This study investigated demographic and lifestyle predictors of serum dioxin, furan and PCB concentrations among adult women of reproductive age living in Chapaevsk, Russia, a town contaminated by previous industrial activity.
Dioxins, furans and PCBs share the properties of being lipophilic chemicals with long half-lives, and consistent with this fact, we found that factors related to bioaccumulation or lipid distribution (i.e. age, duration of breastfeeding, and recent increase in BMI) were significantly associated with serum concentrations of almost all groupings of dioxins, furans and PCBs. In addition, certain external factors were similarly associated with all dioxin, furan and PCB concentrations (i.e. current residential distance from SVZH, and farm plot use duration), suggesting that some exposure pathways are shared by these different classes of chemicals. The moderate to strong correlations between dioxin, furan and PCB concentrations (similar to those reported by other studies (9
)) are indeed consistent with their having a broadly similar set of predictors in Chapaevsk. However, these chemicals also have some different sources: dioxins were produced as by-products of industrial activities and incineration, whereas PCBs are released into the environment consequent to their past industrial use. This may explain why certain factors were only significantly associated with a subset of dioxin, furan and PCB concentrations (e.g. duration of local residence, and consumption of various local foods), suggesting the existence of some chemical-specific exposure pathways in this community.
There were substantially fewer significant predictors for the total C-PCB concentrations than for any other dioxin, furan, or PCB variable, as well as a low model R2
of 0.13. This may be due to the large percent contribution by PCB 77 (mean contribution = 48%), which has a half-life of only 0.1 years (8
), and therefore may vary on a shorter time-scale than the predictors measured here. In contrast, the total C-PCB TEQ is on average 90% PCB 126, whose relatively longer half-life of 1.6 years (8
) may explain the greater number of significant predictors for this variable, and higher model R2
of 0.28. The C-PCBs may also have different exposure patterns that were not adequately captured by our data; for example, total C-PCBs and C-PCB TEQs were the only measures that were not associated with closer residence to SVZH.
A later date of blood draw was associated with lower dioxin, furan and PCB concentrations in multivariate analyses adjusting for age (approximately 10% lower for each additional year for most dioxins, furans and PCBs). This suggests a decreasing trend in exposure over time, which is consistent with decreasing production at the SVZH plant since 1991 (14
) and cessation in 2003, as well as with the measured decline in dioxin levels in Chapaevsk soil samples between 1994 and 2006 (25
). However, temporal trends in other lifestyle and behavioral predictors of serum dioxin, furan, and PCB concentrations (such as local food consumption), may have contributed to the association of blood draw date with serum concentrations, and may not have been adequately controlled for in our statistical models.
Previous research in other populations has shown that diet is an important source of non-occupational exposure to dioxins and PCBs (26
). In this study, consumption of local eggs or fruit at least once/week, and of local beef at least once/month, was associated with significantly higher concentrations of certain dioxins, furans and PCBs, although the strong correlations between the consumption of various types of local foods makes it difficult to reach definitive conclusions about which are most responsible for dioxin, furan and PCB intake. Although elevated dioxin levels have been found in fish from Chapaevsk (25
), no associations with eating fish ≥once/week were significant. However, additional analyses showed that total TEQs were elevated in the 17 women who reported eating fish every day (p <0.01), compared to all other women. This finding indicates that within low and moderate fish consumption categories there is wide variability in serum concentrations of dioxins, furans, and PCBs, which provides insufficient power to detect all but the largest differences between groups.
Limitations of our study include that all dietary data was self-reported, and also that no information was collected on the species of fish consumed. In addition, only the current residential distance from SVZH was available, precluding examination of whether distance from SVZH in certain historical eras was more strongly associated with serum dioxin, furan, and PCB concentrations.
One unexpected finding is that doing laundry by hand was associated with lower serum dioxin, furan and PCB concentrations. This finding was based on a small reference group of only 13 women who reported not doing laundry by hand, and could be due to unknown additional demographic or lifestyle characteristics of these women, or represent a chance finding resulting from the large number of associations that were examined. However, the magnitude of the association was relatively consistent across dioxin, furan and PCB measures, and the relationship could be plausible if doing laundry cleaned the hands of contaminated soil, and therefore decreased incidental ingestion.
Smoking was significantly associated only with lower concentrations of C-PCB TEQs and total TEQs. It has been suggested that cigarette smoke accelerates the elimination of dioxins (8
), possibly due to the induction of the enzyme CYP1A2, which sequesters dioxins into the liver, leading to faster elimination. However, the exact mode of action remains unknown. Several recent studies have suggested stronger inverse associations between smoking and levels of C-PCBs than of PCDDs and PCDFs (27
), however other studies have reported that PCDD and PCDF half-lives were also shorter among smokers (29
Research by Wolff et al (30
) has suggested that increased adiposity can affect lipid concentrations of organochlorines either by reducing their elimination or by providing a larger volume of distribution. Our results are consistent with this observation, as increases in the woman’s BMI were significantly associated with lower serum concentrations of all dioxins, furans, and PCBs (except for C-PCB concentrations), whereas the only significant association with BMI at the time of blood draw was with increased C-PCB TEQs, possibly reflecting slower elimination in individuals with higher BMI.
Comparison of dioxin, furan and PCB concentrations in this population to other studies
The serum dioxin, furan and PCB concentrations seen in this cohort are elevated compared to the US general population. Both the 90th
percentile total TEQ and the median total PCBs in these women were higher than among the 20–39 year old US population in 2003–2004 (90th
percentile total TEQ: 51 vs. 16 pg TEQ/g lipid; median total PCBs: 260 vs. 75 ng/g lipid; (31
); the 90th
percentile was shown for total TEQs since median values were not available for the US population due to the high percentage of non-detects). The women in this cohort also have similarly elevated 90th
percentile TEQs of total PCDDs, PCDFs, C-PCBs, and M-PCBs compared to the 20-39 year old female US population in 2001–2002 (23 vs. 14, 9.0 vs. 4.3; 14 vs. 4.8, 3.2 vs. 1.1 pg TEQ/g lipid, respectively; (32
The individual congeners comprising the highest percentage of the total TEQ were TCDD, 12378-PeCDD, 23478-PeCDF, and PCB 126 (mean contribution of 76% from these 4 congeners). These predominant congeners are similar to those reported in a national representative sample of the US population (32
), as well as in the University of Michigan Dioxin Exposure Study (33
), which described a population with potential non-occupational exposure to dioxins from a Dow Chemical plant, as well as a comparison population living approximately 100 miles away.
Comparison of predictors in mothers and sons
Predictors of maternal serum dioxin, furan and PCB concentrations are similar to those identified among their sons in our recent publication (13
). Maternal employment at SVZH was more strongly associated with the sons’ dioxin, furan and PCB concentrations than with the mothers’ levels. For the sons the percent increases in total PCBs and total TEQs associated with maternal SVZH employment were 29% (p
= 0.02) and 26% (p
= 0.05), respectively, whereas for the mothers they were 17% (p
= 0.054) and 11% (p
= 0.28). Possible explanations for the difference include higher background dioxin, furan and PCB concentrations among the mothers, or the greater number of covariates included in our analysis of the mothers’ samples.
Public health recommendations
Our finding that average serum concentrations of dioxins, furans and PCBs decreased in the course of this study is an encouraging sign that exposure in this region may be trending downward. Certain modifiable factors were nonetheless associated with higher concentrations of dioxins, furans and PCBs, especially residential distance from SVZH, duration of farm plot use, and consumption of local foods. In spite of our findings about local diet, it would be premature to suggest that intake of local foods or fish should be reduced without a fuller assessment of the net health tradeoffs of such a recommendation, especially in a relatively resource-poor environment such as Chapaevsk. Alternate possible ways to reduce dioxin, furan and PCB intake, without potential unintended adverse effects on local nutrition, include remediation of contaminated soil, shifting farm plots to less contaminated locations, or thorough washing of fruits and vegetables before consumption.