Dallaire, F, E Dewailly, G Muckle and P Ayotte. 2003. Time trends of persistent organic pollutants and heavy metals in umbilical cord blood of inuit infants born in Nunavik (Quebec, Canada) between 1994 and 2001. Environmental Health Perspectives, on line 2 July 2003.

An analysis of trends in body burdens of Inuit infants born in eastern arctic Canada reveals dramatic decreases in concentrations of several persistent organic pollutants, most notably PCBs, DDT, DDE and HCB. Lead and mercury were reduced, but there were no trends evident for chlordanes. The scientific team that conducted the work attributed the decline to a combination of world-wide efforts reining in the emmissions of the compounds, plus local changes in diet.

What did they do? In this paper, Dallaire et al. combine data from two studies by the same research team in the Canadian arctic that measured umbilical cord blood of Inuit infants over the period 1994-2001.

The samples come from three villages on the eastern shore of the Hudson Bay (right). All laboratory techniques were "rigorously the same for the entire study period," with a total of 251 samples analyzed for 14 PCB congeners, 11 chlorinated pesticides (aldrine, a-chlordane, g-chlordane, cis-nonachlor, p,p'-DDE, p,p'-DDT, hexachlorobenzene, mirex, oxychlordane, trans-nonachlor and b-BHC), lead and mercury. Slightly different sample sizes were obtained for each different contaminants. The organochlorine measurements were reported per gram of lipid. Figure to right: The location of villages Puvirnituq, Inukjuaq and Kuujjuarapik on the eastern shore of Canada's Hudson Bay. Map adapted from Dallair et al. 2003.

What did they find? With the exception of chlordane and two of 14 PCB congeners, all measured contaminants decreased significantly over the time period of the samples.

The two metals measured, lead and mercury, both declined by more than 8% per year, as did total PCBs, DDT and DDE. HCB's decrease was somewhat less, 6.4% per year. These calculations were adjusted statistically to take into account the village of residence, the age of the mother, parity, and the season of birth, factors all known to influence contaminant concentration.

The time course of DDE decline (graph to left) was similar to that of DDT (not shown) and PCBs (graph to right). Points shown are the average concentrations for each birth year, adjusted as noted above.

What does it mean? The organochlorine contaminants studied by Dallaire et al., and mercury, have reached relatively high concentration levels within cord blood because of long-range atmospheric transport and subsequent contamination of native foods eaten by Inuit. Because those foods typically come from the top of the food chain, bioaccumulation has been especially intense, leading to high levels in Inuit mothers.

The source of high lead is less clear, but is possibly due to lead poisoning from lead shot and bullets used to kill game.

Dallaire et al. acknowledge that two possible factors may be contributing to the declines they are reporting in contamination of umbilical cord blood: increasing control of emissions leading to lower contamination of the food chain, and changes in diet away from contaminated native foods. Unfortunately, they lack sufficient data on contamination trends in native foods to be able to distinguish between these two intepretations with certainty. They believe that both trends are contributing. Indeed, in their estimation, "the decline is mainly due to a diminution of food contamination and, to a lesser extent, to dietary changes."

The declines they observe in the organochlorines and lead are consistent with observations elsewhere and with expectations based on bans and restrictions now in place for these chemicals for several decades.

The mercury trend is more puzzling. Insufficient data are available from arctic animals to establish trends, although a study from 1981-1994 noted an increase. Data from elsewhere in the world to not show a strong decrease. Indeed the decrease in Dallaire et al. is not the result of a gradual decrease, as with the organochlorines, but (as they note) instead two low years in 1998 and 2000.

In summary, these data establish that infants born to Inuit mothers along the eastern shore of Hudson Bay are experiencing less contamination in the womb now than in the early 1990s. This is good news. The only caveat to that assessment arises from concerns about the nutritional impact of shifting to market foods, with added carbohydrates, junk food, pork, chicken, milk products, and other “foreign” food items.

Dallaire et al. end by calling for additional international efforts to reduce environmental inputs. This study's data indicate that decades of efforts to reduce releases of persistent organic pollutants into the environment are paying off with reduced exposures in the womb.