Evaluating sufficient similarity for drinking-water disinfection by-product (DBP) mixtures with bootstrap hypothesis test procedures.

In chemical mixtures risk assessment, the use of dose-response data developed for one mixture to estimate risk posed by a second mixture depends on whether the two mixtures are sufficiently similar. While evaluations of similarity may be made using qualitative judgments, this article uses nonparametric statistical methods based on the "bootstrap" resampling technique to address the question of similarity among mixtures of chemical disinfectant by-products (DBP) in drinking water. The bootstrap resampling technique is a general-purpose, computer-intensive approach to statistical inference that substitutes empirical sampling for theoretically based parametric mathematical modeling.

Chemical measures of similarity among disinfection by-product mixtures.

There are few measures that can be used to distinguish among mixtures of disinfection by-products (DBPs) produced in the chlorination or chloramination of drinking water. Objective measures of similarities among DBP mixtures would greatly simplify judgments about the risk that may be associated with exposure to DBPs in a given water supply. Major by-products of chlorination/chloramination include the trihalomethanes (THMs) and haloacetic acids (HAAs), which are routinely measured for compliance to regulations.

Evaluating sufficient similarity for disinfection by-product (DBP) mixtures: multivariate statistical procedures.

For evaluation of the adverse health effects associated with exposures to complex chemical mixtures in the environment, the U.S. Environmental Protection Agency (EPA) (2000) states, "if no data are available on the mixture of concern, but health effects data are available on a similar mixture .