Transcript Estimation_of_Mercury_Bioavailability_Dean_021808

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?
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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
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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.
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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
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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
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 in presence of sulfide
%Bioavailable
100
pH 7
pH 6
pH 5.5
pH 5
10
1
0
2
4
6
DOC (mg/L)
8
10
Bioavailability Estimation Using
Literature Values
Water Type/Source
Atmospheric Deposition
Mining Runoff
Range of estimated
bioavailable Hg fraction
0.2 to > 0.9
< 0.1
Impacted Sediment Porewater
0.15 to 0.45
Unimpacted Sediment Porewater
0.2 to 0.45
Urban Runoff
Non-urban Runoff
Wastewater Treatment Plant Effluent
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Watershed Science & Simulation
< 0.1
0.2 to 0.3
< 0.2
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
[email protected]
Mr. David Dean – Co-PI
(864) 409-0188
[email protected]
Jane M. Casteline – Program Manager
(703) 684—2470
[email protected]