Ecological health assessments based on whole effluent toxicity tests and the index of biological integrity in temperate streams influenced by wastewater treatment plant effluents

Abstract

Whole effluent toxicity (WET) tests and ecosystem health assessments, based on test guidelines of U.S. Environmental Protection Agency (U.S. EPA) and index of biological integrity (IBI), were conducted on various streams located in Youngsan River watershed, Korea. The WET tests showed that about 33 and 82% of wastewater treatment plants (WWTPs) exhibited significant toxicity to Daphnia magna and Selenastrum capricornutum, respectively. Small WWTPs with low discharge volumes contributed less than 1% to the total stream toxicity. Fish community compositions and trophic guild analysis showed that the diversity index was greater in the control than in impacted streams, and the proportion of omnivore species was less in the control. Also, ecosystem health assessments, based on the IBI, showed distinct differences between the control and impacted sites of WWTPs. Model values of the IBI, based on 12 stream data sets, averaged 28, which is judged as a fair to poor condition according to the U.S. EPA criteria. The mean IBI in the control sites was 42, indicating good stream condition, whereas the impacted sites was scored 21, indicating poor condition. Overall, WET tests and ecosystem health assessments suggested the WWTP effluents had evident toxic effects on the biota, and impacted the species compositions and trophic guilds, resulting in degradation of the stream ecosystem health.