DIRECT TOXICITY ASSESSMENT OF 2 SOILS AMENDED WITH SEWAGE-SLUDGE CONTAMINATED WITH HEAVY-METALS USING A PROTOZOAN (COLPODA-STEINII) BIOASSAY

A rapid bioassay involving growth of the common soil ciliate Colpoda s teinii was used to study the toxicity and bioavailability of heavy met als in soil solutions extracted from air-dried soils from two long-ter m experiments that were amended with sewage sludge. The sludges were p redominantly contaminated with either Ni, Cu, or Zn. Growth of C. stei nii was strongly inhibited in all the metal-amended soils compared wit h the equivalent unamended control soils. The bioassay responses were regressed with metal concentrations in soil and soil pore water to rel ate the biological response to heavy metal regulatory limits for soils receiving sewage sludges. (C) 1997 Elsevier Science Ltd.