RISKTargets:

1. Explain risk, toxicology, toxins and factors that affect chemical risks.

2. Explain how toxicity is measured and methods of determining the toxicity of a chemical.

What is risk, risk assessment, and risk management?

Risk is the possibility of suffering harm from a hazard. Hazard: situation that poses a level of threat

to life, health, property or the environment. Ex. cultural, biological, physical, and chemical.

Risk assessment determines insurance rates. Expressed in terms of probability

Risk management determines safety plans and regulations.

What is toxicology and toxicity? What factor impact toxicity?

Toxicology is the study of adverse effects of chemicals on living organisms.

Toxicity is the measure of how harmful a substance is in causing injury illness or death to a living organism.

© 2004 Brooks/Cole – Thomson Learning

Verysensitive

Majorityof population Very

insensitive

0 20 40 60 80

Dose (hypothetical units)

Nu

mb

er o

f in

div

idu

als

affe

cted

Individual responses to chemical hazards

Toxicity depends on

-dose

-frequency

-time

-size/age

-immune system

-genetics

What are the guiding principles for determining toxicity?

1. Any synthetic or natural chemical can be harmful if ingested in a large enough quantity. Ex. lethal dosage of caffeine = 100 cups of coffee

2. How much exposure to a particular toxic chemical causes a harmful response?- The dose makes the poison.- The dose makes the poison, but differently for different individuals.- The dose of a usually unknown mixture of chemicals makes the poison, but differently for different individuals.

Describe five factors that affect harm caused by substances.

1. Solubility 2. Persistence3. Bioaccumulation 4. Biomagnification 5. Chemical interactions

DDT in fish-eatingbirds (ospreys)

25 ppm

DDT in largefish (needle fish)2 ppm

DDT in smallfish (minnows)0.5 ppm

DDT inzooplankton0.04 ppm

DDT in water0.000003 ppm,Or 3 ppt

Table 9-1 Toxicity Ratings and Average Lethal Doses for Humans

Toxicity Rating

Supertoxic

Extremely toxic

Very toxic

Toxic

Moderately toxic

Slightly toxic

Essentially nontoxic

LD50 (milligrams perkg of body weight)*

Less than 0.01

Less than 5

5–50

50–500

500–5,000

5,000–15,000

15,000 or greater

Examples

Nerve gases, botulism toxin,

mushroom toxins, dioxin (TCDD)

Potassium cyanide, heroin, atropine,

parathion, nicotine

Mercury salts, morphine, codeine

Lead salts, DDT, sodium hydroxide,

sodium fluoride, sulfuric acid, caffeine,

carbon tetrachloride

Methyl (wood) alcohol, ether,

phenobarbital, amphetamines (speed),

kerosene, aspirin

Ethyl alcohol, Lysol, soaps

Water, glycerin, table sugar

Average Lethal Dose†

Less than 1 drop

Less than 7 drops

7 drops to 1 teaspoon

1 teaspoon to 1 ounce

1 ounce to 1 pint

1 pint to 1 quart

More than 1 quart

*Dosage that kills 50% of individuals exposed†Amounts of substances in liquid form at room temperature that are lethal when given to a 70.4-kg (155-pound) human

What is the difference between an acute effect response and a chronic effect response?

Response: type and amount of health damage resulting from exposure to a chemical or other agent. Acute: immediate or rapid. ex. dizziness to

death Chronic: permanent or long-lasting or single

or multiple dose. ex. kidney damage

LD50

0 4 8 12 16

Dose (hypothetical units)

Per

cen

tag

e o

f p

op

ula

tio

n k

illed

by

a g

iven

do

se

What dose would be right for a pesticide?

Top 5 toxicsarsenicleadmercuryvinyl chloridePCBs (polychlorinated biphenyls)

141062

25

50

75

100

How do dose-response curves relate to estimating toxicity?

Dose-response curves are one way to compare the toxicity of different

chemicals developed from acute toxicity tests use mathematical models to extrapolate

low-dose and high-dose levels

© 2004 Brooks/Cole – Thomson Learning

Eff

ect

Dose

Nonlineardose-response

Lineardose-response

No threshold

Eff

ect

Threshold

Thresholdlevel

Dose

Dose-response curves

What are some problems with estimating toxicity?

1. We are constantly exposed to a variety of different chemicals.

2. It is difficult to estimate the toxicity of one chemical and determine all possible interactions.

3. The effect of a particular chemical can be dependent on when the exposure occurred.

Should we avoid using all chemicals until they have been tested?

"When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically. In this context the proponent of an activity, rather than the public, should bear the burden of proof. The process of applying the precautionary principle must be open, informed and democratic and must include potentially affected parties. It must also involve an examination of the full range of alternatives, including no action."

- Wingspread Statement on the Precautionary Principle, Jan. 1998

Fig. 11-2 p. 229Fig. 11-2 p. 229

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