Evaluation of Municipal Effluent Toxicity Using Higher Plants and Invertebrates
Toxicity of Kaunas municipal effluent was evaluated using bioassays with aquatic invertebrates and terrestrial higher plants. Toxicity tests were performed on samples of both untreated and mechanically and biologically treated wastewater. Wastewater toxicity was assessed using seed germination and short-term early seedling growth tests of lettuce (Lactuca sativa L.) and acute microcrustaceans Thamnocephalus platyurus (24 h) assays. Undiluted untreated wastewater was severely toxic to T.platyurus and led to death of all exposed organisms. Twofold decrease in wastewater concentration in the solution (from 100 % to 50 %) led to sharp transition between extremely toxic to medium toxic to tested organisms. In four and more times diluted wastewater only 10-20 % of the total exposed T. platyurus died. Measured endpoints in higher plants tests were: seed germination, root length, shoot height and total biomass. Raw sewage was slightly toxic (0.6 TU) to the root growth of lettuce, but mechanically and biologically treated effluents exhibited no adverse effects or even started to stimulate the growth. The growth of shoots and total biomass were stimulated due to exposure to effluents. Stimulation effect was determined by sufficiently high concentrations of nutrients.