New Analytical Method for Analysis of 6PPD-Q

ALS are at the forefront of the analysis of emerging contaminants including capabilities to test for 6PPD-quinnone (6PPD-Q) also called 2-anilo-5-[(4- methylpentan-2-yl)amino]cyclohexa-2,5-diene- l,4-dione, or N-(1,3-Dimethylbutyl)-N'-phenyl-p­ phenylene-diamine-quinone.

6PPD-Q can leach from tyre-wear particles and has been found to be extremely toxic to species of fish. In urban stormwater runoff, 6PPD-Q can exceed acute toxicity thresholds for several salmonid species. Analysis of 6PPD-Q is gaining increasing interest in the UK following the publication of ‘Highway Runoff and the Water Environment’ (CIWEM, 2024)

Transformation Byproduct from Tyre Anti-Oxidant:

6PPD is a very reactive compound and is intended to preferentially react with ozone at the road surface to prevent tyre degradation, to extend tyre lifespan, and to improve tyre safety characteristics. When 6PPD reacts with ozone, it converts to 6PPD-Q.

_{Figure 1 Ozonation Transformation of 6PPD to 6PPD-Q}

Ozonation Transformation of 6PPD to 6PPD-Quinone

Due to its relatively high solubility in water, 6PPD-Q dissolves into runoff and finds its way into streams, and rivers during storms and high rainfall events.

Environmental testing for the 6PPD source material is expected to be of much greater difficulty and lesser value in comparison to testing for 6PPD-Q. 6PPD has low water solubility and is highly reactive by design; its aqueous half-life has been reported as being only a few hours under neutral pH conditions, even in sterile water. In comparison, 6PPD-Q has much higher toxicity, mobility and persistence.

Fate and Transport Characteristics  

Stormwater is the primary transport mechanism for 6PPD-q to surface water. Tyre wear products are generated as tyres roll across the road, particularly during acceleration, braking, and turning. These particles, and the chemicals they contain, collect in road dust until stormwater transports them into the aquatic environment. Stormwater is diverted to wastewater treatment works (WWTW) through combined sewer and stormwater systems. Studies investigating 6PPD-q removal in WWTW have had mixed results. Several studies showed a strong reduction or removal of 6PPD-q to non-detect levels Maurer et al, (2023), Seiwert et al, (2020) Zhang (2023), and another study showed an increase in mass in the effluent from WWTW Johannessen (2022). More research is needed to follow up on this. The presence of 6PPD and 6PPD-q in biosolids from WWTP remains a data gap.

LC/MS/MS Analysis of 6PPD-Q

ALS laboratory in Canada now offers routine testing for 6PPD-Q in environmental waters, using an extensively validated in-house method. The test protocol uses Liquid Chromatography with Tandem Mass Spectrometry (LC-MS/MS), utilising Multiple Reaction Monitoring (MRM) of 3 independent mass transitions as shown in Figure 2. In combination with a selective Solid Phase Extraction and clean-up protocol, this robust analytical method offers definitive, confirmed identification and measurement of 6PPD-Q to ultra-trace levels of 0.001 µg/L (lower levels are possible). We ensure the highest possible accuracy and precision is achieved by using Isotope Dilution quantitation, where a deuterium-labelled 6PPD-Q analog is added to all samples prior to concentration and analysis to correct for any sample matrix effects or sample processing losses.

The method may be used to characterise source inputs such as urban runoff or even landfill leachate, but also has more than enough sensitivity to support temporal monitoring of 6PPD-Q concentrations in surface waters, tracking concentrations before, during, and after rainfall events, with detection limits well below thresholds expected to cause acute toxicity to salmon.

_{Figure 2 LC-MS/MS MRM Chromatogram}

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