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Lecture 11

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BIOL 354
Bruce Greenberg

BIOL354 – Environmental Toxicology I Spring 2012 Lecture 11: Assessment of Toxicology Risk assessment: mostly depends on the response of the target organism (bio-receptor) [+ve or -ve] - “The dose makes the poison, and the endpoint makes the experiment” o E.g. Jimi Hendrix (L50) vs. Keith Richards 50D ) - Categorizing Responses to Toxicants o Degree: Lethal vs. Sub-lethal (Disturbed environment return to equilibrium)  E.g. Dundus spencer creek: Newspaper headline; fertilizer spill; dead fishes (Uncommon) o Types: Population > Whole organism > Biochemical/Metabolic o Timing:  Acute: Severe, Rapid (<96 hours), [] applied > environmental []  Chronic/Sub-acute: Less severe, Prolonged (>10% life span), [] applied < environmental []  Cumulative: Periodical addition (time & method varies) (Hard to do, good results)  E.g. Chronic: Mick (Discontinued-Control) vs. Keith (Treated) o Life stage (Toxicant Sensitivity):  Life cycle: Lethality, growth, reproduction & development over ENTIRE life cycle  Critical life stage: Important stages (Pre-adult: more physiological changes)(e.g. Repro)  Early life stage: Early in development (Most sensitive) o Physiological changes -> Chronic -> Population Structure  Weakest Link Incongruity: Extrapolation of critical life stage (worst case scenario) results leads to over-estimation of potential risk - Bioassay Strategies o Definition: Biological assay, to estimate the nature, constitution & potency of a chemical by means of the observed response shown by the biological organism o Time: Time for response with set []/dose (hours to days, rarely months) o []/dose: Amount for response within set time  µg/moL (pure); mg/L & ppm (mixture of chemicals, different compounds) o Test types: Static toxicity; static renewal & flow through (difficult to setup & measure) - Dose/Concentration Response Curves o Purpose: Quantify effects of contaminants  Constant: time or []/dose  Higher potency = lower []/dose or time required for response (lower E/50 or E/L50)  Used with or without bioassay (Only need a quantifiable endpoint)  Individual effective dose: Smallest dose needed to affect or kill 1 random individual of the test population o Terminology:  Concentration: Toxicant surrounding/external to the organism  Dose: Toxicant applied internal/taken up by the organism  LC50 EC :50oncentration that cause 50% death/effect of the organisms  NOEC/NOEL: No observed effect concentration/dose  LOEC/LOEL: Lowest observable effect concentration/dose  Preferred, statistically measurable “Lack of proof is not proof of l
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