Time trends of persistent organic pollutants and heavy metals in umbilical cord blood of Inuit infants born in Nunavik between 1994 and 2001 - Quebec, Canada - Children's Health

Environmental Health Perspectives, Oct, 2003 by Frederic Dallaire, Eric Dewailly, Gina Muckle, Pierre Ayotte

Discussion

In this study, we identified an exponential decrease in most of the contaminants analyzed. Knowing that the major source of exposure in our study population is the ingestion of traditional food items of high trophic level, the decrease observed could be explained by a decrease in food contamination, by changes in dietary habits, or by a combination of both.

In Canada, the use of chlorinated pesticides and PCBs has been severely restricted since the 1970s. The use of most chlorinated pesticides is banned, and only closed-use PCBs in already existing equipment are still allowed. Today, it is believed that local sources of PCBs, mainly from abandoned contaminated arctic military sites, do not contribute significantly to human exposures in the Arctic. The comparison of PCB congener signature in soil showed that the impact of arctic contaminated sites was limited to their immediate vicinity, a halo of a few kilometers (Bright et al. 1995). The situation is similar for chlorinated pesticides. They have been used in the 1940s and the 1950s for insect control in Nunavik but are unlikely to be used today because of regulations (although information on the use of pesticides in the Arctic is scarce).

Nevertheless, release in the environment still occurs because of storage leakage and ongoing use in certain parts of the world. OC contaminants are distributed throughout the globe and reach arctic regions by long-range atmospheric transport and oceanic currents (Barrie et al. 1992; Burkow and Kallenborn 2000; Thomas et al. 1992). They accumulate in the food chain, and it is now well accepted that the high trophic level of the traditional Inuit diet is mainly responsible for the high exposure of Inuit populations to biomagnified substances such as POPs (Bjerregaard et al. 2001; Dewailly et al. 1993; Kuhnlein et al. 1995).

The eating habits of Inuit populations have changed enormously during the last 50 years. Since market-bought food has been introduced in their diet, added carbohydrates, junk food, pork, chicken, milk products, and other "foreign" food items have become increasingly popular, especially among adolescents and young adults (Blanchet et al. 2000; Moffatt et al. 1994; Murphy et al. 1995; Olsen 1985). Market food usually has a lower trophic level than does traditional Inuit food and is consequently less contaminated by POPs. This is reflected by the much lower mean concentrations of PCBs and chlorinated pesticides detected in cord blood samples from populations whose diet is almost exclusively composed of market-bought food, such as those in southern Quebec (Rhainds et al. 1999). However, although a gradual switch from traditional food to market food would result in a decrease in blood concentrations of food chain contaminants, it seems unlikely that dietary modifications would be of such magnitude that they alone would cause an annual decrease of 5-10% in the body burden of contaminants.

Information on OC time trends in wildlife is scarce. Since the 1980s, there seems to be a decline in tissue concentrations of arctic marine and terrestrial mammals (Muir et al. 1999; Muir and Norstrom 2000). Scattered reports also underline a general decrease in OCs for various species in different regions of the world: cod, flounder, mussels, and shrimp (Roose et al. 1998), foxes (Georgii et al. 1994), freshwater fishes (Schmitt et al. 1999), and herring gulls (Hebert et al. 1994; Ryckman et al. 1994). In environmentally exposed humans, almost all studies addressing the question of temporal trend of OCs have found a decreasing tendency (Dallaire et al. 2002; Harris et al. 1999; He et al. 2001; Noren 1993; Noren and Meironyte 2000; Schade and Heinzow 1998; Waliszewski et al. 1998). In these studies, the time required to halve the mean contaminant concentrations in the population ([t.sub.1/2]) for PCB and DDT/DDE ranged from 4 to 7 years, except for PCBs in breast milk of Swedish women, which had a [t.sub.1/2] of 14 years (Noren and Meironyte 2000). These results are slightly lower but remain similar to what we observed in the present study ([t.sub.1/2] = 7.8 years and 7.1 years for PCBs and DDE, respectively). The generalized downward tendency of OC concentrations observed in wildlife and human tissues throughout the world strongly suggests that the environmental contaminant burden is steadily declining and that this tendency can be observed in all levels of the food chain. We believe that most of the decrease of OC concentrations observed in this study can be attributed to descending concentrations in the traditional food items of the Inuit diet.