Effects of 3-chlorobiphenyl on photosynthetic oxygen production, glutathione content and detoxication enzymes in the aquatic macrophyte Ceratophyllum demersum

Organic contaminants of environmental concern such as polychlorinated biphenyls have dispersed widely throughout the ecosystems and accumulate in living organisms, and a variety of adverse biological effects have been reported. In this study, we investigated the effects of 3-chlorobiphenyl in the aquatic macrophyte Ceratophyllum demersum and the capacity of its detoxication system. After 24 h of exposure to various concentrations of 3-chlorobiphenyl, the total glutathione content (tGSH) was determined and the dose-response curves for glutathione reductase (GR) and microsomal/cytosolic glutathione S-transferases (m- and c-GSTs, respectively) were established. C. demersum showed a decrease of photosynthesis after exposure to 3-chlorobiphenyl, although only significantly at 5 μg l−1. At 0.005 and 0.05 μg l−1 the GR, m-GST and c-GST activities were significantly increased and concomitantly a non-significant effect on total GSH was observed. At 0.5 μg l−1, GR as well as c-GST were still significantly induced, while at 5 μg l−1 none of the enzymes were activated. These results show that detoxication through glutathione conjugation takes place at low concentrations of 3-chlorobiphenyl, while concentrations in the order of parts per billion cause the inactivation of the enzymatic systems evaluated, enough to place C. demersum in an important physiological stress condition.