, 2011). Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Many pesticides can be considered as POPs. Global DNA methylation levels have been reported to be inversely associated with blood levels of persistent organic

pollutants (POPs), xenobiotics that accumulate in adipose tissue. Kim Trametinib et al. found that low-dose exposure to POPs, in particular organochlorine pesticides, was associated with global DNA hypomethylation, estimated by the percent 5-methyl-cytosine (%5-mC) in Alu and LINE-1 assays, in healthy Koreans (Kim et al., 2010). The same relationship between plasma POP concentrations and blood global DNA methylation, estimated in Alu repeated elements, was evaluated in 70 Greenlandic Inuit, a population presenting some of the highest reported levels of POPs worldwide. In this work, a significant inverse linear relationship was

found for DDT, DDE, β-BHC, oxychlordane, α-chlordane, mirex, several PCBs, and sum of all POPs (Rusiecki et al., 2008). The levels found in this Arctic population, although extremely high, are comparable to those found in other regions. For example, an environmental assessment conducted in a Lacandon Maya community in the Southeast part of Mexico (Perez-Maldonado et al., 2006) showed levels of exposure to DDT comparable to those reported by Rusiecki et al. (2008). Arsenic and its compounds, Gefitinib especially the trioxide, have been widely used in the past in the production of biocites for wood conservative treatments, herbicides, Fenbendazole and insecticides, however arsenical pesticides are still used in some countries and are still present in several wood products. Arsenic is a non-mutagenic human carcinogen that induces tumors through unknown mechanisms. A growing body of evidence suggests that its carcinogenicity may result from epigenetic changes, particularly in DNA methylation. Changes in oncogenes or tumor suppressor genes methylation can lead to long-term changes in the activity of genes controlling cell transformation (Laird,

2005). In arsenic-treated cells, arsenic exposure was associated with the global hypomethylation (Chen et al., 2004, Sciandrello et al., 2004 and Zhao et al., 1997). Arsenic is metabolized through repeated reduction and oxidative methylation. In the presence of high arsenic exposure, this detoxification process can compete with DNA methylation for methyl donors, thus causing hypomethylation (Mass and Wang, 1997). Inorganic arsenic is enzymatically methylated for detoxification, using up S-adenosyl-methionine (SAM) in the process. The observation that DNA methyltransferases also require SAM as their methyl donor suggested a role for DNA methylation in arsenic carcinogenesis and other arsenic-related effects.