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A Unified Aquatic Life Framework forAddressing the Affected Percentages
of Individuals, Species, and Time
Charles DelosGreat Lakes Environmental Center
Two Approachesfor Addressing Time Variability
• Simple approach uses distribution of exposureconcentrations.
• Complex approach uses a long time series ofconcentrations.
An Actual Application Applying theSimple Distribution of Concentrations
• State of Utah adopted a selenium criterion for theGreat Salt Lake, Gilbert Bay.– Applies to the Se concentration in bird eggs.
– Set at 12.5 mg/kg, the State’s estimate of the EC10 formallard duck, the most sensitive known species.
– Applies as the geometric mean concentration.
• Question: What is the aggregate level of effect ifthe water body geometric mean rises to the EC10and the variability of concentrations (expressed asa CV or log standard deviation) remains as present?
Combining Ambient Concentration Distributionwith a Species Concentration-Response Curve:
Aggregate Effect = ∑ probabilityi x Effecti
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Egg Conc (mg/kg)
Allowable ConcProb Density(left axis)
Conc-Resp Curve(right axis)
Hypothetical Illustration: Selecting aReturn Interval for Exceeding a Criterion
• Possible application: let’s say a state wants toallow the annual reproductive season mean Sefish tissue concentration to exceed thecriterion only once in “X” number of years.
• We ask: for various values of the returnfrequency, X, what is the level of aggregateeffect on the hypothetical 5th percentilespecies having EC10=Criterion?
Trial 1: Once in 2 Years
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Annual Mean Concentration Relative to Criterion
Probability Density ofAnnual Concentration
Conc-Response Curve
Trial 2: Once in 3 Years
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Annual Mean Concentration Relative to Criterion
Probability Density ofAnnual Concentration
Conc-Response Curve
Trial 3: Once in 5 Years
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0.25 0.5 1 2
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nn
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Annual Mean Concentration Relative to Criterion
Probability Density ofAnnual Concentration
Conc-Response Curve
Trial 4: Once in 10 Years
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0.25 0.5 1 2
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Annual Mean Concentration Relative to Criterion
Probability Density ofAnnual Concentration
Conc-Response Curve
Results forVarious Exceedance Frequencies
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%R
ep
roIn
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%ile
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Return Interval of Exceedances for Repro Season (yr)
Long-term Avg Effect
10% Effect Line (EC10)
Influence ofAnnual Concentration Variability
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%R
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roIn
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5th
%ile
Spe
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Return Interval of Exceedances for Repro Season (yr)
Avg Effect, CV=0.52
Avg Effect, CV=0.31
Avg Effect, CV=0.13
Avg Effect, CV=0.05
Avg Effect, CV=0.00
Complex Approach
• The next set of slides addresses the complexapproach, which uses a time series ofexposures rather than the statisticaldistribution of exposures.
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Higher Tier Assessment: Combined Applicationof Kinetic Toxicity Model and Population Model
- For Each Species, Apply Two Models -
• Kinetic toxicity model to translate from lab testexposures to continuously variable concentrations.
• Life-stage structured population model.
• The combination allows discerning:– How sensitivity differs among individuals and between life
stages.
– How reductions in survival, growth, and reproduction differin their effect on populations.
– How population effects differ between species that recoverrapidly and species that recover slowly.
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Higher Tier Assessments: Combined Applicationof Kinetic Toxicity Model and Population Model
- For Each Species, Apply Two Models -
• Kinetic toxicity model to translate from lab testexposures to continuously variable concentrations.
• Life-stage structured population model.
• The combination allows discerning:– How sensitivity differs among individuals and between life
stages.
– How reductions in survival and reproduction differ in theireffect on populations.
– How population effects differ between species that recoverrapidly and species that recover slowly.
• Toxicant concentration,short example
• Accumulation of stressin individuals of onespecies
• Population response inone species
Co
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am
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op
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Days
Density Dependent
Generating an Assemblage Toxicity Indexfor Tested Representative Species
Kinetic Toxicity Model
• Needed to predict toxicity of continuouslyvariable concentrations
• Provides input (such as death rates) topopulation model.
Minimum Data Needed to CalibrateToxicity Model for Each Animal Species
- Required
• Acute LC50
• Chronic survival EC50 or EC20
• Chronic EC50/EC20 ratio (conc-response slope)
- Desirable
• Chronic ECx differences between early life stagesand juvenile-adult stages
- Optional
• Chronic ECx differences between lethal andsublethal effects (growth-reproduction)
Simple Use of the Kinetic Modelto Help Understand Acute-Chronic Ratios
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Effe
ctC
on
cen
trat
ion
(mg
/L)
Exposure Duration (days)
Juv EC50
Juv EC20
ELS EC20
Components of Ammonia ACRfor Fathead Minnow
Stage-Structured Population Model
Population Model Input Parameters
• Decide how many life stages you want todivide the species lifespan into.
• For each life stage, specify its:
– Duration
– Background survival rate
– Reproductive rate – for adult stage(s) only.
Modeling Effects on Populations
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opula
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Toxi
cS
tress
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Daphnia
Bluegill
Toxic Stress
Mortality v. Repro EffectsDaphnia response to 30-day Pulse Exposure at EC50
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daphnid mortality - all life stages
dapnid repro impairment
30-day exposure to EC50
Mortality v. Repro EffectsBluegill response to 30-day Pulse Exposure at EC50
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bluegill mortality - all life stages
bluegill ELS mortality / repro impairment
30-day exposure to EC50
Comparing the Simple and Complex Approaches:
Coupled Concentration Distribution & Response Curvevs.
Coupled Toxicity Model & Population Model
Co
ncen
trati
on
Dam
ag
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op
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Density Dependent
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DF
Egg Conc (mg/kg)
Comparing the Simple and Complex Approaches:
Coupled Concentration Distribution & Response Curvevs.
Coupled Toxicity Model & Population Model
• Simple approach:
– Bypasses kinetics of toxicity.
– Bypasses sequencing of events.
– Cannot discern life-stage sensitivity differences.
– Cannot discern chronic lethal from sublethal effects.
– Omits persistence of loss concepts (recovery time):cannot discern short-lived from long-lived species.
