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Toxicity Testing

Toxicity Testing. and Environmental Risk Assessment. Dimensions of the Toxic Chemical Problem. Chemical entities 4-10 million Developed annually ~ 6000 In commerce ~ 65,000 In common use ~ 6,000 Regulated water 129 air 25 .

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Toxicity Testing

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  1. Toxicity Testing and Environmental Risk Assessment

  2. Dimensions of the Toxic Chemical Problem • Chemical entities 4-10 million • Developed annually ~6000 • In commerce ~65,000 • In common use ~6,000 • Regulated water 129 air 25

  3. Toxicology – Historical Perspective • Human (Mammalian) toxicology • White Rat • Rabbit • Dog/Cat • Computer simulation?

  4. Toxicology – Historical Perspective • Environmental toxicology • Before 1950  chemical data superior to biological data • Needed methods to indicate level of biological effects of chemicals

  5. History of Aquatic Toxicology • Prior to 1962 – pollution laws focused on sewage and nutrients • 1962 – Silent Spring published (pollution by synthetic organic chemicals) • Environmental regulations developed • Point-source pollution • Non-point source pollution

  6. Point source discharge into a fly ash collection pond

  7. Toxicity test The means by which the toxicity of a chemical or other test material is determined

  8. Toxicity testing Simultaneous chemical detection and biological effects Acute toxicity test • Short time frame exposure (96h) • “kill ‘em and count ‘em” Chronic toxicity test • Longer time frame exposure (1 week to 3 years) • reproduction, physiology, behavior, biochemistry • More ecologically relevant

  9. Chronic toxicity testing Reproduction Fish – life cycle at least 3 to 6 months (fathead minnow) Invertebrates – complete life cycle in 3 days (water flea -Ceriodaphnia dubia)

  10. Algae toxicity test, EPA laboratory, Cincinnati, Ohio Photo by R. Grippo

  11. Survival Growth Reproduction Behavior (avoidance) Abundance Diversity Biomass Processing rate Endpoints ToxicologyEcology

  12. Environmental Toxicology • Dose - response (effect) relationships • Ecological Dose-Response relationships

  13. Mechanism of ToxicityTargets and Effects • Cell membranes • Enzymes • Lipids • Protein synthesis • Microsomes • Regulatory processes (hormones) • Carbohydrate metabolism

  14. What is the purpose of bioassays? • Rank hazards • Set discharge limits  regulate hazards • Predict environmental consequences • Protect important species • Reason why rainbow trout tested (commercially and recreationally important) • Reason why Zn, Cl standards based on toxicity to rainbow trout even if stream has none

  15. Criteria for Selecting Test Organisms • Broad range of sensitivities • Widely available and abundant • Indigenous or representative • Recreationally, commercially, or ecologically important • Laboratory tolerant • Adequate background information

  16. Ecologically realistic testing • Greater sensitivity? • Improved extrapolation? • Replicability and reproducibility? • Variability and detectability”? • Suitable endpoints?

  17. Ecotoxicological testing Single species Multi-species Mesocosm

  18. LOEC = lowest observable test concentration The lowest test concentration that is significantly different from control

  19. NOEC = no observable effect concentration The highest test concentration that is not significantly different from control

  20. MATC = geometric mean of NOEC and LOEC • Often referred to as the chronic value ____________ • MATC = √NOEC * LOEC

  21. Hypothesis testing • All types of testing need to hypothesis testing  what concentration is significant? • All bioassays try to determine level of toxicant which will or will not cause an effect

  22. Variability Detectability

  23. Need to be careful! • False negative  system insensitive? • False positive  unconfirmed predictions?

  24. Who said it? “The significant problems we face cannot be solved at the same level of thinking we were at when we created them” - Albert Einstein

  25. Who will watch the watchers?

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