Rubber-related chemicals detected in Swiss raw milk

Seven of 17 Swiss milk samples contained at least one targeted rubber-related chemical, according to a study involving researchers from EPFL, Agroscope and the Federal Office for Food Safety and Veterinary Affairs. The results place an unexpected part of the dairy chain under scrutiny: the equipment that moves milk from the cow to the tank.

Researchers collected raw milk from 17 farms across Switzerland and tested for four chemicals associated with rubber materials. At least one substance appeared in seven samples. The concentrations were generally low, and the researchers have not established whether the levels pose a health risk to consumers.

The findings, published in Food Chemistry X and reported by EPFL on September 14, 2026, do not identify a confirmed contamination source. They do show that food safety investigations need to examine the full production process, including components that meet current legal requirements for food contact.

For Swiss consumers, the immediate significance lies in the uncertainty. The study does not advise people to avoid milk, and it does not establish that the detected chemicals cause harm at the measured levels. It gives researchers a starting point for tracing how these compounds reach raw milk.

Milking equipment emerged as a possible source after researchers identified 14 chemicals in hoses, seals and other rubber components. The equipment is designed to handle milk and is legally approved for contact with food, making the result significant for dairy producers and regulators.

Rubber parts are used throughout milking systems. Milk passes through hoses and fittings before it reaches storage tanks, creating several points where compounds can migrate from aging or worn materials. The study does not prove that the equipment transferred every chemical found in the milk, but the overlap gives investigators a clear pathway to examine.

Study leader Florian Breider described the finding as surprising because the materials comply with existing food-contact rules. Those rules regulate approved materials and substances, yet the study suggests that chemicals formed or released during use may deserve closer attention.

The researchers also detected 6PPD-quinone, a compound created when a rubber additive called 6PPD oxidises as the material ages. The substance is known to harm certain fish species. Its presence in milking-system materials does not establish a comparable risk to humans, and the study did not determine how much, if any, entered the milk from those components.

Three samples from Alpine farms far from busy roads contained none of the four substances tested. That result points to traffic exposure as one possible factor, while also showing why the contamination picture cannot be reduced to a single source.

Tyres and road surfaces shed rubber particles as vehicles travel. Those particles can move through air, runoff water or agricultural inputs before reaching fields and entering food chains. The study cites an estimated 6 million tonnes of rubber particles released worldwide each year through tyre and road-surface abrasion.

Road proximity may help explain differences between farms, but the Alpine samples also strengthen the case for examining farm equipment. If traffic were the only pathway, researchers would expect the most isolated farms to provide a clearer comparison. Instead, the study leaves open several routes, including deposition on feed or pasture, contaminated water and contact with rubber components during milking.

The sample is too small to support conclusions about all Swiss dairy farms. Switzerland’s geography, farming systems and traffic patterns vary sharply from canton to canton. Researchers will need broader sampling to separate regional conditions from equipment-specific effects.

The health implications remain unknown because researchers have not yet established a safe-risk assessment for the chemicals detected in milk. The measured concentrations were generally low, but low detection does not answer questions about repeated exposure, combined effects or how the compounds behave during processing.

The study examined raw milk, which is the material collected directly from farms before industrial treatment. Further work will need to determine whether the chemicals persist through common dairy processes and whether they appear in products such as pasteurised milk, cheese or yoghurt. The current findings do not provide those answers.

6PPD-quinone has attracted scientific attention because of its toxicity to some fish species, particularly when tyre-derived pollution reaches waterways. Toxicity in fish cannot be directly translated into a human health assessment. Researchers must examine dose, exposure route and biological effects in people before drawing conclusions for consumers.

Swiss food safety authorities and dairy organisations now have a defined research agenda. It includes testing equipment materials, comparing new and aged components, and measuring chemicals in milk at different stages of production. The work could also expose gaps in how food-contact materials are evaluated over their working life.

Seasonal testing and pathway studies are planned to determine when and how rubber-related chemicals enter Swiss milk. Researchers will investigate whether concentrations change with weather, traffic, pasture use, equipment age or farm management practices.

That next phase matters for both consumers and farmers. If equipment proves to be a major source, manufacturers may need to develop more stable rubber compounds, while farms could receive clearer replacement and maintenance guidance. If environmental deposition plays a larger role, monitoring may need to extend beyond the milking parlour to feed, soil, water and roadside land.

The study also raises a regulatory issue. Materials can comply with food-contact rules when they are manufactured and tested under defined conditions, yet their chemical profile may change as rubber ages and oxidises. Regulators will need evidence on real-world use before deciding whether standards or testing methods require revision.

For now, the evidence supports continued surveillance rather than a broad warning about Swiss milk. The researchers found chemicals in 7 of 17 samples, at generally low concentrations, and did not establish harm to consumers. The planned studies will determine whether the result is an isolated signal or part of a wider issue in dairy production.