estimation of mercury bioavailability in wastewater treatment plant effluents j. david dean san...
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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
ArcTellusWatershed 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
ArcTellusWatershed 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?
ArcTellusWatershed 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
ArcTellusWatershed 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
ArcTellusWatershed 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
ArcTellusWatershed 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.
ArcTellusWatershed 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
ArcTellusWatershed Science & Simulation
Mercury Source ProfilesSelected Sources
• Atmospheric Deposition• Mining• Mercury-containing Sediments• Urban Runoff• Non-urban runoff• Wastewater Treatment Plants
ArcTellusWatershed Science & Simulation
Bioavailability Estimation:Fraction Bioavailable Hg
fHgB = (MeHg + HgR)/HgT
MeHg is total aqueous MeHg HgR is reactive Hg (filtered)
ArcTellusWatershed 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)
ArcTellusWatershed Science & Simulation
Reactive Mercury Estimation:Dissolved Hg-S not complexed by DOC
Bioavailability in presence of sulfide
DOC (mg/L)
0 2 4 6 8 10
%B
ioav
aila
ble
1
10
100
pH 7 pH 6 pH 5.5 pH 5
Bioavailability Estimation Using Literature Values
Water Type/Source Range of estimated bioavailable Hg fraction
Atmospheric Deposition 0.2 to > 0.9
Mining Runoff < 0.1
Impacted Sediment Porewater 0.15 to 0.45
Unimpacted Sediment Porewater 0.2 to 0.45
Urban Runoff < 0.1
Non-urban Runoff 0.2 to 0.3
Wastewater Treatment Plant Effluent < 0.2
ArcTellusWatershed 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
ArcTellusWatershed Science & Simulation
Questions?
Dr. Robert Mason – Co-PI
(860) 405-9129
Mr. David Dean – Co-PI
(864) 409-0188
Jane M. Casteline – Program Manager
(703) 684—2470