The effects on Chlorella sp. and Phaeodactylum tricornutum of two indu
strial wastewaters known to contain the herbicide residues of Triflura
lin and Propanil have been determined by monitoring the number of cell
s, the chlorophyll fluorescence and the carbon dioxide assimilation si
multaneously for a period of 14 days. The growth of the diatom, Phaeod
actylum tricornutum, was inhibited by concentrations of herbicidal was
te of the order of 0.1-0.5%, apparently because the rate of reproducti
on was reduced. Chlorella sp. cells, on the other hand, whilst dramati
cally inhibited by 1% concentrations of herbicidal waste, were able to
recover over a period of 14 days. If discharged at concentrations bel
ow 0.01%, the industrial wastes appeared not to affect phytoplankton.