Unit 3 – Environmental Chemistry

TOPIC 2

DDT – The Good News• Dichlorodiphenyltrichloroethane = DDT• Invented by Paul Hermann Muller who was

given the Nobel prize.• Used to kill lice that carried typhus killing allied

troops in WWII.• Was thought to be able to control mosquitos that

carried malaria• Crops thrived as pests declined.

DDT – The Bad News

• Too wide spread, killed good insects as well• Does not biodegrade quickly, hangs around• Enters the food chain and concentrates killing

larger animals like birds, made egg shells very fragile.

• When a chemical moves up the food chain and concentrates it is called biomagnification.

• Pests can become resistant to pesticide, so they no longer work.

ORGANIC AGRICULTURE• Growing crops:

• without the use of pesticides and commercial fertilizers

• using natural, renewable resources• conserving water • without endangering workers

PESTICIDES AND ORGANIC FARMING

DOMESTIC CROPS WERE SELECTED FOR MAXIMUM PRODUCTIVITY AND HAD LITTLE NATURAL PEST RESISTANCE

• Pests attack and eat our food crops

• This problem is due, in part, to not selecting for pest resistance during domestication

Today’s Pests

Based on: National Geographic, February 1980

DDT WAS INVENTED IN THE 1940’S AND VIEWED AS:- MIRACLE FOR FARMERS- SAFE!

“THE MOST DISCUSSED OF THE NEW INSECTICIDES IS DICHLORO-DIPHENYL-TRICHLOROETHANE, SHORTENED TO DDT BUT ALSO CALLED GUESAROL. THIS COMPOUND HAS REMARKABLE POWER TO KILL INSECTS, PARTICULARLY BODY LICE-THE ‘COOTIES’ OF WORLD WAR I. THE PREVALENCE OF TYPHUS, CARRIED BY BODY LICE, IN THE MEDITERRANEAN THEATER OF THIS WAR HAS EMPHASIZED ITS VALUE. DDT’S EFFECTIVENESS IN WAR MAY WELL BE OVERSHADOWED BY ITS VALUE IN PEACE. PAINSTAKING INVESTIGATIONS HAVE SHOWN IT TO BE SIGNALLY EFFECTIVE AGAINST MANY OF THE MOST DESTRUCTIVE INSECTS THAT FEED UPON CROPS.”

SCIENTIFIC AMERICAN, JULY 1944.

Arial crop sprayers were used to spray

tons of DDT on crops across the

U.S.

Pests became resistant to DDT

Based on: National Geographic

Pesticide Resistance:• In the beginning,

most pests were sensitive to DDT but a few were resistant

• The resistant forms survived and reproduced

• In the end, most pests were resistant to DDTBased on: National Geographic, February 1980

BIOMAGNIFICATIONTHE CONCENTRATION OF

PESTICIDES IN HIGHER LEVELS OF FOOD CHAINS

Most food chains consist of four trophic levels

Trophic Levels

DDT is concentrated as it moved up food chain

This is because energy is lost (from respiration) as go up food chain but DDT is not

Based on: Campbell et al, Biology: Concepts and Connections, Benjamin Cummings

DDT in Food Chain

Bald Eagle•Once was widely distributed over U.S.

•As a top carnivore it feeds on fish

•Swoops down and captures fish off the surface of the water

•Scientists discovered that DDT was concentrated in the bald eagle

•DDT affected the eagle’s ability to reproduce

Scientists found that the eagle eggs had thin egg shells and broke easily

Nests contained broken, rotten eggs

The number of young produced per breedingpair was reduced

Population of adult eagles declined to 4,000 and the eagle was listed as “Endangered”

The Environmental Protection Agency (EPA) banned DDT in 1972

Eagle reproduction before and after DDT ban- What do you notice?

Based on: Grier, J., Science, 1982

Eagle populations increased rapidly and the eagle is now listed as “Threatened”

From: Time, July 11, 1994

Peregrine Falcon •Occurred naturally over most of continental U.S.•Nests on cliffs•Keen eyesight (Ex. If human, they could read newspaper print at 110 yards)•Feeds on other birds, knocking them out of the sky at 200 m.p.h.

•After DDT was introduced in the 1940s, DDT weakened the birds’ egg shells and devastated the population

•By early 1970s, the entire U.S. population was down to 12 breeding pairs

•Peregrines were declared federally endangered and DDT banned

•Peregrines were bred in captivity and reintroduced successfully in cities

DDT & Peregrine

“In the United States at least 500species and subspecies of plantsand animals have become extinctsince the 1500s.”

Douglas Chadwick, H., National Geographic, March 1995

DEFINITIONS – ENDANGERED SPECIES ACT

• Endangered Species: Any species that is in danger of extinction throughout all or a significant portion of its range

• Threatened Species: Any species that is likely to become an endangered species within the foreseeable future

OTHER COMEBACKS ESA is

having some success, but there are more than 600 endangered or threatened species in the U.S. today

Gray whale (California population)

Aleutian Canada gooseAmerican alligatorBrown pelicanUtah prairie dotGreenback cutthroat trout

1994

1985

1990

1987

1984

1978

Date of change

Species removed from endangered list or reclassified as threatened

Based on: Time, July 11, 1994

Defining “Organic”Foods produced without hormones, antibiotics, herbicides, insecticides, chemical fertilizers, genetic modification or germ-killing radiation

The USDA labels such foods “certified organic”

From: Newsweek, Sept. 30, 2002

AVAILABILITY OF ORGANIC PRODUCTS

Based on: Newsweek, Sept. 30, 2002

Can organic farming help the

environment?• Pesticides now kill 67 million

American birds per year

• The Mississippi River dumps enough fertilizer into the Gulf of Mexico to maintain a 60 mile “dead zone” devoid of fish