Ecological risk assessment of emerging chemicals in Gwangju landfill leachate and tributary

Abstract

Each day, landfills have an influx of over-prescribed medicines, pesticides, industrial chemicals, and personal care products in the form of waste. Rainwater, especially on rainy days, percolates through these wastes, extracting various chemicals. Therefore, this landfill leachate is a highly contaminated liquid. This landfill leachate has a potential exposure risk as a significant point source of Emerging Chemicals (ECs) within the aquatic environment by leaking or runoff. However, our understanding of ECs composition in raw and treated landfill leachate is limited. Hence the objective of this study is to conduct a quantitative analysis of ECs in raw and treated leachate from the active landfill site in Gwangju using UHPLC QTOF MS/MS. Additionally, this research aims to assess the potential impact of landfill leachate on the adjacent tributary. Finally, an ecological risk assessment is conducted with Risk Quotient (RQ) values. Three sampling campaigns were completed targeting pharmaceuticals (n=9), pesticide/fungicide/herbicide (n=8), industrial chemicals (n=1), and other organic chemicals (n=3). Each ECs (n=21) was detected in both raw leachate (9.16±7.79 ug/L) and treated leachate (3.84±2.16 ug/L). Pharmaceuticals (ketoprofen(KET), cetirizine(CET), valsartan(VAL), niflumic acid(NFU)), pesticide(DEET), industrial chemicals (triethyl phosphate(TEP)), and diphenylphosphinic acid(DPPA) were identified with high concentrations in landfill leachates. The ECs were treated by Modified Ludzack-Ettinger (MLE) treatment in the landfill, with an average removal efficiency of 66.98%. The chemical compounds with poor treatment efficiency in landfills showed no statistically significant differences between the raw and treated leachates within the landfill (p>0.05). Temporally, pharmaceuticals consistently flowed into the landfill without significant fluctuations, contrasting with pesticides. Near the tributary, 7 chemicals out of 21 chemicals were detected, with CET having the highest concentration at 11.61 ug/L. Metolachlor(MTC), a pesticide known for high usage in May and June, was observed in June with the highest concentration in the tributary. Predicted No Effect Concentration (PNEC) was derived by probabilistic and deterministic approaches in case of sufficient data. When data were insufficient, the QSAR toolbox and ECOSAR were used for predicted toxicity values. The RQ for pharmaceuticals within the landfill indicated a higher value compared to other chemicals. Although the average RQ of raw leachate (6.96) tended to decrease after treatment (5.45), the leachate was still highly contaminated (RQ>1). There was no correlation between landfill leachate and tributary. MTC, galaxolidone(GLX), and metalaxyl(MTX) in the tributary were impacted by non-point sources. In tributary, CET, MTC, and GLX emerged as candidates requiring monitoring (RQ>1). This research contributes to the understanding of ECs contamination in landfill leachate in Gwangju highlighting the importance of pharmaceutical management in landfills.