Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model...

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Biotic Ligand Models Application to data poor metals Adam Peters

Transcript of Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model...

Page 1: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Biotic Ligand Models Application to data poor metals

Adam Peters

Page 2: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

What are Biotic Ligand Models and where do they come from?

Gill Surface Interaction Model – Pagenkopf 1983

Describes interaction of metals with fish gills and competition from other ions

Humic Ion Binding Model V – Tipping 1992

Describes binding of metals with natural organic matter and competition from other ions

Biotic Ligand Model – Di Toro 2001

Combines both of these models to describe toxicity as a function of water chemistry

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Page 3: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Comparability Between Different BLMs

Similarities between BLMs for different metals and different organisms

Consistency of Biotic Ligand stability constants for competing ions

Suggests similarity of interaction between many different fish and invertebrate species

Similarity of interaction between many algal species to metal toxicity

Page 4: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Comparability Between Different BLMs

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Log10KBL

Metal Organism Toxice Ca Mg H

Mn Fish 2.63 3.93

Mn Invertebrate 2.23 3.07 3.08

Cu Invertebratea 8.02 6.67

Zn Fishb 5.5 3.6 3.1 6.3

Zn Invertebratec 5.3 3.2 2.7 5.8

Ni Invertebrated 4.0 3.53 3.57

a - De Schamphelaere & Janssen 2004 Environ Toxicol Chem 23:1365 b - De Schamphelaere & Janssen 2004 Environ Sci Technol 38:6201

c - De Schamphelaere et al. 2006 Environ Toxicol Chem 24:1190 d - Deleebeeck et al. 2008 Environ Toxicol Chem 27:2097

e - Binding constant for the toxic metal

Page 5: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

“Biotic Ligand” Interactions

Consistency in binding constants for major competing ions (e.g. Ca2+, H+)

For different toxic metals

For different test species

Consistency of biological interaction?

Predictability for other cases?

Page 6: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Metal Bioavailability

Large effect due to DOC for many metals

For both acute and chronic toxicity

Effect of DOC predictable using speciation models

WHAM6, VisualMINTEQ

Relative importance of DOC and competing ions depends on the metal

Strength of binding to DOC is important

Page 7: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Metal bioavailability

Metal

Pb

Cu

Zn

Ni

Cd

Increasing importance of DOC

Increasing importance of competing ions

Expectations based on strength of binding to DOC based on information from Tipping 1998 Aquatic Geochemistry 4:3-48.

Page 8: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Metal bioavailability

Metal

Pb

Cu

Zn

Ni

Cd

Simple bioavailability correction based on DOC only

Effects from both DOC and competing ions

Simple bioavailability correction based on hardness only

Effects from both DOC and competing ions

Principal bioavailability effect due to DOC, some effects of competing ions

Page 9: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Lead Bioavailability

Clear effect of DOC on toxicity

Lead speciation complicated by precipitation with phosphate

BLM development complicated by precipitates

Proposed EU approach applies a DOC correction

Effect of DOC on Pb toxicity to L. stagnalis (snail) and P. rapida (rotifer)

Page 10: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Iron and Aluminium

Chemistry dominated by precipitation behaviour

Toxic effects under some conditions

Testing to assess effect of water chemistry

Toxicity reduced by DOC

BLM development for aluminium

Empirical model for iron

Page 11: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Manganese Bioavailability

Evidence of a protective effect from hardness

Chronic BLM development

Competition from Ca2+ for fish and invertebrates

Competition from H+ for algae

Limited effect of DOC (limited binding of Mn)

0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

0 5 10 15

C. d

ub

ia E

C10

(M

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DOC (mg/l)

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C.d

ub

ia E

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Ca (mg/l)

Page 12: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Cadmium Toxicity

Effect of water hardness on cadmium toxicity, derivation of a PNEC as a function of water characteristics. ESR RAR Cd (2007)

Page 13: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Silver

Relatively abundant acute ecotoxicity data

Clear effects of some water quality parameters on toxicity

Acute BLMs for fish and invertebrates

Validation studies suggest relatively poor performance at low hardness and low sulphide levels

Moderate predictive ability

Page 14: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Predicting Chronic Silver Toxicity

No organised chronic testing for silver

Chronic tests available for a range of species

Chronic bioavailability effects less pronounced than acute bioavailability effects

Limited effect of competing ions (Na+, Cl-)

Bioavailability effects due to DOC and sulphide

Alternative approach for chronic toxicity

Page 15: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Chronic Toxicity of Silver

Silver is strongly bound by both DOC and sulphide in freshwaters

Sulphide expressed as Chromium Reducible Sulphide (CRS)

CRS is typically related to DOC

High CRS tends to be associated with high DOC

CRS is typically present at higher concentrations than Ag

Page 16: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Silver and CRS Concentrations

Comparison of dissolved silver (red) and CRS, either measured (green) or estimated from DOC (blue). Monitoring undertaken in the UK between Jan 2010 and April 2011. CRS concentrations are higher

than silver concentrations in all cases. Data from European Precious Metals Federation.

Time (months)

Page 17: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Chronic Silver Bioavailability?

Accounting for bioavailability effects on chronic silver toxicity

Silver will be toxic under conditions where the molar concentration of silver exceeds the molar concentration of CRS

Comparable to SEV/AVS approach for sediments

Validation using chronic testing required

Page 18: Biotic Ligand Models - OECD · What are Biotic Ligand Models and where do ... Biotic Ligand Model – Di Toro 2001 Combines both of these models to describe toxicity as a

Summary

BLMs combine 2 important components to describe metal bioavailability

One of these components may be more important than the other in many cases

Focus on the most important bioavailability modifying effects

Validation of the models likely to be required prior to adoption by regulatory agencies

Assessing Ecotoxicological Impacts Using LCIA | INERIS Workshop on LCIA, Creil | 15th June 2011 18


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