1. Quantifying the Role of Ecological Uncertainty in a Public Health Policy Decision Annual Meeting American Association for the Advancement of Science Seattle, Washington February 14, 2004 Bruce Hope Oregon Department of Environmental Quality Portland, Oregon

2. AAAS Seattle (2/04) Overview  Humans are exposed to methylmercury primarily through fish consumption.  Fish consumption advisories for mercury have been in effect within the Willamette River Basin (Basin) since 1979.  U.S. EPA’s Total Maximum Daily Load (TMDL) process will establish a target level for mercury in surface water.  Meeting the target level will, eventually, permit unrestricted fish consumption.

3. The Basin is located in northwest Oregon and drains into the Columbia River near Portland, Oregon. It holds the 13 th largest river in the continental U.S. and all of Oregon’s major urban areas are located within it. Willamette Basin

4. AAAS Seattle (2/04) Project objectives  Use a Basin-specific food web biomagnification model to estimate a methylmercury (MeHg) biomagnification factor (BMF) for the region.  The model should l Focus on fish (and other aquatic) species resident in the Basin and of which are of concern to stakeholders, and l Be calibrated with fish tissue data collected during 25+ years of water quality monitoring in the Basin.  Use this BMF and probabilistic techniques to calculate a range of Basin-specific target levels.

5. AAAS Seattle (2/04) Target level is based on…  A tissue criterion or the acceptable concentration of methylmercury in fish tissue. l 80-100% of the Hg in fish tissue is in the methylated form.  A biomagnification factor (BMF) which relates mercury surface water concentrations to tissue levels in higher trophic level species, and  A distribution ratio of methylmercury to total mercury in surface waters in which edible fish reside.

6. AAAS Seattle (2/04) Tissue criterion  U.S. EPA’s acceptable level for methylmercury in fish tissue assumes: l A reference dose for methylmercury of 0.0001 mg/kg-d, intended to protect all sensitive human sub-populations in the general population, l A fish ingestion rate of 17.5 g/d, every day, for 70 years, and l A body weight of 70 kg, the adult average.  Current criterion is 0.30 mg MeHg / kg fish, ww.  This value is controversial but was a given for this project.

7. AAAS Seattle (2/04) Biomagnification factor  A BMF describes the increase in concentration across two or more trophic levels. l Encompasses bioaccumulation - uptake into an organism at a given trophic level.  U.S. EPA national BMF values exist but these: l May not adequately reflect local conditions, and l Cannot be linked directly to specific fish species of concern to specific stakeholders.  A four-trophic level food web model was used to estimate Basin-specific BMF values.

8. AAAS Seattle (2/04) Basin-specific food web model  Includes 8 fish species commonly found in the Basin, selected based on measured Hg levels in tissue, feeding guild, and trophic level.  Biomagnification is estimated with Thomann algorithms and Fordham-Regan pathways analysis.  Monte Carlo methods are used to show how ecological uncertain influences tissue concentration and target level estimates.

9. SURFACE WATER AQUATIC MACROPHYTES PHYTO- PLANKTION DETRITUS ZOO- PLANKTON AQUATIC INSECT LARVAE HUMAN CONSUMERS PERIPHYTON LEVEL 2 (1° Consumers) AQUATIC CRUSTACEANS OMNIVOROUS FISH JuvenileAdult PISCIVOROUS FISH INVERTIVOROUS FISH JuvenileAdult LEVEL 3 (2° Consumers) LEVEL 4 (3° Consumers) AQUATIC INSECTS LEVEL 1 (1° Producers) LEVEL 0 (Exposure Media) Northern pikeminnow (A) Largemouth bass (A) Smallmouth bass (A) Rainbow trout (J,A) Cutthroat trout (J,A) Bluegill (J,A) Largescale sucker(J,A) Common carp (J,A) Northern pikeminnow (J) Largemouth bass (J) Smallmouth bass (J) AQUATIC MOLLUSKS AQUATIC WORMS

10. AAAS Seattle (2/04) Thomann model equations Trophic Level 1 Trophic Level 2 Trophic Level 3 Trophic Level 4 Food Term

11. AAAS Seattle (2/04) Pathways analysis equations Trophic Level 2 Trophic Level 3 Trophic Level 4 Lifespan Term

12. AAAS Seattle (2/04) Model calibration  Takes advantage of 1000+ fish tissue samples collected over 25+ years.  Calibration was done at two levels: l Measured tissue EDFs were aligned with modeled tissue CDFs. l Modeled body length~tissue concentration regressions were aligned with those observed in measured data.  Methylmercury assimilation factors and elimination rates were variables most frequently modified during calibration.

13. CONCENTRATION CALIBRATION - NORTHERN PIKEMINNOW

14. CONCENTRATION-LENGTH CALIBRATION - NORTHERN PIKEMINNOW

15. AAAS Seattle (2/04) Monte Carlo analysis  Provides decision makers with a credible range of target levels and the probability of any given target level achieving the tissue criterion.  For 1-D analysis… l Initial values for distributions of physicochemical and species life history variables from the literature. l All variables influenced by stochastic variability and lack of knowledge combined. l For 2-D analyses, 11 measurable variables were considered driven by lack of knowledge, rather than stochastic variability.

16. 2-DIMENSIONAL MONTE CARLO RESULTS - NORTHERN PIKEMINNOW

17. AAAS Seattle (2/04) Distribution ratio  The ratio of dissolved MeHg to total mercury in surface water is highly variable. l Lakes v. streams/rivers (flow) l Epilimnion v. hypolimnion (depth) l Total v. dissolved (sample processing) l Nationally, it is reported as ranging from 30%.  Values measured (n = 64) in the Basin have a mean of 6% (median = 3%), with a 90% confidence interval of 1% to 18%.

18. AAAS Seattle (2/04) COMPARISON OF WILLAMETTE BASIN EMPIRICAL RATIO VALUES TO USEPA GENERIC VALUES

19. AAAS Seattle (2/04) Target level calculation  Given a tissue criterion, a Basin-specific BMF estimate, and an estimate of distribution ratio in surface water, a target level can be calculated as: l where: CTL= Mercury target level; TC = Tissue criterion; BMF = Biomagnification factor;  = Distribution ratio; CF = Conversion factor

20. AAAS Seattle (2/04) Target level estimates (ng/L)

21. AAAS Seattle (2/04) Choosing a target level  Target tissue levels were calculated for each fish species using model estimated BMF values.  There are a number of choices. l Largemouth bass, for example:  Upper bound  15.16 ng/L (5% of individuals)  Lower bound  0.11 ng/L (95% of individuals)  Median  1.27 ng/L (50% of individuals)  Mean  0.39 ng/L  Actual target level selection is a public policy matter requiring stakeholder input. l Even with uncertainty quantified, the challenge is still in making the choice.