Estimation of Mercury Bioavailability in Wastewater Treatment Plant Effluents

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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 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
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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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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

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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

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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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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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Bioavailability Enhancers/MitigatorsKey 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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Mercury Source ProfilesSelected Sources

• Atmospheric Deposition
• Mining
• Mercury-containing Sediments
• Urban Runoff
• Non-urban runoff
• Wastewater Treatment Plants

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Bioavailability EstimationFraction Bioavailable
Hg
fHgB (MeHg HgR)/HgT MeHg is total aqueous
MeHg HgR is reactive Hg (filtered)
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Bioavailability EstimationFraction Bioavailable
Hg
fHgB MeHg (HgT HgP unreactive
Hg)/HgT where HgP is particle bound Hg
or HgB MeHg (100 - HgP - unreactive
Hg)
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Reactive Mercury EstimationDissolved Hg-S not
complexed by DOC
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Bioavailability Estimation Using Literature Values
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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

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• Questions?
• Dr. Robert Mason Co-PI
• [phone]
• robert.mason_at_uconn.edu
• Mr. David Dean Co-PI
• [phone]
• j.david.dean_at_earthlink.net
• Jane M. Casteline Program Manager
• (703) 6842470
• jcasteline_at_werf.org