Chronic intoxications. Persons subject to high levels of exposure because of their occupation may be poisoned without manifesting symptoms, which means they are not warned of the high risk they run of suffering severe intoxication and dying from a small additional exposure, which in normal conditions would not cause a critical intoxication. According to the most recent documentary research by PAN International (Pesticide Action Network), contained in its position paper on the elimination of pesticides (PAN, 2007), the main chronic effects caused by chemical pesticides include cerebral lesions and lesions of the nervous system in general, such as peripheral polyneuropathies and Parkinson's disease (Semchuk and Love, 1992; McConnell et al., 1993; Baldi, 2003; PAN Germany, 2003; Isenring, 2006); cardiovascular diseases; kidney and liver disorders; cancer (Brody and Rudel, 2003; Flower et al., 2004); genetic mutations; teratogenesis (congenital functional malformations or abnormalities) (Levario et al., 2003); endocrine or hormonal problems; reproductive problems (sterility, impotence, abortions, stillborn children, development problems in offspring) (Colborn et al., 1996; Figà-Talamanca, 2006; Bretveld et al., 2007); and suppression of the immune system. All pesticides produce chronic effects, particularly those known as persistent organic pollutants (POPs), which include DDT and other organochlorinated insecticides, which are targeted for control by the Stockholm Convention approved at the United Nations in 2001 and which entered into force in May 2004 (UNEP, 2001; UNEP, 2007).

Health effects of contamination of the environment and foods. There are growing concerns not only about the presence of pesticide residues in foods and their health effects, but also about the "cocktail effect" of multiple pesticide residues, along with food additives, hormones and antibiotics used in breeding livestock and poultry and due to the use of chemical fertilizers. Chemical fertilization in conventional agriculture results in higher levels of nitrates, which can have negative effects on health, because in certain conditions they can be converted to nitrosamines, which are

carcinogenic. They may also reduce the ability of the blood to transport oxygen and pose a risk of methemoglobinemia (FAO, 2000). An effort has begun to look for multiple pesticide residues and nitrates in food samples, because the evidence suggests that when they act in combination in foods, the harmful effects may be compounded. Combinations of low levels of insecticides, herbicides and nitrates have proven toxic at levels at which the chemicals individually are not (Cleeton, 2004).

Hormonal or endocrine effects. The greatest harm from exposure to pesticides occurs during pregnancy, when toxics with endocrine effects or xenohormones limit or block the delicate natural signals that the hormonal systems of the mother and fetus send the cells and organs to guide their development. The endocrine alteration in the womb during the stage of fetal development may result in cancer, endometriosis, learning disorders, behavioral disorders, immunological and neurological disorders and other problems such as low sperm count, genital malformations and infertility. These hormonal problems may originate in fetal exposure and not manifest until puberty (Colborn et al, 1996; Figà-Talamanca, 2006; Bretveld et al., 2007). In addition, it is suggested that they may contribute to higher rates of hormone- dependent cancers such as breast and prostate cancer, in women and men occupationally exposed to pesticides. It is likely that women with breast cancer will have five to nine times more pesticide residue in their blood than those not afflicted with the disease (Bejarano, 2004; Cleeton, 2004).

      Children may be particularly susceptible to pesticide residues because they consume more food and water per unit of body weight than adults and their relatively immature organs may have a limited ability to detoxify these substances. In a comparative study with children ages 2 to 4 years in Seattle, six times more pesticide residue was found in children fed conventional foods than those fed organic foods. In another comparative study in Sweden with 295 children ages 5 to 13 years from schools with different approaches to education and food, it was found that in the