This study was conducted with the objective of determining whether there is a depuration of organochlorine pesticides in breast milk according to breastfeeding time. In total, 171 samples from mothers that lived in the State of Guerrero, Mexico were analyzed. There was a weak negative relationship between pp'DDE (r = -0.216) and Σ-DDT (r = -0.222) concentrations with the days of lactation. In a comparison analysis, a statistically significant decrease of pp'DDT and pp'DDE levels was observed, as well as the Σ-DDT from the first to the fifth week of lactation. A reduction of 0.188 mg/kg lipid of pp'DDE and 0.181 mg/kg lipid of Σ-DDT per week was obtained. HCB, β-HCH and op'DDT concentrations were low and had no major fluctuations between subgroups. The low levels found and the observed reduction in time involve less exposure to the infant to these pollutants. Through this methodology changes in levels of certain organochlorine pesticides in various stages of human milk production may be shown.

In Mexico, organochlorine pesticides were used in public health and agriculture programs, causing chronic exposure to the population. Human breast milk samples were collected from 171 mothers who were residents from Guerrero, Mexico. Analysis was carried out by gas chromatography. Median concentrations (mg/kg on fat basis) for the following pesticides were: HCB, 0.009; β-HCH, 0.004; pp'DDE, 0.760; op'DDT, 0.016; pp'DDT, 0.045; and Σ-DDT, 0.833. These values are lower than in other States in Mexico, and in some countries where the use of these pesticides was banned more than 30 years ago. Differences were found in HCB, pp'DDE and pp'DDT concentrations in groups divided according to age (p < 0.05). The older age groups had higher concentrations, except for the comparison between groups 21-23/24-28 years, which were 0.913 and 0.530 mg/kg of pp'DDE, respectively. Given the restrictions on use, a greater decrease in organochlorine pesticide levels in human milk is expected in a few years.