| dc.description.abstract | Prenatal exposure to environmental toxicants is of major concern, as foetal development is one of the most sensitive life stages for endogenous and exogenous insults. Permeability of the placenta allows not only for environmental contaminants, but also contaminants released from maternal body stores during pregnancy, to be transferred to the foetus. Most of the exposure assessments in pregnant women and birth outcome studies have been performed in developed industrialised countries, mainly in the northern hemisphere. There is a lack of such assessments from developing countries and countries that are in transition, therefore the study was initiated. In addition, the reintroduction of controlled indoor residual spraying (IRS) of DDT for malaria control in 2001 in malaria endemic regions in South Africa (SA), provided an opportunity to assess prenatal exposure and enhance the current understanding of DDT and other selected contaminants in malaria and non-malaria regions situated along the coast.
This thesis evaluated the extent of concomitant exposure to selected organic compounds and mercury (Hg) in utero in three very distinctive rural study sites, namely, site 1 - a malaria endemic site; site 2 - a non-malaria site; and site 3 - an intermittent malaria site. In the malaria endemic site, as expected, elevated levels of DDT from IRS were found. In addition, substantial concentrations of Hg, γ-HCH and endosulfan were also detected. In the intermittent and non-malaria sites, the p,p'-DDE/p,p'-DDT ratios indicate recent on-going use of DDT, possibly illegal use, since DDT use is only allowed in designated areas. Furthermore, high levels of the now banned γ-HCH and endosulfan were also found in the intermittent malaria site, with lower levels in the malaria endemic site and non-malaria sites. Although Hg was detected in 100 % of maternal and cord blood samples analysed, it was found to be in lower concentrations than in some other countries. However, continuous low levels exposure to Hg may have the negative parallel neurotoxic effects for vulnerable groups such as the foetus, newborns and growing children.
This study has confirmed that pregnant women in these study sites were exposed concurrently to a mixture of chemicals, many classified as endocrine disruptors, indicating the need for the implementation of policies that curtail the use of these chemicals. | en |
| dc.description.popularabstract | Background: Prenatal exposure to environmental toxicants is of major concern, as foetal development is one of the most sensitive life stages for endogenous and exogenous insults, due to rapid cell division and apoptosis, morphogenesis, and cellular differentiation. Due to limited renal and biliary elimination, and the inability to metabolise toxicants in utero, prenatal exposure affects birth outcomes and early childhood development. Permeability of the placenta allows not only for environmental contaminants, but also contaminants released from maternal body stores during pregnancy, to be transferred to the foetus. At present, exposure to multiple chemicals amongst pregnant women has been studied, but more research is required on the subject.
Most of the exposure assessments in pregnant women and birth outcome studies have been performed in developed industrialised countries, mainly in the northern hemisphere. There is a paucity of such assessments from developing countries and countries that are in transition (UNEP, 2011). Populations of the southern hemisphere, where most of these developing countries are situated, may be more susceptible to toxic effects of pollutants, due to their compromised health and economic status, as well as changes in climatic conditions, including a rise in temperatures which may lead to an increase in the number of malaria mosquitoes and changes in their geographic distribution. The same trends may be observed for other insect vectors as well, with the final outcome being an increased use of 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane (DDT). It is predicted that coastal populations in the southern hemisphere will be most affected.
The reintroduction of controlled indoor residual spraying (IRS) of DDT for malaria control in 2001 in malaria endemic regions in South Africa (SA), permitted an opportunity to assess prenatal exposure and enhance the current understanding of DDT and other selected contaminants in malaria and non-malaria regions situated along the coast.
This study was initiated as a follow up to a pilot study which evaluated the extent of prenatal exposures to persistent toxic substances (PTS) and birth outcomes in selected geographical regions of SA. The regions under study consisted of three very distinctive rural study sites situated along the western coast of the Indian Ocean, in the KwaZulu Natal province, namely, site 1 - a malaria endemic site; site 2 - a non-malaria site; and site 3 - an intermittent malaria site.
Results and discussion: In the malaria endemic site, high concentrations of DDT, in particular p,p'-1,1-bis-(4-chlorophenyl)-2,2-dichloroethene (p,p'-DDE) and p,p'-DDT, were found in the maternal plasma. These levels were significantly higher when compared with the other two sites (i.e. intermittent malaria and non-malaria). In addition, subjects in the malaria endemic site, were not only exposed to elevated levels of DDT, but also exposed to mercury (Hg), γ-Hexachlorocyclohexane (γ-HCH) and endosulfan, although to a lesser extent. In both the intermittent malaria and non-malaria sites, elevated levels of p,p'-DDE and p,p'-DDT were also found in maternal plasma. A p,p'-DDE/p,p'-DDT ratio of 5 and 4 was found in the intermittent and non-malaria sites, respectively, indicating recent exposure, and suggesting that food is not the only source of DDT exposure in these two areas. The reason for the elevated levels of DDT in these areas is not clear, considering the long residence time of participants in each site. Overall, maternal age and weight negatively influenced p,p'-DDE levels, whereas, having one’s home sprayed by the malaria vector control personnel, using wood for cooking and consuming tinned fish significantly increased the p,p'-DDE levels.
The γ-HCH and endosulfan 1 and 2 were elevated in all three regions, however, significantly higher levels of endosulfan and γ-HCH were found in the intermittent malaria site, possibly due to the large commercial and subsistence farming activities in the area. The two compounds, endosulfan and γ-HCH correlated strongly with each other, indicating a similar source of exposure. For γ-HCH, drinking borehole water (positive), weight (positive), age (negative) and consumption of processed meat (negative) were strong predictors. Growing one’s own food, self-reported poor air quality or exposure to environmental pollution around the home, were all positively associated with endosulfan levels. Consumption of processed meat and dairy products was a negative predictor of endosulfan levels. γ-HCH levels were much higher when compared with some other regions, such as Australia, Mexico and Poland. As γ-HCH and endosulfan are now listed as banned and persistent substances by the Stockholm Convention, efforts must be made to reduce sources of exposure in SA.
The other isomers of Hexachlorocyclohexane (HCH) (α, β- HCH), and the pyrethroid pesticides (cis-permethrin, cyfluthrin, cypermethrin and deltamethrin) were detected in less than a fifth of the samples, and Hexachlorobenzene (HCB) was not detectable in any of the samples. This study found low levels of β-HCH compared to those in Russia and Spain.
Very low maternal concentrations of the Polybrominated Diphenyl Ether (PBDE) isomers, 28, 49, 71, 47, 66, 77, 100, 119, 99, 85, 154, 153, 138, were observed across all three sites, although PBDEs have been reported in other studies in breast milk, leachates and catchment areas in South Africa.
Hg was detected in 100% of maternal and cord blood samples in the malaria endemic site, with significantly higher concentrations than the intermittent and non-malaria sites. There was a strong positive correlation (r2 = 0.66) between maternal and cord blood Hg levels. For umbilical cord blood Hg concentrations, the following were strong predictors in the multivariate regression model: maternal blood Hg levels, living in the malaria endemic site, environmental pollution in the home and a household member being involved in fishing.
Conclusion: This thesis evaluated the extent of concomitant exposure to selected organic compounds and Hg in utero. Although, as expected, elevated levels of DDT from IRS were found in the malaria endemic site, substantial concentrations of Hg, γ-HCH and endosulfan were also found. In addition, DDT was also found in the intermittent and non-malaria sites, although to a lesser extent. The p,p'-DDE/p,p'-DDT ratios in the two sites indicate recent on-going use of DDT, possibly illegal use, since DDT use is only allowed in designated areas. Furthermore, high levels of the now banned γ-HCH and endosulfan were found in the intermittent malaria site, with lower levels in the malaria endemic site and non-malaria sites. In the intermittent malaria site, there is an indication of recent use of DDT, as well as significant exposure to γ-HCH and endosulfan. This study has confirmed that pregnant women in these study sites were exposed concurrently to a mixture of chemicals, many classified as endocrine disruptors, indicating the need for the implementation of policies that curtail the use of these chemicals. | en |
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