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Toxicity Test Methods. Chapter 4. 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

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Toxicity Test Methods

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  • 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 ’80’s with some modifications since then
  • Most “old” tests have not been replaced with new tests but rather have been “tweaked” over the years
  • 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
single species toxicity testing
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
single species toxicity testing con t
Single species toxicity testing (con’t)
  • 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
single species toxicity testing con t11
Single species toxicity testing (con’t)
  • 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
single species toxicity testing con t13
Single species toxicity testing (con’t)
  • 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
single species toxicity testing con t16
Single species toxicity testing (con’t)
  • 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
multi species toxicity test
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
microcosms and mesocosms
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
uses of microcosms and mesocosms
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