Overview: Biotic Ligand Model - ACWI

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Monitoring Implications of Using the
Copper Biotic Ligand Model (BLM)
and EPA’s Update of Ambient Water
Quality Criteria for Copper

Lauren Wisniewski
Christina Jarvis
May 10, 2006

U.S. Environmental Protection Agency
Office of Water, Office of Science & Technology
Standards & Health Protection Division

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ƒ Background: Water Quality Criteria

ƒ Biotic Ligand Model (BLM)

ƒ Comparison of 1986 and Updated Copper Criteria

ƒ Copper BLM Implementation Project

ƒ Monitoring Implications

ƒ Summary, Conclusions, and Next Steps

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ƒ National Criteria Recommendations: Scientifically

defensible guidance developed and published by
EPA per Clean Water Act Section 304(a)

ƒ Criteria: Adopted part of State/Tribal Water Quality

Standards under Clean Water Act Section 303(c)

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ƒ There are currently 629 rivers and streams listed as

impaired for copper and 5 for contaminated sediments due
to copper

ƒ The existing aquatic life criteria for copper are

underprotective for some waters and overprotective for
others

ƒ The current criteria relies on expensive Water Effects Ratio

(WER) testing to develop site specific criteria. A study
showed using the Biotic Ligand Model will cost on average
15% of the cost of WER testing

ƒ The updated criteria utilizes the best available science,

including the scientifically established relationships between
copper toxicity and water chemistry parameters

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ƒ 1986 Copper Criteria are a function of hardness

Š Acute Copper Criteria: e((00..88554455[[llnn((hhaarrddnneessss))]]--11..446655))
Š Chronic Copper Criteria: e((00..99442222[[llnn((hhaarrddnneessss))]]--11..446644))

Effect of Hardness on Copper Toxicity to
Fathead Minnows (Erickson et al., 1996)

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Copper LC50 (umol/L) 4 R2=0.954
3

2

1

0 200

0 50 100 150

Hardness (mg/L as CaCO3)

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ƒ Potentially under-protective at low pH
ƒ Over-protective at higher dissolved organic carbon (DOC)
ƒ The same copper concentration exerts different degrees of

toxicity from time to time and from place to place

ƒ Criteria do not typically reflect the effects of other water

chemistry factors that are also known to affect metal toxicity

ƒ Requires site-specific water quality criteria adjustments

using Water Effect Ratio (WER) procedure

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Draft Update Released December 2003

ƒ Uses the Biotic Ligand Model (BLM) to calculate

freshwater criteria on a site-specific basis

ƒ BLM model used as a replacement for the

hardness equation

ƒ Predicts acute freshwater water quality criteria

using an approach similar to that of predicting
organism toxicity; chronic criteria derived from
acute using acute to chronic ratio

Final Update Release Expected Nov/Dec 2006

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The Biotic Ligand Model (BLM) is a bioavailability model
that uses receiving water body characteristics and
monitoring data to develop site-specific water quality
criteria.

Biotic: of or relating to living organisms

Ligand: any molecule that binds to another

Model Background and Development

ƒ Free Ion Model (1980s): Chemical model
ƒ Gill Model (1996):Toxicological model
ƒ Refinement and incorporation into criterion (2000-2004)

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BLM Input Data
•Temperature
•pH
•Dissolved Organic Carbon (DOC)
•Major Cations (Ca, Mg, Na, & K)
•Major Anions (SO4 & Cl)
•Alkalinity

BLM Output Data
•Site-Specific Copper Criteria
•Copper Speciation

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ƒ pH 7.8 ƒ SO44 3.4 mg/L
ƒ DOC 5.0 mg/L ƒ Cl 1.2 mg/L
ƒ Ca 11.8 mg/L
ƒ Mg 5.0 mg/L ƒ Alkalinity 43 mg/L
ƒ Na 1.5 mg/L
ƒK 0.6 mg/L ƒ Hardness 50 mg/L

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H+ Gill Surface
Ca+2 (biotic ligand)
Na+

Organic Competing Cations Free Copper Binding
Ligand Metal ion Site
Complexes Free
Metal ion Cu+2
Cu - DOC
Cu+2

Inorganic
Ligand
Complexes

Cu OH+

Cu CCOl+ 3+ 12
Cu

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10000 Fathead minnows, Lab
1000 Fathead minnows, Field
+ D. pulex (CT DEP, Dunbar, 1996)

PREDICTED LC50 (ug/L) 100 +
++
10
++ +
+ ++ +

1 ++
1
++ +
+

+

10 100 1000 10000
MEASURED LC50 (ug/L)
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Copper CMC (ug / L) 250 Comparison of CMC calculated by BLM or Hardness Equation
200 Alkalinity and pH Covary with Hardness
150
100 CMC by Hardness Equation
CMC by BLM
50
0 BLM, DOC = 10 mg/L
0
BLM, DOC = 5 mg/L

BLM, DOC = 2 mg/L

50 100 150 200 250 300 350 400 450

Hardness (mg / L) 14

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ƒ 1986 Criteria with Water Effects Ratio (WER)

Adjustment is comprehensive in scope, but sampling
error is high and precision is low

ƒ BLM is limited in model formulation, but sampling error

low

ƒ Comparison WER-adjusted and BLM-derived site-

specific copper criteria in Colorado and
Massachusetts showed the two methodologies
resulted in similar values

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Advantages
ƒ BLM-derived criteria utilizes the best available science and

will likely result in more appropriate site-specific criteria

ƒ Improves our understanding of how water chemistry affects

metal availability and toxicity

ƒ Water chemistry data are cheaper to obtain than site-

specific toxicology data

ƒ BLM can be combined with streamlined WER testing

Disadvantages
ƒ The BLM requires more monitoring data and 1-2 days of

training and practice before using

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This workgroup-based project that involves EPA
Regions and States to meet these goals:

ƒ Implementation Information

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ƒ BLM Training Resources

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ƒ Communications and Stakeholder Outreach

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ƒ How will the BLM affect state water quality monitoring programs?

ƒ How could states refine future monitoring efforts to use the BLM?

ƒ How much does it cost to measure the BLM parameters?
ƒapproximately $150-$200 for all 10 parameters

ƒ When and how will the updated copper criteria be implemented?
ƒSome states have already started using a phased approach (CO)

ƒ Will there be regional defaults or regression equations to fill in data gaps?

ƒ How many data sets are enough to develop site-specific criteria?

ƒ What will be the impact on ambient assessments?

ƒ Can the criteria be developed on a site-specific, seasonal basis?

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ƒ Increased precision of the BLM (compared to the hardness-

based criteria) will lead to increased efficiency

ƒ BLM-based criteria can be as much as 10 times less stringent

than hardness-based criteria in waters with high DOC and
neutral pH (which are typical of many water bodies)

ƒ The cost savings of using the BLM instead of WER testing will

be considerable for wastewater treatment plants

ƒ Increased monitoring costs will pay greater dividends for

environmental protection programs

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ƒ The BLM uses the best available science to develop

site-specific criteria that are neither overprotective nor
underprotective

ƒ The BLM simulates the interactions between chemical

parameters (e.g., pH, DOC) and copper toxicity

ƒ The BLM can be used to calculate site specific copper

criteria that agrees remarkably well with bioassay-
based WER studies

ƒ BLM may eliminate the need for WER testing

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Biotic Ligand Model

ƒ Saltwater BLM is under development
ƒ EPA plans to update the zinc and silver aquatic life criteria

using the BLM

Stakeholder Outreach

ƒ EPA is open to hearing the ideas, concerns, and questions of

States and other stakeholders.

ƒ States are invited to participate in the next Copper BLM

Implementation Working Group Call:

Thursday May 18tthh, 1-2 PM ET

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