IIn the 1980s, there were isolated reports of something fishy going on: Koho salmon near towns in the Pacific Northwest died more often than salmon farther from town. Since then, scientists have suspected that urban runoff was to blame, and a study was published in science last week (December 3rd) supported their hypothesis. Urban watersheds contain a chemical called 6PPD quinone, which is a derivative of tire rubber and is toxic to Koho salmon.
The scientist spoke to Washington University chemical engineer Edward Kolodziej, a co-author of the study, about the results.
WASHINGTON UNIVERSITY TACOMA
Anecdotes report that urban rainwater has been around since the 1980s, killing Koho salmon. From the 1990s onwards, much more extensive documentation of these annual mortality phenomena began in the Seattle area. There was a research team led by Jay Davis, Nat Scholz, and Jen McIntyre, who are all co-authors [of the latest study]Considering the toxicology of this phenomenon and its frequency in the field for about 20 years. I joined them in 2014 and did some sophisticated water quality studies to better understand the chemical makeup of the waters that killed the Koho salmon.
EK: Salmon are born in fresh water, and then Koho salmon live in fresh water for about a year. Then they go to the sea and come back two or three years later. They don’t come back until autumn in a relatively short time – the adults return to breed. After they reproduce, they die, so people are used to seeing dead salmon in the stream because the assumption was, “They laid their eggs, they died, that’s completely natural.” 1990s found out they actually came back to breed and when it rained they died. You could cut them open, they were full of eggs so they hadn’t reproduced, and this is where these observations really began. Much work was done to understand where it happened, how much and if water was related.
EK: We combined water quality analyzes and toxicological observations. In this way, we found road-derived chemicals in the water that were in very good agreement with some landscape models and GIS-based statistical analyzes. These are actually present during periods when the salmon died.
Toxicological observations, meanwhile, indicated that among all these different possible sources of chemicals, tire rubber was the only one that killed Koho salmon. If we just soaked pieces of tire rubber in water, it was very fatal to the Coho salmon. It’s a very complex mix – our instrument sees more than 2,000 chemicals there. We just had to start separating it and isolating it into chemically simpler fractions. We were just starting to follow toxicity as we kept breaking up and breaking up and breaking up. Finally, we identified a chemical in the tire leachate that was highly toxic to the Koho salmon. We could then replicate the phenomena with just a standard exposure.
EK: All tires require a variety of preservatives to make them durable, longer lasting, and stronger. It has been known at least since the 1930s that ground level ozone – this low concentration of ozone in the air – really degrades tire rubbers. There have always been compounds in tires that are supposed to absorb the ozone before it can react with the tire rubber. This antioxidant chemical, 6PPD, was identified in the early to mid-1950s. I’m not entirely sure when it spread into tire manufacturing, but it’s one of the most common, if not most common, antioxidants added to tires to soak up ozone. Essentially, the reaction product – what is present after the ozone reaction – is what we saw in the tire leachate and what has been found to be very toxic to the Koho salmon.
Toxicological observations, meanwhile, indicated that among all these different possible sources of chemicals, tire rubber was the only one that killed Koho salmon.
EK: I can’t answer that properly. It is a huge question that people devote their entire lives to. All aquatic organisms fighting often face multiple stressors, multiple threats, and multiple difficulties. For systems where road drains come in contact with habitats important to Koho salmon, this seems pretty important near Seattle. Some of the population models predict localized extinction of Koho from these exact streams within 20 or 30 years because of this constant mortality in the returning fish. They just can’t feed their population and every year they get smaller and smaller.
EK: We know that in the same basins where koho salmon dies, chum salmon and cutthroat trout coexist and they don’t seem to die from the same storms that kill the koho. This field data shows that we can foresee differences in species sensitivity. Aside from Coho salmon, we just don’t know how sensitive other species are. Hence, this is a job that requires follow-up examination.
EK: Pretty soon we will look at these ingesting waters and understand the dynamics of this connection – how does it persist, what breaks it down, how much of it [there is]what its fate is in the environment – so we have a lot to do to understand the basic water quality elements of this compound once we know about it.
At the same time, I am sure there will be a number of related toxicological studies that understand the biology of these exposures. We are working to generate data in the hope that we can improve and solve problems and I definitely hope we can have a conversation about chemical ingredients used in consumer products like tires that are compatible with this type of Work related. I would assume that people will ponder whether or not this chemical is the best choice for the desired properties in consumer products like tires.
The disposal of used tires is a major problem when transporting materials. We can reuse and recycle sustainable products. Tires are reused on playing fields, mixed into asphalt, and used in building materials. To make sustainable products better possible, we also need to consider their end use and reuse. Chemical safety is very important to the decisions we make regarding reuse. In order to enable the sustainability of the products, it must be ensured that everything in these products is environmentally friendly and environmentally friendly for the people. That’s one aspect of that realization that I need to ponder.
EK: It’s a very motivating problem to work on. It’s devastating to me, my whole group, and all of the people who work every year on how adult salmon die when they return to spawn. I mean, these are really nice fish. If you went to the store you could buy these fish. It is very motivating for all of us to try to understand what harms these fish because they really are the 1 percent of salmon that actually make it back to survival and then they just cannot survive our waters. My entire group is very motivated and excited about the prospect of improving our management of these important species.
E.P. Kolodziej et al., “A ubiquitous Tire Rubber Chemical Induces Acute Mortality in Koho Salmon.” science, doi: 10.1126 / science.abd6951, 2020.
Editor’s note: The interview has been edited for brevity.