1 incorporation of bioavailability patrick van sprang – arche oecd workshop on metals...

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Incorporation of bioavailability

Patrick Van Sprang – ARCHE

OECD Workshop on Metals Specificities in Environmental Hazard Assessment, Paris, 7-8 september 2011

2• Metals are found in different forms in the environment • These are referred to as metal “species”• Changing in the environment is called “ (chemical) speciation” or

“transformation”• Kinetics and chemical speciation under environmentally relevant

conditions crucial for PNEC derivation & read-across• Important point: Not all metal species are toxic

Introduction

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– with inorganic ligands (OH-, CO32-, HCO3

-,..)

– with dissolved NOM2 (measured as DOC3: humic and fulvic acids) each of these processes may reduce metal bioavailability/toxicity

Dissolved Metal ComplexesDissolved Metal Complexes

Metals exist in the environment…

– Free-ion forms tend to bind to biological ligands, e.g.physiologically active sites at the gill these species mainly causes metal toxicity

Dissolved Free Metal Dissolved Free Metal

– adsorbed to suspended solids (POC1 or mineral surfaces) each of these processes may reduce metal bioavailability/toxicity

Particulate MetalParticulate Metal

1POC: Particulate Organic Carbon2NOM: Natural Organic Matter3DOC: Dissolved Organic Carbon

4For terrestrial and sediment systems, the concentration of a metal that is determined after destruction of the mineral matrix. For aqueous systems: the total amount of metal present, including the fraction sorbed to particles and to dissolved organic matter and the fraction in the mineral matrix; = particulate (sorbed + precipitated) + dissolved (inorganic complexes + organic complexes + free ionic forms)

Total Metal ConcentrationTotal Metal Concentration

Metal toxicity can be expressed as…

Dissolved Metal Concentration*Dissolved Metal Concentration*most often, the dissolved fraction in ecotoxicity tests refers to the fraction that passes through a filter of 0.45 µm. = inorganic complexes + organic complexes + free ionic forms

* It should be noted, however, that this definition may not necessarily refer to the metals in solution. In the range of 0.01- 0.45 µm colloid inert particles containing metal ions that remain suspended, may still exist;

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- the degree to which a metal species is available to interact with the biotic ligand (e.g. physiologically active sites at the gill) to exert its effect.

= free ionic forms (mainly)

Bioavailable Metal ConcentrationBioavailable Metal Concentration

- Biotic Ligand* Model (BLM): assumes that both the free metal ion activity and the interaction of the available cationic forms with the organism reflect the toxicity.

- Free Ion Activity Model (FIAM): assumes that the free metal ion activity reflects the chemical reactivity and toxicity of the metal

Metal toxicity can be expressed as…

* A "biotic ligand" is a biochemical receptor that is metal-binding and is treated similarly to other ligands in the exposure water, except that it is on the organism. An example of a biotic ligand is a fish gill.

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Why incorporate bioavailability in CSR of metals?

• NOEC/EC10 in laboratory test media which often maximizes bioavailability (e.g. low DOC in water; low OC in soil) may not reflect ‘real environment’ (rivers may have different DOC, pH) !

• Database often contains NOEC/EC10 obtained in test media with widely varying chemistry (= very different bioavailability) which toxicity values to select (species mean ?, lowest NOEC/EC10 ?) ?

• Generic/uncorrected SSD does not represent ‘intrinsic sensitivity’ alone but rather a mix of ‘intrinsic sensitivity’ + bioavailability effects toxicity values should therefore be normalized towards similar physico-chemical conditions !

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Why inorporate bioavailability in CSR of metals?

Incorporationbioavailability

Concentration (µg/l)

Cum

ula

tive D

istr

ibuti

on

Funct

ion (

%)

Generic PNEC

Concentration (µg/l)

Cum

ula

tive D

istr

ibuti

on

Funct

ion (

%)

Normalized PNEC

• Bioavailability models ‘remove’ the variability in sensitivity due to differences in physico-chemistry

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Does bioavailability matter in EU waters ?

0

100

200

300

400

01 02 03 05 06 07 07 08 09 10 11

48h-

EC

50 in

µg

Cu/

L648

Acute effects (LC50 in µg/l) of copper to Daphnia magna,tested in 11 different EU surface waters

Factor 30 difference in acute Cu-toxicity across EU surface waters !!

De Schamphelaere et al., 2002

Sampling location

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Soil pH (CaCl2) Nitrific. Glucose Maize Barley Tomato Eisenia Folsomia

Houthalen 3.6 87 24 24 55 32Zegveld 4.1 196 226 226 966 619Montpellier 4.1 38 59 71 27 78 113Rhydtalog 4.2 68 603 91 48 179 510Jyndevad 4.5 26 14 31 87Kövlinge II 5.1 39 37 109 27 282 22Aluminusa 5.6 62 191 185 47 309 103Borris 5.6 89 16 46 110 54 31 183Woburn 6.1 104 555 297 416 136 303 884Ter Munck 6.7 97 97 54 103 103 169 298Souli ** 7.0 253 425 169 283 283 378 559Marknesse 7.6 66 148 84 233 233 299 583Brécy 7.5 156 457 801 504 504 609 941Cordoba 2 7.6 196 712 712 396 72 514 875Cordoba 1 7.6 61 190 68 105 105 195 79Guadalajara 7.7 33 54 411 192 192 312 542

Does bioavailability matters in EU soils ?Chronic effects of nickel (NOEC/EC10 in mg/kg) to soil

organisms/processes tested in 16 different EU surface soils

Factor between 10-45 difference in chronic Ni-toxicity across EU soils !!

10TOTAL METAL LEVELS (MONITORING DATA)

KD, SS

Ca, pH, DOC,…(speciation model)

SEM, AVS

Toxicity-based models (Biotic Ligand Model, Regression Models,…)

PHYSICO-CHEMICAL SPECIATION MODELLING

SEDIMENT

TotalMe-concentration

WATER


Porewater or free ion model

Free ionicMe-fraction

BIOAVAILABILITY ASSESSMENT MODELLING

Bioavailable Metal Fraction

Biogeochemical Region X1 Biogeochemical Region X2 Biogeochemical Region Xn

DissolvedMe-fraction

SEM – AVSMe-fraction

SOIL


TOTAL METAL LEVELS (MONITORING DATA)

KD, SS

Ca, pH, DOC,…(speciation model)

SEM, AVS

Toxicity-based models (Biotic Ligand Model, Regression Models,…)

PHYSICO-CHEMICAL SPECIATION MODELLING

SEDIMENT


SEDIMENT


WATER


WATER


Porewater or free ion model

Free ionicMe-fraction

BIOAVAILABILITY ASSESSMENT MODELLING

Bioavailable Metal Fraction

Biogeochemical Region X1 Biogeochemical Region X2 Biogeochemical Region XnBiogeochemical Region X1 Biogeochemical Region X2 Biogeochemical Region Xn

DissolvedMe-fraction

SEM – AVSMe-fraction

SOIL


SOIL


Approaches for bioavailability ?

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1. Transformation from total to soluble fraction - approach

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2. Use of speciation models - approach

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3. Toxicity related bioavailability models: approach

The BLM requires a description of water chemical parameters that can influence metal toxicity: - pH- DOC (a convenient measure of NOM)- Major ions: Calcium, Magnesium- Others: e.g. Sodium (Cu)

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MeOH+

MeCO3

Me-DOC

pH

[Me] on ‘biotic ligand’

Toxic effect

Water Organism

H+

pH

Me2+

Ca2+

Na+

Mg2+

‘biotic ligand’ e.g. gill, cell surface

Speciation (WHAM)Intrinsic sensitivity

Competition (log K’s)

Log KCaBL

Log KMgBL

Log KNaBL

Log KHBL

Log KHBL

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De Schamphelaere & Janssen, 2002

R2 = 0.9672

R2 = 0.9559

0

1020

30

40

5060

70

0.0 0.5 1.0 1.5 2.0

Cation activity (mM)

48h

EC50

(Ni

2+) (

µM) Acute

R2 = 0.9918

R2 = 0.8086

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.5 1.0 1.5

Cation activity (mM)21

d EC

50 (N

i2+

) (µM

) Chronic

Ca Mg

BLM: development (1)3. Toxicity related bioavailability models

16 De Schamphelaere et al., 2002

Sampling of waters

Chemical analyses (pH, DOC, Ca, Na,…)

Adding ≠ concentrationsDetermine toxicity

Test

BLM

Factor 2

BLM: validation (1)3. Toxicity related bioavailability models

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Factor 10 to 30 variability in toxicity… reduced to factor 2 in > 90% of the cases

10

100

1000

10000

10 100 1000 10000

observed EC50 (µg/L)

pre

dic

ted

EC

50 (

µg

/L)

Daphnia - acute - Cu

Daphnia - chronic -Cu

Daphnia -acute -Zn

Daphnia - chronic -Zn

Daphnia - acute - Ni

Field cladocerans -acute - CuRainbow trout -chronic - Zn

..for invertebrates and fish


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10

100

1000

10000

10 100 1000 10000

observed EC50 (µg Cu/ L)

pred

icte

d EC50 (

µg C

u/L)

P. subcapitataChlorella sp.C. reinhardtiiP. subcapitata (NOEC, fi eld)

..for algae

Factor 10 to 30 variability in toxicity… reduced to factor 2 in > 90% of the cases


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BLM: similar response across metals ? (1)

InvertebratesAlgae Fish

Invertebrates, fish & algae

NO

EC

(µ

g/l Z

n)

NO

EC

(µ

g/l Z

n)

algae

pHDOC

invertebrates fish

pH

NO

EC

(µ

g/l Z

n)Invertebrates, fish

& algae

NO

EC

(µ

g/l Z

n)

Hardness

Ca > Mg


NO

EC

(µ

g/l N

i)

NO

EC

(µ

g/l N

i)

Invertebrates, fish, algae

pHDOC

Mg > Ca


NO

EC

(µ

g/l N

i)Hardness

- Zn

- Ni

3. Toxicity related bioavailability models

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NO

EC

(µ

g/l C

u)

NO

EC

(µ

g/l C

u)

algae

pHDOC

invertebrates fish

pH

NO

EC

(µ

g/l C

u)

Hardness does not

significantly affect chronic

toxicity

- Cu

- Toxicity response = f(organism; phys-chem parameter)- Toxicity response = pH: similar for algae; different for

invertebrates & fish= DOC: similar for all

organisms= H: ± similar for all

organism (> Ca for Zn; > Mg for Ni; less significant for Cu)

BLM: similar response across metals ? (2) 3. Toxicity related bioavailability models

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BLM: applicability domain

• BLMs developed & validated within 90th % of phys.-chem from EU waters and should therefore only be applied within such boundaries !!

• Specific conditions outside boundaries need special attention (e.g. model extrapolation, additional specific testing….


22• BLM developed for limited number of species:

– P. subcapitata (green alga)– D. magna/C. dubia (cladoceran, invetebrate),– O. mykiss/P. promelas (fish)

• Ecotoxicity database contains NOEC/EC10 for other species/taxonomic groups (e.g. molluscs, rotifers, insects)

• Given that individual development for all existing aquatic species is impossible, can a BLM developed for one species be used for another species?...

• Extrapolation assumes similar mechanism of actions (e.g. similar stability constants between the cations (Ca, Mg, H) and the biotic ligands, similar site of action)

BLM: extrapolation across other species ? (1)3. Toxicity related bioavailability models

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Read across?

Read across?

Read across?

BLM model fish (rainbow trout)

BLM model algae (Raphidocelis)

BLM model water flea (Daphnids)

BLM: extrapolation across other species ? (2)3. Toxicity related bioavailability models

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How ?: perform ‘spot checking’ of the BLMs for species for which no validation had been undertaken.

BLM: extrapolation across other species ? (3)

- Insect: Chironomus tentans- Rotifer: Brachionus calyciflorus- Molluscs: Lymnaea stagnalis- Higher plant: Lemna minor

BLM predictions were within a factor ± 3


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BLM: Implementation in risk assessment (1)

Yes

Yes

No

No


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Eco-region HC5

0

10

20

30

40

50

60

70

80

90

100

1 10 100 1000 10000

NOEC (µg/l)

perc

entil

e

Scenario ditchThe Netherlands

Scenario lake Monate Italy

Scenario river Rhine The Netherlands

Scenario river Otter United Kingdom

Scenario river Teme United Kingdom

Scenario acid lake Sweden

Scenario river Ebro Spain

10,9/11,8 µg/l

57,3 µg/l25,4 µg/l

17,5 µg/l

14,7 µg/l9,9 µg/l

DOC = 2,5 3,2 3,7 2,8 2,5 8,0 12,0 mg/lpH = 7,7 8,1 8,2 7,8 6,7 7,6 6,9

BioFwater,X NOECrefNOECx

2. Calculate the bioavailability factors (BioF) for the BLM species

PECbioavailable=PEC * BioFwater,X

1. Normalise the NOEC for the BLM species towards site specific conditions (NOECx) and towards EU reference water chemistry conditions (NOECref)

3. Select the highest BioF for the BLM species

4. - Calculate the bioavailable PEC concentration

- Use D. magna/C. dubia BLM to normalise all other invertebrates (e.g. molluscs, rotifers,..)- Use O. mykiss/P. promelas to normalize all fish/amphibians - Use R. subcapitata to normalize all other algae

BLM: Implementation in risk assessment (2)


- Or calculate the bioavailable PNEC concentration

PNECbioavailable=PNECgeneric /BioFwater,X

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- Coastal/open sea waters are characterised by… - high pH (typically between 7.8–8.3), high salinity (35‰), high ionic strength. - DOC levels may vary considerably between marine waterbodies- Freshwater and marine organisms face very different iono- and osmo-regulatory

issues related to living in either a very dilute or concentrated salt environment. freshwater BLMs can NOT directly be used for marine environments

- Me-DOC binding freshwater different then marine waters = Speciation modelling to be modified with the ionic strength

DOC normalization if applicable = bioavailability correction = not species-specific

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4. Bioavailability models in marine waters

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4. Bioavailability models in marine waters

Model accuracy - Bioavailability prediction within a factor of 2

Toxicity - DOC regressions for 6 marine species

1 incorporation of bioavailability patrick van sprang – arche oecd workshop on metals...

Documents

metal metal toxicity

metal species

metal ions

metal present

dissolved metal concentration

free metal ion activity

dissolved fraction

environment freeion