1 / 26

Toxicity Testing II P erforming a toxicity test

Toxicity Testing II P erforming a toxicity test. Toxicity testing. Acute toxicity test Short time frame exposure (96h) “kill ‘em and count ‘em” LC 50 , TLM (median tolerance limit EC 50 (effective concentration) Chronic toxicity test Longer time frame exposure (1 week to 3 years)

wayland
Download Presentation

Toxicity Testing II P erforming a toxicity test

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Toxicity Testing II Performing a toxicity test

  2. Toxicity testing Acute toxicity test • Short time frame exposure (96h) • “kill ‘em and count ‘em” • LC50, TLM (median tolerance limit • EC50 (effective concentration) Chronic toxicity test • Longer time frame exposure (1 week to 3 years) • Endpoints are reproduction (brood size) physiology, behavior, biochemistry • More ecologically relevant

  3. Analysis • Analysis of Variance (hypothesis testing) • Test for significant difference from control (C + 5 doses) • Regression analysis • EC20 (concentration that causes 20% reduction relative to control)

  4. Determination of EC20 Control response 10 μg Response (growth) 20% reduction relative to control 8 μg Control EC20 eg. 1 mg/L = discharge limit Dose

  5. Ecosystem Tests(microcosms, mesocosms) • AOV design (4 reps X 3 treat., 3 rep X 4) • Time = 1 – 2 years • $106 /year • Endpoints are • Biomass • Diversity • Species richness • Etc.

  6. Normal distribution # Responding Log Dose Dose Probit Analysis • Response of organisms to toxic chemicals = normal distribution • Cannot measure normal distribution directly because effect is cumulative, so graph as cumulative distribution Cumulative distribution

  7. Log Dose • Difficult to evaluate a curved line • Conversion to a straight line would make evaluation easier Cumulative distribution # Responding

  8. Relationship between normal distribution and standard deviations 34.13% Mean 13.6% 2.13% -2 -1 0 1 2 Standard deviations

  9. Difficult to deal with SD (34.13, 13.6, etc) so rename SD to probits 34.13% Mean 13.6% 2.13% 3 4 5 6 7 Probits

  10. Probits • Based on SD so each probit has a percentage attached to it • Mean response defined as probit = 5 so all probits are positive  easier to visualize • Can use probit analysis to calculate LC50 because probit transformation will straighten the cumulative distribution line

  11. Cumulative distribution Probit transformed # Responding Log Dose Log Dose • Cumulative distribution is curvilinear • Probit transformation straightens the cumulative distribution line • Easier to calculate LC50 50% response LC50

  12. Note: probit forces data towards middle of distribution  good because most organisms are “average” in their response

  13. Aquatic toxicity testing Daphnia (water flea) “White rat of aquatic toxicity testing” Daphnia toxicity test

  14. Example problem Dose% alive 0 mg/L (control) 100 1 100 3 90 10 30 30 20 100 0

  15. If there is magic on earth, it is in water Photo by R. Grippo

  16. This slide purposely left blank

  17. Today’s laboratory exerciseAcute toxicity test – Daphnia pulex • Use neonates (<24 h old) • All females (parthenogenetic) • Class will break up into 3 groups of 2 • 1 person in group will calculate dilutions, other will select neonate Daphnia

  18. Calculation of Dilutions • Have stock solutions at a given concentration (10 mg/L Zn, 1 mg/L Cu, 100% effluent) • Want to make 100 ml test solutions at correct concentrations • Use C1 V1 = C2 V2 10 mg/L changes 100 ml Where C1 = concentration of stock solution V1 = volume needed of stock solution for ea. concentration C2 = desired concentration of test solution V2 = final volume needed in test chamber

  19. To make up solutions in cups • Put correct volume of toxicant into graduated cylinder • Add MH water to ~98-99 ml • Top off with squirt bottle of MH water (bottom of meniscus) • Pour into plastic cup • Start with lowest concentration 1st, work up to highest (why?) • Rinse graduated cylinder with MH water when done

  20. To count out Daphnia • Work on light table, easier to see. • Arrange 6 small plastic sample cups. • Put 2-3 ml in each sample cup (large drop). • Suck up Daphnia from brood container (2-3 at a time, neonates only). • Express Daphnia into large drop. Note: take care to release Daphnia under water  if just drop in may get caught in surface tension and die • Put 2-3 in 1st cup, 2-3 in next cup, until all cups have 10  random distribution will prevent putting all easiest to capture in 1st cup, next easiest all in 2nd cup, etc • After have 10 in ea. Cup and test chambers are ready, carefully lower cup into test chamber and release animals under water. • Record # dead/alive 24 and 48 hrs

  21. Estimate LC50 • If have at least two partial kills  use computer program • If one or less partial kills  use probit paper

More Related