Antibiotics In Two Municipal Sewage Treatment Plants In Sri Lanka

During the past few decades,the occurrence of antimicrobials in the aquatic environment becomes a worldwide issue and a growing environmental concern as thousands of tons of pharmacologically active substances are used yearly to treat or prevent infective diseases in human and veterinary medicine and in agriculture.Most of the monitoring data on the occurrence of antibiotics in sewage treatment plants(STPs)have been reported from Europe,North America and some countries in Northeast Asia,while very limited data can be found in Southeast Asian countries.As a pioneering research in Sri Lanka,24 h composite wastewater samples were collected at the influent and effluent of two municipal STPs for consecutive 7 days to investigate occurrence,consumption and removal efficiency of seventeen antibiotics.The STP was located in Colombo and Hikkaduwa,respectively,representing two kinds of communities.Colombo STP mostly collects wastewater from local households in the Greater Colombo area which is the major center of employment in manufacturing,trade,business services and government service sectors.Hikkaduwa is a rapidly tourist center in the southwest of Sri Lanka where the STP treats domestic wastewater from the tourist hotels.In this study occurrence and removal and seventeen antibiotic compounds from the groups of sulphonamides and synergist(SAs),fluoroquinolones(FQs),tetracyclines(TCs),macrolides(MLs)and phenicols(PCs)were investigated in two sewage treatment plants(STPs)featuring different treatment technologies.The compounds were extracted from sewage samples by solid-phase extraction(SPE).For the detection and quantitative determination of the analytes,High-performance liquid chromatography coupled with tandem mass spectrometry(HPLC–MS/MS)(1290/6470QQQ)was performed in the multiple reaction monitoring(MRM)mode.As a result,the majority of the antibiotics can be always detected from both STPs,except for chlortetracycline,doxycycline and florfenicol.Fluoroquinolones(FQs)were detected at highest concentrations with ciprofloxacin(CIP)being the dominant compound.Concentrations of CIP in the influent samples were in the range of 433-6010 ng/L.In general,the removal efficiency varied significantly from-1100%-100% depending on the compound and treatment process.The activated sludge system of Colombo exhibited better elimination and more stable performance than the constructed wetland process of Hikkaduwa.The consumption of antibiotics was estimated on the basis of influent mass load and catchment population data.We found a difference in consumption patterns between the two served areas.Compared to local people in Colombo,tourists in Hikkaduwa appeared to take more antibiotics during the study period with the estimated daily dose of 0.25 g per 1000 persons.Moreover,macrolides accounted for a larger portion than FQs in Hikkaduwa,with azithromycin(AZM)being the most prevalent antibacterial agent.After comparison with an official report by Medical Supplies Division of Sri Lanka,we conjected that AZM was not commonly used among local people and it was mainly introduced by foreign arrivals.However antibiotics are only partially eliminated during the sewage treatment process and the residual antibiotics may be discharged into the environment.Further study required to be applied to test whether these levels in this study could disrupt aquatic and marine ecology or promotion of antibiotic resistance.