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Incorporation of bioavailability

Incorporation of bioavailability. Patrick Van Sprang – ARCHE OECD Workshop on Metals Specificities in Environmental Hazard Assessment, Paris, 7-8 september 2011. Introduction. Metals are found in different forms in the environment These are referred to as metal “species”

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Incorporation of bioavailability

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  1. Incorporation of bioavailability Patrick Van Sprang – ARCHE OECD Workshop on Metals Specificities in Environmental Hazard Assessment, Paris, 7-8 september 2011

  2. Introduction • 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

  3. Metals exist in the environment… Particulate Metal • 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 • adsorbed to suspended solids (POC1 or mineral surfaces)  each of these processes may reduce metal bioavailability/toxicity Dissolved Metal Complexes Dissolved Free Metal • Free-ion forms tend to bind to biological ligands, e.g.physiologically active sites at the gill •  these species mainly causes metal toxicity 1POC: Particulate Organic Carbon 2NOM: Natural Organic Matter 3DOC: Dissolved Organic Carbon

  4. Metal toxicity can be expressed as… Total Metal Concentration For 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) 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;

  5. Metal toxicity can be expressed as… Bioavailable Metal Concentration • - 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) - Free Ion Activity Model (FIAM): assumes that the free metal ion activity reflects the chemical reactivity and toxicity of the metal - 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. * 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.

  6. 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 !

  7. CumulativeDistribution Function (%) CumulativeDistribution Function (%) Concentration (µg/l) Concentration (µg/l) Normalized PNEC Generic PNEC Why inorporate bioavailability in CSR of metals? • Bioavailability models ‘remove’ the variability in sensitivity due to differences in physico-chemistry Incorporation bioavailability

  8. Does bioavailability matter in EU waters ? Acute effects (LC50 in µg/l) of copper to Daphnia magna, tested in 11 different EU surface waters De Schamphelaere et al., 2002 Sampling location Factor 30 difference in acute Cu-toxicity across EU surface waters !!

  9. 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 !!

  10. Approaches for bioavailability ?

  11. 1. Transformation from total to soluble fraction - approach • Assumption: Dissolved metal concentrations more closely approximate the biologically available fraction than does total metal concentrations Total metal concentrations = dissolved metal concentrations (e.g. Ni, Cu, Zn) ≠ dissolved metal concentrations (e.g. Pb) Conversion needed No conversion needed • Speciation model (e.g. Minteq: requires phys-chemcharacterisation of medium (pH, Hardness,..)) • Analytical measurements testing (filtration, then e.g. ICPMS/AAS)

  12. 2. Use of speciation models - approach • Assumption: chemical species (mainly free metal ion activity) is able to explain the observed toxicity FIAM Dissolved metal concentrations • Speciation model (e.g. Minteq/WHAM: requires phys-chemcharacterisation of medium (pH, Hardness,..)) • Analytical measurements testing (filtration, then e.g. Ion Selective Electrode (ISE), Donnan membrane technique (DMT))

  13. 3. Toxicity related bioavailability models: approach • Assumption: chemical species (mainly free metal ion activity) and the interaction of the available cationic forms with the organism reflect the toxicity BLM • Chronic BLM’s have been developed & validated for several metals (e.g. Ni, Zn, Co, Cu in freshwater)/ Acute BLM’s also exist for other metals (e.g. Ag, Cd) Dissolved metal concentrations • FIAM - speciation model (e.g. Minteq/WHAM) • Gill Surface Interaction Model (e.g. CHESS) • 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)

  14. Ca2+ Log KCaBL Water Organism Log KMgBL Log KNaBL Mg2+ Log KHBL H+ pH Me-DOC Log KHBL [Me] on ‘biotic ligand’ Toxic effect Me2+ Na+ pH MeCO3 MeOH+ Competition (log K’s) Intrinsic sensitivity Speciation (WHAM) ‘biotic ligand’ e.g. gill, cell surface

  15. Acute Chronic 3. Toxicity related bioavailability models BLM: development (1) Ca Mg • De Schamphelaere & Janssen, 2002

  16. Sampling of waters Factor 2 Test BLM Chemical analyses (pH, DOC, Ca, Na,…) Adding ≠ concentrations Determine toxicity BLM: validation (1) 3. Toxicity related bioavailability models • De Schamphelaere et al., 2002

  17. BLM: validation (2) 3. Toxicity related bioavailability models • ..for invertebrates and fish • Factor 10 to 30 variability in toxicity… • reduced to factor 2 in > 90% of the cases

  18. BLM: validation (3) 3. Toxicity related bioavailability models • ..for algae • Factor 10 to 30 variability in toxicity… • reduced to factor 2 in > 90% of the cases

  19. 3. Toxicity related bioavailability models BLM: similar response across metals ? (1) Algae - Zn Invertebrates Fish invertebrates fish Invertebrates, fish & algae algae Invertebrates, fish & algae NOEC (µg/l Zn) NOEC (µg/l Zn) NOEC (µg/l Zn) NOEC (µg/l Zn) Ca > Mg pH pH DOC Hardness - Ni Invertebrates, fish, algae Invertebrates, fish & algae Invertebrates, fish & algae NOEC (µg/l Ni) NOEC (µg/l Ni) NOEC (µg/l Ni) Mg > Ca pH DOC Hardness

  20. 3. Toxicity related bioavailability models BLM: similar response across metals ? (2) - Cu invertebrates fish Invertebrates, fish & algae algae Hardness does not significantly affect chronic toxicity NOEC (µg/l Cu) NOEC (µg/l Cu) NOEC (µg/l Cu) pH pH DOC • - 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)

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

  23. 3. Toxicity related bioavailability models BLM model fish (rainbow trout) Read across? Read across? Read across? BLM model algae (Raphidocelis) BLM model water flea (Daphnids) BLM: extrapolation across other species ? (2)

  24. 3. Toxicity related bioavailability models BLM: extrapolation across other species ? (3) How ?: perform ‘spot checking’ of the BLMs for species for which no validation had been undertaken. Literature toxicity data (e.g. Cu) Toxicity testing (e.g. Ni) • - Insect: Chironomus tentans • - Rotifer: Brachionus calyciflorus • - Molluscs: Lymnaea stagnalis • - Higher plant: Lemna minor BLM predictions were within a factor ± 3

  25. 3. Toxicity related bioavailability models BLM: Implementation in risk assessment (1) 3 BLM’s (alga, invertebrate, fish) available ? Partial BLM normalization allowed No Yes Partial BLM normalization or BioF approach ‘Spot checks’ available for at least 3 other species ? No Yes Full BLM normalization across all species

  26. 3. Toxicity related bioavailability models BLM: Implementation in risk assessment (2) Partial BLM normalization or BioF approach (e.g. Zn RA) Full BLM normalization across all species (e.g. Ni, Cu-RA) 1. Normalise the NOEC for the BLM species towards site specific conditions (NOECx) and towards EU reference water chemistry conditions (NOECref) • 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 2. Calculate the bioavailability factors (BioF) for the BLM species 3. Select the highest BioF for the BLM species 4. - Calculate the bioavailable PEC concentration PECbioavailable=PEC * BioFwater,X - Or calculate the bioavailable PNEC concentration PNECbioavailable=PNECgeneric /BioFwater,X

  27. 4. Bioavailability models in marine waters - 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

  28. 4. Bioavailability models in marine waters Bioavailability correction (DOC): derivation of normalized PNEC value – e.g. Cu Model accuracy - Bioavailability prediction within a factor of 2 Toxicity - DOC regressions for 6 marine species

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