Estimation of Mercury Bioavailability in Wastewater Treatment Plant Effluents J. David Dean San Francisco Estuary Institute Mercury Coordination Conference.

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

[email protected]

Mr. David Dean – Co-PI

(864) 409-0188

[email protected]

Jane M. Casteline – Program Manager

(703) 684—2470

[email protected]