting lessons
The researchers carried out in-depth analyses of over 10,000 measurements of POPs in the global oceans over the past five decades. They found that not only are the chemicals being driven northwards by sea currents, but also some coastal areas are seeing a rise in POPs as chemicals embedded in river sediments slowly make their way to the oceans.
"Oceans have become the sinks for these chemicals, and ocean circulation is contributing more to their global transport to the Arctic now that the sources for atmospheric circulation have been restricted by the Stockholm Convention of 2001," he explains.
He notes that the oceans are now both sinks and sources of POP contaminants as they move the chemicals northwards. Compared to the world's other oceans, the Arctic counts the highest concentration of HCH, DDT and OCP pesticides in its waters.
These legacy POPs will take decades to degrade but they do offer some lessons for the present, Zhang says.
"We now have a clearer understanding of the processes these legacy POPs experience in the global environment, so we can largely reduce environmental and health impacts by considering the properties and processes that make chemicals into POPs even before a new chemical is produced or used in large quantities. Global partnership with different stakeholders is essential to achieve the goal" he says.
Different from POPs covered in this study, PFAS, so-called "forever chemicals," are more concerning in term of their environmental and health impact disclosed by relatively recent studies including those by the Zhang group. Zhang says their research aims to understand sources, processes and impact of legacy and new POPs can help shape policy and legislative guidelines around them to minimize the hazards they pose to the environment.
"We need to point out that even though the Arctic is not seeing reduced concentrations of these POPs two decades after global source regulations, it does not mean that global chemical regulations are not working," says Zhang. "Without those regulations, the situation would have been much worse."
Read the cited paper: "Exploring global oceanic persistence and ecological effects of legacy persistent organic pollutants across five decades"
