Leaching of Retorted Oil Shale: Assessing the Toxicity to Colorado Squawfish, Fathead Minnows, and Two Food-Chain Organisms

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Abstract
Development of a large shale‐oil industry in Colorado, Utah, and Wyoming would result in disposal of large volumes of retorted shale. Water percolating through these wastes could leach toxicants into surface waters of the upper Colorado River system. Leachate from field lysimeters containing shale that had gone through the Paraho retorting process 6 years before had high concentrations of K, Li, Mg, Mo, Na, SO 4, and NO 3. Total concentrations of organics in leachate were low; nitrogen‐containing aromatic hydrocarbons approximated background concentrations. In 96‐h exposures, undiluted leachate was not toxic to fathead minnows Pimephales promelas or Colorado squawfish Ptychocheilus lucius, and was only slightly toxic to the mayfly Hexagenia bilineata and to Daphnia magna. In 30‐d exposures to different concentrations of the leachate, a concentration of 6:94 (percent leachate:percent dilution water) caused reduced growth of fathead minnows and reduced survival of mayflies. The highest test concentration not causing toxic effects was 3:97. This dilution represented conductivity of 1,080 μS/cm and total dissolved solids of 750 mg/L–values that are 1.2 to 2.0 times higher than in the Colorado and White rivers at the Colorado‐Utah border. The elements Li and Sr appeared to be selectively accumulated by the two fish species. Deleterious effects of leachates from retorted oil shale appear to be unlikely in major rivers with large dilution factors. Feeder streams and backwater areas with less flushing may require protection.

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