Lecture 2 - DA Flashcards
What is the dose response relationship, and what kind of curve does it produce? What can be calculated from the curve?
Dose refers to the amount of toxicant exposed to.
Response is the observed effect/endpoint measured.
A series of doses/concentrations are used to generate a sigmoidal curve.
LC50/LD50 is calculated from the curve.
What is done to linearlise the dose response curve?
Put on a log axis to linearise it, to better make predictions.
Describe an essential toxicant. What is the most typical essential toxicant?
Needed in trace amounts, but toxic at high concentrations.
Essential for growth and survival.
Copper is the most typical.
What is the reference toxicant for essential organic and inorganic toxicants?
Inorganic - copper
Organic - phenol
Describe a non-essential toxicant.
Not required for survival or growth, and as dose/concentration increases, adverse effects increase.
Name some endpoints (9).
Death - lethality test Growth inhibition Cellular stress Respiratory changes Developmental toxicity Reproductive effects Immunotoxicity Genotoxicity
What are the problems with using endpoints? What is needed to be accurate (6)?
May not always be a statistically significant effect. To be accurate you need appropriate: -sample size and replication -number of endpoints observed -number of dosages/concentrations -ability to measure the endpoint -little variability in the endpoints -statistical methodology
What effect will a very low dose/concentration, very long exposure time have on a population?
No effect.
What effect will a low dose/concentration, long exposure time have on a population?
Sensitive individuals are affected.
What effect will an intermediate dose/concentration, intermediate exposure time have on a population?
Equal number of deaths and survivors.
What effect will a high dose/concentration, short exposure time have on a population?
Few resistant individuals, with many deaths.
What effect will a very high dose/concentration, very short exposure time have on a population?
Entire population dead.
What two tests are used to simulate field conditions?
Microcosm and mesocosm tests.
What do field studies measure?
Measures effects at a population level.
What 4 factors does a toxic effect depend on?
Dose/concentration
Length of exposure
Lifestage of the organism
Previous exposure
What is a reference toxicant? What is its purpose?
Known toxicant used as a positive control.
Used to determine viability of test organisms and to assess consistency.
Are acute toxicity tests short term, or long term?
Short term test, takes days.
What are some endpoints of an acute toxicity test (4)?
Mortality
Immobilisation
Loss of equilibrium
Growth inhibition
Are chronic toxicity tests short term, or long term? What does it involve?
Long term, involves partial or full life cycle test.
What are some endpoints of chronic toxicity tests (3)?
Reproduction viability
Growth
Mortality
Which lifestages are very sensitive?
Early lifestages.
What can happen if exposed to toxicants during early lifestages?
The toxic effects may carry over to older lifestages.
Are sublethal toxicity tests short term or long term?
Can be both.
What do sublethal toxicity tests measure?
Effects at sublethal levels.
What are some endpoints of sublethal toxicity tests (3)?
Biochemical/physiological changes
Histological changes
Behavioural changes
How many endpoints can a given acute toxicity test have? What about chronic and sublethal?
Acute - single only
Chronic - single or multiple
Sublethal - multiple only
How do acute toxicity tests differ from chronic and sublethal in terms of complexity and data analysis?
Acute tests are more simpler than chronic and sublethal.
Sublethal is the most complex of the three.
In which of the three toxicity tests (acute, chronic, or sublethal) can toxic mechanisms be identified?
Chronic and sublethal, but not acute.
Some chemicals are less toxic in the environment than lab conditions. Explain why. Is this always the case?
Reduced persistence and lower bioavailability.
This is not always the case, some chemicals may show enhanced toxicity, and are more toxic in the environment.
How many endpoints does a single species test have?
Single finite endpoint.
How many environmental factors does a single species test have? What about microcosm/mesocosm tests?
Single environmental factors.
Microcosm/mesocosm tests have multiple environmental factors.
What species are used in single species tests?
The most sensitive one available.
How do microcosm and mesocosm tests differ?
Microcosm - small to large tanks, mainly outdoors
Mesocosm - same as microcosm, but larger scale
What are 8 advantages of a mesocosm test?
Is a completely functioning ecosystem.
Can be characterised and maintained for a defined time
Can replicate in appropriate statistical design
Components of the system can be isolated or supplemented.
Conditions are more realistic than lab setting
Effect of a chemical can be seen on many species at once
Ecosystem level effects and interactions can be investing
What are 5 limits of mesocosm tests?
Difficult to establish realistic community, especially higher trophic levels
Very expensive to construct/maintain
Replicated system can change and diverge over time
Scaling factors may not always add up to the natural system
Difficult to interpret results and characterise endpoints
When selecting a species for toxicity testing, what is the criteria (6)?
Should have range of sensitivities
Species should be abundant and widely available
Should be native
Should be recreationally, financially, or ecologically important
Background information on the species should be well known
Should be adaptable to lab conditions
Do organisms respond to an absolute increase in dose/concentration or a proportional increase?
Proportional increase.
What is a probit? Can a probit analysis analyse quantal data and continuous data?
A probit is one unit of standard deviation.
Probit analysis can analyse quantal data, but not continuous data.
Give an example of quantal data and continuous data.
Quantal - germination, death, tumour induction
Continuous - change in protein levels, oxygen consumption
What can be used to measure acute toxicity?
Vertebrates, invertebrates, and luminescent bacteria.
When using bacteria for toxicity tests, what is used?
Vibrio fischeri
Has a lux operon, with luciferase carrying out lumination.
What kind of bacteria is vibrio fischeri?
Marine, gram negative rod.
When using luciferase luminescence for bacterial toxicity testing, what indicates toxicity?
Toxicity reduces metabolic activity, so reduced light indicates toxicity.
What are some examples of using bacterial toxicity testing?
Wastewater treatment plants Monitoring raw drinking water Waste streams Industrial effluents Pollutants in soil
What is easier, detecting a mutagen, or proving the substance is carcinogenic?
Detecting a mutagen.
What are 2 benefits of bacterial test systems? Can they detect both mutagenicity and carnogenicity?
Advantages
-Short generation times - short test
-Cheap and easy to grow
Only detects mutagenicity and not carcinogenicity.
What bacterial strain does the ames test use?
Salmonells typhimurium His-strain.
What does the ames test involve?
Exposes the mutant bacteria to a test chemical
Revertants form - called reverse mutants, normal strains of bacteria
They grow on minumum agar
The stronger the mutagenic effect, the more revertant colonies on the minimum agar.
What is background reversion? When does the rate of reversion become significant?
All strains have natural mutations, therefore we expect a predictable rate of reverse mutants.
Rate varies between strains.
If the background reversion is doubled, then it is thought to be significant.
What is a promutagen?
Mutagenic when metabolised.
What does a daphnid acute toxicity test involve?
Daphnids reproduce by parthenogenesis, males produced in adverse conditions.
Culture should have no males if no toxicity is present.
Are daphnids suitable for both chronic and acute tests?
Yes.
Why are daphnids so sensitive?
They are filter feeders.
What are the four types of exposure conditions used in chronic toxicity testing?
Static
Static-renewal
Recirculation
Flow-through
What are some marine test species?
Shrimps, molluscs, fish, bivalves.
Are algal toxicity test more chronic or acute?
Mostly chronic tests.
What is an algicidal concentration? What about algistatic concentration?
Concentration that is lethal to the algae population.
Algistatic concentration is the concentration that completely inhibits growth, but allows regrowth when resuspended in normal media.
Is there a preferred algal test species?
No consistently sensitive species found yet.
What are two plants used for vascular plant toxicity tests?
Duckweed and lemna
What are 3 advantages of using vascular plants in toxicity tests?
Small size, rapid growth, and structural simplicity.
Can rooted vascular plants be used in a toxicity test with an aquatic medium?
There is no standardised test for aquatic media.
What bioconcentrates more, plants/algae or terrestrial/aquatic animals? What is this useful for?
Plants and algae. Used for bioremediation.
