STRUCTURE-ACTIVITY-RELATIONSHIPS OF CHLOROBENZENES USING DNA MEASUREMENT AS A TOXICITY PARAMETER IN ALGAE

This study investigated the effects of chlorobenzenes on the diatom Cyclotella meneghiniana using DNA measurement as a toxicity parameter and related toxicity to different physicochemical properties of chlorobenzenes. The organisms were exposed to chlorobenzene solutions for 48 h to obtain effective concentration (EC50) values (in terms of percent DNA reduction). The toxicity (EC50) increased with increasing degree of chlorination, as follows: monochlorobenzene (235.74 mg/L), dichlorobenzenes (23.33-51.88 mg/L), trichlorobenzenes (0.59-6.42 mg/L), tetrachlorobenzenes (0.27-1.39 mg/L), pentachlorobenzene (0.008 mg/L) and hexachlorobenzene (0.002) mg/L). Quantitative structure-activity relationships were developed showing high correlations, as follows: water solubility (r2 = 0.96); molecular volume (r2 = 0.92); zero-order connectivity index (r2 = 0.92); second-order connectivity index (r2 = 0.92); molecular surface area (r2 = 0.92); octanol/water partition coefficient (r2 = 0.86); bioconcentration factor (r2 = 0.86); and inorganic/organic character (r2 = 0.83). A poor correlation, however, was obtained with the molecular negentropy index (r2 = 0.25). The toxic effect (EC50) was explained in terms of a partitioning process as a function of the aqueous solubility of the chlorobenzenes and was found to occur at similar degrees of exposure saturation.