The sociodemographic characteristics of the sample are shown in . Most of the women and men sampled were between 20 and 46 years of age. Household incomes were generally low, with many reporting a total household income less than $25,000. The women in the sample had on average 8.2 years of formal education, whereas the men had on average 9.6 years of education. However, some participants (25 women (32%) and 12 men (19%)) reported having no formal education. Among the 70 of 79 women for whom pregnancy history was available the average was 5 pregnancies (range 0-15). PCB (Spearman r = .08) and DDE (Spearman r = .18) concentrations were not significantly correlated with gravidity (Reliable data on parity and breast feeding were not available.). A majority of the participants (67.1% of women and 77.8% of men) were born in Laos or Thailand. Education was negatively correlated with age (Spearman r =−.30, p<.001) and positively correlated with years in the United States (Spearman r = .59, p<.0001). As expected, the subset of participants born in the United States were younger (mean age 21.5 years) than those born outside the United States (mean age 34.5 years) and better educated; 77.1% had at least a high school education compared with 50% of those born outside the United States. Most participants born in Laos or Thailand had been in the United States for an extended period (about 20 years on average).
Demographic Characteristics of the Samplea.
Most participants (85%) reported eating sport-caught fish, with women reporting an average of 6.6 years of consumption and men 7.9 years of consumption. Fewer participants (65%) reported having eaten sport caught fish within the 12 months immediately preceding collection of the blood sample. Fish consumption during the most recent 12 months was relatively modest, with women reporting a median of 6 fish meals and men reporting a median of 8 fish meals over the 12 months. PCB contamination in the Fox River was widely publicized in the local media during the time frame of the study and that was reflected in the participants’ awareness of the fishing advisories. Virtually all respondents (134 of the 138 who answered the question) were aware of the fishing advisories for local waters. Only 9.7% of respondents reported no change in their fishing habits in response to the advisories. Others reported one or more of the following changes: stopped consuming local fish (49.5%), reduced consumption of local fish (31.5%), changed fishing locations (31.5%), changed types of fish eaten (14.4%) or changed how the fish is cleaned or prepared (7.2%).
Tables and show exposure data for total PCBs, p,p’-DDE, and total Hg. Men had higher serum PCB and DDE concentrations than women, but this difference did not reach statistical significance. Hg exposure was low in this population overall, but Hg concentrations were significantly higher in men than in women. Only 21 of the 142 people who provided a blood sample were not sport-caught fish consumers, but fish eaters had much higher total serum PCB concentrations (arithmetic mean of 347.6 ng/g lipid) than non-fish eaters (arithmetic mean of 87.8 ng/g lipid). The individual with the highest PCB concentration was a women who reported consuming locally caught fish for 15 years. This one extreme value was excluded before calculating the summary statistics shown in . Similarly, two extreme DDE values, one male and one female, were excluded prior to calculation of means and confidence intervals. The participants born in Laos or Thailand had higher serum PCB concentrations and much higher serum DDE concentrations than the smaller subset of individuals born in the United States. Thirty two participants had Hg concentrations below the detection limit of the method and only five of the 142 participants who provided blood samples had total Hg concentrations above 5.8 ng/ml, the blood concentration upon which the EPA reference dose (RfD) was based (Rice et al. 2003
Total serum PCB and DDE (ng/g lipid) in 79 women and 63 men who provided baseline blood samples.
Total Hg (ng/ml) in 79 women and 63 men who provided baseline Blood samples. Values for 32 participants with levels below the detection Limit were excluded.
shows the Spearman correlation coefficients among total PCBs, DDE and Hg. Moderate correlations between PCBs and DDE, PCBs and Hg, and DDE and Hg were observed. Among fish eaters serum PCB concentration was positively correlated with years of sport-caught fish consumption (Spearman r = 0.43; p <0.0001), but surprisingly, serum DDE and blood total Hg concentrations were not (see ). The strongest predictor of serum DDE concentrations was the number of years spent in a Thai refugee camp prior to coming to the US (Spearman r= .60; p<0.0001).
Spearman correlations for selected variables.
shows the lipid-adjusted serum concentrations of individual PCB congeners that were detectable in at least 40% of the participants. PCB congeners 118, 138, 153, and 180 accounted for a relatively large percentage (44%) of the total PCBs. However, a number of lightly chlorinated congeners including PCB 28, PCB 33-20-53, PCB 66-95, and PCB 74 that are not routinely detected in human serum were detected in over 40% of the participants and each of these accounted for, on average, about 3-7% of the total PCBs.
Congener profile of baseline blood samples in 142 Hmong participantsa