Exposure assessment of persistent organic pollutants and metals in Mexican children
Introduction
In Mexico, contamination sources of metals, persistent organic pollutants (POPs) and persistent toxic substances (PTS) exist in different areas, such as those associated with mining, agriculture, major industry, small-scale industry, oil fields, and non-controlled waste disposal sites. In this scenario, it is important to assess the exposure of children to different toxins, considering that they are one of the populations most susceptible to chemicals (IPCS, 2006). Biomonitoring in children is a useful instrument in formulating environmental health policies. For example, in Mexico during the last decade, studies in children led to the reduction or elimination of different chemicals such as lead, DDT and lindane. Furthermore, the biomonitoring of susceptible populations is a valuable method for the identification of critical contaminants, as has been shown in the United States with the National Health and Nutritional Examination Survey (NHANES III, 2005, Needham et al., 2005).
Information about human exposure to chemicals is very limited; besides, in relation to children, the information is even more scarce. In this regard, four programs are particularly relevant as they do include children. Two are German studies, one in the Federal State of Baden–Wuerttemberg in Southwest Germany (Gabrio et al., 2005, Link et al., 2005, Link et al., 2007) and the second in North Rhine–Westphalia (Wilhelm et al., 2007), and two program in the United States of America, the Human Exposure to Environmental Chemicals (NHANES III) and a study performed in Minneapolis that evaluated 50 environmental chemicals in children (Sexton et al., 2006).
Children appear to be particularly suitable for a monitoring program, as they are not directly exposed to occupational pollution; thus, children normally reflect present trends of environmental exposure more accurately than do adults (Link et al., 2005). Moreover, it is well established that children are potentially at a higher risk than adults for adverse health effects from exposure to many environmental chemicals (Guzelian et al., 1992, Bearer, 1995, Carlson, 1998, Galson et al., 1998, Aprea et al., 2000, Needham and Sexton, 2000, Adgate and Sexton, 2001, Brent et al., 2004, IPCS, 2006).
Taking into account the above points, we studied children’s exposure to metals, POPs and PTS in nine hot spot areas in Mexico. In general, POPs and metals are receiving international attention, and very recently, new resolutions designed to eliminate or restrict POPs use were drafted at the Stockholm Convention on Persistent Organic Pollutants (Mintz, 2001, UNEP, 2004).
Section snippets
Population
The sampling sites were selected considering previous knowledge of contamination at each site and their distribution throughout the country. Sites included in the study are recognized for their industrial activity, agricultural practices with past and current use of pesticides, waste disposal or brick production using different materials as fuel sources (Fig. 1 and Table 1). During the year 2004, we studied a total of 229 healthy children (aged 6–12 years old). The children attending public
Results
Blood concentrations of organochlorine pesticides and PCBs are depicted in Table 2; an important finding is that all children included in this study had detectable levels of DDE, indicating a generalized past exposure to DDT. Moreover, the pesticide DDT, which is less persistent than its main metabolite (DDE), was detected in 14.5% of the population studied (Table 2). The highest concentrations for both compounds (DDT and DDE) were recorded in Chis (Table 3). While the mean level of DDE for all
Discussion
The extraordinary stability and persistence of the POPs, together with their lipophilic properties, leads to their accumulation in the food chain and causes considerable health and ecotoxicological effects (Ratcliffe, 1967, Colborn et al., 1993, Peakall, 1993, Olsson et al., 1994, Hays and Aylward, 2003). Therefore, production prohibition or stronger restrictions in the application or emission of persistent organochlorines have been necessary; this was the aim of the Stockholm Convention on
Acknowledgments
This work was supported by grants from the National Institute of Ecology, and from Consejo Nacional de Ciencia y Tecnología, Mexico, CONACYT-SALUD 13841. Dr. A. Leyva provided English editing of manuscript.
The work described in the manuscript was conducted in accordance with national and institutional guidelines for the protection of human subjects.
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