May 12, 2025

expert reaction to study identifying nanoparticles in human breast milk

A study published in PNAS looks at the identification of nanoparticles in human breast milk. 

Prof Oliver Jones, Professor of Chemistry, RMIT University, said:

“There were two parts to this study. The first was an attempt to separate nanoparticles from human breast milk. Here, they found some material that may have been nanoparticles, but I don’t think the results were conclusive. The human samples also all came from China, so don’t tell us anything about the rest of the world. 

“The other thing to remember is that detection by itself does not mean much. Today’s analytical equipment is so sensitive that we can detect almost anything anywhere. However, just because something may be present in tiny amounts does not mean it is causing harm.

“The second part of the study aimed to create a specific type of nanoparticle (silicon dioxide or silica) and administer it to mice to investigate its passage into milk. While this sort of experiment has its use, the keywords are “in mice”. Mice are not mini-humans, and lab-made nanoparticles, as well as the amounts they used, may not accurately reflect what is found in the environment. The results, while interesting, are thus not directly comparable.

“We have actually known that nanoparticles can enter the body through the lungs for over 20 years [1]. Many types of nanoparticles, including carbon, gold, silver, zinc oxide, titanium dioxide, and manganese oxide, have been shown to do this [2], so in that sense, the findings aren’t new.

“Another thing to keep in mind is that the authors did not assess any potential effects of the particles; they just looked at how they might get into milk. Breathing particles in is different from ingesting them. The tissue in the lung is thin to facilitate gas exchange. This makes it relatively easy for small particles to enter the body this way. In contrast, the tissue in the intestinal tract is relatively thick and well-controlled. It is quite possible that ingested nanoparticles pass through and so don’t cause any effect. 

“In short, while particulate pollution is a real problem that should be studied, I don’t think we need to panic over nanoparticles in milk just yet.”

References

1. Oberdörster G.  Sharp Z.  Atudorei V.  Elder A.  Gelein R.  Lunts A.  Kreyling W. Cox C. Extrapulmonary translocation of ultrafine carbon particles following whole-body inhalation exposure of rats. Journal of Toxicology and Environmental Health Part A 2002 65 (20) 1531-1543.

2. Oberdörster G.  Oberdörster E. Oberdörster J. Nanotoxicology: an emerging discipline evolving from studies of ultrafine particles. Environmental Health Perspectives, 2005, 113 (7), 823-839″.

Prof Tamara Galloway, Professor of Ecotoxicology, University of Exeter, said:

“This interesting paper combined human biomonitoring with animal studies to understand more about the circulation of nanoparticles in the human body and their uptake into breast milk. The paper is well presented and supports previous findings with additional data. It does not offer anything new to report on potential harm to humans or babies, but aids understanding of routes of nanoparticle uptake into the body and how changing the nanoparticles themselves (e/g/ altering their surface charge) could alter how they are taken up.

“It’s been known for some time that nanoparticles of various types can enter the human body and circulate to different tissues and locations, including to breast milk. For example, micro and nanoplastics, carbon black (an air pollutant linked to traffic fumes) and other metals have been found both in human tissues and breast milk. Mostly, the concentrations of nanoparticles found in the body are very small and there is no indication that they lead to adverse health effects at these concentrations.

“The real world implications of this paper are in offering a more in-depth characterisation of the particles themselves, including their shapes, sizes and surface charge. The combined approach of human and animal studies, allowed the authors to firstly identify the most abundant nanoparticles in breast milk (silicon) and then to explore how they got there, a good illustration of the ‘One Health’ approach.

“They found:

“• Nanoparticles were present in 42/53 breast milk samples

“• Nanoparticles could be getting into breast milk by a pathway of uptake into and through cells (including immune cells). via airways/intestine/blood to breast milk

“• Eating flour-containing food might put you more at risk (this was more tentative but not altogether surprising, a lot of flours and powdered foods have anticaking agents and whiteners in them, it’s not particularly new or conclusive)

“• Changing the surface charge on the nanoparticles could modify their uptake – this is good news at it offers a future way of designing drug delivery or of reducing unwanted exposures”

‘Identification of nanoparticle infiltration in human breast milk: Chemical profiles and trajectory pathways’ by Qing Yang et al. was published in PNAS at 20:00 UK time on Monday 12 May 2025.

DOI: 10.1073/pnas.2500552122 

Declared interests

Prof Tamara Galloway: No conflicts to declare.

Prof Oliver Jones:I have no conflicts of interest to declare.