Toxicity of Saline Wastewater from Oil and Gas Development in the Bakken Shale Region of North America

Improvements in oil and gas technologies, such as directional drilling and hydraulic fracturing, have led to an extraction boom in the U.S.  Oil and gas extraction results in large quantities of waste water.  On average, oil wells produce 10 barrels of wastewater for every 1 barrel of oil, and this water is the single largest waste stream associated with oil and gas production.  The Williston Basin lies within the prairie pothole region, an area with thousands of perennial and seasonal wetlands, ponds, lakes and streams.   Waste water from oil and gas production in the Williston Basin is highly saline (>250,000 mg/L).   Surface and groundwater within the region is hard and high in sulfates, whereas waste waters from oil production are chloride dominated.  We investigated the effects of NaCl on Daphnia magna and  Lemna gibba (duckweed), and are currently  experimenting with Ceriodaphnia dubia.  Experiments were conducted in reconstituted, hard waters simulating the surface waters of the prairie pothole region.  Acute toxicity of NaCl in hard water to D. magna was 6,355 mg/l and duckweed growth was inhibited at approximately 5,500 mg/L.   These results indicate that chloride toxicity from waste water present a threat to the health of surface waters if released.