Perturbation of lipid membranes by organic pollutants

The ability of a range of organic pollutants--hexachlorobenzene, mirex(1,1a,2,2,3,3a,4,5,5,5a,5b,6-dodecachlorooctahydro-1,3,4-metheno-1H cyclobuta(cd) pentalene), 1,3,5-trichlorobenzene, 2,4,6-trichlorophenol, p-nitrophenol, p-chlorophenol, DDT, and pentachlorophenol--to perturb liposomes of dipalmitoyl phosphatidylcholine (DPPC) has been measured by differential scanning calorimetry. The degree of perturbation was measured by the increase in breadth of the main DPPC phase transition in both heating and cooling scans. DDT and the phenol derivatives were effective perturbers of phospholipid, broadening the transition by as much as 12-fold. Hexachlorobenzene and mirex did not perturb at all when mixed with DPPC at concentrations as high as 20 mol%, although 1,3,5-trichlorobenzene caused slight broadening of the main transition at this concentration. Perturbation is facilitated by the presence of a hydroxyl group on the benzene ring and hindered by increasing degrees of chloride substitution. An apparent correlation exists between the extent of phospholipid perturbation measured by differential scanning calorimetry and LD50 values for these compounds taken from the literature. This suggests the possibility of formulating an "index of perturbation" which could be used to screen certain classes of organic compounds for potential biological toxicity on a routine basis.