Thousands of unknowns – tackling the chemical complexity in plastics

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Many products we use on a daily basis are made of plastic. Photo: Stefan Schweihofer (stux – pixabay).

The detrimental health impacts of certain plastic chemicals, such as phthalates and bisphenol A (BPA), have received attention both scientifically and politically. However, plastic contains many more, in fact thousands of additional chemicals that are similarly toxic to organisms – including humans. This story outlines ways in which the chemical complexity of plastics can be problematic and introduces current examples trying to address this complexity.

Written by Molly Mcpartland, Norwegian University of Science and Technology (NTNU),

Plastic is a chemically complex material

Beyond what is known as plastic additives – such as antioxidants, plasticizers, and flame retardants – thousands of chemicals called ‘processing aids’ are also used during the manufacturing and production of plastic.

In addition to intentionally added chemicals that give plastic its unique durability, flexibility, and utility, many non-intentionally added substances (NIAS) are also present (Wiesinger, Wang, and Hellweg 2021).

This chemical complexity is problematic for several reasons:

  • First, it is estimated that approximately 90 percent of all chemicals added to plastic are unknown (Zimmermann et al. 2021) (Wiesinger, Wang, and Hellweg 2021). The European Chemicals Agency (ECHA) has implemented a legislation for evaluating chemicals, such as the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation. However, REACH regulations are limited to known substances and therefore the hazard of unknown chemicals cannot be evaluated, classified, or subsequently restricted.
  • A second problem is that plastic chemicals can leach out of the plastic product and into the surrounding medium, whether that be our oceans, soil, food, or beverages. Research has demonstrated that up to 88 percent of the chemicals in a product may leach out of plastic (Zimmermann et al. 2021). This serves as a relevant source of human exposure to plastic chemicals and has been addressed by European regulations in the past (EU, 2004). Safe leaching thresholds have been established for chemicals of a known hazard. Although such regulations cannot keep up with the thousands of chemicals, both known and unknown, being used in plastic manufacturing and production.
  • Finally, defining the health hazards caused by plastic chemicals is a daunting task as we are exposed to many chemicals, often simultaneously. Chemical testing is commonly carried out on single chemicals at a time, which ignores the likelihood that chemicals are interacting within our bodies. Testing all the chemicals in a plastic product at once is a solution that has been presented by scientists (Groh and Muncke 2017) and may provide a clearer picture of the health impacts caused by this chemical complexity.

How does plastic impact human health?

Exposure to plastic chemicals is linked to numerous negative health impacts, including the development of cancer and obesity, decreased reproduction, and neurotoxicity. Currently for REACH to consider a chemical of very high concern, it must be carcinogenic, mutagenic, or reproductively toxic. This criterion is useful, though leaves out endocrine disrupting chemicals (EDCs).

Plastic chemicals often have similar shapes and sizes to the chemicals naturally produced by our bodies. Therefore, they can act as EDCs – meaning they alter the normal hormone processes within our bodies, including hormone production, metabolism, fertility, and development – just to name a few.

This can be especially dangerous during pregnancy and for young children whose bodies are still growing and developing. This early life exposure is also linked to disease in adult life, such as cardiovascular disease and dementia (Gillman 2005).

BPA, for example, has been detected in over 90 percent of US, European, and Asian populations (Vandenberg et al. 2010, NHANES, 2015) and the associated health costs are estimated at 340 billion US dollars and 160 billion euros, annually (Attina et al. 2016).

Addressing chemical complexity

Numerous strategies to address chemical complexity are underway.

The Regulation on classification, labelling and packaging of chemicals (CLP) has implemented the Chemicals Strategy for Sustainability (CSS) which is dedicated to removing endocrine disrupting and other hazardous chemicals from everyday products (Zimmermann et al. 2022). With this goal, the CLP has defined four new hazard classes of chemicals. These classes have been developed via a fast-track procedure and have been introduced as of April 20th, 2023. There is now a defined hazard class for endocrine disrupting chemicals.

Another approach is being carried out in Norway via the PlastChem project. Here, the Norwegian University of Science and Technology has coordinated with several partners from across Europe to group plastic chemicals based on structure and hazard with the goal of eliminating entire groups of chemicals, including those with an unknown identity. This approach removes the time-consuming – and often impossible – task of testing every single chemical and instead assumes that chemicals with similar characteristics will be similarly toxic.

Perhaps some of the most important steps being taken is the overall reduction of plastic production, usage and disposal. The global plastics treaty is an international, legally binding agreement that aims to address the production, usage, and disposal of plastic. Negotiations on what the treaty would include are currently underway, and the scientific community has strongly recommended that the treaty must address the chemical complexity in plastic. The Minderloo-Monaco Commission on plastics and human health specifically recommends health-protective standards for chemicals associated with plastics and a mandatory disclosure of the full chemical composition in all plastic products.

Backed by scientific research, we can inform developing policies that promote the safe and sustainable usage of plastic.

Edited by: Sara Plassnig and Caroline Enge



Attina, Teresa M. et al. 2016. “Exposure to Endocrine-Disrupting Chemicals in the USA: A Population-Based Disease Burden and Cost Analysis.” The Lancet Diabetes & Endocrinology 4(12): 996–1003.

Gillman, Matthew W. 2005. “Developmental Origins of Health and Disease.” New England Journal of Medicine 353(17): 1848–50.

Groh, Ksenia J., and Jane Muncke. 2017. “In Vitro Toxicity Testing of Food Contact Materials: State-of-the-Art and Future Challenges.” Comprehensive Reviews in Food Science and Food Safety 16(5): 1123–50. (August 21, 2020).

NHANES IIII (2015) Fourth national report on human exposure to environmental chemicals. Department of Health and Human Services Centers for Disease Control and Prevention, Atlanta

Vandenberg, Laura N. et al. 2010. “Urinary, Circulating, and Tissue Biomonitoring Studies Indicate Widespread Exposure to Bisphenol A.” Environmental Health Perspectives 118(8): 1055–70.

Wiesinger, Helene, Zhanyun Wang, and Stefanie Hellweg. 2021. “Deep Dive into Plastic Monomers, Additives, and Processing Aids.” Environmental Science and Technology 55(13): 9339–51.

Zimmermann, Lisa et al. 2021. “Plastic Products Leach Chemicals That Induce In Vitro Toxicity under Realistic Use Conditions.”

Zimmermann, Lisa et al. 2022. “Implementing the EU Chemicals Strategy for Sustainability: The Case of Food Contact Chemicals of Concern.” Journal of Hazardous Materials 437(May): 129167.