Halogen Substitution Patterns among Disinfection Byproducts in the Information Collection Rule Database

Disinfection byproduct halogen substitution patterns were examined using Information Collection Rule data. A new metric was developed to quantify and compare extents of specific halogen substitution in different byproduct classes. Bromine substitution in four byproduct classes ranged widely across 6565 samples but strong interdependencies existed between classes on an individual sample basis. Bromine substitution in dihaloacetic acids and trihalomethanes was comparable whereas bromine substitution in trihaloacetic acids and dihaloacetonitriles tended to be 10% lower and 60% higher than in trihalomethanes, respectively. However, these bromine substitution measurements were significantly impacted by censored data handling because reporting limit left-censoring increased with the number of bromine substituents in each class and minimum reporting levels varied between and within classes. Correlation among extents of bromine substitution in the four byproduct classes examined motivated their treatment as a multivariate response with application of a test for multivariate outliers. The test was effective at exposing inconsistencies indicative of data entry or analytical error. This work shows that disinfection byproduct data with full homologue series for multiple compound classes contain redundant information in the form of expected interdependencies among species. Application to quality assurance is demonstrated in this paper. Further applications to modeling and monitoring design are anticipated.