Relative half lives of chloranil and dichlone in different tropical milieux

Abstract Chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) and dichlone (2,3-dichloro-1,4-naphthoquinone), organic fungicides widely used as seed dressings in Nigeria, were investigated to assess persistence in four tropical ecosystems. Sterile and non-sterile samples of sewage water, fresh water, agricultural soil and sea water were incubated with 50 μml −1 of each of the fungicides under glasshouse conditions. Colorimetric assays and TLC analyses were used to determine residual proportions at appropriate intervals. Chloranil disappeared in sewage water, fresh water and agricultural soil after 28, 28 and 41 days of incubation respectively, while traces of the fungicide were still present after 8 months' incubation in sea water. The disappearance of both pesticides in the samples seems to be supported by biotic factors but chemical degradation is not precluded.