Figures (3)  Tables (2)

    • Figure 1. 

      Schematic diagram illustrating emerging contaminant generation during shale gas extraction, showing primary waste streams at each stage (drilling, fracturing, and production/treatment), estimated generation volumes, and carrying emerging contaminant categories. Names of all the pollutant abbreviations listed above: POPs (persistent organic pollutants); PAHs (polycyclic aromatic hydrocarbons); PFAS (per- and polyfluoroalkyl substances); OCPs (organochlorine pesticides); EDCs (endocrine disrupting chemicals); PAEs (phthalate esters); OPEs (organophosphate esters); AEOs (alcohol ethoxylates); NPEOs (nonylphenol ethoxylates); QACs (quaternary ammonium compounds); ARGs (antibiotic resistance genes); MPs (microplastics).

    • Figure 2. 

      Process flow diagram of the FPW treatment plant in China. Blue boxes show emerging contaminants that can be removed by the treatment processes; red boxes represent new pollutants generated during these processes. Blue indicates harmless components; red denotes toxic products, including by-products formed during treatment processes and sludge concentrated through evaporation. Full names of all the pollutant abbreviations listed above: PAHs (polycyclic aromatic hydrocarbons); PFAS (per- and polyfluoroalkyl substances); OCPs (organochlorine pesticides); OPEs (organophosphate esters); NPEOs (nonylphenol ethoxylates); QACs (quaternary ammonium compounds); ARGs (antibiotic resistance genes).

    • Figure 3. 

      Sources, treatment methods, transformation, environmental fates, and release risks of emerging contaminants in shale gas extraction.

    • Category Contaminant Concentration Primary source Sample
      size      		 Analytical method Region
      (basin)      		 Detection frequency Ref.
      POPs TPHs 26,700–79,300 mg/kg (OBDC) Base fluid (Diesel/Oil) 5 GC-MS Sichuan Basin, China 100% [26,28,36]
      PAHs 1.25–2.37 mg/kg (OBDC) 6 67%
      BTEXs 8.18–8.39 mg/kg (OBDC) 4 75%
      EDCs PAEs Up to 877 μg/kg (WBDC)
      Up to 5.6 μg/kg (OBDC)      		 Plasticizers, lubricants 8 (WBDC)
      5 (OBDC)      		 UHPLC-Q-TOF-MS Sichuan Basin, China 100% [24]
      OPEs Up to 527 μg/kg (WBDC)
      Up to 18.5 μg/kg (OBDC)      		 Flame retardants 100%
      AEOs 1.48–3.22 mg/kg (WBDC) Surfactants 100%
      NPEOs 14.4–26.3 mg/kg (OBDC) Surfactants 100%
      Biocides (like antibiotics) QACs 1.40–2.73 mg/kg (WBDC)
      21.8–42.5 mg/kg (OBDC)      		 Biocides 8 (WBDC)
      5 (OBDC)      		 UHPLC-Q-TOF-MS Sichuan Basin, China 100% [24]
      Microplastics Polyacrylamide polystyrene / Friction reducers, lubricants / / / / [33,34]
      '/' indicates that the corresponding information was not explicitly reported in the references.

      Table 1. 

      Emerging contaminants detected in drilling cuttings from shale gas extraction

    • Category Contaminant Concentration Primary source Sample size Analytical method Region (basin) Detection frequency Ref.
      POPs PAHs 1.5–65671 μg/L Fracturing fluid, thermal cracking, Natural release / / Sichuan Basin, China, and Marcellus Shale, the United States / [31]
      PFAS PFOA Up to 1.00 ng/L Degradation of fluoropolymer materials 46 LC/MS/MS Permian Basin, the United States 100% [39]
      PFOS Up to 1.20 ng/L
      PFBS 0.17–2.00 ng/L
      PFHpA Up to 0.35 ng/L
      PFHxA Up to 1.20 ng/L
      PFTeA Up to 0.24 ng/L
      NEtFOSE Up to 0.98 ng/L
      OCPs 15.33–29.22 μg/L Leaching from formation strata 5 GC–MS/MS Sichuan Basin, China 100% [40]
      EDCs NPEOs 211–12,400 ng/L Surfactants 24 UHPLC-Q-TOF-MS Sichuan Basin, China 100% [24]
      PAEs Up to 6,725 μg/L plasticizers, solvents / HPLC/Q-TOF-MS the United States / [21]
      Biocides QACs 260.1 μg/L Biocides 1 HPLC-MS/MS Sichuan Basin, China 100% [41]
      ARGs ARGs 0.36 copies/cell - 16 Metagenomic sequencing Sichuan Basin, China 100% [44]
      Microplastics Polyacrylamide / Drag reducers / / / / [45]
      '/' indicates that the corresponding information was not explicitly reported in the references.

      Table 2. 

      Emerging contaminants detected in wastewater from shale gas extraction