Ecological risk assessment of microplastics and heavy metals in central industrial wastewater treatment plant

Abstract

Microplastics become a big concern in environment. Their small particle size can absorb a variety of pollutants from the nearby environment when discharged into the environment, especially heavy metals. Central industrial wastewater treatment plant (WWTP) is an important source of microplastics in the environment. In this study, wastewater and sludge were collected from two industrial estates in Thailand. Wastewater was collected from 4 points i.e., influent, post grit chamber, post aeration tank, and post sedimentation tank while sludge was collected from sludge storage. Concentration of microplastics, heavy metals and heavy metals on microplastics were examined to evaluate ecological risk assessment. Based on the results, microplastics concentration in effluent and sludge were 11.04 ± 0.08 particles/L, 2,398.00 ± 11.37 particles/kg from WWTP A, while 33.53 ± 0.55 particles/L, 1,930.00 ± 7.57 particles/kg from WWTP B, respectively. In addition, main shape, size, colors, and polymer were pellet, range 100 – 500 µm, white/clear, and polypropylene polymer from both sites, respectively. In terms of heavy metals, zinc was the most detected in wastewater, sludge, and on microplastics. The risk assessment was carried out. The result found that polymer risk index (H) showed 35,835 in WWTP A and 45,652 in WWTP B, which high toxic level. High risk of pollution load index (PLI) with category IV (97.82) was showed in WWTP A, while PLI of WWTP B were presented in category II (12.76). For geo-accumulation Index (Igeo), all heavy metals presented in low degree level, except Cd and Se from WWTP A presented as low toxic (0.7) and moderate toxic (1.2), respectively. Potential ecological risk (PER) of microplastics presented extreme danger (48,893 and 20,087 from WWTP A and WWTP B, respectively.), while PER of heavy metals also showed low toxic level with 70.71 and moderate toxic with 96.61 from WWTP A and WWTP B, respectively. Furthermore, PER of heavy metals on microplastics exhibited 48,936.63 and 20,183.61 from WWTP A and WWTP B, respectively, which extreme danger level.