Toxicity Test Methods

1
Toxicity Test Methods

• Chapter 4

2
Introduction

• Working knowledge of standard test methods very
  important in understanding the field of
  environmental toxicology
• Both strengths and weaknesses needed to interpret
  test results
• Methods were mostly developed in the 80s with
  some modifications since then
• Most old tests have not been replaced with new
  tests but rather have been tweaked over the
  years

3
Overview

• Toxicity tests can range from cell cultures to
  ecosystem function
• Most tests fall under two general classifications
• Single-species
• Relatively cheaper, shorter, low ecological
  realism
• Multi-species
• Tend to be longer, more expensive and have higher
  ecological realisms

4
Single species toxicity testing

• Daphnia 45-h Acute Toxicity Test
• Most widely used test for evaluating toxicity of
  water
• Three primary species
• Daphnia magna general testing
• Ceriodaphnia dubia chronic testing over an
  acute time period
• Daphnia pulex evaluation of stormflow toxicity
• All are easy to culture when published guidelines
  are followed but some differences in testing
  procedure
• Note algal tests are most likely to show
  hormesis effect

5
D. magna vs. C. dubia
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Ceriodaphnia dubia toxicity test
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Daphnia magna toxicity test
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Single species toxicity testing (cont)

• Algal 96-h growth toxicity test
• Examines toxicity to freshwater and marine algae
• Algae are extremely important because they
  generate most of the primary productivity in
  aquatic and marine sytems ? effects on algae can
  have high impact at higher trophic levels in
  ecosystem

9
Microalgae 96-h toxicity test
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Algal toxicity test
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Single species toxicity testing (cont)

• Acute toxicity tests with aquatic organisms
• Multiple tests using a variety of fish,
  amphibians and macroinvertebrates
• Endpoint is either death or immobilization
• More difficult to culture or obtain as test
  organisms so often use animals collected from the
  wild or available commercially as bait
• Test organisms may need to be acclimated to
  laboratory conditions
• More variability in response because of increased
  heterogeneity of gene pool
• Locally collected organisms may provide better
  indication of effect of xenobiotics on local
  ecosystems
• See table 4.5 (p. 80-82) for specific test
  organisms and test conditions

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Fathead minnow culture
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Single species toxicity testing (cont)

• Terrestrial vertebrate toxicity test
• Mammals, birds
• Toxicant usually introduced in food (gelatin
  capsule or gastric lavage)
• Mammals ? surrogate for human health effects
• Birds ? effect of pesticides on non-target
  species
• Both animal groups are usually tested for 90 days
• Endpoint death, test may include urinalysis,
  hematology, necropsy

14
Small mammals collected from the wild may not be
suitable for toxicity testing
15
Beware of using large wild rats!
16
Single species toxicity testing (cont)

• Frog Embryo Teratogenesis Assay Xenopus (FETAX)
• One of few standardized amphibian-based toxicity
  tests
• Designed to test teratogenicity of chemicals or
  effluent using the African Clawed frog as a
  surrogate for humans
• Good correlation between known human teratogens
  and FETAX results

17
Xenopus life cycle
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Multi-species toxicity test

• Artificially contained communities
• Must contain two or more interacting species
• Trying to simulate environmental realism but
  often want to reduce heterogeneity in test
  conditions
• Wide range of size and complexity in
  multi-species test protocols

19
Microcosms and Mesocosms

• Microcosms
• Small (can usually be picked up)
• Assembled to include specific components
• Highly defined artificial ecosystem
• Easy, cheap to replicate
• Moderate level of environmental realism
• Mesocosms
• Larger (kiddie wading pool to 3 acre ponds)
• May include volunteer components so system is
  less defined
• Expensive, hard to maintain
• High level of environmental realism

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Microcosms
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Mesocosms
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Uses of microcosms and mesocosms

• 1 - Test for ecosystem level effects of
  pesticides (FIFRA microcosms)
• Effects of oil spills on marine ecosystem
• Effect of draining aquaculture ponds into
  adjacent stream
• Any ecosystem level test