Heavy metal toxicity is associated with a wide range of diseases. The problem is magnified when toxic metals are found in breast milk, the main source of nutrition for a vulnerable age group [1]. Metals can reach breast milk through different routes, including dietary intake, environmental contamination, occupational and living habits, and household and cosmetic products [2]. In this study, the levels of seven essential metals (Co, Cu, Mn, Mo, Se, Zn, and V) and 13 toxic metals (Sb, As, Ba, Be, Cd, Cs, Pb, Hg, Ni, Pt, Th, Tl and U) were assessed in the breast milk of 118 lactating mothers participating in a Spanish human biomonitoring project (BETTERMILK). For the determination of all analytes, except for Hg, samples were subjected to microwave digestion using an ETHOS 1 system with a Q-20 rotor and quartz vessels. Approximately 1.0 g of breast milk was weighed into a quartz digestion vessel and 3 ml of HNO₃ (1:1) and 0.5 ml of 30% H₂O₂ were added. The digested solutions were adjusted to a final weight of 10 g with deionised water. Chemical analysis was then performed on an iCAP RQ Thermo Scientific inductively coupled plasma mass spectrometer (ICP-MS). In the case of Hg, 500 mg of breast milk was weighted in a quartz boat for its determination in the direct mercury analyser (DMA-80). The highest detection frequency (DF) was 100% for Cu, Zn, Se and Cs, 93% for As and 84% for Hg. The remaining elements had DFs below 40%. The geometric mean (GM) concentrations were below the LoQ for 13 elements and the maximum value found was 2856 ng/g for Zn. The study identified as the main factors associated with metal levels in breast milk the pre-pregnancy BMI, maternal age, use of cosmetics and deodorants, food consumption, and living near industrial activities. The estimated weekly/daily intake of toxic and essential metals in newborns via human milk was compared with the PTWI/UL/BMDL0.1 established by EFSA and FAO/WHO, all of which were lower, except for Zn at 95th percentile and As at the most restrictive range value. To the best of our knowledge, this is the first study to evaluate the risk of newborns to the most toxic metals such as Hg, As, Cd, Pb, Se and Zn via breast milk in Spain.

Acknowledgements

The authors would like to thank Eva Villoldo, responsible for the collection of samples, who performed her work with great efficiency. The study would not have been possible without the participating mothers and the Division of Neonatology of the Department of Pediatrics at the University and Polytechnic La Fe Hospital. We want to particularly acknowledge the donors and the IBSPCV BioBank (PT13/0010/0064) integrated in the Spanish National Biobank Network and the Valencian Biobanking Network for their collaboration. We also would like to University of Alicante (UAIND21-03C) and Generalitat Valenciana (GV/2015/008) for the financial support.

References

[1] Exclusively breastfeed for 6 months. World Health Organization - Regional Office for the Eastern Mediterranean. http://www.emro.who.int/nutrition/breastfeeding/exclusively-breastfeed-for-6-months.html (accessed 2024-09-22)

[2] Mathiesen, L.; Buerki-Thurnherr, T.; Pastuschek, J.; Aengenheister, L.; Knudsen, L. E. Fetal Exposure to Environmental Chemicals; Insights from Placental Perfusion Studies. Placenta, 2021, 106, 58–66. https://doi.org/10.1016/j.placenta.2021.01.025.