Why scientists still cannot say how much plastic infants are actually consuming

by · News-Medical

From feeding bottles to formula and breast milk, researchers traced where plastic particles and oligomers appear and why reported exposure levels can vary so widely.

Paper: Evidence, implications and mitigation of plastic-derived contaminants in infant food: a systematic review. Image Credit: Irina Gutyryak / Shutterstock

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Researchers recently conducted a systematic review, published in the journal NPJ Science of Food, to evaluate evidence on infant dietary exposure to plastic-derived contaminants, including nanoplastics and oligomers, and to assess the state of current research.

Infant Exposure to Plastic-Derived Contaminants

Plastics have become ubiquitous in manufacturing, packaging, and consumer products because of their cost-effectiveness and versatility. Their widespread use has also contributed to environmental contamination and human exposure to plastic-derived chemicals and particles.

Infants may experience MNP exposure at least an order of magnitude higher than adults. Their potential exposure is increased by their smaller body size, greater food intake per kilogram of body weight, and frequent reliance on plastic-based feeding products.

The detection of plastic-derived contaminants across breast milk, formula, solid infant foods, and feeding products, together with evidence of MNP contamination in the wider environment, points to multiple exposure pathways. Feeding products are often marketed as safe, but inconsistent testing and significant gaps in toxicological evaluation, especially concerning sub-micron particles and chemical leachates, remain unresolved.

Current regulatory measures provide limited coverage of MNPs and do not set infant-specific exposure or migration limits for plastic contaminants. Clear infant-specific guidance is lacking. Economic and practical barriers further limit the adoption of non-plastic alternatives. These shortcomings highlight the critical need for systematic research and targeted risk assessment to guide effective mitigation strategies for this vulnerable population.

Literature Synthesis

A systematic review was conducted of all primary, peer-reviewed studies reporting new data on MNP and oligomer concentrations in infant foods and feeding equipment, following PRISMA guidelines. Relevant articles were identified through searches of Web of Science, Scopus, and PubMed up to October 12, 2025. Keyword screening yielded 92 papers for manual relevance assessment by two researchers, of which 26 were then read in full.

Inclusion criteria required primary studies to report new quantitative data on MNP or oligomer concentrations or release rates in infant food or feeding equipment. Eligible literature reviews had to contain sections focused on plastic-derived contaminants in or from infant food and feeding equipment. Studies without migration experiments, quantitative data, or a clear distinction between plastic and non-plastic oligomers were excluded. Data extraction was performed independently by two reviewers, followed by bibliometric analysis.

Methodological quality was evaluated using 14 core criteria addressing sample preparation, contamination mitigation, and experimental design, with adjustments for the differing properties of particulate MNPs versus dissolved oligomers, and food matrices versus container simulants. Variation in sampling, analysis, and reporting prevented a meta-analysis, so the authors used a qualitative synthesis rather than calculating an average contamination rate.

Research Trends and Outputs

Comprehensive database searches identified 22 primary research articles and four review articles examining plastic contamination in infant food. This area of research is rapidly developing, with most studies published within the last four years. Since 2021, the annual publication rate has risen, averaging more than four studies per year over the past four years and suggesting growing recognition of the issue among researchers, regulators, and industry.

The bulk of research focuses on infant feeding bottles (IFBs), while fewer studies address formula and solid-food containers. Investigations into breast milk, solid foods, and breast milk storage bags remain scarce.

Four recent reviews evaluated infant exposure to MPs from food, with primary emphasis on breast milk and formula. While some reviews analyzed MPs from feeding bottles and storage bags, none examined nanoplastics or contamination in solid foods.

Several reviews overlooked or misinterpreted key primary studies, and the authors identified several factual inaccuracies. Only one review systematically compared findings across studies and addressed other contamination sources, such as airborne microplastics. Most reviews offered limited recommendations for reducing infant exposure, with only one proposing dietary modifications for breastfeeding mothers.

Lack of Standardized Methodologies and Consistent Reporting

Data on MPs in breast milk and formula are limited and often inconsistent, largely because of variations in study design and analytical rigor. Methodological biases can contribute to reports of elevated MP concentrations, while some higher-reliability studies report lower concentrations and show the importance of environmental controls. One study found that airborne deposition during formula preparation was 1.7 times the inherent MP concentration in the formula.

Plastic contaminants in solid infant foods have been investigated in only two studies, with results differing by product type and fat content. Across the breast milk and formula evidence base, some studies lacked sufficient blank controls or used preparation methods that could fragment particles, while one otherwise high-reliability study relied on visual pre-screening that favored larger particles. Overall, inconsistencies in data quality and methodology account for much of the variation in reported contamination levels, keeping the evidence base fragmented.

Several widely cited studies may overestimate contamination by misclassifying fatty acid esters as microplastics or by failing to verify polymers in sub-micron particles. Studies using stronger contamination controls, polymer verification, and better-validated analytical procedures provide more reliable estimates and have challenged some previously reported high exposure values.

Feeding Equipment and Container Contamination

Multiple studies demonstrate that contaminant release from IFBs is closely tied to bottle material, brand, and preparation method. For example, formula prepared in polypropylene (PP) bottles at 70°C has been reported to release up to 16 million MPs per liter, but the review notes that this widely cited estimate has been disputed, with other studies reporting much lower concentrations and one attributing the particles to fatty acid esters. In one abrasion study, glass bottles released fewer particles than plastic bottles, while mechanical abrasion in both types generated up to 112 MPs/mL.

Temperature is a key factor, with three independent studies confirming that higher formula preparation temperatures substantially increase MP release, but the researchers did not recommend lower temperatures, likely because such advice must also account for World Health Organization and European Food Safety Authority guidance on microbial contamination. Brand differences are also significant; one study found that IFB brand was the dominant factor in MNP release, with statistical confidence exceeding 99%.

For breastmilk storage bags, exposure estimates range from 0.62 to 0.86 mg/day, the highest reported for this source, but the true proportion of plastic versus non-plastic material remains uncertain because gravimetric measurements have limitations.

Studies on food storage containers and pouches indicate that heating and acidic foods can accelerate plastic migration. For example, estimated cumulative exposure to cyclic polyethersulfone (PES) oligomers exceeded thresholds of toxicological concern by up to 533% in high-consumption scenarios, while one study estimated that microwave heating of plastic food containers could release up to 2.15 billion particles/cm² of food-plastic contact area. That study was rated low reliability because it lacked procedural blanks and compositional analysis for submicron MNPs. Reported migration estimates differed by up to nine orders of magnitude between studies using markedly different analytes and analytical approaches.

Conclusions

This systematic review found evidence of plastic-derived contaminants across several infant foods and feeding products, but the scale of infant exposure remains difficult to determine. Inconsistent methodologies and limited regulatory oversight continue to impede clear risk assessment. The review does not establish that measured exposures cause adverse health effects in infants, and health effects at environmentally relevant exposure levels remain uncertain. Coordinated research and standardized testing protocols are needed to improve exposure estimates, strengthen toxicological evidence, and inform infant-specific risk assessment and policy.

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