title: Potential impact of flowback water from hydraulic fracturing on agricultural soil quality: Metal/metalloid bioaccessibility, Microtox bioassay, and enzyme activities.
abstract: Hydraulic fracturing has advanced the development of shale gas extraction, while inadvertent spills of flowback water may pose a risk to the surrounding environment due to its high salt content, metals/metalloids (As, Se, Fe and Sr), and organic additives. This study investigated the potential impact of flowback water on four representative soils from shale gas regions in Northeast China using synthetic flowback solutions. The compositions of the solutions were representative of flowback water arising at different stages after fracturing well establishment. The effects of solution composition of flowback water on soil ecosystem were assessed in terms of metal mobility and bioaccessibility, as well as biological endpoints using Microtox bioassay (Vibrio fischeri) and enzyme activity tests. After one-month artificial aging of the soils with various flowback solutions, the mobility and bioaccessibility of As(V) and Se(VI) decreased as the ionic strength of the flowback solutions increased. The results inferred a stronger binding affinity of As(V) and Se(VI) with the soils. Nevertheless, the soil toxicity to Vibrio fischeri only presented a moderate increase after aging, while dehydrogenase and phosphomonoesterase activities were significantly suppressed with increasing ionic strength of flowback solutions. On the contrary, polyacrylamide in the flowback solutions led to higher dehydrogenase activity. These results indicated that soil enzyme activities were sensitive to the composition of flowback solutions. A preliminary human health risk assessment related to As(V) suggested a low level of cancer risk through exposure via ingestion, while holistic assessment of environmental implications is required.
authors.affiliation: Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors.forename: Season S
authors.initials: SS
authors.lastname: Chen
authors.affiliation: Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China; State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China. Electronic address: dan.tsang@polyu.edu.hk.
authors.forename: Daniel C W
authors.initials: DCW
authors.lastname: Tsang
authors.affiliation: Environmental and Water Resources Engineering, Department of Civil and Environmental Engineering, Imperial College London, South Kensington, London SW7 2AZ, UK.
authors.forename: Nigel J D
authors.initials: NJD
authors.lastname: Graham
authors.affiliation: School of Natural Resources and Environmental Science, Korea Biochar Research Center, Kangwon National University, Chuncheon 24341, Republic of Korea.
authors.forename: Yong Sik
authors.initials: YS
authors.lastname: Ok
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China. Electronic address: yujief@hit.edu.cn.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Feng
authors.affiliation: Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
authors.forename: Xiang-Dong
authors.initials: XD
authors.lastname: Li
mesh_terms: D001681:Biological Assay; D004784:Environmental Monitoring; D000067071:Hydraulic Fracking; D058955:Metalloids / Q000032:analysis* / Q000633:toxicity; D008670:Metals / Q000032:analysis* / Q000633:toxicity; D018570:Risk Assessment; D018675:Toxicity Tests; D062065:Wastewater / Q000737:chemistry* / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000633:toxicity
chemical_list: D058955:Metalloids; D008670:Metals; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Enzyme activity; Fracturing fluids; Metal mobility; Microbial toxicity; Soil interaction