| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 95 === In aquatic ecosystems, algae population plays a important role as a primary producer. Once surface waters are contaminated by chemicals, like herbicides, often cause negative effects to algae populations. The major objective of this study is to assess the toxicity of herbicides to algae (Pseudokirchneriella subcapitata) by close-system algal toxicity tests.
Twenty herbicides were divided in two groups based on their modes of action (ACCase and ALS inhibition) by Herbicide Resistance Action Committee (HRAC). The toxicity tests were conducted with an exposure period of 48 hours. Three response endpoints were considered: production of dissolved oxygen (ΔDO), final yield, and growth rate.
Results indicate that cyclosulfamuron is the most toxic herbicide and clodinafop-propargyl is the least one. According to EC50 values, cyclosulfamuron demonstrated a much higher toxicity than clodinafop-propargyl by more than 1,000-fold. Among the three response endpoints, ACCase inhibitors are more sensitive to ΔDO and ALS inhibitors are more sensitive to final yield. On the other hand, growth rate is always the least sensitive endpoint.
Comparison between algae and other aquatic species shows that L. gibba is more suitable for assessing the toxicity of the two groups of herbicides. However, the application of our close-system BOD bottle tests offers a variety of benefits including savings of cost and time.
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