Phytotoxicities of selected chemicals and industrial effluents to Nitellopsis obtusa cells, assessed by using a rapid electrophysiological charophytetest

The acute phytotoxicities of seven heavy metals (Cd2+, Cu2+, Hg2+, Ni2+, Zn 2+, Cr6+ and Co2+), three phenolic compounds (phenol, 3,5-dichlorophenol an d pentachlorophenol) and nine industrial effluents were appraised by using a rapid electrophysiological test with cells of the charophyte, Nitellopsis obtusa. The EC50 values (concentrations causing a 50% decrease in resting potential) obtained for reference chemicals were compared with those of fiv e microbiotests (Polytox(R), Microtox(R), Selenastrum capricornutum growth inhibition, Daphnia magna immobilisation and Rotoxkit F(TM)) taken from the scientific literature. The 45-minute charophyte test, the freshwater Algal toxkit F(TM), Daphtoxkit F(TM) and Rotoxkit F(TM) were conducted simultaneo usly to assess the toxicities of effluents. The Toxkit microbiotests were t ypically two orders of magnitude more sensitive than the electrophysiologic al charophyte test to pure chemicals. The electrophysiological charophyte t est was generally more sensitive than the Toxkit microbiotests to complex e ffluents. The rapid electrophysiological test, employing the 45-minute memb rane depolarisation of N. obtusa cells as an endpoint, demonstrated similar sensitivity to heavy metals and phenolic compounds as the 20-minute bacter ial Polytox(R) test, but less sensitivity than the 15-minute Microtox(R) te st. Therefore, this rapid macroalgal test appears to be valuable as a suble thal toxicity screening tool for effluents.