Breast milk intake and mother to infant pesticide transfer measured by deuterium oxide dilution in agricultural and urban areas of Mexico

Vector-borne diseases have increased pesticide use in urban areas (UA) and agricultural areas (AA) in Mexico. Breast milk can be contaminated by pesticide exposure. The objective of the study was to measure breast milk intake by deuterium oxide dilution as well as organochlorine and pyrethroid transfer from mother to infant in AA and UA of Sonora, Mexico. Human milk intake was determined by the ’dose-to-mother’ technique using deuterium oxide (D₂O) dilution. Mothers’ body composition was also assessed by this technique and the intercept method. Pyrethroids (deltamethrin, cypermethrin and cyhalothrin) and organochlorine pesticide residues (p,p’- DDT, p,p’- DDE, p,p’- DDD) in breast milk samples were measured by gas chromatography. Sixty-two lactating women and their infants participated in the study, 32 lived in the UA and 30 lived in the AA. Breast milk intake was approximately 100 mL higher in the AA than in the UA 799 ± 193 and 707 ± 201 mL/day, respectively (p < 0.05). The concentrations of p,p’- DDT and cypermethrin levels in breast milk were higher in the UA than in the AA (p < 0.05 and p = 0.001, respectively). None of the pyrethroids and organochlorine pesticides studied surpassed the Acceptable Daily Intake (ADI) in milk for humans according to EPA and FAO/WHO. In conclusion, breast milk intake was higher in the AA compared to the UA. The p,p’- DDT and cypermethrin levels in breast milk were higher in the UA compared to the AA. Since pesticide levels in human milk did not exceed the ADI, breastfeeding is still a safe practice and should be encouraged.