Effects of 2,4-Dichlorophenol on the Net-Spinning Behavior of Hydropsyche slossonae Larvae (Trichoptera; Hydropsychidae), an Early Warning Signal of Chronic Toxicity

In order to assess the potential of hydropsychid capture net anomalies as a bioindicator of chronic toxicity in streams and rivers, the effects of 2,4-dichlorophenol (2,4-DCP) exposure on the net-spinning behavior of Hydropsyche slossonae were examined for anomalies after 0, 5, 10, 15, and 20 exposure days to gradient concentration of 2,4-dichlorophenol. The net-spinning behavior was significantly affected when larvae were exposed to 1.0, 10, 25, and 50 μg·L−1, as expressed by the occurrence of two distinct abnormalities. The first one was a distortion of the midline meshes, where the normal diamond-shape structure is disrupted and the meshes are separated by extra strands (called “midline” anomaly). The second aberration observed was called “chaotic” net, where the nets are highly irregular without any real structure or well-defined areas. A good correlation was found between the chaotic net frequencies and the reduction of ATP concentrations in the larvae, indicating possible uncoupling effects of 2,4-DCP on the oxidative phosphorylation process. Toxicity curves demonstrate that the sensitivity threshold of chaotic net frequencies ranged from 3.5 to 7 μg·L−1, which is highly sensitive compared with other sublethal effects of 2,4-DCP on other aquatic species.