Assessing dermal exposure risk to workers from flowback water during shale gas hydraulic fracturing activity

Hydraulic fracturing is a well stimulation technique used in the production of natural gas from shale. While hydraulic fracturing has been in use for decades as a method for oil and gas recovery, recent advances in horizontal drilling techniques and fracturing fluid production have made previously unattainable natural gas reservoirs accessible and economically recoverable. Flowback water produced from the hydraulic fracturing process can pose environmental and human health risks. The objective of this study is to assess cancer risk following dermal exposure to flowback water among workers at hydraulic fracturing sites. Median, 2.5th percentile, and 97.5th percentile concentrations for high priority constituents in flowback water were collected from a previous study and used to estimate cancer risk from dermal exposure to carcinogenic agents in water compared to a target lifetime cancer risk value of 10−6. Hazard quotients, which compare exposure dose to dose at which no adverse effects are expected, were also calculated for non-carcinogenic components of flowback water and compared to an acceptable value of 1. The cancer risk estimate for median concentrations did not exceed the target lifetime cancer risk of 10−6 except for benzo(a)pyrene where the cancer risk of full hand exposure to flowback water for 3 h (one event per week for 4 years) falls within this range (2.9 × 10−6 - 1.4 × 10−5), which exceeds the target risk level even at the 2.5 percentile value. The upper limit of cancer risk form exposure to heptachlor also exceeds 10−6 in this model. Hazard quotient for barium in the same model exceeds 1 (1.7) and results in a total hazard index of 2.