Chlorinated benzo-1,2-quinones: an example of chemical transformation of toxicants during tests with aquatic organisms.

An analytical procedure specific for chlorinated benzo-1,2-quinones has been developed to examine the stability of these compounds under conditions used for investigating their toxicity to aquatic organisms. Solutions of the compounds in a number of organic solvents were unstable in the light, and addition of acetone solutions to water brought about rapid decomposition of the chloroquinones which had half-lives less than 0.5 hr: the corresponding chlorocatechols were the principal products. The kinetics of decomposition of tetrachlorobenzo-1,2-quinone in aqueous solutions were studied in detail and showed the formation of tetrachlorocatechol, 2,5-dichloro-3,6-dihydroxybenzo-1,4-quinone, 1,2,3-trihydroxy-4,5,6-trichlorobenzene, 1,2,4-trihydroxy-3,5,6-trichlorobenzene, dichloromaleic acid, and a trichlorocyclopentendione. In organic solvents in the light, 3,4,5-trichlorobenzo-1,2-quinone underwent a dismutation reaction with formation of 3,4,5-trichloro- and tetrachlorocatechol; in a comparable reaction, 4,5-dichlorobenzo-1,2-quinone formed 4,5-dichlorocatechol and 3,4,5-trichlorocatechol. The toxicity of aqueous solutions prepared by dilution of freshly prepared acetone solutions of tetrachlorobenzo-1,2-quinone was examined in the zebra fish embryo/larvae test, and it was found that the threshold toxic concentration could be accounted for entirely by the analytically established concentration of tetrachlorocatechol produced as a chemical transformation product. It is concluded that in toxicological examination of reactive compounds, exposure to the toxicant should be assessed from concentrations analytically determined during the experiments and that attention be directed to both the nature and the toxicity of the transformation products.