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and Environmental Risk Assessment
Toxicity Testing and Environmental Risk Assessment
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Dimensions of the Toxic Chemical Problem
Chemical entities million Developed annually ~6000 In commerce ~65,000 In common use ~6,000 Regulated water air
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Toxicology – Historical Perspective
Human (Mammalian) toxicology White Rat Rabbit Dog/Cat Computer simulation?
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Toxicology – Historical Perspective
Environmental toxicology Before 1950 chemical data superior to biological data Needed methods to indicate level of biological effects of chemicals
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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
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Point source discharge into a fly ash collection pond
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Toxicity test The means by which the toxicity of a chemical or other test material is determined
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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
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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)
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Algae toxicity test, EPA laboratory, Cincinnati, Ohio
Photo by R. Grippo
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Endpoints Toxicology Ecology Survival Growth Reproduction
Behavior (avoidance) Abundance Diversity Biomass Processing rate
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Environmental Toxicology
Dose - response (effect) relationships Ecological Dose-Response relationships
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Mechanism of Toxicity Targets and Effects
Cell membranes Enzymes Lipids Protein synthesis Microsomes Regulatory processes (hormones) Carbohydrate metabolism
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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
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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
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Ecologically realistic testing
Greater sensitivity? Improved extrapolation? Replicability and reproducibility? Variability and detectability”? Suitable endpoints?
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Ecotoxicological testing
Single species Multi-species Mesocosm
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LOEC = lowest observable test concentration
The lowest test concentration that is significantly different from control
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NOEC = no observable effect concentration
The highest test concentration that is not significantly different from control
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MATC = geometric mean of NOEC and LOEC
Often referred to as the chronic value ____________ MATC = √NOEC * LOEC
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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
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Variability Detectability
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Need to be careful! False negative system insensitive?
False positive unconfirmed predictions?
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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
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Who will watch the watchers?
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