Based on the fact that EDTA complexes free metal ions, a method combin
ing algal assays, electron microscopy and EDX-ray microanalysis was de
veloped to determine total and metal toxicity in full strength effluen
t water. By adding a sufficient amount of EDTA into a test water to bi
nd the free metal ions, metal and 'organic' toxicities could be differ
entiated in assays, as observed from tests with two industrial wastewa
ters and a solution containing a mixture of Cu, Zn and Hyamine. Metal
toxicity could be verified by the presence of free metal ions in the w
ater and by excess metals in the polyphosphate bodies of affected alga
l cells where altered chloroplasts were observed, Damage to the thylak
oidal membranes in the chloroplast was characteristic of metal toxicit
y in Chlorella cells.