Absorption, disposition and metabolism of di-isononyl phthalate (DINP) in F-344 rats

Di-isononyl phthalate (DINP; CAS no. 68515-48-0) is a general-purpose plasticizer for polyvinyl chloride. It produced liver and kidney effects when given to rodents at high oral doses, but there were no target organ effects in primates treated under similar conditions. To assist in understanding the basis for these species differences, the pharmacokinetic properties of DINP were evaluated in rodents following both oral and dermal administration. These studies demonstrated that the pharmacokinetic properties of DINP are similar to those of other high-molecular-weight phthalates. When orally administered to rodents, DINP is rapidly metabolized in the gastrointestinal tract to the corresponding monoester, absorbed and excreted, primarily in the urine. Shortly after administration, DINP is found primarily in liver and kidneys, but it does not persist or accumulate in any organ or tissue. It is very poorly absorbed from the skin, but once absorbed it behaves in the same way as the orally administered material. The results of these rodent studies contrast with data from studies involving humans or other primates, which indicate low absorption at low oral doses and much more limited total absorption at high doses. It appears that many, if not all, of the effects of DINP in rodent studies are associated with internal doses that would be difficult, if not impossible, to achieve in humans under any circumstances. Thus, the results of rodent studies may not be very useful in assessing the potential risks to humans from high-molecular-weight phthalates.