WWRC 84-15
Chemistry and Aquatic Toxicity of Raw Oil Shale Leachates from Piceance Basin, Colorado
Abstract
Leachates were collected during the period of 1981 to 1983 from several depths in two
surface piles of raw, mined oil shale in the Piceance Basin of northwest Colorado. Although both
piles were subject to similar climatic conditions, the composition of major inorganic ions in the
leachates differed considerably because of different shale compositions. Acute toxicity to Daphnia
magna and fathead minnows (Pimephales promelas) occurred when leachate conductivity
exceeded 7,000 to 8,000 umhos/cm and total dissolved solids exceeded 6 to 7 g/L (0.6 to 0.7%
salt). D. magna were more sensitive than fathead minnows in acute toxicity tests, and D. magna
48-h LC50 values were as low as 13% of full-strength leachate. The lowest no observed effect concentration
determined in D. magna 21-d chronic toxicity tests was 0.9% of full-strength leachate.
Because of interactions among the major ions, the contributions to toxicity by trace elements and
organic compounds in the oil shale leachates could not be differentiated from contributions by
MgS04, the major toxicant. This study demonstrated that toxic mechanisms occurring within complex
chemical mixtures cannot always be identified on the basis of single-compound toxicity values,
and that reconstituted mixtures of principal chemical components are useful in identifying toxicants
and their interactions with other mixture constituents.
Keywords — Daphnia magna Pimephales promelas Acute toxicity Chronic toxicity
Field leachates
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