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Bioavailability correction for sediments: concepts, implementation and examples
Eurometaux‐ECHA workshop “Metals” evaluation under REACH
Helsinki
21‐24 March 2011
ECHA workshop “Metals evaluation under REACH”
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CONCEPTS
ECHA workshop “Metals evaluation under REACH”
Similar need for bioavailability correction as
for the water compartment
PNEC sediment
Risk assessment sediment considering bioavailability
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Different site specific characteristics
RWC PNEC
High
Medium
Bioavailability
Low
ECHA workshop “Metals evaluation under REACH”
Key parameters influencing bioavailability
• Sulfides: bind metals to form insoluble metal complexes. 4
• Organic carbon: strong adsorption of metals to the organic carbon pool in sediments
• Iron/Mangeneseoxy/hydroxides: adsorption/precipitation/inclusion of metals by formed Fe/Mn (O)OH precipitates
ECHA workshop “Metals evaluation under REACH”
Conceptual model sediment compartment
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Water
phase
Different metal species
Oxic Layer
Sediment
phase
MnO, FeO...
Me2+
Me2+
Me2+
Me- OC
Mineral bound
metal
Anoxic Layer
MeS
MeS
Complex matrix with many factors controlling metal availability
ECHA workshop “Metals evaluation under REACH”
Acid Volatile Sulfides (AVS)
• The availability of some divalent cationic metals (Hg, 6
Cd, Cu, Pb, Zn, Ni,..;) in sediment has been shown to be strongly influenced by the presence of acid volatile sulfides (AVS) as they form insoluble complexes with these metals.
• AVS (Acid Volatile Sulfides) are those sulfides which are readily extracted by cold extraction (1 M HCL) of sediments. • AVS can be determined by measuring the release of sulfides after acidification with HCl (photometric ECHA workshop “Metals evaluation under REACH”
determination with dimethyl‐p‐phenylenediamine)
Bioavailability sediment: SEM‐AVS concept
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Typical AVS concentrations in EU range from 0.3 ‐ > 100 µmol/g dry wt
Typical oxic sediments: 0‐1 µmol g/dry wt Typical oxic/anonoix sediments 1‐10 µolg/dry wt ECHA workshop “Metals evaluation under REACH”
Bioavailability sediment: SEM‐AVS concept
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Water
phase
Different metal species
Oxic Layer
Sediment
phase
MnO, FeO...
Me2+
Me2+
Me2+
Me- OC
Mineral bound
metal
Anoxic Layer
MeS
MeS
1M HCl extraction
SEM (Simultaneously Extracted Metals) + AVS (Acid Volatile Sulfide)
ΣSEM = SEMCu + SEMPb +SEMCd + SEMZn + SEMNi (AVS affinity Hg>Cu >Pb>Cd>Zn>Ni)
Excess SEMCu = SEMCu – (AVStotal – SEMHg)
ECHA workshop “Metals evaluation under REACH”
potentially bioavailable
SEM‐AVS model
Data treatment
(SEM, AVS)
(10,5)
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Probability of exceedance (%)
(1,10)
(20,70)
0
Paired measured data
0
(SEM‐AVS)
SEM –AVS < 0 = no risk
ECHA workshop “Metals evaluation under REACH”
Bioavailabilitysediment: other sediment phases
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Sediment
phase
Water
phase
Different metal species
MnO, FeO...
= Future research
Me2+
OxicLayer
Me2+
Me2+
MeMe-OC
OC
Mineral bound
metal
AnoxicLayer
MeS
MeS
Other sediments sediment sorption phases have also been
identified as important such as particulate organic carbon
and the oxides of Fe and Mn.These phases have a large
ECHA workshop “Metals evaluation under REACH”
adsorption capacity.
Reduction in variability: incorporation bioavailability e.g. Cu
Total
100
AVS low
Max/Min ratio
120
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AVS/OC low
80
60
40
20
0
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Most sensitive endpoints
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ECHA workshop “Metals evaluation under REACH”
Bioavailability model development for sediments‐Ni case
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• Clear quantitative and significant relationships could be established for Ni between observed toxicity and different sediment parameters (AVS; Fe; OC)
• Multi‐factorial models could not be derived due to co‐
variance sediment parameters
• Again AVS can be considered the predominant parameter controlling for most divalent metals as evidenced from both laboratory studies and field recolonizationstudies
ECHA workshop “Metals evaluation under REACH”
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IMPLEMENTATION IN THE REACH FRAMEWORK: TIERED APPROACH
ECHA workshop “Metals evaluation under REACH”
Incorporation of bioavailability sediment (MERAG)
TOTAL METAL LEVELS (MONITORING DATA)
SEDIMENT
Sulfide
Non-sulfide
Total
Me-concentration
binding metals
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binding metals
KD, SS
PHYSICO-CHEMICAL
SPECIATION MODELLING
SEM, AVS
SEM – AVS
Me-fraction
Organic carbon
normalisation
Pore
water
Fe/Mn(oxy)hydroxides
SEM, AVS/FOC
Toxicity-based models (Biotic Ligand Model,
Regression Models,…)
Bioavailable Metal Fraction
BIOAVAILABILITY ASSESSMENT MODELLING
ECHA workshop “Metals evaluation under REACH”
Biogeochemical Regions X1, X2, Xn,…
Bioavailability Normalization Approach
‐effects side
Chronic
Database
Toxicity data expressed as total metal
concentrations
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Select appropriate normalization factor (AVS, OC, Fe,…) and normalize chronic database
Bioavailability
Models
PNEC
Calculation
In absence of model select tox data performed with sediments representing RWC condition (e.g. low AVS, low OC)
Outcome: HC5 value/lowest bioavailability corrected EC10 value from normalized database divided by AF ECHA workshop “Metals evaluation under REACH”
Normalization procedure
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Log EC10
Normalization equation
Variability
RWC AVS = 0.77 µmol/g dry wt
AVS
ECHA workshop “Metals evaluation under REACH”
Organic carbon normalization
¾ Differences in toxicity responses within a species can be mainly explained by organic carbon content of the sediment.
PNEC, total (mg Me/kg dry wt.)
fOC = fraction organic carbon
PNEC, OC normalized (mg Me/g OC)
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Regional
assessment
Local
assessment
ECHA workshop “Metals evaluation under REACH”
Bioavailability Normalization Approach
‐exposure side
Exposure
data
Exposure data expressed as total metal
concentrations
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Measure locally bioavailability parameters (SEM‐AVS, OC, ….)
Bioavailability
correction
PEC bioavaible
Calculation
In absence of these use default worst case assumptions for Eu (e.g. 10 P AVS = 0.77 µg/kg dry wt.)
Derivation of PEC bioavailable and comparison with PNEC bioavailable
ECHA workshop “Metals evaluation under REACH”
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IMPLEMENTATION IN THE REACH FRAMEWORK: EXAMPLES
ECHA workshop “Metals evaluation under REACH”
Bioavailability incorporation EU‐CdRAR (1)
• PNEC derivation:
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– SEM‐AVS normalized PNEC
– Based on two sediments tests. Study which yielded the lowest total NOEC ( Chironomus) was used further to perform a SEM‐AVS analysis
– AVS content was low (0.5 µmol/g dry wt.). SEM‐AVS difference was positive
– AF approach used
ECHA workshop “Metals evaluation under REACH”
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Bioavailability incorporation EU‐CdRAR (2)
• Total PNEC derivation
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PNEC sediment = 115 mg kg‐1/50 = 2.3 mg Cd kg‐1
• PNEC Cd, bioavailable
‐ 115 mg = 1.02 µmol
‐ AVS test = 0.5 µmol (SEM Pb and Cu = 0.13 µmol). AVS available to bind with Cd = 0.5 – 0.13 = 0.37 µmol)
‐ SEM Cd – Excess AVS = 1.02 – 0.37 = 0.67 µmol
PNEC bioavailable = 0.67/50 = 0.013 µmol Cd/g dry wt. (1.5 mg Cd/kg dw)
ECHA workshop “Metals evaluation under REACH”
Bioavailability incorporation EU‐CdRAR (3)
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Local SEM and AVS data available?
yes
Risk factor= (SEMCd-ΔAVSCd)/PNECavailable
no
Risk factor= (PEClocal-10th perc.ΔAVSCd)/PNECavailable
ECHA workshop “Metals evaluation under REACH”
Bioavailability incorporation EU‐CdRAR (4)
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SEM‐AVS implementation in regionalrisk characterization
– Default 10th percentile of ∆AVSCddistribution (0.49 µmol/ g. dry wt.)
– Sensitivity analysis: 10th percentile ∆AVSCd Germany (0.061 µg/g dry wt.)
ECHA workshop “Metals evaluation under REACH”
Bioavailability incorporation EU‐Cu RAR (1)
• PNEC derivation:
–
–
–
–
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SSD approach (6 species, 106 NOECS)
NOECs related to OC and AVS
However, SEM Cu overestimated (artefact)
Member states wanteds worst case PNEC for “aerobic”
sediments
• Trimmed database
– Select NOECS of low AVS sediments: 62 NOECS remained
– Selection criterium: < 0.77 µg/dry wt (10th P‐flanders dataset). In ecotox tests: median value: 0.15 µmol/g dry wt.
• Implementing OC normalization (NOEC total/fOC) further reduced the intra species variability
• SEM‐AVS implementation in risk characterization
– Default 10th percentile of AVSdistribution (0.77 µmol/ g. dry wt.)
ECHA workshop “Metals evaluation under REACH”
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Bioavailability incorporation EU‐Cu RAR (2)
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Conclusion : HC5‐50 sediment (benthic SSD) = aerobic 1741 ‐ 2021 mg Cu/kg OC (log normal‐best fitting)
87‐101 mg Cu/kg dry weight (5% OC) (log normal‐best fitting)
ECHA workshop “Metals evaluation under REACH”
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Example Ni Case study (1): development of bioavailability models
• Identification of key sediment parameters driving nickel toxicity in sediments
• Development of bioavailability models for three sediment species:
– Hyalellaazteca
– Gammaruspseudolimneaus
– Hexagenia species
• Correlations and simple linear regressions
• Sediment parameters examined were:
– AVS, TOC, pH
– Fetot ,Mntot , FeSEM , MnSEM
– CEC, sand, silt, clay
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ECHA workshop “Metals evaluation under REACH”
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Example Ni Case study (2): development of bioavailability models
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•
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Several sediment parameters were significantly correlated with the observed ecotoxicity values (expressed as total recoverable nickel or SEM nickel)
The significant relationships between the ecotoxicity values and AVS for all three species suggest that a bioavailability model based on AVS AVS was the driving parameter but co‐variance was seen with several other parameters (e.g., Total Fe, TOC)
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ECHA workshop “Metals evaluation under REACH”
Example Ni Case study (3): development of bioavailability models
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Normalization data with AVS model reduces intra‐species variability significantly
76.8 %
reduction
42.2 %
reduction
31.4 %
reduction
ECHA workshop “Metals evaluation under REACH”
Conclusions sediment bioavailability
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• Bioavailability plays important role in sediment toxicity
• Mechanistic understanding is increasing
• Different tools are available and/or under development and relevant databases on the key parameters (AVS/OC/Fe) are being developed
ECHA workshop “Metals evaluation under REACH”