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A Statistical Approach for Judging Stability of Whole Mixture Chemical Composition over Time for Highly Complex Disinfection By-Product Mixtures from EPA's Four Lab Study
Citation:
TEUSCHLER, L. K., L. S. Aume, G. E. RICE, J. E. SIMMONS, J. G. PRESSMAN, M. G. NAROTSKY, T. F. SPETH, R. J. MILTNER, E. S. HUNTER, A. McDonald, J. Craft, P. I. Feder, A. Fristachi, S. Parvez, AND S. D. Richardson. A Statistical Approach for Judging Stability of Whole Mixture Chemical Composition over Time for Highly Complex Disinfection By-Product Mixtures from EPA's Four Lab Study. Presented at Society for Risk Analysis 2011 Annual Meeting, Charleston, SC, December 04 - 07, 2011.
Impact/Purpose:
To inform the public.
Description:
Chemical characterization of complex mixtures and assessment of stability over time of the characterized chemicals is crucial both to characterize exposure and to use data from one mixture as a surrogate for other similar mixtures. The chemical composition of test mixtures can vary due to natural variations of the collected environmental mixture, concentration procedures, preparation of the mixture for testing, and chemical reactions during storage; these variations can affect toxicity. This presentation describes a statistical approach for evaluating chemical stability of highly complex disinfection by-product (DBP) mixtures resulting from disinfection of water concentrates used in EPA’s Four Lab multigenerational rodent bioassay. Complex DBP mixtures were produced by concentrating natural source water with reverse osmosis membranes, storing the concentrate in 16 drums, and chlorinating the concentrate prior to placement on animal cages. At time intervals dictated by water demand, concentrate was chlorinated. Chemical analyses were conducted for each chlorination event; concentrate was sampled prior to use (day 0), at various time periods from arbitrarily selected cages, and upon removal from cages. Mixed linear models were used to evaluate stability of 44 individual DBPs, total organic halide (TOX), and 18 DBP mixture subgroups across and within drums, and over time. Three hypothesis tests evaluated whether: average chemical concentrations were stable across drums over time; concentrations were stable within drums over time; and chlorination events were reproducible across drums on day 0. A judgment of instability required a >20% change in chemical concentrations from Day 0 to Day 14 or a >20% coefficient of variation on Day 0. Results showed a high degree of stability and reproducibility for 32 single DBPs, TOX, and 11 DBP mixture subgroups, including the halomethane, haloacid, and haloaldehyde chemical classes.