Natural gas has become a leading source of alternative energy with the advent of techniques to economically extract gas reserves from deep shale formations. Here, we present an assessment of private well water quality in aquifers overlying the Barnett Shale formation of North Texas. We evaluated samples from 100 private drinking water wells using analytical chemistry techniques. Analyses revealed that arsenic, selenium, strontium and total dissolved solids (TDS) exceeded the Environmental Protection Agency's Drinking Water Maximum Contaminant Limit (MCL) in some samples from private water wells located within 3 km of active natural gas wells. Lower levels of arsenic, selenium, strontium, and barium were detected at reference sites outside the Barnett Shale region as well as sites within the Barnett Shale region located more than 3 km from active natural gas wells. Methanol and ethanol were also detected in 29% of samples. Samples exceeding MCL levels were randomly distributed within areas of active natural gas extraction, and the spatial patterns in our data suggest that elevated constituent levels could be due to a variety of factors including mobilization of natural constituents, hydrogeochemical changes from lowering of the water table, or industrial accidents such as faulty gas well casings.

Accumulation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) by crop plants from contaminated soils may pose health risks. A greenhouse pot experiment using lettuce (Lactuca satuva L.) as a representative vegetable was conducted to assess the concentrations of PAHs and HMs in vegetables grown in wastewater-contaminated soils. The concentrations of total PAHs were ranged from 1.5 to 3.4 mg kg −1 in the contaminated soils, while 1.2 mg kg −1 in the reference soil. Linear regression analyses showed that the relationships between soil and shoot PAH concentrations were stronger for LMW-PAHs (R 2 between 0.51 and 0.92) than for HMW-PAHs (R 2 0.02 and 0.60), suggesting that translocation for LMW-PAHs is faster than HMW-PAHs. Furthermore, the data imply that root uptake was the main pathway for HMW-PAHs accumulation. The plant shoots were also highly contaminated with HMs, particularly Cd (0.4-0.9 mg kg −1 ), Cr (3.4-4.1 mg kg −1 ), Ni (11.7-15.1 mg kg −1 ) and Pb (2.3-5.3 mg kg −1 ), and exceed the guidance limits set by State Environmental Protection Administration (SEPA), China and the World Health Organization (WHO). This study highlights the potential health risks associated with cultivation and consumption of leafy vegetables on wastewater-contaminated soils.

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