Crumb rubber made from end of life car tyres is a common waste product in urban societies and a nuisance for the parents of football players, whose children bring particles home in their clothing and shoes. It can also end up in seas and oceans. What happens if marine animals mistake crumb rubber for food?
By: Fanny Hägg and Claudia Halsband // Akvaplan-niva, Dorte Herzke and Vladimir Nikiforov // NILU – Norwegian Institute for Air Research, Andy Booth // SINTEF Ocean, Sophie Bourgeon // UiT The Arctic University of Norway
Crumb rubber is produced from old vehicle tyres and contains a complex mixture of chemical additives and residual production chemicals. The re-use of car tyre rubber as crumb rubber granulate on artificial sports fields entails the loss of millimetre-sized particles to the surrounding environment. Demands for cheap infill materials have increased the use of crumb rubber in artificial surfaces such as playgrounds and football fields. Loss of crumb rubber from football fields happens mainly through removal of snow, at least in Scandinavian countries, but it also escapes in players’ clothing and shoes, as well as wind and water runoff from the pitches.
Removed snow is sometimes dumped into the ocean, potentially a direct pathway for crumb rubber to the marine environment. This makes crumb rubber particles an important source of marine microplastics.
As tyre-derived particles and chemicals are harmful to various aquatic organisms, it is important to evaluate the exposure of marine organisms to crumb rubber and understand the associated risks to animal health.
Crumb rubber highlights truck tracks outside a football field in Tromsø. Crumb rubber escapes from the turf through snow removal and rain/meltwater runoff. Particles can be transported by streams and municipal drainage systems, ultimately reaching the marine environment. Photos: Fanny Hägg / Akvaplan-niva
In this context, the Fram Centre-funded project RubberTox investigated whether lumpfish ingest crumb rubber when exposed to the material through food. We further investigated the consequences of this ingestion. In her MSc thesis at UiT The Arctic University of Norway, Fanny Hägg studied how long ingested crumb rubber particles stay in the gastrointestinal tract of lumpfish, and whether the ingested rubber releases tyre-related organic chemicals into the tissues of exposed fish.
An exposure experiment was conducted in early autumn of 2020 at the Akvaplan-niva R&D station (FISK) outside Tromsø, Norway. A group of 180 lumpfish were distributed across six tanks; 90 fish were exposed to 1-3 mm sized crumb rubber added to the tanks together with food for one week. Another 90 lumpfish that did not receive crumb rubber served as controls. Then, the fish were fed regular food without rubber for another two weeks. Three fish were taken randomly from each tank and sacrificed on ten selected sampling days throughout the three-week experiment. Fish intestines were visually examined for ingested crumb rubber particles, then dissected, and rubber particles were counted. Blood samples were taken for analysis of organic chemicals at NILU’s lab in the Fram Centre by gas chromatography and mass spectrometry (GC-MS).
Fanny was especially interested in a compound called 6PPD (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine), a chemical antioxidant used in tyre manufacturing that transforms in the environment into a derivative known as 6PPD-quinone. The latter has been shown to be lethally toxic to coho salmon (Oncorhynchus kisutch) and hence, addressing concerns about the potential toxicity of 6PPD and 6PPD-quinone to other aquatic organisms was one of the goals in the RubberTox project.
The results showed that most of the exposed lumpfish ingested crumb rubber. A continuous increase in the number of rubber particles found in fish guts indicated that the ingestion was more rapid than the excretion, illustrated by a peak on day 8, the day following the one-week exposure period.
Crumb rubber was found in fish intestines from the first day of the experiment, showing that the lumpfish did not avoid the rubber and thus did not discriminate against non-edible particles. After a two-week cleansing period in clean water on a rubber-free diet, rubber particles were still found in some of the guts. There was, however, a wide variation in the number of particles ingested per fish: some lumpfish had eaten more than 80 rubber particles each, while other individuals had no rubber in their gut.
Although some fish may have accumulated rubber particles over time, others may have evacuated the rubber in their faeces, while yet others may have rejected the rubber as food altogether. What drives such individual differences in behaviour needs further investigation.
The chemical analysis of the blood samples showed uptake of tyre-derived chemicals in exposed lumpfish.
Six chemicals, including 6PPD, were detected in significantly higher concentrations in blood from exposed fish compared to non-exposed controls. The transformation product 6PPD-quinone was not detected. The concentrations of the detected chemicals were elevated in the blood of exposed lumpfish after the exposure on day 7 but decreased during the cleansing period until the experiment ended on day 21. This indicates that these chemicals do not accumulate in blood and are metabolised or transferred to other organs quite quickly. Two of these chemicals were identified as ditolylphenylenediamine, C20H20N2 and tolylphenylphenylenediamine, C19H18N2, which are known constituents of anti-degradant mixtures used in tyre production.
In fact, the same chemicals were found in a positive control of the commercially available mixture Vulcanox-3100. A positive correlation was found between the number of crumb rubber particles recorded in the fish guts and the concentration of rubber-derived chemicals in the blood. These results demonstrate that ingestion of particles is an important pathway in the uptake of chemical additives from anthropogenic sources by aquatic organisms.
Organisms that are opportunistic or non-selective in their feeding behaviour are at increased risk of exposure to chemical additives.
More research is needed to elucidate the toxicity of these substances and possible negative effects on the health and fitness of ingesting animals.