Salmon under Threat – Detecting a New Contaminant of Concern
Developing the first test for 6PPD-quinone
Each spring and autumn, millions of salmon migrate along the American West Coast from the Pacific Ocean, returning to their native rivers and streams to spawn. Unfortunately, a significant number of these salmon mysteriously die before they reach their destination, threatening the future of the wild salmon population. Scientists believe that 6PPD-quinone, a toxic compound that is polluting waterways, is to blame. Eurofins Environment North America was the first in the world to develop a commercial testing method for 6PPD-quinone in aqueous and solid matrices.
This problem of wild salmon dying suddenly while migrating has worsened over time and the underlying cause has puzzled experts for decades. However, a late-2020 publication by the University of Washington and other organisations in Science made a major breakthrough in understanding the threats faced by wild coho salmon (Oncorhynchus kisutch).
The study has identified a compound that is toxic to the salmon, even at low concentrations, called 6PPD-quinone. This compound begins as 6PPD, a member of a group of compounds known as anti-degradants, which are used as additives to protect tyres and other rubber products from damage from ozone. In doing so, 6PPD is oxidised and transformed into 6PPD-quinone. As the tyres then wear, the worn rubber is continuously deposited on roadways and makes its way into waterways through run-off from rain.
Several follow-up studies have confirmed toxic effects of 6PPD-quinone to aquatic life, but not all species are affected equally, with some creatures exhibiting a 6PPD-quinone tolerance over 100x greater than that of coho salmon. However, acute toxicity has also been observed in rainbow trout (Oncorhynchus mykiss); while coho salmon are isolated to the Pacific Northwest, rainbow trout are found in over 50 countries worldwide. This discovery makes it clear that 6PPD-quinone is a global issue. As trout is closely related to char, another widespread and economically important genus of fish, there is a need for additional toxicological and transport studies on every continent.
Eurofins Environment North America’s world-first commercial method tests for 6PPD-quinone in aqueous and solid matrices, including both sediments and consumer/construction products. Recently, the company pushed the aqueous detection limit from 10ppt (parts per trillion or ng/L) to 2ppt in aqueous samples. This is achieved from only 250mL of aqueous matrices.
The science behind
The technique used exhaustively extracts the contaminant and utilises solid phase extraction (SPE) to concentrate the compound and remove bulk interferences. Analysis is carried out on an LC-MS/MS (Liquid Chromatography-Tandem Mass Spectrometer), utilising isotope dilution quantitation. This approach employs a stable isotope of 6PPD-quinone, which is added to samples prior to extraction. Isotope dilution is considered the gold-standard approach for trace-level environmental analysis because it can loss-correct sample concentrations and mitigate both enhancement and suppression caused by the matrix.
