TOXICOLOGY IV

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TOXICOLOGY IV

• ECOLOGICAL RISKS

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Chemical Risks

• Rachel Carsons book Silent Spring (1962) first
  made people really think about chemical
  pollution.
• About DDT and how birds were being killed.

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Silent Spring

• On the mornings that had once throbbed with the
  dawn chorus of robins, catbirds, doves, jays,
  wrens, and scores of other bird voices there was
  now no sound only silence lay over the fields
  and woods and marsh. No witchcraft, no enemy
  action had silenced the rebirth of new life in
  this stricken world. The people had done it
  themselves.
• (Rachel Carson 1962)

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DDT

• Early 2nd generation (man made) pesticide
• Saved millions of people by killing disease
  carrying mosquitoes, ticks, bed- bugs, etc.
• 1950s- Death of birds noticed.

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DDT

• Stayed in soil and decomposing leaves
• Worms and insects ate leaves and soil
• Birds ate worms.
• Birds egg shells were too thin and broke
• DDT banned by EPA in 1972

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EFFECTS OF CHEMICAL PROPERTIES

• Most chemicals quickly decompose in to simpler
  compounds. Called degradation.
• Degradation occurs from
• Sunlight
• Moisture
• Warmth
• DDT degrades very, very slowly.

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EFFECTS OF CHEMICAL PROPERTIES

• DDT dissolves better in fats and oils than in
  water.
• ? DDT absorbs into animals bodies
• Once in a body it stays there.
• ? DDT builds up through the food chain.
• It Bioaccumulates.

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EFFECTS OF CHEMICAL PROPERTIES

• Bioaccumulation causes some chemicals to
  concentrate in animal fat.
• Through Biomagnification some chemicals build up
  at each level in the food chain.

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Biomagnification
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Biomagnification
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EFFECTS OF CHEMICAL PROPERTIES

• Many other chemicals cause problems
• The 1st pesticides were arsenic, lead, mercury,
  etc.
• They absorb (tightly bound to) soil particles.
• Many farms still have them in the soil.

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EFFECTS OF CHEMICAL PROPERTIES

• New pesticides are supposed to absorb to soil and
  then quickly break down.
• Some dont and then leach down to the groundwater.

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Movement and Fates of Pesticides in the
Environment
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Movement and Fates of Pesticides in the
Environment
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Testing Environmental Impacts of New Compounds

• 6 questions for a pesticides review.
• How rapidly does it break down?
• Does it dissolve better in water or in oil?
• How quickly does it evaporate?

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Testing Environmental Impacts of New Compounds

• Does it bind to soil particles or leach out as
  water percolates through?
• Does it tend to build up in fish, birds, and
  other wildlife?
• How toxic is it to humans and to organisms in the
  environment?

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Testing Environmental Impacts of New Compounds

• The Toxic Substances Control Act (1976) tracks
  75,000 industrial chemicals.
• Pesticides
• Herbicides
• Detergents
• Solvents
• Industrial Waste Products