Near-road particulate matter from Washington D.C. has variable levels of 6PPD and 6PPD-quinone: acute and...

Tire wear is a significant contributor to near-road ambient air pollution, particularly in urban areas. Recently, attention has been directed to the tire tread chemical N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), an anti-ozone agent, and its chemical byproduct 6PPD-quinone (6PPDQ), which has been linked to toxicity responses in several fish species from roadside runoff. Although near-road particulate matter (PM) has been linked to toxicity, the contribution from 6PPDQ remains uncertain due in part to the limited evidence for its presence in airborne PM and to the hundreds of other chemical constituents known to be present in such complex mixtures. We hypothesized that (1) near-road PM would contain appreciable levels of 6PPD and 6PPDQ and (2) near-road samples that vary in the levels of these compounds would cause differential concentration-dependent toxicity responses in zebrafish (Danio rerio), a model organism widely used to assess acute and developmental toxicity. To address this, ambient PM samples collected near a highway in the Anacostia neighborhood of Washington, D.C., USA, in the Summer of 2023 were pooled into two groups (near-road samples 1 (NR1) and 2 (NR2)), methanol-extracted, and assessed for acute and developmental toxicity (0.3 to 30 µg/mL). The samples were analyzed for 6PPD, 6PPDQ, ions, inorganic elements, and elemental and organic carbon ratios. Chemical determinations revealed the presence of 6PPDQ in both samples, although levels were 41% higher in NR1 and only NR1 had detectable levels of 6PPD. NR1 also had higher concentrations of the elements Cu and Fe, while NR2 had greater levels of organic carbon, sulfates, and nitrates. Wind trajectory and elemental analysis indicated that NR1 was enriched by non-exhaust emissions from traffic. The NR1 sample elicited greater irritant locomotor responses after acute exposure and higher prevalence of uninflated swim bladders after developmental exposure relative to NR2. NR1 and NR2 elicited similar increases in other morphological abnormalities, although responsiveness to changes in light after developmental exposure was diminished to a greater extent with NR2 compared to NR1. In summary, 6PPDQ was consistently present in PM from a near-highway ambient airshed, although 6PPD was more variable. However, variable chemical composition among these PM samples, including the presence of 6PPD and 6PPDQ, did not result in large differences in potency in zebrafish.