Incorporating New Exposure Model In Drinking Water Calculations Katherine Pelch, PhD April 24, 2019 CHE-Alaska
Calculating MCLs 1 2 3 Target Human Serum Level Dosimetric Adjustment Factor Animal serum level Volume of distribution Reference Dose X ÷ Ln(2) / human half-life Uncertainty factors 5 4 Exposure Estimates Maximum Relative source contribution Contaminant Level ÷ (MCL) Ingestion rate 2 @endo_exchange
Exposure Estimates Relative source contribution (RSC) Ingestion rate RSC Example RSCs Used • Proportion of the total daily exposure to a NJ NH chemical that is attributed to or allocated PFOA 0.2 0.4 to tap water PFOS 0.2 0.5 • US EPA guidance on RSC * : PFHxS na 0.5 • Use values between 20%-80% (0.2-0.8) PFNA 0.5 0.5 • Default to 20% if inadequate data *Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (2000) https://www.epa.gov/sites/production/files/2018-10/documents/methodology-wqc-protection-hh-2000.pdf 3 @endo_exchange
Exposure Estimates Relative source contribution (RSC) Ingestion rate Ingestion Rate Ingestion Rates Used • How much water is consumed on a per L/kg/day Based on: body weight basis non-pregnant, non-lactating NJ 0.029 • We consume different volumes of water at adult different life stages * NH 0.055 lactating woman • Infants and children drink more water on a VT 0.175 first year of life per body weight basis than adults based on combined direct and indirect water intake *U.S. EPA. Exposure Factors Handbook 2011 Edition (Final Report) https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=236252 4 @endo_exchange
These Exposure Estimates Are Inadequate For PFAS 1. Many PFAS are bioaccumlative 2. PFAS cross the placenta 3. PFAS are transferred to infants in breastmilk 4. Infants are particularly vulnerable • Highest exposure estimates on a per body weight basis • Susceptible to developmental programming 5 @endo_exchange
A New Exposure Model For PFAS MDH PFOA HBGV MDH PFOS HBGV MDH PFHxS HBGV 6 @endo_exchange
Two Exposure Scenarios • Infant consumes formula • BOTH MODELS: reconstituted with PFAS • PFAS crosses placenta –born contaminated water with existing body burden • Continues drinking PFAS • Infant exclusively breastfed contaminated water throughout for 6 months with life breastfeeding tapered to zero by 12 months 7 @endo_exchange
Using the Model INPUT OUTPUT 70 • Half life Serum Concentration (µg/L) 50% of the reference serum concentration 60 • Placental transfer ratio 50 Dependent on target • Breast milk transfer ratio human serum level 40 • Volume of distribution 30 20% of the reference serum concentration • Target human serum level 20 10 0 0 10 20 30 40 50 Age (years) 8 @endo_exchange
What Are The Predicted Serum Concentrations Over Time Given A Particular Drinking Water Concentration? 100 90 0.050 µg/L 80 (50 ppt) Serum Concentration (µg/L) 70 50% of reference serum concentration 60 0.040 µg/L 50 (40 ppt) 40 0.035 µg/L 30 20% of reference serum concentration (35 ppt) 20 10 0 0 10 20 30 40 50 Age (years) 9 @endo_exchange
Model Outputs Based on MDH Target Human Serum Level Formula-fed Infant Scenario PFOA Serum Concentration Breastfed Infant Scenario PFOA Serum Concentration at at Water Concentration 0.150 µg/L Water Concentration 0.035 µg/L 70 70 Serum Concentration (µg/L) Serum Concentration (µg/L) 50% of reference serum conc. 60 50% of reference serum conc. 60 50 50 40 40 30 20% of reference serum conc. 20% of reference serum conc. 30 20 20 10 10 0 0 0 10 20 30 40 50 0 10 20 30 40 50 Age (years) Age (years) The drinking water level suggested for formula-fed infants (150 ppt), would not have been protective for breastfed infants, so MDH set a health based guidance value of 35 ppt based on breastfed infants. MDH PFOA HBGV 10 @endo_exchange
Impacts of Exposure Assumptions in NHDES MCL Calculations Modeled Serum PFOA Concentrations Modeled Serum PFOS Concentrations 70 90 Serum Concentration (µg/L) Serum Concentration (µg/L) 70 ppt (NHDES proposed MCL) 80 60 38 ppt (NHDES proposed MCL) 70 50 60 40 50 50% 38 ppt (using model for breastfed infants) 40 30 10 ppt (using model for breastfed infants) 30 50% 20 20% 20 20% 10 10 0 0 0 10 20 30 40 50 0 10 20 30 40 50 Age (years) Age (years) >50% for 9 years >50% for 8.5 years 11 @endo_exchange
Impacts of Exposure Assumptions in NHDES MCL Calculations Modeled Serum PFHxS Concentrations Modeled Serum PFNA Concentrations 30 80 Serum Concentration (µg/L) Serum Concentration (µg/L) 70 23 ppt (NHDES proposed MCL) 85 ppt (NHDES proposed MCL) 25 60 20 50 50% 15 40 7 ppt (using model for breastfed infants) 30 50% 10 20 5 20% 20% 10 49 ppt (using model for breastfed infants) 0 0 0 10 20 30 40 50 0 10 20 30 40 50 Age (years) Age (years) >50% for 11.5 years >50% for 9.5 years 12 @endo_exchange
Conclusions • The new exposure model created by MN Dept. of Health more fully considers the • long half life of PFAS • ability to cross the placenta and pass through breastmilk. • The new model is protective of a vulnerable population – infants and children. • The model predicts that current MCLs proposed by NHDES will not protect children for the first 10 years of their life. 13 @endo_exchange
www.tedx.org Funding • Arkansas Community Foundation • Winslow Foundation • Cornell Douglas Foundation • Wallace Genetic Foundation • Forsythia Foundation • Marisla Foundation • Tides Foundation Carol Kwiatkowski Christina Ribbens Kim Schultz Executive Director Business Manager Oil & Gas Program Coordinator View our full comments to NHDES at: https://endocrinedisruption.org/assets/media/documents/TEDX_NHDES_comments.pdf 14 @endo_exchange
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