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 wrt bioavailable 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 wrt bioavailable 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 Profiles Selected Sources Atmospheric Deposition Mining Mercury-containing Sediments Urban Runoff Non-urban runoff Wastewater Treatment Plants ArcTellus Watershed Science & Simulation

Bioavailability Estimation: Fraction Bioavailable Hg fHg B = (MeHg + Hg R )/Hg T MeHg is total aqueous MeHg Hg R is reactive Hg (filtered) ArcTellus Watershed Science & Simulation

Bioavailability Estimation: Fraction Bioavailable Hg fHg B = [MeHg + (Hg T – Hg P – unreactive Hg)]/Hg T where Hg P is particle bound Hg or %Hg B = %MeHg + (100 - %Hg P - %unreactive Hg) ArcTellus Watershed Science & Simulation

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

Bioavailability Estimation Using Literature Values Water Type/SourceRange of estimated bioavailable Hg fraction Atmospheric Deposition0.2 to > 0.9 Mining Runoff< 0.1 Impacted Sediment Porewater0.15 to 0.45 Unimpacted Sediment Porewater0.2 to 0.45 Urban Runoff< 0.1 Non-urban Runoff0.2 to 0.3 Wastewater Treatment Plant Effluent< 0.2 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) Mr. David Dean – Co-PI (864) Jane M. Casteline – Program Manager (703)