It’s January 2018 in Iqaluit, Nunavut, and the temperature is -50C even before the wind chill. But cold is not the only danger. Scientists at remote sampling sites “need to be very alert for bears and wolves,” warns research scientist Hayley Hung. In order to fend off large predators lurking nearby and camouflaged against the snowy expanse of white, these researchers travel in groups, armed with a gun.
Hung, a scientist with Environment and Climate Change Canada based in Toronto, removes her gloves just long enough to snap a picture of her colleague Chris Spencer opening up the air sampler they are here to check. His thin nitrile-gloved hands numbed by cold and strong winds, it takes 15 minutes with freezing fingers to swap in the new foam disk and remove the old one from the sampler affixed to a chain link fence. From this absorbent collector they will open a precious window into the chemical soup circulating in Arctic air, adding to a timeline of data stretching from past to future.
Chris Spencer, of Environment and Climate Change Canada, changes the air pollution collector disk in a sampler in Nunavut. Photo credit: ECCC
Distant and sparsely populated, the Arctic is nevertheless a sink for persistent organic pollutants (POPs) originating in cities and industrial sites around the world. The atmosphere, oceans, and rivers are conduits carrying contaminants poleward, where they are a recognized health concern for Arctic-dwelling indigenous peoples.
Hung and Spencer gather data for the federal Northern Contaminants Program run by Crown-Indigenous Relations and Northern Affairs Canada. The program, established in 1991, provides a long-term window into Arctic atmospheric pollutant trends. And Canada is one of many nations that contributed data to the most comprehensive analysis thus far of how deposition and circulation of POPs in the Arctic has changed over time.
Many previous studies have published data about Arctic POPs, but a study published in February 2019 in Science of the Total Environment consolidated all available raw data to probe whether trends over time were consistent Arctic-wide. Led by Frank Rigét of the Arctic Research Centre at the University of Aarhus, in Roskilde, Denmark, he and his 17 colleagues amassed data from samples collected over two to three decades, as far west as Alaska, all the way across the Canadian Arctic and to northern Scandinavia, with some acknowledged data gaps in the Russian and Finnish Arctic.
The team, based in Denmark, Greenland, Sweden, Canada, Faroe Islands, Norway, Iceland, and USA, analyzed 1,074 long-term time-series and 735 short-term time-series for many POPs. Their list was extensive and comprehensive, including notorious agents such as polychlorinated biphenyls (PCB) dichlorodiphenyltrichloroethane (DDT), and perfluoroalkyl substances (PFASs), along with hexachlorocyclohexanes (HCH), hexachlorobenzene (HCB), hexabromocyclododecane (HBCDD), and more.
“The real strength of this is that we are analysing a lot of data series using the same statistical methods,” says Rigét, who contrasts that strategy with the more typical piecemeal approach.
Cynthia de Wit, an environmental chemist at Stockholm University who was not involved in the study, agrees.
“Previously everyone did their own statistical evaluation of their datasets, and published them separately,” she says. Someone might do an analysis on polar bears, or bird eggs, or fish, “and the problem was that it was difficult to compare these, because they might have used slightly different methods and statistical tests, and maybe not the best statistical methods.”
POP history
As a family of long-lived globe-trotting chemicals, POPs were manufactured for use in industry, consumer products and agriculture. PCBs, for example, were formerly used in electrical transformers, coolants, and carbonless copy paper, while DDT was originally developed as an insecticide and used on mosquitoes, lice, and agricultural pests. DDT was linked to eggshell-thinning in fish-eating birds such as eagles, pelicans and peregrine falcons. In the 1960s and 70s, reproductive failures for these birds saw many species decline towards the precipice of extinction. Both became linked to reproductive, developmental, neurological and immunological problems for humans and wildlife, as famously highlighted in Rachel Carson’s 1961 book Silent Spring.
As the scientific understanding of POP impacts grew, some of these chemicals were banned or phased out of production. In 2001, 152 countries signed onto a United Nations treaty in Stockholm to eliminate, restrict or minimize unintentional production of a dozen widely used POPs. Later amendments added more. Today, more than 33 POP chemicals or groups are covered by this “Stockholm Convention,” now recognized by 182 countries, including Canada but not the USA.
POPs exhibit a spectrum of behaviours, explains paper co-author John Kucklick of the National Institute of Standards and Technology in Charleston, South Carolina, which has a biorepository of samples used in this latest study.
“Some are more persistent than others, but as a class, the reason they are a problem is that…their persistence allows them to accumulate in the food web,” he says.
Their persistence links to their affinity to glom onto fats, so when a polar bear chomps on a seal, “it’s eating much of the seal’s fat,” adds Kucklick. This phenomenon of taking on a prey animal’s POP burden is called bioaccumulation, whereby these chemicals build up in the body faster than they can be excreted and their concentration gets a boost with each meal up the food chain. Plankton exposed to POPs in seawater, for example, are eaten by small fish, which are eaten by bigger fish, which in turn are eaten by seals and whales.
The mounts ultimately can add up significantly. A 2003 study in Nature led by University of Ottawa toxicologist Eva Krümmel showed that PCB concentrations can be 2,500 times more concentrated in salmon fat than in ocean water.
The devil in the details
Rigét’s team analysed multiple long-term datasets from a variety of freshwater and marine species, including blue mussels, Atlantic cod, Arctic char, ringed seals, belugas, orcas, thick-billed murre, black-legged kittiwakes, and polar bears. The results showed a general trend for legacy POPs such as HCH and HCB, which have been decreasing in concentration to varying degrees over the last several decades. A few of these time series showed increasing trends but only at sites suspected to be influenced by some specific source. For instance, levels of the brominated flame retardant congener BDE-47 increased through the mid-2000s but then dropped — consistent with a phase-out of commercial BDE mixtures in Europe and North America at that time, just before these agents were added to the Stockholm Convention in 2009. A similar trend was found for perfluorooctane sulfonic acid, reflecting the voluntary US phase-out of its production in 2000 and its subsequent addition to the Stockholm Convention.
Those studying Arctic POPs emphasize how much this kind of trend detection relies on consistent long-term data collection. As Rigét explains, power analysis suggests that due to natural between-year variability, at least 20 years of data, collected annually, is often needed to detect trends. Indeed, many time series available for analysis were insufficient in this regard and could not be used to confirm a trend.
This same challenge was cited by another one of the paper’s authors, Birgit Braune of Environment and Climate Change Canada’s National Wildlife Research Centre in Ottawa, whose seabird studies are supported by the Northern Contaminants Program.
“The longer you monitor, the better you’re in a position to pick up subtle changes,” she says, emphasizing the value of steady government support for this long-term data collection, which contrasts with the less consistent funding from academia or non-governmental organizations.
As for the ecological impacts of these downward trends, “it’s different for different animals,” says de Wit. Things like fish now have lower contaminant loads, but long-lived mammals like polar bears, seals, and whales are “still carrying a burden of what they were exposed to even as a fetus,” she says.
If an animal’s mother was exposed to high levels, they were transferred to young via fetal exposure and nursing, which means they will not disappear in short order. They are “recycling them on into their offspring,” suggests de Wit, who has seen levels of some chemicals decline but in some cases too slowly to help. She still sees enough PCBs in top predators to make them health risks, for example, with Inuit populations consuming these animals experiencing reproductive, cardiovascular, and immune system effects.
Overall though, Hung remains optimistic about POPs trends. So too does Kucklick, although he cautions against complacency. Regardless of the decline in legacy POPs, he explains, newer POPs like perfluorinated compounds have not declined much. Meanwhile, the world’s chemical marketplace continues to welcome new substances, many of them similar to legacy POPs and most not subject to global regulation.
“There are still a lot of unknowns,” says Hung, who emphasizes the ongoing need for long term monitoring, international discussions, and toxicology research.
His perspective is echoed by Environment and Climate Change aquatic toxicologist Magali Houde. “We’re just starting to understand how contaminants are moving around and accumulating in animals, and with all of the changes happening up north,” she says. “It makes our job a lot harder.”
So too does a rapidly evolving climate, which Braune describes as “a new stressor that’s already changing the dynamics of contaminant cycling.” As new species move into a warmer Arctic, shifting dietary patterns will complicate the interactions between chemistry and biology.
“You need long term datasets to detect changes that have occurred in the past and are bound to occur in the future,” she concludes.
Global Atmosphere Watch Observatory at Alert, Nunavut, the key site of persistent organic pollutant monitoring in the Canadian Arctic. Photo credit: ECCC