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Effects of Heavy Metal and Other Elemental Additives to Activated Sludge on Growth of Eisenia foetida¹

ABSTRACT

The approximate level at which added concentrations of certain elements would cause an activated sludge to induce a toxic effect upon the growth of Eisenia foetida was determined. During 43 trials on sludge samples obtained throughout 1 year of study, earthworms grew from 3 to 10 mg live wt at hatching to 792 mg ± 18% (mean ± C.V.) in 8 weeks, when sludge was 24°C and contained no additives. None of several elements commonly used in microbial growth media enhanced the growth rate of the earthworm. At salt concentrations up to about 6.6% on a dry wt basis, none of six anions tested was in and of itself toxic, while five of 15 cations—Co, Hg, Cu, Ni, and Cd—appeared specifically to inhibit growth rate or cause death. Manganese, Cr, and Pb were innocuous even at the highest levels of application—22,000, 46,000, and 52,000 mg/kg, respectively. Neither the anionic nor cationic component of certain salts, such as NaCl or NH₄Cl, could be said to inhibit growth, which occurred only at high concentrations of these salts (about 3.3 and/or 6.6%). Below 7 mmho/cm, toxicity could not be correlated with electrolytic conductance, though higher values may help to explain the nonspecific growth inhibitory effects of salts like NaCl and KCl. Nor could toxicity ever be ascribed to hydrogen ion activity, since sludge pH was not altered even at the highest salt dose. It is concluded that except under very extreme conditions, the levels of heavy metals and salts generally found in activated sludges will not have an adverse affect on the growth of E. foetida.

Key Words: earthworms • cadmium • copper • nickel • lead • chromium • zinc • cobalt • mercury • salts

¹ Work supported by the National Science Foundation, in cooperation with SUNY Coll. of Environ. Sci. and Forestry, Syracuse, NY 13210.

² Professor of Biology, State Univ. Coll. of Environ. Sci. and Forestry, Syracuse, N.Y.; Research Associate, Dep. Agric. Eng., Cornell Univ., Ithaca, NY 14853; and Biology Student, State Univ. Coll. of Environ. Sci. and Forestry, respectively.

Received for publication August 1, 1980.