Phytotoxicities of Selected Chemicals and Industrial Effluents to Nitellopsis obtusa Cells,Assessed by Using a Rapid Electrophysiological Charophyte Test

Abstract

The acute phytotoxicities of seven heavy metals (Cd²⁺, Cu²⁺, Hg²⁺, Ni²⁺, Zn²⁺, Cr⁶⁺ and Co²⁺), three phenolic compounds (phenol, 3,5-dichlorophenol and 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 five microbiotests (Polytox®, Microtox®, Selenastrum capricornutum growth inhibition, Daphnia magna immobilisation and Rotoxkit F^™) taken from the scientific literature. The 45-minute charophyte test, the freshwater Algaltoxkit F^™, Daphtoxkit F^™ and Rotoxkit F^™ were conducted simultaneously to assess the toxicities of effluents. The Toxkit microbiotests were typically two orders of magnitude more sensitive than the electrophysiological charophyte test to pure chemicals. The electrophysiological charophyte test was generally more sensitive than the Toxkit microbiotests to complex effluents. The rapid electrophysiological test, employing the 45-minute membrane depolarisation of N. obtusa cells as an endpoint, demonstrated similar sensitivity to heavy metals and phenolic compounds as the 20-minute bacterial Polytox® test, but less sensitivity than the 15-minute Microtox® test. Therefore, this rapid macroalgal test appears to be valuable as a sublethal toxicity screening tool for effluents.