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Efficiencies of Extractants Used in Analyses of Heavy Metals in Sludges¹

ABSTRACT

A comparison of extractability was made for three solvents commonly used in estimating availability of heavy metals in soils to living plants. Small, intermediate, and large amounts of heavy metals were removed, respectively, from an anaerobic digest of a sewage sludge with 2.5% acetic acid, 0.1N HCl, and 1.0N HCl respectively. With 10, 20, 30, and 40 ml 1N HCl per g sludge, approximately the same amount of each heavy metal was extracted during 1 hour of shaking, while for 0.1N HCl and 2.5% acetic acid increasing amounts were extracted at 10, 20, and 30 ml/g, with somewhat higher or lower amounts being obtained at a ratio of 40 ml extractant per g sludge. With 0.1N HCl, an extraction period of 0.5 hour appeared to be sub-optimal, while periods longer than 1 hour did not yield significantly greater extractability except for Cd, extracted for 3 hours. Extraction of Ni for 5 hours and Pb for 5 or 7 hours resulted in significantly less metal than was obtained at 1 hour. Since it is highly likely that availability of heavy metals to plants will depend on numerous and unpredictable variables, it is proposed that until such factors are resolved, a standard extraction procedure be used by all workers on sludges and soils. This would provide a basis for comparisons of published data.

Key Words: anaerobic sludge • cadmium • chromium • copper • lead • nickel • zinc • heavy metals availability

¹ This study was supported by the Natl. Sci. Found. Program Res. Applied to Natl. Needs (RANN) Grant ENV 76-17225.

² Postdoctoral Associate and Professor of Zoology, respectively, School of Biology, Chemistry and Ecology, State Univ. of New York, College of Environ. Sci. and Forest., Syracuse, NY 13210.

Received for publication May 30, 1978.