Fate and effects of 4-chlorophenol and 2,4-dichlorophenol in marine plankton communities in experimental enclosures.

The fate and effects of 4-chlorophenol (4CP) and 2,4-dichlorophenol (DCP) added to North Sea coastal plankton communities enclosed by large plastic bags were studied in three experiments of 4 to 6 weeks duration. The biodegradation of the compounds was studied in laboratory experiments using water from the enclosed ecosystems. 4CP and DCP, added at initial concentrations of 0.1-1.0 mg X liter-1, disappeared from the water in the enclosures in 5 to 23 days, 4CP generally being the less persistent. Degradation rates were generally comparable to those found in laboratory tests with the same water. 4CP was removed by biodegradation, and DCP was probably removed by a combination of biodegradation, photodegradation, and/or chemical degradation. Results indicated that biodegradation rates could be limited by lack of inorganic nutrients, leading to much lower degradation rates than would be expected from routine laboratory tests. Faster degradation after repeated addition of 4CP showed adaption of the bacterial community. Addition of 0.3 mg liter-1 4CP or DCP inhibited the phytoplankton growth rate slightly. The 1 mg liter-1 4CP or DCP inhibited the phytoplankton, changed the species composition, and also influenced the zooplankton. In two of the three experiments 1 mg liter-1 DCP resulted in a temporary lowering of bacterial numbers following the addition. In one experiment inhibitory effects were found after 4CP and DCP had disappeared from the water, pointing to the formation of a more toxic intermediate during the degradation of these compounds. The laboratory tests also indicated the formation of relatively stable intermediates. The concentrations causing the effects in the different bag experiments were quite similar. This indicates that, although the development of the plankton communities during the different experiments was different, the concentrations resulting in ecological effects are quite reproducible.