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Toxicity assessment of herbicides of two different modes of
action by a closed-system algal test
StudentYu-Sheng Lin AdviserChung-Yuan Chen
Institute of Environmental Engineering National Chiao Tung Unversity
ABSTRACT
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 ( DO), 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 DO 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.
