Tyre Anti-degradants
Tyre anti-degradants are additives in the rubber manufacturing process, enhancing materials but posing environmental risk when leached. 6PPD-Quinone, linked to Coho Salmon mortality, draws attention alongside other chemicals, raising broader environmental concerns.
Tyre anti-degradants are crucial in rubber manufacturing for vehicle tyres, bolster material endurance. However, tyre usage releases particles that enter our stormwaters, causing two distinct environmental concerns: firstly, the particles themselves, categorised as microplastics. Secondly, the abundance of tyre anti-degradants. These compounds leach into the environment, with some having been identified as toxic to aquatic ecosystems. Moreover, the use of recycled tyres on sports fields and children's playgrounds introduces enhances the leaching on these chemicals into the surrounding environments.
Presently, these compounds below have garnered attention as contaminants of emerging concern. Nevertheless, ongoing research is underway to examine additional compounds.
N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine quinone (6PPD-Q)
6PPD-Q is the ozonation product of 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine). 6PPD is used as an antiozonant engaging in more rapid reactions with ozone compared to ozone's interaction with the rubber. Despite 6PPD being used in tyres since the mid-1960s, this transformation to quinones was first identified in 2020. It had been discovered in freshwater streams that 6PPD-Q is toxic to Coho Salmon (LC50 = 95 ng/L), killing them before they spawn. Further studies also identified the toxic impact on species like brook trout (LC50 = 0.59 μg/L) and rainbow trout (LC50 = 1.0 μg/L).
Figure 1: 6PPD ozone-oxidation to 6PPD-Q
Hexamethoxymethyl melamine (HMMM)
HMMM is used as a crosslinking agent in the production of coatings and tyres. It improves the adhesion between the rubber and the steel reinforcing cords. HMMM has shown an acute toxic effect on daphnia. It is also linked to toxicity and mortality events of aquatic organisms. However, there are currently no published concentrations for aquatic animals yet.
Figure 2: HMMM
1,3-Diphenylguanidine (DPG)
DPG is used as primary and secondary accelerator in the vulcanization of rubber but also improves the physical and mechanical properties of the vulcanizate. DPG has been found in urban runoffs and has been classified by ECHA as a substance toxic to aquatic life with long lasting effects.
Figure 3: DPG
Our Capabilities
Eurofins Environment Testing is at the forefront of analysing new Emerging Contaminants. Thus, we have developed an analysis method for identifying 6PPD-Q, HMMM and DPG using isotope dilution LC-MS/MS. This approach enables us to analyse various sample types, including drinking water and stormwater, sand, sediment, rubber materials, and leachates. These analyses are very important to understand the extent of the problem, especially here in Australia and Aotearoa New Zealand, where little data is available on their impact on native fish species.
