**4. Organochlorinated contaminants and their toxic effects**

Organochlorine pesticides (OCP) are among the most abundant global pollutants with high concern. According to the Stockholm Convention, POPs included nine internationally produced and extensively used in agricultural crops or vector control. These compounds are highly toxic and potentially carcinogenic according to the US Environmental Protection Agency (USEPA) stated since 1980 [15]. One of these compounds is pentachlorophenol, which is toxic to any living organism, as it is an inhibitor of oxidative phosphorylation. It is also a pollutant recalcitrant to degradation due to its stable aromatic ring and high chloride content, thus persisting in the environment [12].

The regulation of exposure to these persistent chlorinated pollutants by the population continues, mainly through the consumption of fatty foods of animal origin that previously where feed with contaminated fodder. The resistance of persistent organic compounds to chemical and metabolic degradation implies that they concentrate more as they move through food networks [9]. Despite the prohibitions imposed on most of these pollutants for several years, numerous investigations have reported the continuing and ubiquitous presence of organochlorines in the global atmosphere [15].

Exposure to these pollutants is associated with effects on human health, including cancer, reproductive defects and behavioral changes, which are related to the alteration of the functions of some hormones, growth factors, enzymes, and neurotransmitters [11]. Organochlorine pesticides such as dichlorodiphenyltrichloroethane (DDT) was widely used before recognizing their toxicity and persistence. Exposure to pesticides has been associated with arthritis, breast cancer, and diabetes [8]. Actually, these organochlorine compounds are bio-magnified through the food chain. In the case of humans, when consuming foods of animal origin such as meat, fish, milk, among others, they are exposed to high levels of these pollutants because their biodegradation is slow and they accumulate in the human body as mentioned above. An example is DDT, which can remain for 50 years in the body, mainly in fatty tissue, its distribution is through the bloodstream in plasma or lipids. Also, these contaminants cross the placental barrier reaching the fetus and is secreted in breast milk [12]. This compound has been detected at high levels in liver, brain, along the food chain [13]. Other examples are dichlorodiphenyldichlorethylene (DDE) and methoxychlor, which, although they are weak as estrogens and antiandrogens. They have been found to accumulate in fatty tissues in organisms and are associated with disease, including cancer [16].

Another problem of the organochlorine compounds due to the low biodegradation, is their sediment deposition, which straight to substantial increases in the residence time of these compounds in aquatic ecosystems, thus facilitating bioaccumulation. These pollutants are known to bind principally with organic matter as the humic acids present in the sediments due to their hydrophobicity [15].
