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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.
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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
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
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
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
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
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
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
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
Mercury Source ProfilesSelected Sources • Atmospheric Deposition • Mining • Mercury-containing Sediments • Urban Runoff • Non-urban runoff • Wastewater Treatment Plants ArcTellus Watershed Science & Simulation
Bioavailability Estimation:Fraction Bioavailable Hg fHgB = (MeHg + HgR)/HgT MeHg is total aqueous MeHg HgR is reactive Hg (filtered) ArcTellus Watershed Science & Simulation
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
Reactive Mercury Estimation:Dissolved Hg-S not complexed by DOC
Bioavailability Estimation Using Literature Values ArcTellus Watershed Science & Simulation
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
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