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?