a practical approach to account for the bioavailability of metals bruce brown wca environment...
DESCRIPTION
Slide 3 Why bother to account for bioavailability? Many new metals EQSs are based on high bioavailability Wide scale failure of EQSs derived for metals if only considering face-value comparison with monitoring data. Enables resources and money to be focussed at those sites at real risk of harmTRANSCRIPT
A practical approach to account for the
bioavailability of metals
Bruce BrownWCA Environment
REPRESENTING Eurometaux
November 25th 2010
Slide 2
Metals EQSs are Evolving• Existing methods based on
total concentrations are poor predictors of potential environmental risk
• Need to monitor dissolved metals
• Biotic Ligand Models (BLMs) developed which predict toxicity extremely well
• BLMs appear complicated to implement – but are not!
Slide 3
Why bother to account for bioavailability?
• Many new metals EQSs are based on high bioavailability
• Wide scale failure of EQSs derived for metals if only considering face-value comparison with monitoring data.
• Enables resources and money to be focussed at those sites at real risk of harm
Slide 4
Perceived practical limitations when using biotic ligand
models (BLMs) in the WFD• Complexity of models• Input hungry• Resource intensity• Practical difficulties• How to use the outputs?
Slide 5
Solutions to the practical problems of implementing bioavailability in a
regulatory frameworks• Development of screening tools –
only 3 inputs for Cu, Ni, Zn – DOC, pH and Ca)
• Tiered compliance assessment for metals
• Full automation possible within laboratory analytical system e.g. UK
• Outputs can be expressed as either bioavailable metal or site specific EQS
Slide 6
Screening Tools
0
5
10
15
20
25
0 5 10 15 20 25
HC5 NiBLM µg l-1
HC5
Scre
enin
g too
l µg
l-1
Comparison of Ni screening tool performance against NiBLM performance (all concentrations in µg dissolved Ni l-1) data from sites across the England and Wales (n ≈ 112) .
Slide 7
Limited input data
Output 1:Bioavailability-basedPNEC
Output 2:Site-specific risk characterization
Slide 8
The Tiered Approach1. Comparison with generic EQSbioavailable
2. Use of screening tool
3. Consideration of local ambient background concentrations
4. Remedial measures
Class
ificati
onPr
ogra
mme o
f Me
asur
es
FAIL
FAIL
FAIL No fu
rther
actio
n nec
essa
ry Pass
Pass
Pass
Slide 9
1. Comparison with generic EQSbioavailable
2. Use of screening tool
3. Consideration of local ambient background concentrations
4. Remedial measures
Class
ificati
onPr
ogra
mme o
f Me
asur
es
FAIL
FAIL
FAIL No fu
rther
actio
n nec
essa
ry Pass
Pass
Pass
Slide 10
Nickel - Great Britain (n = 183)
1. Comparison with generic (100% bioavailable) EQS
2. Use of screening tool
FAIL
FAIL
Pass
Pass
Percentage pass rate = 97 %
(n =122) (n = 61)
(n =6)(n =116)
Slide 11
Nickel - France (n = 249)
1. Comparison with generic (100% bioavailable) EQS
2. Use of screening tool
FAIL
FAIL
Pass
Pass
Percentage pass rate = 95 %
(n =29) (n = 220)
(n =12)(n =17)
Slide 12
Nickel - Austria (n = 1779)
1. Comparison with generic (100% bioavailable) EQS
2. Use of screening tool
FAIL
FAIL
Pass
Pass
Percentage pass rate = 91 %
(n =646) (n = 1133)
(n =158)(n = 488)
Slide 13
Data Requirements• Typically DOC, pH & Ca as minimum• Potential need for guidance on best
practice for producing DOC data?• Can estimate DOC from dissolved Fe
or UV absorbance but adds uncertainty
Slide 14
DOC Estimation by UV
Slide 15
Summary• Accounting for metal bioavailability provides a robust
metric by which to assess potential risks – and is linked to biology!
• Bioavailability can be applied within a tiered approach • Simplified screening tools are available that:
– Process large numbers of samples– Have only 3 inputs (in the case of Cu, Ni and Zn)– Fully automated
• Accounting for bioavailability does NOT present significant practical challenges
• Some changes to routine monitoring requirements probably needed e.g. Dissolved metals and DOC
• Implementation Guidance next year?