title: PBPK-Based Probabilistic Risk Assessment for Total Chlorotriazines in Drinking Water.
abstract: The risk of human exposure to total chlorotriazines (TCT) in drinking water was evaluated using a physiologically based pharmacokinetic (PBPK) model. Daily TCT (atrazine, deethylatrazine, deisopropylatrazine, and diaminochlorotriazine) chemographs were constructed for 17 frequently monitored community water systems (CWSs) using linear interpolation and Krieg estimates between observed TCT values. Synthetic chemographs were created using a conservative bias factor of 3 to generate intervening peaks between measured values. Drinking water consumption records from 24-h diaries were used to calculate daily exposure. Plasma TCT concentrations were updated every 30 minutes using the PBPK model output for each simulated calendar year from 2006 to 2010. Margins of exposure (MOEs) were calculated (MOE = [Human Plasma TCTPOD] ÷ [Human Plasma TCTEXP]) based on the toxicological point of departure (POD) and the drinking water-derived exposure to TCT. MOEs were determined based on 1, 2, 3, 4, 7, 14, 28, or 90 days of rolling average exposures and plasma TCT Cmax, or the area under the curve (AUC). Distributions of MOE were determined and the 99.9th percentile was used for risk assessment. MOEs for all 17 CWSs were >1000 at the 99.9(th)percentile. The 99.9(th)percentile of the MOE distribution was 2.8-fold less when the 3-fold synthetic chemograph bias factor was used. MOEs were insensitive to interpolation method, the consumer's age, the water consumption database used and the duration of time over which the rolling average plasma TCT was calculated, for up to 90 days. MOEs were sensitive to factors that modified the toxicological, or hyphenated appropriately no-observed-effects level (NOEL), including rat strain, endpoint used, method of calculating the NOEL, and the pharmacokinetics of elimination, as well as the magnitude of exposure (CWS, calendar year, and use of bias factors).
authors.affiliation: *Syngenta Crop Protection, LLC, Greensboro, North Carolina, 27419-8300; charles.breckenridge@syngenta.com.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Breckenridge
authors.affiliation: The Hamner Institutes for Health Sciences, 6 Davis Drive, Research Triangle Park, North Carolina, 27709;
authors.forename: Jerry L
authors.initials: JL
authors.lastname: Campbell
authors.affiliation: The Hamner Institutes for Health Sciences, 6 Davis Drive, Research Triangle Park, North Carolina, 27709;
authors.forename: Harvey J
authors.initials: HJ
authors.lastname: Clewell
authors.affiliation: The Hamner Institutes for Health Sciences, 6 Davis Drive, Research Triangle Park, North Carolina, 27709;
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Andersen
authors.affiliation: 3131 Texas A&M University, College Station, Texas, 77843-3131;
authors.forename: Ciriaco
authors.initials: C
authors.lastname: Valdez-Flores
authors.affiliation: Sielken and Associates Consulting Inc, 1200 Beacon Court, College Station, Texas, 77845.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Sielken
mesh_terms: D001280:Atrazine / Q000032:analysis / Q000097:blood / Q000493:pharmacokinetics* / Q000633:toxicity; D060766:Drinking Water / Q000737:chemistry* / Q000592:standards; D004784:Environmental Monitoring / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D008954:Models, Biological; D011336:Probability; D018570:Risk Assessment; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000097:blood / Q000493:pharmacokinetics* / Q000633:toxicity
chemical_list: D060766:Drinking Water; D014874:Water Pollutants, Chemical; D001280:Atrazine
keywords: PBPK model; Safe Drinking Water Act; atrazine; atrazine monitoring program; chlorotriazines; drinking water; pharmacokinetics; probabilistic risk assessment; sensitivity analysis.