Acute, Chronic, Sublethal Effects to Individuals Flashcards
Single Species Testing Benfits
Control and isolation of variables
* Sensitivity (overestimate toxicity?)
* Provide insight into effects seen at
higher levels of organization
* Simplicity allows rapid incorporation
of new chemicals into testing
Microcosms
Microcosm: laboratory systems intended to Microcosm: laboratory systems intended to
physically simulate an ecosystem or major physically simulate an ecosystem or major
subsystem of an ecosystem while permitting subsystem of an ecosystem while permitting
control of conditions and replication of control of conditions and replication of
treatments
** Microcosm: small studies, usually in the lab
Mesocosm:
Mesocosm: large, containing many species,
usually outdoorsusually outdoors
** ‘‘Cosms used to study changes at population, Cosms used to study changes at population,
community, ecosystem levels and contain at least community, ecosystem levels and contain at least
2 trophic levels (primary producers, grazers)
Cosms benefits
Validate single species lab studies or
mathematical models
* Predict potential fate and effects of
chemicals
–Degradation of compound Degradation of compound
–Bioaccumulation/Biomagnification Bioaccumulation/Biomagnification
–Detect disturbances among populations Detect disturbances among populations
and/or communities and/or communities
* Cheaper than field studies Cheaper than field studies
Field Evaluations Advantages
- Site-specific testing
- Realistic
- Account for functional redundancies
Field Evaluations Disadvantages
Not predictive (not applicable to other sites)
* Not replicative
* Studies are often long-term
* Temporal and spatial variability
Single Species 4 main beniftis
Uncertainty
Reproducibility
Interpretability
Sensitivity
Field Test 4 main benefits
Complexity
Cost
Realism
Acute exposures time
Exposures 48-96 hours
Acute exposures advantages
Rapid building of comparative databases (species and chemical)
* Manipulate water quality to evaluate interactions with toxicity
* Rapid screening of new chemicals, formulations, mixtures, etc…
Acute exposures disadvantages
Some acute exposures can take long periods to manifest effects
* Miss sub-lethal effects that may occur
Chronic exposures time
10 percent duration of the lifespan of the test organism.
Chronic test advantages
More ecologically relevant
* Examine sub-lethal endpoints (growth, reproduction)
* Shows effects at lower doses
Chronic test disadvantages
Expensive to run
High maintenance
Life cycle study
determines lethality, growth, reproduction, development, or other important qualities at all life stages.
Critical life stage test
Focuses on a particular life stage such as neonates. Often, the most critical stage is assumed to be an early life stage.
Early life stage (ELS) tests
Often done under the assumption that the most critical stage is often the earliest stages. Embryo to larval stage.
Weakest Link Incongruity
Early life stage testing is applied to the
premise that the population will remain viable
if the weakest link in an individual life stage is
protected
– False paradigm
– Early life stage not always the most crucial relative
to the population
– r/K spectrum of reproduction strategies
Static toxicity tests
Individuals are placed in a series of exposure concentrations. Exposure water not changed during the test.
Static-renewal test
Test solutions are completely or partially replaced periodically
Flow-through test
Continuous flow or intermittent flow of toxicant solutions
Static Advantages
cheap, easy, minimal waste
Static Disadvantages
loss of chemical, poor
water quality/BOD, metabolic products
Static-Renewal
Test solutions completely
or partially renewed periodically (typically or partially renewed periodically (typically
every 48 hours)
Flow-Through
test solution flows
into and out of test chambers on a
once-through basis
Flow-Through Advantages
maintain chemical
concentration, better water quality
Flow-Through Disadvantages
expensive, high
maintenance, large volume of waste, maintenance, large volume of waste,
require more space
Model Test Species Fresh Water Invertebrates
Daphnia magna
Daphnia pulex
Ceriodaphnia dubia
Model Test Species Fresh Water Fish
- Rainbow trout
*Bluegill
*Fathead minnow
Model Test Marine Invertebrates
Mysid shrimp
Urchin
Sand dollar
Model Test Marine Fish
Silverside
Top smelt
Sheepshead minnow
Acute Endpoints
Survival
Analyses: LCx
Chronic Endpoints
Survival, growth, reproduction
Other endpoints: histology, behavior, etc..
Analyses: NOEC, LOEC, MATC, LCx, ECx
Where to start a test
Concentrations
-from Literature
-EPA databases
- Ecotox EPA database
-IRS EPA database
-Hazardous substance database (NIH)
-Pilot Study
Dose-Response Models
Standard test method
* Serial dilution of test concentrations (50% dilutions)
* Replicate containers for each treatment
* At least one control treatment
* Individuals randomly placed into the containers
* Mortality tallied in each tank/cage at a set time
* Data used to calculate a measure of lethality
– proportion dying (#dead/#exposed)
– relate to exposure concentration
Median lethal dose (LD50) or LC50
The LD50 is the dose resulting in death of 50% of
exposed individuals by a predetermined time, e.g.,
96 h.
INCIPIENCY OR THRESHOLD
Lowest concentration (or dose) at which an increase in
toxicant concentration (or dose) begins to produce an
increase in the measured effect or effect metric.
Incipient median lethal concentration
(incipient LC50)
Concentration below which 50% of exposed individuals
will live indefinitely relative to the lethal effects of the
toxicant.
