Are certain chemicals from car tires responsible for occasional acute deaths of salmon in Norwegian rivers?

After an episode of acute salmon deaths in the river Homla in autumn 2018, it had been speculated whether a rotenone treatment further up the watercourse could be the cause of the observations. This hypothesis has however been investigated thoroughly and was excluded as a probable cause. So far, it has not been possible to determine what led to the fish death. We later discovered an American report, which describes an organic compound in car tires that is linked to acute fish death [1].

A highway crosses Homla river, and there is additional runoff from the Stavsjøfjell tunnel to Homla. Runoff from the tunnel after washing has been launched as a possible factor that may have contributed to the fish deaths. The American study linked acute fish death to a specific chemical found in car tires (Figure 1), which when exposed to ozone becomes a substance that may be highly toxic for fish. The compound «6PPD», which is added to car tires in up to 2% acts as an antioxidant and is oxidised to «6PPD quinone», or «6PPDQ» (Figure 1). Although ozone concentrations are assumed to be small in tunnels, there are many other substances in car exhaust with oxidative properties, such as nitrogen oxides, which may oxidize 6PPD. A very low LC50 for 6PPDQ has been established in coho salmon (Oncorhynchus kisutch), which is reported at 0.8 µg /L.

Funded by a grant from the Norwegian Environment Agency, and in collaboration with the Norwegian Institute for Nature Research, we established an LC-MS/MS based isotope-dilution assay for the quantification of 6PPDQ in water samples and analyzed a set of water samples (e.g. tunnel runoff). We were surprised to see that the compound could be widespread, and detected a maximum concentration of ca. 32% of the reported LD50. These preliminary findings emphasize the need for a more comprehensive survey of the contamination of the Norwegian environment with 6PPDQ as well as toxicological investigations into the acute and chronic effects in salmon.

Reference

[1] Tian, Z., Zhao, H., Peter, K. T., Gonzalez, M., Wetzel, J., Wu, C., Hu, X., Prat, J., Mudrock, E., Hettinger, R., Cortina, A. E., Biswas, R. G., Kock, F. V. C., Soong, R., Jenne, A., Du, B., Hou, F., He, H., Lundeen, R., Gilbreath, A., Sutton, R., Scholz, N. L., Davis, J. W., Dodd, M. C., Simpson, A., McIntyre, J. K., Kolodziej, E. P. A ubiquitous tire rubber-derived chemical induces acute mortality in coho salmon, Science 2021, 371, 185–189.