A Breast Milk Pathway Model for Nonlipophilic Compounds. Jeff Swartout, NCEA-Cin, U.S. EPA, 26 W. M.L. King (MS-190), Cincinnati, OH 45268
The U.S. EPA is revising its Multiple Pathway Exposure Model (MPEM; formerly the Indirect Exposure Model) for predicting human exposures to contaminants in combustor emissions. The MPEM includes exposure to nursing infants from consumption of breast milk. The breast milk pathway model (BMPM) is designed to predict the concentration of contaminants in breast milk following uptake by lactating women. Published breast milk pathway models address lipophilic compounds only. A simple pharmacokinetic model is proposed here for predicting the concentration of nonlipophilic compounds in the aqueous phase of breast milk (BMPMaq). The performance of the model is tested, in part, with data from methylmercury (MeHg) ingestion. The form of the BMPMaq is a modification of the Smith (1987) model for predicting milk fat concentrations of ingested lipophilic compounds. The fundamental assumption of the BMPMaq is that the concentration of contaminant in the aqueous phase of breast milk (Caq) is proportional to the concentration of the contaminant in plasma. The mathematical form of the BMPMaq is given as: Caq = (DI x Fp x PCpm) (Ke x Fpm), where DI = daily contaminant intake (mg/kg-day), Fp = fraction of contaminant in plasma, PCpm = Caq:Cplasma ratio, Ke = biological elimination constant (per day) and Fpm = plasma weight/body weight. When contaminant concentrations are given only on a whole blood basis, Fp must be estimated with consideration of the RBC:plasma concentration ratio. Data are available for estimating Fp, PCpm and Ke for Hg species following ingestion of MeHg. The BMPMaq predicts pathway models address lipophilic compounds only. A simple pharmacokinetic model is proposed here for predicting the concentration of nonlipophilic compounds in the aqueous phase of breast milk (BMPMaq). The performance of the model is tested, in part, with data from methylmercury (MeHg) ingestion. The form of the BMPMaq is a modification of the Smith (1987) model for predicting milk fat concentrations of ingested lipophilic . . . . . . [RiskWorld Note: Submitted abstract incomplete]