Hazard assessment of hydraulic fracturing chemicals using an indexing method.

The rapid expansion of unconventional natural gas production has triggered considerable public concerns, particularly regarding environmental and human health (EHH) risks posed by various chemical additives used in hydraulic fracturing (HF) operations. There is a need to assess the potential EHH hazards of additives used in real-world HF operations. In this study, HF additive and fracturing fluid data was acquired, and EHH hazards were assessed using an indexing approach. The indexing system analyzed chemical toxicological data of different ingredients contained within additives and produced an aggregated EHH safety index for each additive, along with an indicator describing the completeness of the chemical toxicological data. The results show that commonly used additives are generally associated with medium-level EHH hazards. In each additive category, ingredients of high EHH concern were identified, and the high hazard designation was primarily attributed to ingredients' high aquatic toxicity and carcinogenic effects. Among all assessed additive categories, iron control agents were identified as the greatest EHH hazards. Lack of information, such as undisclosed ingredients and chemical toxicological data gaps, has resulted in different levels of assessment uncertainties. In particular, friction reducers show the highest data incompleteness with regards to EHH hazards. This study reveals the potential EHH hazards associated with chemicals used in current HF field operations and can provide decision makers with valuable information to facilitate sustainable and responsible unconventional gas production.