Transcript Ecological Linkages in Risk Assessment: Evaluating

Ecological Linkages in Risk Assessment:
Evaluating Risk in Natural Ecosystems
T.L. Yankovich
27 June 2007
ETB-07-###
Outline:
 Background Information
 Key Aspects and Framework
 Risk Assessment Approach
 Conclusions and Future Considerations
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Ecological Risk Assessment (ERA) Framework
(from Environment Canada 1997)
PROBLEM FORMULATION
Risk Managers and
Stakeholders
Data Collection and
Generation
Ecological Risk Assessment:
Analysis
Entry
Exposure
Effects
Characterization
Characterization
Characterization
Risk Characterization
If CEPA-“toxic”
Risk Management
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Key Components of Problem Formulation
i.e.: ‘What’ we
want to protect.
 Identification of Valued Ecosystem Components
(VECs)  and corresponding/comparable
receptor species.
 Screening/identification of contaminants of
potential environmental concern (COPECs).
 Evaluation of the potential overlap between
i.e.: ‘What’ we
want to protect
from.
COPECs and biota.
i.e.: ‘Where’ we
should focus
our efforts.
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Weighing Out the Risks
The level at which potential for
exposure and effects is typically
assessed using a multi-tiered approach.
Initially, a hyper-conservative
approach is undertaken for
SCREENING purposes.
A more detailed assessment of
exposure and in some cases,
effects, is then performed.
Mitigation and/or remediation
may then be considered,
depending upon the outcomes.
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Key Components of Entry Characterization
 Identification of key contaminant entry
pathways  key compartments.
 Characterization of source/emissions
through monitoring.
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Assessment of process.
Evaluation of source pathways.
Consideration of expected contaminant
behaviour.
Identification of contaminants of
potential environmental concern
(COPECS).
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Key Components of Exposure Characterization
 Characterization of exposure COPEC
concentrations in key compartments
for key receptor species.
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Characterization of species inventory.
Identification of valued ecosystem
components (VECs) and corresponding
receptor biota.
Compilation of relevant biological attributes
and parameter values for selected species.
Where possible, measurement of site-specific
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transfer parameters.
Estimation of Total Dose
DTOT or EEV = DE + DI
where:
• DTOT is the total dose to biota;
• DE is the total external dose from all radionuclides to which
biota are being exposed; and
• DI is the total internal dose from all radionuclides to which
biota are being exposed.
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Estimation of Total External Dose
to Aquatic Biota
DER = [COR,W  UW  DCCEWR] + [COR,S  US  DCCESR] + [COR,V  UV  DCCEVR]
where:
• COR,(W,S,V) is the concentration of radionuclide (R) in water
(W), sediments (S) or vegetation (V) (Bq·L-1 or Bq·kg-1);
• UW, US and UV are the habitat-use factors of biota for water,
sediments and vegetation, respectively (dimensionless); and
• DCFEWR, DCFESR and DCFEVR are the external dose
conversion factors for water, sediments, and vegetation,
respectively (based on Amiro, 1997).
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Estimation of Total Internal Dose
to Aquatic Biota
DIR = BAFR x COW x DFR x DCCIR
where:
Radionuclide (R)
Concentration In
Biota Tissue
• BAFR is the bioaccumulation factor for radionuclide, R (L/kg fresh
weight);
• COW is the concentration of radionuclide, R, in the water (Bq/L);
• DFR is a distribution factor to account for a disproportionate internal
distribution of radionuclide, R (dimensionless); and
• DCCIR is internal dose conversion coefficient for radionuclide, R.
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Unlike Aquatic Biota
Terrestrial biota are sub-divided into those
that spend time aboveground and those
that spend time belowground, or a
combination of the two with respect to
external dose estimation (as recommended
by Sample et al., 1997).
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Estimation of Total External Dose to
Aboveground Terrestrial Biota
Dabove  Fabove  Froughness Csoil, R  DC ground, R  CFb  ECF
ground
ground
factor
R
where:
• Daboveground represents the external dose rate from aboveground exposure to
contaminated soil (Gy/a);
• Faboveground is the proportion of time spent above ground (dimensionless);
• Froughness factor is the dose rate reduction factor accounting for surface roughness of soil
(dimensionless), which is assumed to have a default value of 0.7 (as recommended by
Sample et al., 1997);
• Csoil,R represents activity of radionuclide, R, in surface soil (Bq/kg dry);
• DCground,R is the dose coefficient factor for radionuclide, R, in soil contaminated to a
given depth (Sv/s per Bq/m3) (from Eckerman and Rymann, 1993);
• CFb is the conversion factor to change Sv/s per Bq/m3 to Gy/a per Bq/kg (is equal to
5.05 x 1010); and
• ECF is the elevation correction factor to adjust dose coefficients to value
representative of effective height of animal aboveground (which is assumed to be 2 for
small mammals and other species that are <1 m from the soil surface and 1 for taller
animals that are >1 m from the soil surface).
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Estimation of Total External Dose to
Belowground Terrestrial Biota
Dbelow  1.05  Fbelow
ground
C
soil, R
 ER  CFa
ground R
where:
• Dbelowground represents the external dose rate to non-human biota from contaminated
soil (Gy/a);
• Fbelowground is the proportion of time spent below ground (dimensionless);
• Csoil,R represents activity of radionuclide, R, in surface soil (Bq/kg dry);
• ER is the total energy of all g emissions (MeV/nuclear transition) (from Blaylock,
1993);
• 1.05 is a conversion factor to account for immersion in soil versus water; and
• CFa is the conversion factor to convert from MeV/nuclear transition to Gy·kg/Bq·a
(5.05x10-6).
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Application of Allometric Models
to Estimate Internal Dose
 For aquatic organisms, such as mammalian and avian species, as
well as similar species in terrestrial environments, exposure is
estimated based on allometric estimation of exposure via key
pathways, with estimation of fractional radionuclide uptake based
on diet.
Where:
n
Cbiota   I m  C m, R  BTF R  ft  fd
m 1
is Cm,R is the concentration of radionuclide R in medium m (Bq/kg fresh or Bq/L);
BTFR is the biotransfer factor of radionuclide, R (d/kg);
ft is the fraction of time an animal spends at the site of interest;
fd is the fraction of the diet of an animal that consists of food from the site of
interest.
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Estimation of Intake Rates for Various
Types of Receptor Biota
y  aWt
b
where:
• Y is the predicted biological function (e.g. food
ingestion rate);
• Wt the fresh weight of the animal (in kg or g);
and
• a and b are fitted empirical coefficients that
were quantified based on data representing
many observations of one broad characteristic
group (e.g. food intake rates measured for
many mammals).
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Assumed Intake Rates for Various
Types of Receptor Biota
Y
Type of Biota
Units
Wt
a
b
Reference
Birds:
Non-Passerine (NP)
Passerine (P)
All birds
All birds*
Food Intake
Food Intake
Water Intake
Inhalation
Rate
g dw food/d
g dw food/d
L/d
m3/d
g
g
kg
kg
0.301
0.398
0.059
0.4089
0.751
0.850
0.67
0.77
Nagy (1987)
Nagy (1987)
Calder & Braun (1983)
Lasiewski & Calder (1971)
Food Intake
Food Intake
Food Intake
Water Intake
Inhalation
Rate
g dw food/d
g dw food/ d
g dw food/ d
L/d
m3/d
g
g
g
kg
kg
0.621
0.577
0.235
0.099
0.5458
0.564
0.727
0.822
0.90
0.80
Nagy (1987)
Nagy (1987)
Nagy (1987)
Calder & Braun (1983)
Stahl (1967)
g/day
g/day
n.a.
n.a.
g
g
n.a.
n.a.
0.019
0.013
n.a.
n.a.
0.841
0.773
n.a.
n.a.
Nagy (1987)
Nagy (1987)
n.a.
n.a.
Mammals:
Rodents (R)
Herbivores (H)
All mammals (A)
All mammals
All mammals
Reptiles and Amphibians:
Herbivores
Insectivores
Food Intake
Food Intake
Water Intake
Inhalation
Rate
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Key Components of Effects Characterization
 Identification of relevant potential
effects to key receptor biota.
 Compilation of relevant effects
benchmarks (typically based on
regulatory guidance and/or
literature).
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Potential Exposure Must Then Be
Considered With Respect to
Potential Risk
Site-Specific
Exposure
Expected Exposure Value
Potential Risk =
Effects Benchmark Value
Regulatory
Guidelines
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. . . . . Thank YOU!
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