Prenatal Exposure to Persistent Organic Pollutants and Its Associated Factors

Abstract

Persistent organic pollutants (POPs) are persistent, toxic and bioaccumulating chemicals, which are regulated by Stockholm Convention on POPs. POPs in the environment are absorbed into the human body via inhalation, oral intake, tran-splacental transport (TPT) and dermal contact, and circulate in the body partitioning among lipid in blood and fatty body compartments. Especially, as fetus is in drastic development and growth, prenatal exposure and its health effects have been a matter of special concern. The aim of this study was to evaluate prenatal exposure to POPs, and its associated factors. Firstly, Heavy metals and POPs, including Pb, Cd, T-Hg, MeHg, PCDD/Fs, PCBs, PBDEs, PCNs, and PBDD/Fs, were analyzed in 20 paired samples of cord blood, maternal blood, maternal urine, and placenta. The samples were collected from pregnant mothers and neonates from South Korea in 2010. The distribution of heavy metals among the samples varied with their physicochemical characteristics. The concentrations of Pb and Hg in the maternal and the cord blood samples were significantly correlated each other, implying efficient transplacental transport (TPT). Cd and Hg were accumulated in the placenta, forming protein conjugates, and T-Hg was higher in the cord blood samples than the maternal blood samples due to the binding affinity of Hg with fetal proteins. POPs generally showed the highest concentrations in the maternal serum samples, and the POPs levels in the cord serum and the placenta samples were dependent on the degree of halogenation. The TPT of POPs was seemingly related to lipoprotein transportation. Some PBDE congeners, however, showed their highest concentrations in the cord serum samples, suggesting an additional TPT mechanism. This is the first study to detect PCNs and PBDD/Fs in the cord serum samples, showing that the PCN levels were comparable to other POPs. According to the principal component analysis (PCA) results of the contaminant levels, POPs and heavy metals showed significantly different characteristics, whereas PBDEs had an intermediate attribute. Despite the limited number of participants, the comprehensive analysis of trace contaminants in the paired sample sets enabled us to infer the distribution and TPT mechanism of various contaminants. Secondly, we investigated associated factors of POPs in the serum of a Korean population. We measured serum levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls PCBs, determined physiological conditions, and surveyed dietary habits using a validated food frequency questionnaire (FFQ) from 180 subjects in South Korea. In the samples, the median concentrations of OCPs and PCBs were 483 and 216 ng g-1 lipid, respectively, which were slightly higher than those reported in previous studies in Korea, but the congener distributions were similar. A stepwise multiple linear regression (MLR) and other statistical analysis revealed that serum POP levels were higher in women and were positively correlated with age. BMI and total cholesterol were positively and negatively associated with serum POP levels, respectively, reflecting the influence of food intake and the diluting effect of body fat. Metabolic syndrome and type 2 diabetes mellitus were significantly associated with serum POP levels. And the intake of animal foods had positive associations whereas phytogenic foods showed negative associations with serum POP levels, seemingly because of high contamination of animal foods and effect of the food matrix, which governs POP absorption and excretion. The results of MRL for the non-patients showed similar trend with those of all participants, but more distinct associations. The MRL results of the MS patients showed higher R2 than those of other participants, and showed eccentric correlation with the intake of beans and dairy products, suggesting MS may alter the influence of food intake on the serum POP levels. Despite the small number of subjects and the other uncertainties, we identified some factors associated with serum POP levels in the Korean population that could be valuable for POP exposure assessments and studies of their health effects. Lastly, we investigated feto-maternal ratio (FM- ratio) of POPs, and its associated factors, which included the physicochemical properties of POPs and the physiological characteristics of the mothers and their fetuses. We employed a new approach to investigate factors affecting partitioning of POPs in the feto-maternal unit, which was based on multiple linear regression (MLR) analysis to predict FM-ratio. We analyzed PCBs, PCDD/Fs, and PBDEs concentrations from 20 pairs of the maternal and cord serum, and calculated FM-ratio. And then we built the preliminary models with the physicochemical properties calculated with Q-chem and the physiological characteristics measured in the hospital. The results of the preliminary models showed that lipid contents in the maternal and cord bloods were significantly associated with FM-ratio, seemingly due to transplacental transport of POPs. The associations of gestational age and birth weight were likely related to toxicokinetics of POPs. The numbers of halogen atoms (nX) and smallest sphere centered from center of mass (span R), molecular physicochemical properties related with molecular size and lipophilicity, were also associated with FM-ratio. Although the results of the preliminary models should be interpreted cautiously, the new approach based on MLR analysis suggested in this study could improve our understanding on the partitioning behavior, prenatal exposures of POPs, and its potential health effect.