Spring 2024

Potential Health Effects of Plastic Additives

By Andrew Yeh, Ph.D., DABT

Plastic is a complex chemical mixture.  The main constituent of plastic is its polymer backbone, but a broad range of chemicals, referred to as plastic additives, can be added to plastic that impart essential functional properties over its lifecycle (e.g., flexibility, flame resistance).  The number of additives in plastic varies substantially, ranging from 0.05 to 70% of the plastic’s weight depending on the polymer and function of the additive (UNEP, 2023; Wagner et al., 2024) (see UNEP Figures).  Without plastic additives, plastic products would not exist as we know them today; however, some chemicals used as plastic additives may be associated with adverse health effects at sufficient exposure levels.  This article discusses what is known about potential migration of plastic additives from plastics, as well as the potential health effects of plastic additives and their implications for human health risk assessment.

Since the earliest reports of plastic in the environment, researchers have sought to evaluate the extent that plastic materials may be vectors of exposure for chemicals.”

Since the earliest reports of plastic in the environment, researchers have sought to evaluate the extent that plastic materials may be vectors of exposure for chemicals.  Migration of additives from plastic, via food packaging, medical products and devices, toys, and other products, can be relevant for human exposures.  Many additives are not bound strongly to the polymer matrix and, therefore, can migrate to the environment (e.g., some phthalates).  In contrast, other additives are bound strongly to the polymer and exhibit limited migration under ambient conditions, such as the flame retardant tetrabromobisphenol A and, in general, heavy metals and other metal compounds (UNEP, 2023).

Extent of migration varies based on physicochemical properties of the polymer and additive and conditions of the external environment.  For example, migration from plastic is slowest when the polymers are in a rigid state.  Hence, at ambient temperatures, migration may be faster from polyethylene and polypropylene, which are less rigid, relative to more rigid polymers, such as polyethylene terephthalate, polyvinyl chloride, and polystyrene (UNEP, 2023).  Factors associated with a lower tendency to migrate from plastic include higher molecular weight (greater than 600 grams/mol) and hydrophobicity (i.e., water repellence) (WHO, 2019).  In contrast, migration can be increased by weathering, acidic or basic pH, high temperatures, high turbulence, and/or long exposures to water (UNEP, 2023).

Finally, in any discussion of plastic exposures, it is important to address nano- and microplastics (NMPs), i.e., plastic particles smaller than 1 micrometer (μm) and 5 millimeter (mm), respectively.  Numerous studies report occurrence of NMPs in various environmental media and human tissues (e.g., atherosclerotic plaque, breast milk, placenta), but whether NMPs are causing any adverse health effects is an area of active research.  To date, available information suggests the contribution of NMPs to exposure to plastic additives is minor compared to other exposure pathways for such chemicals (WHO, 2019).

Regarding toxicological hazards, UNEP (2023) identified nine groups of “chemicals of concern in plastics” based on association with toxicity hazards and potential for migration (see Table).

“Chemicals of Concern in Plastics” Identified by UNEP (2023)

Potential adverse health effects are well researched for some chemicals in these diverse groups of additives.  For example, some heavy metals and polycyclic aromatic hydrocarbons (PAHs) can cause cancer or non-cancer effects in various organ systems in humans.  In addition, potential effects on the liver and immune system, thyroid disease, and reproductive cancers have been investigated for certain per- and polyfluoroalkyl substances (PFAS), such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS); however, there is inadequate evidence to establish any causal associations in humans and, generally, insufficient toxicity data for other PFAS.  Endocrine disruption is a common concern for several of the identified groups, including some polybrominated diphenyl ether and organophosphorus flame retardants, and phthalate (e.g., di-2-ethylhexyl phthalate [DEHP]) and bisphenol (e.g., bisphenol A [BPA]) plasticizers.  To date, no causal association with endocrine disruption in humans has been established for any of these chemicals.

Of the 16,000 plastic-associated chemicals identified by the Norwegian Research Council in March 2024, 10,000 were lacking hazard information.”

Collectively, some chemicals used as plastic additives may be associated with adverse health effects at sufficiently high exposure levels.  However, the mere presence of these chemicals in plastics does not, by itself, imply risks of adverse health effects.  For example, although some metal compounds can cause toxicity hazards, they may present limited health risks as plastic additives because, as mentioned previously, metals tend to be bound strongly to polymers and exhibit limited migration under ambient conditions.  Overall, the diversity of chemicals and functions, as well as data gaps in understanding exposure and toxicity, underlie the complexity of human health risk assessment of plastic additives.  In fact, of the 16,000 plastic-associated chemicals identified by the Norwegian Research Council in March 2024, 10,000 were lacking hazard information (Wagner et al., 2024).  Overcoming these challenges will be a significant effort, presumably requiring cooperation between academia, industry, and regulators.