Toxicity of unwanted intermediates and products formed during accidental thermal decomposition of chemicals.

The problem of the formation of unwanted substances that can occur during thermal decomposition of chemicals is studied from a toxicological point of view. Two species, ethyl parathion (a widely used pesticide) and cumene hydroperoxide (an intermediate for the industrial production of phenol and acetone), are selected for this investigation. The hazards associated to their accidental thermal decomposition are estimated on the basis of the (known) intermediates and products formed by means of a computational tool (ECOSAR programme) and assessed experimentally by means of algal bioassays. Green alga Pseudokirchneriella is used as target organism for all the toxicological assessments. The results of these tests on the samples collected during the thermal decomposition of the two studied species indicate that in the case of ethyl parathion the decomposition process gives rise to a mixture of compounds which are more toxic than the parent species. On the other hand, the decomposition of cumene hydroperoxide in cumene results into the formation of different species whose toxicity towards the adopted organism is lower than that shown by the starting compound. A procedure is proposed to ascertain when it is necessary or it is avoidable to carry out further investigations that involve the analytical resolution of mixtures resulting from the thermal decomposition process. This approach is suggested as a preliminary screening to identify the hazards associated with an accidental decomposition either of pure chemicals or of mixtures of compounds.