Acute Toxicity of 6PPD‐Quinone to Early Life Stage Juvenile Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) Salmon

Abstract

The breakdown product of the rubber tire antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD)-6-PPD-quinone has been strongly implicated in toxic injury and death in coho salmon (Oncorhynchus kisutch) in urban waterways. Whereas recent studies have reported a wide range of sensitivity to 6PPD-quinone in several fish species, little is known about the risks to Chinook salmon (Oncorhynchus tshawytscha), the primary prey of endangered Southern Resident killer whales (Orcinus orca) and the subject of much concern. Chinook face numerous conservation threats in Canada and the United States, with many populations assessed as either endangered or threatened. We evaluated the acute toxicity of 6PPD-quinone to newly feeding (~3 weeks post swim-up) juvenile Chinook and coho. Juvenile Chinook and coho were exposed for 24 h under static conditions to five concentrations of 6PPD-quinone. Juvenile coho were 3 orders of magnitude more sensitive to 6PPDquinone compared with juvenile Chinook, with 24-h median lethal concentration (LC50) estimates of 41.0 and more than 67 307 ng/L, respectively. The coho LC50 was 2.3-fold lower than what was previously reported for 1+-year-old coho (95 ng/L), highlighting the value of evaluating age-related differences in sensitivity to this toxic tire-related chemical. Both fish species exhibited typical 6PPD-quinone symptomology (gasping, increased ventilation, loss of equilibrium, erratic swimming), with fish that were symptomatic generally exhibiting mortality. The LC50 values derived from our study for coho are below concentrations that have been measured in salmon-bearing waterways, suggesting the potential for population-level consequences in urban waters. The higher relative LC50 values for Chinook compared with coho merits further investigation, including for the potential for population-relevant sublethal effects.

Establishing an In Vitro Model to Assess the Toxicity of 6PPD-Quinone and Other Tire Wear Transformation Products

“…Our results confirm the high sensitivity of juvenile coho salmon to 6PPDQ as well as the substantially greater tolerance to acute toxicity in closely related species. ,, The relative order of sensitivity seen here (coho > Chinook > sockeye) is also consistent with exposure to undiluted urban stormwater runoff . Interestingly, in that study, undiluted stormwater elicited low-level mortality (∼13%) in young of the year Chinook salmon with the common suite of URMS symptoms.…”

“…Interestingly, in that study, undiluted stormwater elicited low-level mortality (∼13%) in young of the year Chinook salmon with the common suite of URMS symptoms. 6PPDQ concentrations from that stormwater source have not been reported to exceed 1 μg/L, well below lethal concentrations reported for both younger swim-up stage Chinook and older juveniles here. Therefore, URMS symptoms and mortality observed in Chinook salmon exposed to runoff was unlikely due solely to 6PPDQ, but rather a result of multiple contaminants in stormwater, which include other PPDs and PPDQs with unknown toxicological profiles.…”

“…Induction of 6PPDQ mortality in aquatic species at concentrations measured in receiving waters (<2.85 μg/L) has only been demonstrated in select teleost fish belonging to the Salmoninae family (coho salmon; rainbow trout, O. mykiss ; brook trout, Salvelinus fontinalis ; white spotted char, S. leucomaenis ). − Confoundingly, many other Salmoninae species are not sensitive, and overall species sensitivity does not appear to have a discernible pattern with established species phylogenies. ,, Within the sensitive species, coho salmon are approximately five times more sensitive (24 h LC 50 95 ng/L) to mortality than any other species that have been evaluated. , The presence of PPDs and quinone transformation products in the water, air, and soils also presents an opportunity for exposure in terrestrial animals including humans. Detection of 6PPD and 6PPDQ in greater than 60% of human urine samples from an urbanized region in China implies pervasive exposure of biota in urban areas .…”

Bioretention Cells Provide a 10-Fold Reduction in 6PPD-Quinone Mass Loadings to Receiving Waters: Evidence from a Field Experiment and Modeling

“…We also calculated the acute risk quotient (RQ) using the LC 50 for adult coho salmon of 95 ng L –1 . We note that an LC 50 of 41 ng L –1 was recently reported by Lo et al for juvenile Coho salmon, using this value would increase all of the reported RQs by 2.3 times. We used the RQ to calculate an average (RQ av ) based on the MEC.…”

“…For coho salmon, the primary toxicant in road runoff was recently discovered to be the compound 6PPD-quinone ( N -(1,3-dimethylbutyl)- N ′-phenyl- p -phenylenediamine-quinone), which is produced as a transformation product when atmospheric ozone reacts with 6PPD, an antiozonant tire additive . 6PPD-quinone has been found at toxicologically relevant levels in many urban streams across North America, − and in road dust in Japan, and further research has shown that a number of other salmonid species are impacted at environmentally relevant concentrations of 6PPD-quinone. − 6PPD-quinone toxicity is an area of evolving research, with results indicating that juvenile salmon are also very sensitive to 6PPD-quinone exposure, that toxicity is not consistent among aquatic organisms, and that the modes of toxicity are not fully understood …”