Municipal effluents toxicity evaluation using higher terrestrial, aquatic plants, and invertebrates

Abstract

The toxicity of Vilnius municipal effluents was evaluated using the bioassays with aquatic invertebrates and terrestrial and aquatic higher plants. Toxicity tests were performed on samples of untreated and biologically treated wastewater. Wastewater toxicity was assessed using seed germination and short-term early seedling growth test of lettuce (Lactuca sativa L.), growth inhibition test of Lemna minor and the acute microcrustaceans Daphnia magna (24-48 h) assay. Undiluted untreated wastewater was severely toxic to D. magna and led to death of all exposed organisms (48 h test). The estimated median lethal concentration was 5% WW (20 TU) for untreated wastewater and biologically treated effluents had only slight acute toxicity to D. magna (0.80 TU). The inhibition of growth of L.minor was detected only in untreated wastewater: EC50 for growth rate was 63.4% WW, for biomass – 52.3% WW. The measured endpoints in terrestrial plants test were seed germination, root length, shoot height and total biomass, but only root length was sensitive one. Untreated and biologically treated effluents inhibited the growth of L.sativa roots by 70 % and EC50 was equalled to be 47.2% WW and 61.1 % WW, respectively. The growth of shoots and total biomass were stimulated due to exposure to effluents; stimulation effect was determined by sufficiently high concentrations of nutrients. The applied bioassays were ranked according to their sensitivity to the effluents as follows: D. magna > L. minor > L. sativa. The treatment of wastewater reduced average toxicity index by 11 times.