In this report the first results of a study on the effect of compound-specific and environment-specific factors on rates of reductive dehalogenation, are shown. The study was carried out to assess the extend to which it is possible to extrapolate rate constants obtained under laboratory conditions to realistic circumstances. Several chlorophenol congeners were incubated in sediment-water systems, while varying seven distinct conditions. Measured half-lives tended to increase with increasing concentrations of the compound incubated, decreasing sediment concentrations, decreasing temperature and both increasing and decreasing pH-values of the sediment. 3,4-Dichlorophenol was shown to be the most persistent of the chlorophenol congeners incubated, while the trichlorophenols were the most easily dechlorinated. It is recommended to further investigate the factors given above and also to include additional chemicals.