Lecture 2 - RH Flashcards
Fundamental to ecotoxicology is the relationship between dose and _______
Response
What is the dose regarding ecotoxicology?
The amount of toxicant to which an organism is exposed
What is the response regarding ecotoxicology?
The observed effect or endpoint that is measured
How is the dose-response curve generated?
A series of concentrations are tested ranging from no deaths to 100% deaths and as a result the LC50/LD50 is calculated
What is NOEC?
No Observed Effect Concentration
What is LOEC?
Lowest Observed Effect Concentration
What are the types of toxicants?
Essential
Non-essential
What is the difference between essential and non-essential toxicants?
Essential toxicants are toxicants that are essential for survival in trace amonts but toxic in large amounts.
Non-essential substances are not required for growth and survival and as concentration increases adverse events occur.
What are the types of responses to toxicants?
Death (lethality tests)
Growth inhibition
changes in metabolism
Cellular stress (induction/inhibition)
Changes in respiration
Developmental toxicity
Reproductive effects (embryo production and viability, and germination in plants)
Immunotoxicity
Genotoxicity (carcinogenicity, mutagenicity)
What are the problems with current endpoints looked for in ecotoxicology?
The endpoints may not be statistically significant. To be accurate we need appropriate:
Sample size and replication
Number of endpoints observed
Number of dosages or concentrations
Ability to measure endpoints
little variability of endpoints
statistical methodology
What is the effect of dose of toxicant on response? How does time affect this?
Very low = no effects
Very high = deaths
Time does nothing to doses that are very low and kills most individuals at higher doses
What are the types of toxicity tests?
Acute toxicity tests
Chronic toxicity tests
Lifecycle/Partial Lifecycle toxicity tests
Sublethal toxicity tests
microcosm and mesocosm tests
Field studies
What is acute toxicity testing?
The tested concentration/dose is severe enough to cause a rapid response (within 24 hours to 4 days)
What is chronic toxicity testing?
Tested concentration/dose causes a response after a longer period of exposure (usually greater than 1/10th of the lifespan of an organism. eg. 21 days for some fish species
What is lifecycle/partial toxicity testing?
Entire lifecycle (embryo-adult) or critical life stages are studied
What is sublethal toxicity testing?
Tested concentrations below level which directly causes death
What are microcosm and mesocosm tests?
Tests that simulate the conditions of the field
What does the toxic effect depend on?
Dose/concentration
Length of exposure
Lifestage
Previous exposure and toxicological interactions
What is used as a positive control in typical toxicology testing?
A reference toxicant
What are the typical endpoints of acute toxicity tests on fish and invertebrates?
Mortality
Immobilisation
Loss of equilibrium
What are the typical endpoints of acute toxicity tests in algae and vascular plants?
Growth inhibition
Mortality
What is the difference between LC50, LD50, and LT50?
Lethal Concentration
Lethal Dose
Lethal time of exposure
*Respectively
What does a higher LC50 value indicate?
Higher tolerance of an organism to tested toxicant
What are the typical endpoints of chronic toxicity testing?
Reproduction (gamete production, egg viability, hatching success, germination)
Growth and Mortality
What is the EC50 of an organism?
Effective concentration causing adverse effects in 50% of tested organisms for endpoints other than mortality.
Why are some toxicant tests conducted on early life stages?
Early life stages are very sensitive and the effects can carry over to later stages
New evidence suggests effects of toxicants on the epigenome
Are sublethal toxicity tests conducted in the short term or in the long term?
May be either
What are the end points of sublethal toxicity tests?
Biochemical/physiological - induction of enzymes and proteins, up/down regulation of genes, hematology, respiration
Histological - tissue necrsis, tumour formation, pathology
Behavioural - locomotion, swimming ability, avoidance, predator-prey interactions, courtship
Why are most chemicals less toxic in field than in tests?
Reduced persistence and bioavailability
What are the chemicals that become more toxic in the field called?
Photoenhanced toxicity
What is the difference between microcosm and mesocosm?
Classified based on size
What are the advantages of using simulated mesocosms?
Systems are tested in a functioning ecosystem in the correct proportions
Can be maintained for a set time
Conditions can be monitored before and after adding toxicant
Components of system can be isolated
Environmental condiitions which is better than simulating in lab
Interactions between species can be investigated
What are the limitations of simulated mesocosms?
Difficult to establish a realistic community
Very expensive to construct and maintain
Replication systems change differently with time and diverge
Scaling factors must be carefully considered
Difficult to interpret results and characterize endpoints
What are the benefits of conducting field studies?
Natural environment is complex, dynamic, and changeable (unlike controlled lab environment)
More realistic evaluation of concentration-response relationship: Interactive effects of physico-chemical facors with toxicants
Can measure indirect effects - predator/prey interactions, biotic and abiotic interactions
How are sites selected for field studies?
Cost, accessibility
Presence of the desired test species
What endpoints are measured in field studies?
Can these effects be detected in field studies? (i.e reproducability of lab experiments)
Laboratory validation using acute and chronic tests
What are the types of test organisms in aquatic systems?
Microorganisms
Primary producers (phytoplankton, micro-algae, and aquatic plants)
Invertebrates (molluscs + crustaceans)
Fishes
Amphibians
Sediments
What are the types of test organisms in terrestrial environments?
Microorganisms
Primary producers
Invertebrates
Reptiles
Birds
Mammals
What are the criteria for selecting organisms for field studies?
Organisms with a range of sensitivities should be tested
Tested species should be widely available and abundant
Test species should be native/ representative of tested environment
Tested species should be recreationally, commercially, or ecologically important
Tested species should be adaptable to lab conditions
Bacnground information on physiology and ecology of tested species should be known
What are the important elements of experimental design regarding ecotoxicology?
Replication
Randomisation
Realisticness
Follow the testing guidelines
What are the test guidelines used for?
Test guidelines provided detailed instuctions on experimental design.
*The test guidelines include: Principles of the test Test validity Description of methods Choice of species, holding vessels Preparation of test chemicals Required observations Data analysis and interpretation
What kind of increase in concentration of toxicants do organisms respond to?
Organisms respond to a proportional increase in toxicant rather than an absolute increase
What is the PROBIT value?
1 unit of standard deviation
How is the response linearised?
X axis uses a log scale
Y axis uses a PROBIT scale
what kind of data can’t be analysed by PROBIT analysis?
continuous data
What are the methods of data analysis used in ecotoxicology?
Exploratory plot analysis:
Histograms, box plots, dot plots, scatterplots, homogeneity of variance, normality, independence, Data transformation (log, arcsine, square root, PROBIT)
Hypothesis testing: Analysis of variance (ANOVA), parametric/non-parametric data analysis, type 1/type 2 error
Correlation and regression analysis
Multivariate analysis
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