Bengt-Erik Bengtsson, Juvy P. Bongo, Britta Eklund
The tropical duckweed Lemna aequinoctialis Welwitsch (Lemnaceae) was collected in Thailand and the Philippines, so that an efficient toxicological bioassay for tropical environments could be developed. Optimal conditions required for conducting ecotoxicological growth tests were investigated and the resulting test manual was used to test the effects of heavy metals (Cd2+, Cr6+, Cu2+, Hg2+, Zn2+), ClO3-, 3,5-dichlorophenol and phenol on the growth of the two strains of duckweed. The effect on growth was measured as 96-hr EC50 for biomass production and the number of fronds (leaf-like process) produced. The sensitivity of the two duckweed strains to the tested compounds was quite similar. Cd2+, Cu2+ and Hg2 demonstrated the highest toxicity, ClO3- and phenol the lowest toxicity, while Cr6+ and Zn2+ demonstrated intermediate toxicity.
Inst. of Appl. Environ. Research, Stockholm University, Lab. for Aquatic Environ. Chemistry, S-106 91 Stockholm, Sweden; Biology Department, University of San Carlos, Cebu City 6000, P. del Rosario St., Philippines
