Chemicals and plastic; exploring the toxic tag-a-longs to nurdles

Despite huge public concern, plastic production is still on the rise, with approximately 350 million tonnes of plastic produced globally1 in 2018. The reason plastic is still so popular is because it is light weight, flexible, colourful and long-lasting. These features are given to plastic by the chemicals in it which are added to plastic when it is being made into pellets – also called nurdles.

Nurdles are the raw material of the plastics industry and are lost to the environment even before they have been melted to make a plastic product. Approximately 230,000 tonnes of nurdles enter our marine environment every year from across the world. That’s billions of microplastic particles. Even if we prevented any end of life plastics from entering our oceans, we would continue to see plastic pollution in the form of these tiny pellets. Nurdles are packed with chemicals that make plastic useful but also make it a long-lasting pollutant that packs a toxic punch. The story doesn’t end there, nurdles in our seas can also attract other chemical pollutants from the surrounding water and play a role in concentrating and transporting harmful chemicals within the environment and if ingested, into the bodies of sea creatures who can mistake nurdles for food. This toxic transfer is the overlooked plastic pollution problem.

What is plastic and what are all these chemicals?

Let’s go back to basics; plastic is not one chemical. The word plastic actually describes a group of materials made from a mixture of chemicals. Plastic contains both additives (intentionally) and contaminants (non-intentionally) added during the production process as well contaminants that come from the raw material, oil, used to make plastic. Once in the environment, plastic can also adsorb contaminants from its surroundings, which further add to the chemical cocktail.

To produce plastic with the desired properties, such as flexibility, colour or flame retardancy, producers use additives such as dyes and plastizers. For example, by weight, up to 75% of PVC can be made up of plasticisers that soften the material. Studies of plastic packaging alone found there could be thousands of additives used and between 4 to 6 non-intentionally added substances for every additive.

These plastic additives and related chemicals contained within these plastic resins are sometimes harmful to wildlife, humans and the environment. Those of environmental concern include) phthalatesBisphenol A (BPA), flame retardants and organotins. Other chemicals might end up in the plastic unintentionally during production such as per- or poly-fluorinated alkyl substances (PFAS). These chemicals are all present in nurdles and are often more reactive and mobile than the plastic polymer itself, with a tendency to leach out of the plastic once in the environment2.

The chemical cocktail

Like plastic pollution most chemical pollution in our seas comes from land-based sources3. Once in the marine environment persistent ocean pollutants, such as PCBs, PAHs and DDT, have been shown to accumulate in marine species and enter the food chain.

Persistent organic pollutants (POPs) are the name given to some of the most toxic chemicals in use today, they have harmful effects on human health and the environment such as endocrine disruption, mutagenicity and carcinogenicity4. These chemicals are persistent, not easily degraded and accumulate in the food chain, so can build up in animal and human tissue causing long term damage. Some of the most harmful POPs, such as polychlorinated biphenyls (PCBs) and DDT, are now banned due to the risks they pose to the environment or human health. Although this ban was almost 30 years ago and current manufacture has been reduced, these chemicals continue to persist in the marine environment with concentrations of PCBs in fish from Antarctica still rising3.

Plastics have been identified as potential carriers of toxic chemicals, like POPs, in the marine environment.  These pollutants are attracted to oily substances such as plastic. This means they are likely to adsorb (attach) onto the surface of plastic once in the environment with potential to transfer them into food chains if ingested.

Toxic tag-a-longs – how do nurdles play a role?

Nurdles and other microplastics are particularly efficient at adsorbing these chemicals because of their large surface area. POPs have been found on nurdles at much higher concentrations than background levels.

On the coast of Japan, Polychlorinated bisphenols (PCBs) and DDE were found to accumulate in plastic pellets in concentrations up to a million times higher than surrounding seawater5. If ingested these pellets could serve as a potential source of toxic chemicals to marine wildlife such as seabirds. A study in 2009, showed how the PCBs from ingested plastics could transfer into the tissue of seabird chicks6.

In the North Pacific Gyre, a part of the ocean seen as a ‘hotspot’ for microplastic pollution, another study showed that PCB levels in Northern Pacific lantern fish within North Pacific Gyre were higher than elsewhere. This indicated that the source of this contaminant may be coming from non-prey (e.g., microplastic) sources, including nurdles7.

The adsorption of chemicals doesn’t stop at PCBs. In fact a whole range of harmful contaminants, including Polyaromatic hydrocarbons (PAHs), DDT, Heavy Metals, and PFAS, have all been shown to have concentrated, to much higher levels than background sediments or seawater, onto the surface of pellets and plastic fragments across the world; from Greece8 to Guadalupe Island in Mexico4.

Harmful additives attracting attention

But that’s not all. Before pellets have even reached the environment or begun to accumulate background chemical contaminants, the specific additives present in virgin plastic pellets may actually cause just as much harm. Not only are they adding to the plastic soup, but these additives are a source of chemical pollution too.

In a Brazilian study, new virgin polyethylene (PET) pellets were shown to be consistently more toxic to sea urchins than older beached pellets9. Another study showed that hard (Scleractinia) coral species ingested tiny fragments of pre-production plastic, of different types and weathered states, found in oceans10; retaining small micrometre sized particles in their bodies for long period impacting them negatively. The authors suggested that the chemicals leaching from plastics might stimulate feeding, encouraging corals to ingest even more.

In Japan, Nonylphenols (NPs) –  hormone disrupting chemicals used as a stabilizer and antioxidant in plastics – were measured in plastic pellets by 2 orders of magnitude higher than that in sediment levels, suggesting NPs were  added to the plastic during production5. The transfer of NPs (and other chemical contaminants) to invertebrates has been demonstrated from various types of plastic 8; a clear indication that once pellets have fragmented into smaller pieces they will add to the potential for chemical transfer.

A case of chemicals caught in the system

Black nurdles found on beaches across the south west of England were shown to contain high levels of Bromine, Lead and Antimony.   These elements are associated with chemical flame retardants that are persistent and harmful in the environment, and the nurdles were probably made of poorly sorted, recycled black plastic electronic waste.

Some birds, such as the Australian short-tailed shearwater, appear to particularly mistake black nurdles for food12, which could be a problem as they are often recycled and are more likely to contain unintended chemical contaminants.

The natural nasties

It’s not just industrial chemicals which like to attach themselves to plastic. The hard surface of plastic provides an environment on which biofilms can form – rich microbial communities that can harbour pathogens such as Escherichia coli (E.coli) and Vibrio spp, but may also make plastic more easily mistaken for food13.

These are present on nurdles studied in the Firth of Forth, Scotland; a clear example of how our bathrooms are linked to the beach.

An overlooked concern

Clearly plastic is a threat to marine wildlife at all sizes, from entanglement to ingestion, but the chemicals plastics harbour pose a further risk that is less obviously visible.

There are questions remaining as to the ecological importance of this toxic transfer from plastics and marine wildlife can also be exposed to hazardous chemicals by other pathways , including prey and natural materials8.

Regardless, chemical pollution is an increasing concern to many in the scientific community. The increasing amount of both plastic and chemicals in the ocean mean that the issue isn’t going away and prevention of both plastic and chemical pollution is paramount.

Check out to find out what we are doing to help tackle both chemical and plastic pollution.





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