An inhalation distribution model for the lactating mother and nursing child.

A rule-of-thumb methodology is presented to assist in assessing risk to a nursing child due to the mother's occupational inhalation exposure. The method represents an example of the use of physiologically based pharmacokinetic modeling using state-of-the-art computational techniques. A computer model is developed to describe distribution of non-metabolized, inhaled contaminants into a mother/child system as a function of the contaminant's blood:air and octanol:water partition coefficients. Risk is assessed in terms of the area under the blood concentration vs. time curve of the exposure chemical. Since low partition values yield low risk for the nursing child and high values yield high risk, the model is exercised over a range of intermediate values (blood:air = [2,25]; octanol:water = [100, 1500]). Results are thus applicable to chemicals for which the mother's dose is a strong factor in estimating the child's risk. The most notable observation is that, for the range of partition values used, this model never predicts a risk for the child greater than 25% of that of the mother. An equation is provided (based on model results) that expresses the child's risk as a fraction of the mother's risk.