1. and Environmental Risk Assessment
Toxicity Testing
and
Environmental Risk Assessment

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

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)

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

13. Endpoints Toxicology Ecology Survival Growth Reproduction
Behavior (avoidance)
Abundance
Diversity
Biomass
Processing rate

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

18. Mechanism of Toxicity Targets and Effects
Cell membranes
Enzymes
Lipids
Protein synthesis
Microsomes
Regulatory processes (hormones)
Carbohydrate metabolism

19. 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

20. 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

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

22. Ecotoxicological testing
Single species Multi-species Mesocosm

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

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

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

26. 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

27. Variability Detectability

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

30. 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

31. Who will watch the watchers?