Long-term fate of organochlorine xenobiotics in aquatic ecosystems. Distribution, residual behavior, and metabolism of hexachlorobenzene, pentachloronitrobenzene, and 4-chloroaniline in small experimental ponds.

Hexachlorobenzene (HCB), pentachloronitrobenzene (PCNB), and 4-chloroaniline (4-CA) were dosed into the water of small experimental ponds in Southern Germany. The average concentration of the chemicals in the pond water during the application period (4-6 weeks) was about 50 micrograms/liter. Chemical residue concentrations were determined in water, sediment, and flora and fauna species up to 166 weeks after application. The decrease of all chemicals in the water phase follows exponential functions and can be correlated to some extent with the physicochemical properties such as volatility from water and vapor pressure. Although chemically quite different, the residual behavior of the model compounds followed a similar pattern resulting in relatively high initial concentrations in biota and a slow buildup and subsequent decline of concentrations in the sediment. As to some fauna species (backswimmers and libellula larvae) and to sediment (0- to 20-cm layers), even 3 years after application, 14C residues of about 0.1 mg/kg could be found. In all analyzed flora species, however, no more residues could be measured in the new vegetation period after application. The amounts of the chemicals used did not cause detectable symptoms of poisoning over the investigation period. Anisols and azo compounds were found to be conversion products of pentachloronitrobenzene and 4-chloroaniline.