A<i>Chlamydomonas</i>Algal Bioassay for Detecting Growth Inhibitor Herbicides

Abstract

The single-celled green alga Chlamydomonas eugametos was found to be well suited for detecting growth inhibitor activity of chemicals. Tests consisted of solubilizing technical grade compounds in 20-ml aliquots of a 1 × 10 5 cells/ml zoospore culture. Commercially available growth inhibitor herbicides significantly inhibited synchronous cell population increases within 48 h at concentrations ranging from 1 × 10 −4 to 1 × 10 −7 M. Examples of compounds that inhibited Chlamydomonas more than 50% were butylate ( S -ethyl diisobutylthiocarbamate) and diallate [ S -(2,3-dichloroallyl)diisopropylthiocarbamate] at 1 × 10 −4 M, CDEC [2 chloroallyl diethyldithiocarbamate] and propham (isopropyl carbanilate) at 1 × 10 −5 M, alachlor [2-chloro-2′,6′-diethyl- N -(methoxymethyl)acetanilide] and trifluralin [α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine] at 1 × 10 −6 M, and bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate] at 1 × 10 −7 M. Ethanol, dimethylsulfoxide (DMSO), or acetone can be used to solubilize herbicides in the aqueous medium. DMSO and ethanol are not detrimental to the cells if the concentration is kept at 1% v/v or less.