Effects of pristine and photoaged tire wear particles and their leachable additives on key nitrogen removal processes and nitrous oxide accumulation in estuarine sediments

Global estuaries and coastal regions, acting as critical interfaces for mitigating nitrogen flux to marine, concurrently contend with contamination from tire wear particles (TWPs). However, the effects of pristine and photoaged TWP (P-TWP and A-TWP) and their leachates (P-TWPL and A-TWPL) on key nitrogen removal processes in estuarine sediments remain unclear. This study explored the responses of denitrification rate, anammox rate, and nitrous oxide (N2O) accumulation to P-TWP, A-TWP, P-TWPL, and A-TWPL exposures in estuarine sediments, and assessed the potential biotoxic substances in TWPL. Results indicate that P-TWP inhibited the denitrification rate and increased N2O accumulation without significantly impacting the anammox rate. A-TWP intensified the denitrification rate inhibition by further reducing narG gene abundance and NAR activity, and also decreased the hzo gene abundance, HZO activity, and Candidatus Kuenenia abundance, thereby slowing the anammox rate. N2O accumulation was lower after A-TWP exposure than P-TWP, with the NIR/NOS and NOR/NOS activity ratios closely associated with N2O accumulation. Batch experiments indicated that photoaging promoted Zn release from TWPL, significantly contributing to the inhibited denitrification rate and increased N2O accumulation by TWP. In addition, TWP drives changes in microbial community structure through released additives, with the abundance of DNB and AnAOB closely linked to the Zn, Mn, and As concentrations in TWPL. This study offers insights into assessing the environmental risks of TWPs in estuarine ecosystems.