Sediment-porewater dynamics of neurotoxin domoic acid in marginal seas of northern China: Seasonal prevalence and ecological risks in mariculture bays.

Elevated concentrations of the neurotoxin domoic acid (DA) in marine environments pose severe threats to benthic fisheries resources and the health of seafood consumers. However, the spatiotemporal dynamics and potential risk levels of DA in marine benthic environments remain poorly constrained. This study represents the first comprehensive investigation of DA in sediment-porewater system across five mariculture bays and adjacent offshore areas in northern China. The results revealed widespread DA in sediments and porewater, with detection rates above 90% in both inshore bays and offshore regions of northern China. The occurrence of DA was higher in mariculture bays than in offshore areas. Notably, DA concentrations in porewater (14.65-3518.95 ng/L, median 142.13 ng/L) was substantially higher than in the water column (4.75-31.32 ng/L, median 9.40 ng/L). In Sishili Bay during 2023, higher concentrations of DA in the sediment-porewater system were observed in spring (March-April) compared to summer and winter sampling periods, with peak values of 3518.95 ng/L in porewater and 5086.27 ng/kg in sediment. At the sediment-porewater interface of mariculture bays, DA was predominantly partitions to the solid phase (mean φsedi-pw = 59.89%), while in marginal seas, DA favored the dissolved phase (mean φsedi-pw = 31.95%). DA concentrations in the benthic environment exhibited a weak negative correlation with temperature across sampling stations during the study period, suggesting that temperature may influence DA distribution. In this study, ecological risk refers to the potential toxic effects of DA, quantified using the Risk Quotient (RQ) method based on the ratio of measured environmental concentration (MEC) to predicted no-effect concentration (PNEC). Overall, the ecological risk of DA was low to moderate, whereas during springtime, DA posed elevated risks to benthic organisms in specific areas of Sishili Bay and Laizhou Bay. These findings demonstrate that the benthic environment represents an underappreciated reservoir of DA in coastal ecosystems and therefore requires greater attention, particularly in mariculture zones.