Antibiotics residues in inland and transitional sediments

This study assesses the concentrations of a range of antibiotics in riverine and transitional sediments in Ireland. A selection of 12 macrolide, fluoroquinolone, sulphonamide, and diaminopyrimidine antibiotics were quantified in 80 grab surficial sediment samples from around Ireland, selected to investigate areas of potentially higher pollution risk (agriculture, aquaculture, industrial emissions, and wastewater emission points) as well as isolated areas where there are no known pollution sources. Several of the macrolides and sulphonamides/trimethoprim were generally detected more frequently above limits of quantification (LoQ). Fluoroquinolones, while frequently detected above limits of detection (LoD), concentrations were mostly below method LOQs. The most prevalent antibiotic detected was clarithromycin, found at the highest mean concentration (6.65 ng/g) and detected in ∼90 % of samples. Comparing levels of quantified antibiotics to levels reported internationally, Ireland is at the lower end for all quantified antibiotics. This is with the notable exception of clarithromycin, which is higher than levels found in comparable studies in Italy, Spain, France, and Argentina. Higher levels of total antibiotics (49.3 ± 24.7 ng/g) were found to be present immediately adjacent to wastewater emission points while moderate degrees of contamination (9.0 ± 9.7 ng/g) were also linked to wastewater, aquaculture, or agricultural pressures. Based on risk quotients calculated from available sediment PNECs taken from the NORMAN ecotoxicology database, clarithromycin was also the only compound to be present at concentrations indicative of a "moderate" degree of environmental risk, with most of the remaining falling below this threshold. Ciprofloxacin was ostensibly found to be of a "high" degree of environmental risk; however, this is based on only a single sample quantified above the LoQ. Overall, antibiotic sediment concentrations suggest a low ecotoxicological risk for most of the target antibiotics, although clarithromycin, ciprofloxacin, and sulfamethoxazole warrant further monitoring in sediments. A final notable finding is the differences in partitioning behaviour of antibiotics between water and sediment: clarithromycin is more likely to be detected in sediment while sulfamethoxazole partitions more to water. Such partitioning behaviour should therefore be taken into consideration for any subsequent monitoring programmes.