We can't find the internet
Attempting to reconnect
Something went wrong!
Hang in there while we get back on track
Electrochemical-oxidative dualism: Decoupling the acute effects of lake water-aged tire wear particles on periphytic biofilm-mediated denitrification
Summary
This study examined how freshly generated and lake water-aged tire wear particles (TWPs) of different types affect denitrification in periphytic biofilms. Neither fresh nor aged TWPs altered nitrate removal or denitrification gene abundance, despite aging increasing the electron exchange capacity and free radical content of particles.
As emerging microplastic pollutants, tire wear particles (TWPs) have unclear photochemical impacts on aquatic nitrogen cycles. This study investigated how three types of TWPs-mechanically generated via rolling (R-TWPs), sliding (S-TWPs), and low-temperature crushing (C-TWPs)-and their aged counterparts (AC-, AR-, AS-TWPs) influenced nitrate reduction in periphytic biofilms. Aging in lake water altered the surface properties of TWPs: AC- and AR-TWPs accumulated inorganic ions and organic coatings, while AS-TWPs facilitated microbial colonization. Aged TWPs exhibited enhanced electron exchange capacity (EEC) and elevated levels of environmentally persistent free radicals (EPFRs). However, neither fresh nor aged TWPs altered nitrate removal, denitrification gene abundance (nirK, nirS), or microbial community structure in a dose-dependent manner; their impacts showed no simple correlation with EEC or EPFRs. Under illumination, TWPs acted as electron shuttles, transferring photogenerated electrons. Quenching hydroxyl radicals (·OH) revealed a strong positive correlation between EEC (specifically, electron donating and accepting capacities) and nitrate removal rates (r = 0.928-0.957, p < 0.01). Variance partitioning analysis identified EPFRs as promoters (contribution: 0.16) and ·OH as inhibitors (contribution: -0.18) of denitrification. At concentrations of 1.0-50.0 mg L over 7 days, TWPs exerted paradoxical effects on urban river nitrogen cycling. This paradox arose from synergistic interactions between surface-active components (e.g., carbon black, zinc oxide) and photosensitive moieties (e.g., EPFRs, redox functional groups). This work highlights the dual role of photoactive TWPs in modulating aquatic nitrogen cycles and underscores the necessity of evaluating their photochemical reactivity and oxidative stress effects when assessing microplastic pollution in urban water systems.