Keywords: 
• herbicides /
• green algae /
• algal growth inhibition /
• toxic effect /
• mechanism action /
• chemical structure

Abstract: The impacts of pesticides on primary producers (i.e., algae) have raised global concerns. However, the toxic effects of herbicides on algae have been hypothesized to be much severe than those of insecticides and fungicides. To verify this hypothesis, this paper selected 36-brands herbicides to document their uses in China for crops of dry and paddy farmlands, and to investigate their effects on algae growth. The results showed that: 1) the effects of the herbicides on algae growth were dependent on their functional mechanisms and chemical composites; the herbicides that inhibit plant cell division and are applied on plant leaves were found to be more toxic that the herbicides that are made of artificially synthetic plant growth hormone; 2) for a given functional mechanism, the herbicides with difference chemical composites had different-level toxicities on green algae. The herbicides were less toxic on the paddy farmlands (e.g., rice) than the dry farmlands (e.g., wheat and corn). The results can be the important scientific information for better use of pesticides/herbicides, evaluation of their ecological effects, and protection of freshwater environment.