Transcript ES 120 TOXICS IN THE ENVIRONMENT

ES 120 TOXICS IN THE
ENVIRONMENT
LECTURE 12-13: Toxicity testing
SCOPE OF LECTURE
• How can we predict the toxic potential of
pollutants?
– Effects on human health
– Impact on environment
STANDARDIZED TESTS
• Expose/ dose test organism to/ with several
levels/ amounts of a pollutant and record
effects (“end point”)
– Environment, pollutant and organism are defined
– Environment is controlled (preferably constant)
– Experiments and results can be replicated by
different researchers in different laboratories
SOME FACTORS AFFECTING TOXICITY:
A SHORT REVIEW
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Dose/ concentration in food and environment
Route of uptake
Lipophilicity of pollutant
Exposure time and animal size
Biotransformation potential
Presence of target sites
Life stage
Volatility/ chemical stability
Environmental conditions
Bioavailability: interaction of physico-chemical
properties of pollutant and environment
CHOICES
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Species of organism
Exposure mode
End point (measured response)
Duration
Environmental conditions
Scale
CHOICE OF IDEAL SPECIES
Factors that determine the choice of ideal test
species include
• Technical factors
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Easy and cheap to grow and handle
Small species with a short life span
Genetic diversity: pro and contra
Ethical issues: vertebrates vs invertebrates
• Relevance
– Representative for many systems: abundant in a wide
geographical range
– Representative for other species
CHOICE OF EXPOSURE MODE
• Direct application
– Topical (via skin)
– Intravenous
• Food
• Ambient (esp. aquatic toxicity tests)
• Frequency of administration
– Single dose
– Intermittent
– Continuous
CHOICE OF END POINT
In order of increasing sensitivity:
1. Mortality
2. Sublethal response
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Reproduction, growth, growth rate, feeding etc
Behavior (mobility)
Mutations (Ames test with bacteria)
Deformation
3. Biochemical lesions
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Reporter genes in cellular systems
In micro and mesocosms: population numbers, juvenile
to adult ratio, community structure, flux of C and N
through system, etc.
CHOICE OF EXPERIMENTAL DURATION
• Acute toxicity tests
– Experiment lasts typically between 1 and 3 days
– End point is usually mortality
– Yields information about proper pesticide application dose and acute
toxic effects
– Problem: bioaccumulation incomplete, i.e. results depend on
experimental duration and cannot be used to predict environmental risks
(at least not directly)
• Chronic toxicity tests
– Experiment lasts more than 1-3 days but less than normal life span
– Any endpoint
– Results more relevant for environmental risk assessment than acute
toxicity tests
• Life cycle tests
– Experiment lasts several generations
– Any end point
CHOICE OF ENVIRONMENTAL CONDITIONS
• Factors affecting bioavailability
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pH: metals
Organic matter: metals and lipophilics
Ionic composition of water: “speciation” of metals
Clay and sand characteristics of soil and sediments
• Factors affecting organisms
– Food supply
• None or only once: acute toxicity tests
• Static renewal: regularly refreshing medium
• flow through systems: constant environment, expensive
– Other factors such as T, volume of container, number of
individuals per container, etc
CHOICE OF SCALE
• Single species in small lab environment
• Microcosm: a few small species (foodchain) in a
relatively small, controlled enclosure
• Mesocosm: multiple species, potentially
including a vertebrate, in a medium sized,
controlled enclosure
• Field study
– Manipulated enclosures in the field
– Field study with controlled release of pollutants
– Field study observing the effects of an existing
pollutant
THERE ARE MANY, MANY
STANDARDIZED TESTS…
• www.epa.gov/opptsfrs/home/guidelin.htm
• www.epa.gov/opptsfrs/publications/OPPTS_Har
monized/850_Ecological_Effects_Test_Guideline
s/Master/850.master.pdf
• Test requirements depend on chemical to be
registered, production volume and intended use
AN EXAMPLE: DAPHNID
CHRONIC TOXICITY TEST
• Static renewal or flow through system
• End points: mortality, reproduction, immobility of
adults and young
• At least 10 daphnids (<24 h old) per pollutant
concentration
• At least 5 pollutant concentrations
• Test duration is 21 days
• Medium is replaced and young are removed
every 2-3 days (i.e. Mon, Wed, Fri)
DAPHNID CHRONIC TOXICITY TEST : EFFECT OF
PHENOL AND CADMIUM ON REPRODUCTION
ANALYSIS OF DATA
• Plot end point (survival, growth, reproduction,
etc) as function of dose or exposure
concentration
• Exposure time is the same for all data in the plot
• With a statistical model, estimate
– LD50: dose at which 50% of test animals survive
– LC50: concentration at which 50% of test animals
survive
– EC50: concentration at which end point is 50% of
control
ESTIMATION OF LC50 OR EC50
LC50, EC50 ARE FUNCTIONS OF EXPOSURE TIME
LC50, EC50 ARE FUNCTIONS OF EXPOSURE TIME
OTHER MEASURES
• LC50 and EC50 are not very relevant
measures for risk assessment
• We want to know the concentrations at
which we see little or no effect
– LCx, ECx: concentration lethal for a small
percentage x/ showing an effect of x percent
– LOEC: lowest observed effect concentration
– NOEC: no observed effect concentration
– NEC: no effect concentration
Relevance Accuracy Foundation
LC50,
EC50
LCx,
ECx
LOEC,
NOEC
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+/-
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Statistical
model
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Statistical
test
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Biological
process
based
model
NEC
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Statistical
model
Remarks
Easy to determine
but of little value;
depends on
exposure time
Depends on
statistical model and
exposure time
Depends on choice
of toxicant
concentrations and
on exposure time
Requires DEB
model; independent
of exposure time;
not yet implemented
in toxicity tests
REMARK ON EC50, LC50
• Ultimate EC50 and LC50 values are related
to toxicity parameters in biological process
based models such as DEB models
• In this context ultimate EC50 and LC50
values are relevant as they can be used to
predict responses other than those
measured
WHICH POLLUTANT IS MORE TOXIC, A OR B?
% Output (growth, reproduction)
WHAT TYPES OF TOXICANTS ARE THESE:
100
75
50
25
0
0
10
20
Toxicant concentration
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SUMMARY
• The goal of toxicity testing is to assess the environmental and
human health hazards of pollutants
• Test organisms are exposed to a range of test concentrations/
doses; response variables (end points) are recorded after (a)
defined time interval(s)
• Dubious premises
– Test conditions represent or can be translated to real world conditions
– Test organisms are representative for other taxa or results can be
interpolated to other taxa
– Results can be interpolated to effects on other response variables
– Results can be interpolated to other levels of organization
• The “better” tests (e.g. flow through systems, mesocosms,
field enclosures) are relatively labor intensive, expensive and
take a long time to complete
• Classical data analysis yields toxicity measures that are not
very relevant, inaccurate and/ or dependent on the exposure
time and method of analysis
Next Lecture
• Biomarkers and Biological Monitoring
• Homework:
– Read PE 10 and 11
– Read paper on ecological indicators