Hydrolysis of norfloxacin in the hyporheic zone: kinetics and pathways

Dredging wastewater discharge caused mangrove sediment antibiotic accumulation and affected functional microbes in carbon and nitrogen metabolism

Antibiotic pollution is a major environmental concern in mariculture activities along coastlines with mangrove forests. However, the content, composition, and ecological impacts of such pollution within mangrove ecosystems have been limitedly explored. In this study, surface sediments and sediment profiles (40 cm deep) were investigated for 14 antibiotics, elemental parameters, and functional gene abundance at mangrove sites affected by dredging wastewater discharge from mariculture ponds along the Jiulong River Estuary. The results revealed that all 14 antibiotics were detected in the surface sediments, with total antibiotics below 6 ng gDW-1 at sites without direct wastewater dicharge. In contrast, sediment profiles from sites receiving wastewater discharge exhibited higher antibiotic contents, reaching up to 19.6 ng gDW-1 in the surface sediments. Fluoroquinolones (ofloxacin and enrofloxacin) were the dominant antibiotic classes of antibiotics, and the deeper sediment layers were also contaminated with antibiotics because of wastewater discharge. Antibiotic accumulation resulting from wastewater discharge significantly affected the functional microbes involved in carbon and nitrogen metabolism. Positive correlations were observed between ofloxacin (florfenicol) and the gene abundance of nosZ and nirK while amoA abundance showed negative correlations. Increased levels of enrofloxacin (terramycin and sulfamethazine), as well as organic carbon and total nitrogen, were associated with higher abundances of narG and mcrA genes. Overall, prolonged wastewater discharge from mariculture activities led to antibiotic accumulation, extending into deep sediment layers, potentially reshaping the functional microbes involved in carbon and nitrogen metabolism. Therefore, future strategies are urgently needed to address antibiotic pollution caused by wastewater discharge near mangrove forests.

Prediction models and major controlling factors of antibiotics bioavailability in hyporheic zone

Recently, antibiotics have been frequently detected in the hyporheic zone (HZ) as a novel contaminant. Bioavailability assessment has gradually attracted more attention in order to provide a more realistic assessment of human health risks. In this study, two typical antibiotics, oxytetracycline (OTC) and sulfamethoxazole (SMZ), were used as target pollutants in the HZ of the Zaohe-Weihe River, and the polar organics integrated sampler was used to analyze the variation of antibiotics bioavailability. According to the characteristics of the HZ, the total concentration of pollutants, pH, and dissolved oxygen (DO) were selected as major predictive factors to analyze their correlation with the antibiotics bioavailability. Then the predictive antibiotic bioavailability models were constructed by stepwise multiple linear regression method. The results showed that there was a highly significant negative correlation between OTC bioavailability and DO (P < 0.001), while SMZ bioavailability showed a highly significant negative correlation with total concentration of pollutants (P < 0.001) and a significant negative correlation with DO (P < 0.01). The results of correlation analysis were further verified by Principal Component Analysis. Based on the experimental data, we constructed eight prediction models for the bioavailability of two antibiotics and verified them. The data points of the six prediction models were distributed in the 95% prediction band, indicating that the models were more reliable and accurate. The prediction models in this study provide reference for the accurate ecological risk assessment of the bioavailability of pollutants in the HZ, and also provide a new idea for predicting the bioavailability of pollutants in practical applications.