Heterocypris incongruens as a tool to estimate sewage sludge toxicity.

The toxicity of 13 sewage sludges was evaluated in relation to the crustacean Heterocypris incongruens. The bioassay used was a commercial, direct contact test that allows evaluation of solid-phase toxicity. Evaluation of sewage sludges included physicochemical properties (pH, total organic C, total N, cation-exchange capacity, total exchangeable bases, available forms of P and K, and electrical conductivity), heavy metal content (cadmium, chromium, copper, lead, nickel, and zinc), and content of polycyclic aromatic hydrocarbons (16 from the U.S. Environmental Protection Agency list). The evaluated parameters were then compared with bioassay results (mortality and growth inhibition). Sewage sludges were characterized by optimal physicochemical properties; low K (<5.64 mg/kg) and total organic C (177-253 g/kg) levels were noted. Contaminant content (heavy metals and polycyclic aromatic hydrocarbons) clearly differed between individual sewage sludges. Polycyclic aromatic hydrocarbon contents ranged from 3.8 to 36.4 mg/kg. Total concentrations of heavy metals in all sewage sludges (with the exception of one sludge) were lower than the pollutant concentration limits for land application. Heterocypris incongruens mortality when sludge was applied at doses of 6, 12, or 24% ranged from 0 to 70%, from 4.7 to 72.1%, and from 0 to 100%, respectively. Average growth inhibition was 39.7 to 46.6% (depending on the sludge dose applied). Any stimulating influence of two sewage sludges on the test organism was recorded. The median lethal concentrations calculated for individual sewage sludges ranged from 88 to 956 g sewage sludge/ kg.