Longitudinal study of pesticide residue levels in human milk from Western Australia during 12‐months of lactation: Exposure assessment for infants
Authors: Geddes Donna T. , Du Jian , Gay Melvin C.L. , Gridneva Zoya , Lai Ching Tat , Hartmann Peter E. , Trengove Robert D. 
Published: November 2023

Persistent organic pollutants (POPs), such as pesticides, are released into the environment and bio‐accumulate in human adipose tissue via inhalation, ingestion or dermal adsorption. The presence of pesticides in human milk (HM) is of great concern due to the potential health effects. Longitudinal monitoring of these pesticides in HM is essential to gauge the maternal environment, to ensure that the daily tolerable intake by an infant is within recommended guidelines and to determine any associations with infant growth outcomes.

Pre‐ and post‐feed milk samples were collected from both breasts of 16 Western Australian (WA) mothers at 2, 5, 9 and 12 months postpartum. A miniaturized QuEChERs extraction optimized for human milk (1mL) was used, followed by quantitative GC‐MS/MS analysis for 88 pesticides. Linear mixed models were used to investigate associations between HM pesticides levels and maternal and infant anthropometrics. One‐way ANOVA and Tukey's all pair comparison testes were used to compare the differences in pesticides concentration and the actual daily intake (ADI) and the estimated daily intake (EDI).

Only 3 pesticides (p,p′‐DDE, p,p′‐DDT and β‐BHC) were detected in this cohort. p,p'‐DDE was detected in 83% of the samples. A significant decrease (68%; P = 0.03) in HM p,p'‐DDE levels was observed between 2 months (70.90 ± 70.58 ng/g fat) and 12 months (22.35 ± 13.96 ng/g fat). p,p'‐DDT and β‐BHC were detected in 2 mothers and 1 mother respectively. No significant relationships were observed between HM p,p'‐DDE and infant growth outcomes such as weight (P = 0.40), length (P = 0.13), head circumference (P = 0.07) and percentage fat mass (ultrasound skinfolds (P = 0.34) and bioimpedance (P = 0.11)). The ADI of the infant (0.16 μg/kg body wt/day) which was calculated based on the actual measurements of infant milk intake, milk lipid and infant weight, was significantly different (P < 0.05) than the conventional EDI (0.23 μg/kg body wt/day).

Overall the levels of p,p'‐DDE in HM decreased significantly over the first year of lactation, and were not related to infant growth outcomes. The more accurate ADI was significantly less than the EDI after 2 months of lactation indicating previous studies are overestimating infant dose. The ADI for women from WA was also 2 to 17 times lower than current recommended guidelines (0.5 μg/kg body wt/day). Whilst concern about the effects of pesticides exposure to infants is warranted, one must take into consideration the relatively short period of exposure via breastfeeding relative to a lifetime. Further, HM POPs serves as an important environmental indicator of population exposure.

Support or Funding Information

This study was supported by an unrestricted research grant from Medela AG (Switzerland). The authors acknowledge Bruker for the provision of SCION GC‐MS/MS system and Bioplatform Australia for pesticide research.