Redistribution of Trace Elements from Contaminated Sediments of Lake Coeur d'Alene during Oxygenation

Abstract

Sediments of Coeur d'Alene Lake in northern Idaho are contaminated with heavy metals as a result of mining in the Coeur d'Alene River basin. Dredging and disposal operations have been suggested as a possible means of environmental remediation; thus, detailed knowledge is required as to how sediment oxygenation can result in the redistribution of trace elements. To simulate changing physicochemical soil conditions, stirred batch experiments were conducted using fresh sediment core material retrieved from the lake. Fifty grams of sediment were added to 750 mL of double deionized water and mixed while being oxygenated for 260 h. The following parameters were monitored as a function of time: pH and E h , contaminant trace‐element release into the aqueous phase, and metal abundance within operationally defined fractions of the solid phase: magnesium chloride (exchangeable), sodium hypochlorite (organic), sodium acetate‐acetic acid (carbonate), ammonium oxalate in the dark (non‐crystalline), hydroxylamine hydrochloride (crystalline), and potassium perchlorate‐hydrochloric‐nitric acid (sulfidic) extractable sediment fractions. In all trials, levels of aqueous‐phase Zn remained high throughout the simulations (6.60 mg L −1 ) and were highly correlated (sigma value = 0.95) with Mn. Oxygenation and disturbance resulted in a shift in trace element partitioning from the sodium hypochlorite (organic) and potassium perchlorate‐hydrochloric‐nitric acid extractable (sulfidic) fractions into the ammonium oxalate in the dark (noncrystalline) extractable fraction. Overall, these results indicate that oxygenation and agitation of anaerobic sediment results in Zn release into solution with concomitant redistribution of trace elements in the solid‐phase.