Although the latest reports on trends in biological levels of POPs are promising, the scenario for the next generations is of concern*. This holds true also for mercury, for which increased exposure owing to increased emissions and increased biological availability is expected. The most sensitive group of people is pregnant women and their foetuses**. Effects on the foetus might be prevented through the provision of good dietary advice to pregnant women based on the results of detailed trend studies of health outcomes in relation to contaminant exposure. The health of the unborn child should have top priority.
In order to reach fetal circulation, foreign chemicals must cross the placenta, the main interface between mother and fetus. Based on analyses made from cord blood, it is known that the fetus is exposed to environmental contaminants present in the maternal circulation. Laboratory studies in ArcRisk investigated the transfer of several contaminants, mainly perfluorinated compounds, in newly delivered human placentas. The overall findings indicated that the fetus can be significantly exposed to perfluorinated compounds in the womb. These findings suggest that environmental contaminants interact with placental transporter proteins, which may affect fetal exposure to chemical contaminants. The clinical significance of these findings is still unclear.
Mother-and-child health studies in ArcRisk investigated the relationship between the diet of pregnant women and contaminant levels in their blood, found that fish consumption was an important factor. A study of the maternal transfer of PBDEs showed that levels in the blood from umbilical cords of newborns were clearly correlated with levels in their mother’s blood serum; this study indicated a broader range of exposure sources than fish, however, as neonates from rural areas had statistically significantly lower levels of contaminants in their blood than those from urban areas. A long-term study of the trends of PCBs and several organochlorine pesticides in human breast milk has shown continually decreasing levels over the 15 years of the study.
Several health effects have been identified as a consequence of the exposure to organohalogen pollutants in the Mediterranean populations studied. Significant decreases in birth weight have been associated with higher cord blood serum concentrations of DDTs and, marginally, HCB and β-HCH. Decreases in birth length have been related to high HCB concentrations and decreases in head circumference to increased DDT. Higher concentrations of β-HCH have also been significantly associated with higher levels of thyroid-stimulating hormone at birth. Health effects of low-level mercury exposure have demonstrated subtle neurobehavioral deficits in children prenatally exposed to methylmercury.
Analyses of POPs in large numbers of individuals are required to assess the possible health effects of long-term exposure to low concentrations of these compounds. New-borns are more sensitive to these effects because their and metabolic functions are under development. Accordingly, new-born/foetus/pregnant women are often chosen for identification of health disturbances and for the examination of long-term effects of past exposures.
Criteria for acceptable concentrations of mercury contaminants in humans are presented in the table below (Donaldson et al., 2010). The maximum allowed concentration of total Hg in urine for exposed population to inorganic Hg set by WHO (1990) is 50 µg/g creatinine.
Most people in coastal areas of Mediterranean countries, and around 1-5 percent of the population in central and northern Europe, are at internationally accepted safe levels for methyl mercury, while large numbers among Mediterranean fishing communities and the Arctic population significantly exceed these levels (EC, 2005).