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Biotic Ligand Models Application to data poor metals
Adam Peters
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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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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
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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
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“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?
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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
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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.
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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
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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)
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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
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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
)
DOC (mg/l)
0.0E+00
1.0E-05
2.0E-05
3.0E-05
4.0E-05
5.0E-05
6.0E-05
0 25 50 75 100
C.d
ub
ia E
C10
(M
)
Ca (mg/l)
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Cadmium Toxicity
Effect of water hardness on cadmium toxicity, derivation of a PNEC as a function of water characteristics. ESR RAR Cd (2007)
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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
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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
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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
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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)
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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
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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