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Study Finds Many Arctic Pollutants Decrease Following Stockholm Convention

An international group of scientists actively monitoring the Arctic region has discovered a decrease in the levels of certain persistent organic pollutants (POPs) regulated by the Stockholm Convention.

Persistent Organic Pollutants, also known as POPs, can have lasting impacts on both people and wild animals in the Arctic. Research shows some POPs are decreasing in the region after being pulled from market or regulated around the globe. (Image credit: Arturo de Frias Marques (

POPs are a diverse class of chemicals with longer life and with the ability to travel long distances from their source of production or use. Several POPs were widely used in consumer products, industry, or as pesticides in agriculture. Familiar POPs include chemicals like polychlorinated biphenyls (PCBs) and DDT, and certain products they were used in include fabric coatings and flame retardants.

Since it was found that POPs lead to health problems for wildlife and people, they were widely phased out of production or banned in various countries. Several of them have been associated with neurological, reproductive, immunological, and developmental problems in mammals. In the late 20th century, the accumulation of DDT, which is a very familiar and extensively used POP, was found to be associated with eggshell-thinning in fish-eating birds, such as pelicans and eagles, and caused a catastrophic decline in the population of those animals.

In 2001, a total of 152 countries signed a United Nations treaty in Stockholm, Sweden aimed at eliminating, restricting, or minimizing unintentional manufacture of 12 of the most extensively used POPs. Through subsequent amendments, more chemicals were added to the original list. At present, over 33 POP chemicals or classes are covered by the well-known “Stockholm Convention,” recognized by182 countries.

This paper shows that following the treaty and earlier phase-outs have largely resulted in a decline of these contaminants in the Arctic. When POP use was curtailed, the change was reflected by declining concentrations in the environment.

John Kucklick, a biologist from the National Institute of Standards and Technology (NIST) and the senior U.S. author on the paper

In general, the contaminants that are being regulated are decreasing,” stated Frank Rigét from the Department of Bioscience, Aarhus University, Denmark, who is the lead author of the study.

POPs specifically cause problems in the Arctic since the ecosystem there is particularly fragile, and pollution could be initiated either by local sources or from longer distances as a result of air and water currents. POPs also have the tendency to bioaccumulate, suggesting that they accumulate more rapidly in humans and animals than they can be excreted, and that exposure can be high up the food chain. Fishes that feed on plankton exposed to POPs in water are eaten by whales or seals, and with increase in each level in the food chain, there is an increase in the amount of POPs. The same holds good for terrestrial animals. Hence, the exposure of a large mammal can be huge and long-lasting.

When compared to an average American, indigenous people who live in northern coastal areas like Alaska usually consume more fish and other animals that are higher on the food chain. Hence, such communities are possibly exposed to increased amounts of such pollutants.

For nearly twenty years beginning in 2000, Kucklick and Rigét worked along with researchers from Sweden, Denmark, Iceland, Canada, and Norway to track POPs in the fat of a number of marine mammals and in the tissue of seabirds and shellfish. They also checked the air in the Arctic Circle for pollution.

To get a complete picture of how the deposition of POPs might have altered over time, the research comprised specimens archived since the 1980s and ’90s in special storage facilities worldwide. The U.S. specimens were provided by the NIST Biorepository, situated in Charleston, South Carolina. Samples archived in that facility are part of the Alaska Marine Mammal Tissue Archival Project (AMMTAP) or the Seabird Tissue Archival and Monitoring Project (STAMP). Both collections are conducted in partnership with other federal agencies.

The study collated over 1,000 samples captured over the course of several decades from many diverse locations across the Arctic Circle. Generally, the so-called legacy POPs—those that have been eliminated or limited from production - were shown to be reducing over the last twenty to thirty years, although some had reduced more compared to others.

The major decreases were in a byproduct of the pesticide lindane, a-HCH, with a mean annual decline of 9% in Arctic wildlife.

The study team found PCBs had reduced as well. Several industrial countries banned PCBs in the 1970s and ’80s, and their production was minimized under the Stockholm Convention in 2004. Formerly, the compounds had been extensively used in electrical systems. In this research, it was discovered that their presence had decreased by nearly 4% per year across the Arctic region since being taken off the market.

Two of the legacy POPs mentioned under Stockholm, β-HCH and HCB, showed only minor declines of less than 3% annually. β-HCH was part of a heavily-used pesticide mixture with the active ingredient lindane and HCB was used in industry as well as in agriculture.

A small number of the legacy POPs had increased in some locations, although a few of those were at sites assumed to be impacted by strong, still-prevailing local pollution sources.

Particularly, the flame retardant hexabromocyclododecane (HBCDD) exhibited a yearly increase of 7.6%. HBCDD was one of 16 extra POPs included into the Stockholm Convention as of 2017 and is suggested for elimination from use, with specific exemptions.

Most of the study conducted for this paper was a direct result of the 2001 treaty requirements, which included a condition that sponsors take part in ongoing, long-term biological monitoring. Although the U.S. contributed to the study, it has not approved the treaty. It is anticipated that work on the treaty will continue as new POPs are detected.

This new work emphasizes the usefulness of long-term data and global scientific partnership, says Rigét. “You really need to gather more than 10 years of data before you can see the trend because in the short term there can be some small fluctuations,” he notes. “Looking at this data also showed us how to be more economical and avoid over-sampling in the future.”

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