Rapid assessment of pesticide toxicity in aquatic ecosystems using deep learning-based automatic duckweed counting method.

Pesticides are widely used in agriculture to control weeds, insects, and diseases that threaten crop yields. However, their extensive use raises concerns about environmental impacts, particularly in aquatic ecosystems, which are vulnerable to contamination through runoff and leaching. To assess the toxicity of pesticides to aquatic plants, we applied an optimized automated duckweed (Wolffia globosa) frond-counting tool based on the StarDist technique. Using this method, we tested twenty-eight commonly used pesticides, including herbicides, fungicides, and insecticides effects on duckweed growth. The herbicide paraquat showed the strongest growth inhibition (IC50 < 10 ppb), followed by diuron (IC50 = 384.2 ppb). Simazine and pendimethalin exhibited moderate toxicity, while glyphosate, triclopyr, and glufosinate showed lower toxicity. Surprisingly, metamifop did not inhibit duckweed growth up to the highest tested concentration (106 ppb). Isoprothiolane was the only fungicide tested that exhibited significant toxic effects on duckweed (IC50 ≈ 924.3 ppb). All others, including azoxystrobin, hexaconazole, difenoconazole, picoxystrobin, tebuconazole, and cyproconazole, only inhibited plant growth at unnaturally high concentrations. Interestingly, cyazofamid promoted duckweed growth under the test conditions. Among 12 insecticides tested, 8 exhibited relatively low toxicity to duckweed (IC50 > 105 ppb). Cypermethrin, carbofuran, fenpropathrin, and nitenpyram showed very low toxicity, with IC50 values exceeding 106 ppb. Our results both enhance understanding of agrochemical toxicity and demonstrate the utility of automated, high-throughput quantification of W. globosa growth, providing a rapid and effective approach for pesticide toxicity assessment in aquatic environments.