Thyroid Hormones in Pregnancy in Relation to Environmental Exposure to Organochlorine Compounds and Mercury

Abstract

Polychlorinated biphenyls (PCBs), chlorinated pesticides, and mercury are global environmental contaminants that can disrupt the endocrine system in animals and humans. However, there is little evidence that they can interfere with endocrine status in pregnant women and neonates at low levels of exposure. The aim of this study was to examine thyroid hormone levels during pregnancy and in cord blood in relation to blood concentrations of organochlorine compounds (OCs) and Hg in healthy women recruited during pregnancy. We found a significant negative correlation between maternal total triiodothyronine levels and three non-coplanar congeners (PCB-138, PCB-153, and PCB-180), three pesticides (p,p´-DDE, cis-nanochlor, and hexachlorobenzene), and inorganic Hg independently, without any other changes in thyroid status. No significant relationships were observed between OCs and cord serum thyroid hormones. Cord serum free thyroxin was negatively correlated with inorganic Hg. These results suggest that at even low levels of exposure, persistent environmental contaminants can interfere with thyroid status during pregnancy.

Serum PCBs, p,p′-DDE and HCB predict thyroid hormone levels in men

“…Consistent with our results was a recent Canadian study of 149 pregnant women found a significant inverse relationship between low, environmental levels of HCB, PCB 153 and ΣPCBs in plasma and total T 3 , but no associations with free T 4 and TSH (Takser et al 2005). Likewise, inverse associations between PCBs and T 3 levels were also previously observed in the wives of Swedish fishermen (Hagmar et al 2001b) and in German schoolchildren (Osius et al 1999), while another study among Dutch women reported an inverse association with T 3 that was also accompanied by an inverse association with T 4 and a positive association with TSH (Sala et al 2001).…”

“…Inconsistent with our findings were results from two other human studies that found no associations between p,p′-DDE and thyroid hormones in adult men (Hagmar et al 2001a;Persky et al 2001). Also inconsistent with our results but consistent with what they reported for HCB and PCBs, Takser et al (2005) found an inverse association between p,p′-DDE and total T 3 with no associations between p,p′-DDE and free T 4 or TSH in pregnant women. Based on the limited amount of available human data, the association between p,p′-DDE and thyroid hormones needs to be explored in other epidemiologic studies to support or refute our findings.…”

“…The study did not measure free T 4 , total T 3 or TSH. In addition, as described earlier, inverse associations between plasma HCB levels and total T 3 were reported in obese men following participation in a weight loss program (Pelletier et al 2002) and among pregnant women (Takser et al 2005). Finally, although animal (rat) studies on HCB and thyroid function primarily show declines in T 4 and increases in TSH (ATSDR 2002b), a study among hamsters dosed with HCB found a marked decrease in T 3 levels (and significant increase in sodium iodide uptake) while T 4 levels remained unchanged (Smith et al 1987).…”

“…In addition, several human studies have investigated associations between levels of these compounds in the body and thyroid hormone levels (Takser et al 2005;Schell et al 2004;Bloom et al 2003;Hagmar 2003;Pelletier et al 2002;Hagmar et al 2001a;2001b;Persky et al 2001;Sala et al 2000;Longnecker et al 2000;Osius et al 1999;Koopman-Esseboom et al 1994;Emmett et al 1988). However, study populations have differed greatly and results have not been consistent across studies.…”

Some evidence of effects of environmental chemicals on the endocrine system in children

“…For all studies, PCB levels (median or mean) are reexpressed in terms of μg/l serum, by the methods of Longnecker (Longnecker, 2001). Except for the study from Germany (Osius et al, 1999) of school children exposed to a toxic waste incineration plant, all other studies are from cohorts of infants or mothers with no particular exposures, from Holland (Koopman-Esseboom et al, 1994;Fiolet et al, 1997), North Carolina (Longnecker et al, 2000;Rogan et al, 1986), Taiwan , and Québec (Canada) (Takser et al, 2005). The combination of the highest exposures and the second largest sample size makes the Faroe Islands study the most useful.…”