Several pollutants found in water inhibit the photosynthetic electron transport chain, and therefore affect the growth of phytoplankton and aquatic plants. In this study, thylakoid membranes isolated from spinach leaves were used in a microelectro‐chemical cell to generate photocurrent. The toxic effect of an inhibitor is observed by a decrease in the photocurrent. To improve the stability of their biological functions, the thylakoid membranes were immobilized in an albumin–glutaraldehyde cross‐linked matrix. The developmental work of this phytotoxicity test was done by using the herbicide atrazine as the reference toxicant. Results on reproducibility were in the range generally accepted for standardized bioassays. The phytotoxicity of herbicides from various chemical classes including photosynthetic and nonphotosynthetic inhibitors was evaluated. Toxicity responses of the immobilized thylakoid test to photosynthetic inhibitors compared favorably with literature data for the algal growth inhibition test using Selen‐astrum capricornutum. The detection capabilities of the photosynthetic microassay for cyanazine, metribuzin, diuron, and propanil met the recommandation for the water quality guidelines for raw water. Characteristics of this in vitro approach such as rapidity, experimental simplicity, and cost effectiveness are also discussed.

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