Estimation of Mercury Bioavailability in Wastewater Treatment Plant Effluents

1. Estimation of Mercury Bioavailability in Wastewater Treatment Plant Effluents J. David Dean San Francisco Estuary Institute Mercury Coordination Conference February 20, 2008 Oakland, CA ArcTellus Watershed Science & Simulation

2. ESTIMATION OF MERCURY BIOACCUMULATION POTENTIAL FROM WASTEWATER TREATMENT PLANTS IN RECEIVING WATERS(WERF Project 05-WEM-1CO) Principal Investigators Dr. Robert P. Mason - University of Connecticut J. David Dean - ArcTellus ArcTellus Watershed Science & Simulation

3. Purpose and Background • Assess the bioavailability of mercury in various effluents and receiving waters • Grew out of SF Bay Hg TMDL • Is Hg from WWTPs more or less bioavailable than Hg from other sources? ArcTellus Watershed Science & Simulation

4. Project Objectives • Develop a working definition of Hg bioavailability • Develop a list of bioavailability enhancers/mitigators • Profile/rank sources wrtbioavailable Hg • Develop a two-tiered guidance document for use by wastewater utilities • Screening level • Detailed assessment level ArcTellus Watershed Science & Simulation

5. Project Elements – Phase 1 • Define bioavailability • Identify enhancers/mitigators • Profile sources wrtbioavailable Hg, enhancers/mitigators • Develop an effluent ranking procedure • Apply the ranking procedure • Estimate the effects of wastewater treatment on Hg removal/bioavailability, data/literature review • Review recent Hg TMDLs ArcTellus Watershed Science & Simulation

6. Project Elements – Phase 2 • Develop a screening procedure for evaluating effluent Hg bioavailability in various receiving water types (i.e. fresh, brackish, saline) • Detailed assessment procedure • Guidance for obtaining necessary data • Guidance for application • Potential modification to Phase II to coordinate bioavailable inorganic mercury estimation with reactive mercury measurement in WWTP effluents ArcTellus Watershed Science & Simulation

7. Bioavailability Defined • Bioavailable mercury - both inorganic and organic forms, readily transported across biological membranes, and subsequently accumulated, and/or biotransformed to a more toxic and bioaccumulative species. • Potentially bioavailable mercury any form that can be converted into bioavailable mercury in a scientifically reasonable time span. ArcTellus Watershed Science & Simulation

8. Bioavailability Enhancers/Mitigators:Key Factors • Total Hg concentration • MeHg concentration and methylation potential • TSS concentration • Dissolved/solid phase partitioning • Mercury speciation • DOM (DOC) / sulfide interactions • Biogeochemistry of receiving waters • Dilution / mixing ArcTellus Watershed Science & Simulation

9. Mercury Source ProfilesSelected Sources • Atmospheric Deposition • Mining • Mercury-containing Sediments • Urban Runoff • Non-urban runoff • Wastewater Treatment Plants ArcTellus Watershed Science & Simulation

10. Bioavailability Estimation:Fraction Bioavailable Hg fHgB = (MeHg + HgR)/HgT MeHg is total aqueous MeHg HgR is reactive Hg (filtered) ArcTellus Watershed Science & Simulation

11. Bioavailability Estimation:Fraction Bioavailable Hg fHgB = [MeHg + (HgT – HgP – unreactive Hg)]/HgT where HgP is particle bound Hg or %HgB = %MeHg + (100 - %HgP - %unreactive Hg) ArcTellus Watershed Science & Simulation

12. Reactive Mercury Estimation:Dissolved Hg-S not complexed by DOC

13. Bioavailability Estimation Using Literature Values ArcTellus Watershed Science & Simulation

14. Status • Bioavailability defined • Enhancers/Mitigators identified • Source profiles developed • MeHg and RHg (where possible) • Enhancers/Mitigators • Effluent bioavailability estimation/ranking procedure completed/tested on Sacramento River data set • Phase I report completed ArcTellus Watershed Science & Simulation

15. Questions? Dr. Robert Mason – Co-PI (860) 405-9129 robert.mason@uconn.edu Mr. David Dean – Co-PI (864) 409-0188 j.david.dean@earthlink.net Jane M. Casteline – Program Manager (703) 684—2470 jcasteline@werf.org