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Toxicity Testing. and Environmental Risk Assessment. Dimensions of the Toxic Chemical Problem. Chemical entities4-10 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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Toxicity testing

Toxicity Testing


Environmental Risk Assessment

Dimensions of the toxic chemical problem

Dimensions of the Toxic Chemical Problem

  • Chemical entities4-10 million

  • Developed annually~6000

  • In commerce~65,000

  • In common use ~6,000

  • Regulated water 129 air 25

Toxicology historical perspective

Toxicology – Historical Perspective

  • Human (Mammalian) toxicology

  • White Rat

  • Rabbit

  • Dog/Cat

  • Computer simulation?

Toxicology historical perspective1

Toxicology – Historical Perspective

  • Environmental toxicology

    • Before 1950  chemical data superior to biological data

    • Needed methods to indicate level of biological effects of chemicals

Toxicity testing

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

Toxicity testing

Point source discharge into a fly ash collection pond

Toxicity test

Toxicity test

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

Toxicity testing

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

Toxicity testing

Chronic toxicity testing


Fish – life cycle at least 3 to 6 months

(fathead minnow)

Invertebrates – complete life cycle in 3 days

(water flea -Ceriodaphnia dubia)

Toxicity testing

Algae toxicity test, EPA laboratory, Cincinnati, Ohio

Photo by R. Grippo





Behavior (avoidance)




Processing rate



Environmental toxicology

Environmental Toxicology

  • Dose - response (effect) relationships

  • Ecological Dose-Response relationships

Mechanism of toxicity targets and effects

Mechanism of ToxicityTargets and Effects

  • Cell membranes

  • Enzymes

  • Lipids

  • Protein synthesis

  • Microsomes

  • Regulatory processes (hormones)

  • Carbohydrate metabolism

What is the purpose of bioassays

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

Criteria for selecting test organisms

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

Ecologically realistic testing

Ecologically realistic testing

  • Greater sensitivity?

  • Improved extrapolation?

  • Replicability and reproducibility?

  • Variability and detectability”?

  • Suitable endpoints?

Ecotoxicological testing

Ecotoxicological testing

Single species Multi-species Mesocosm

Loec lowest observable test concentration

LOEC = lowest observable test concentration

The lowest test concentration that is significantly different from control

Noec no observable effect concentration

NOEC = no observable effect concentration

The highest test concentration that is not significantly different from control

Matc geometric mean of noec and loec

MATC = geometric mean of NOEC and LOEC

  • Often referred to as the chronic value



Hypothesis testing

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

Toxicity testing

Variability Detectability

Need to be careful

Need to be careful!

  • False negative  system insensitive?

  • False positive  unconfirmed predictions?

Who said it

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

Toxicity testing

Who will watch the watchers?

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