Possible Effects of Pesticide Washout on Microalgae Growth

Aquatic ecosystems are threatened by various anthropogenic activities, including those exacerbated by pesticides leaching from agricultural lands. Although legislation and regulations regarding pesticides aim to eliminate the risk of eutrophication and pollution, only a few studies have examined the impact of these substances on non-target organisms, such as microalgae, which are highly involved in biogeochemical cycles and critical for ecosystem integrity. We studied the effect of the agricultural insecticide Teppeki based on flonicamid, the fungicide Ortiva with azoxystrobin, and the herbicide Basar with (S)-metolachlor on the green microalga Chlorella vulgaris and the cyanobacterium Synechococcus leopoliensis. Ortiva and Basar were more toxic at lower doses than Teppeki, with (S)-metolachlor demonstrating the most instantaneous and potent inhibition. Half maximum effective concentration (EC50) values confirmed the strong inhibitory effect of the herbicide on both strains on days 3 and 8, and highlight the differing temporal responses, especially for Ortiva. This observed pattern of toxicity is consistent with pulse-amplitude-modulated fluorescence measurements of photosystem II, which indicate that both species are more sensitive to (S)-metolachlor and azoxystrobin than to flonicamid. We claim that the side effects of pesticides on non-target organisms must be given more attention. It is well established that herbicides can impair photosynthetic organisms such as microalgae, but pesticides targeting other pests can also cause adverse effects on these communities. Such unwanted side effects are directly related not only to the reduction of biodiversity, but also to human health.