Opening Questions
• Name two kinds of bias.
• Name three sources of bias.
• What are some important aspects of DDT?

Lesson 1 Review Points
• Using Science as Evidence
– When science is used as evidence it is important to
identify possible sources of bias.
– Bias may be due to sampling bias or measurement
bias.
• Background of DDT
– DDT is a pesticide used for mosquito control and
pest control in agricultural crops.
– DDT accumulation in some bird species resulted in
death, nervous system damage, and reproductive
failure.
– As a result DDT was banned in the United States in
1972.

What are some sources of bias?
• Applying the results of a study too broadly
(generalizing)
• Taking research results out of context
• Not taking a random sample
• Taking too small of a sample
• Measurement error

Lesson 2
Food Webs, Bioaccumulation, and
Visualizing Data

What kind of damage can DDT
cause to birds?

In the body of an animal, DDT is changed
(metabolized) to DDE.
DDE dissolves in fat, not in water, and is
stored in fatty tissues. Thus, DDE tends to
remain in the body and can cause several
problems.

DDE: Kinds of Damage
• Reproductive failure (in birds- eggshell
thinning)
• Immune system problems
• Nervous system damage
• Death

How does DDT move into
lakes, streams and oceans?

After DDT is applied, some DDT volatizes, some
remains on the plant, and some washes off the
plant into the soil, eventually making its way to a a
stream, river, or lake.
The DDT that remains on the leaves of plants may
be ingested by primary consumers such as
insects and rodents.
DDT that has washed into a waterbody, remains in
the sediment or is consumed by bottom-feeding
organisms or absorbed by fish gills and skin.

Is DDT still used today?

YES
DDT is still used in some countries
for insect control on crops.
In countries where mosquitoes carry
malaria, DDT is currently used for
mosquito control.

What is a Food Web?

Food Web = A summary of the feeding
relationships within an ecological
community.
ORGANIC DEBRIS
Osprey
Water Plants
Sucker
Bay
Shrimp
Trout
Plankton
Silverside

Food Chain = One thread of the food web
ORGANIC DEBRIS
Osprey
Large Mouth Bass
Crayfish

Cast of Food Web Characters
• Tertiary Consumers –
Animals that eat animals that
eat animals
• Secondary Consumers –
Animals that eat animals that
eat plants
• Primary Consumers –
Animals that eat plants
• Primary Producers – Plants
and Phytoplankton:
organisms using the sun for
energy

Why is food web knowledge
important for understanding the
impact of DDT on ospreys and
eagles?

Ospreys and eagles are tertiary consumers
and this makes them particularly vulnerable
to DDT because of
bioaccumulation and biomagnification.

What is bioaccumulation?

Bioaccumulation = the accumulation of a
contaminant or toxin in or on an organism
from all sources (e.g., food, water, air).
An increase in the concentration of a chemical in a biological
organism over time, compared to the chemical's
concentration in the environment. Compounds accumulate in
living things any time they are taken up and stored faster
than they are broken down (metabolized) or excreted.

What is biomagnification?

Biomagnification = the increase in
concentration of toxin as it passes through
successive levels of the food web
DDE accumulates at higher levels in organisms that are
higher in the food chain

Biomagnification of a DDE in Aquatic
Environment
Tertiary Consumer 3-76 µg/g ww
(fish eating birds)
Level Amount of DDE in Tissue
Secondary Consumers 1-2 µg/g ww
(large fish)
Primary Consumers
(small fish)
0.2-1.2 µg/g ww
Primary Producers
(algae and aquatic
plants)
0.04 µg/g ww

Considering biomagnification,
how could DDE harm an
osprey?

Osprey Food Web
Large Mouth Bass
Crayfish
Plant material and algae
3-76 µg/g ww
1-2 µg/g ww
0.2- 1.2 µg/g ww
0.04 µg/g ww
DDE Concentration
Osprey

Units of Measurement
1 gram = 1000 milligrams (mg) = 1,000,000 micrograms (µg)
microgram (µg) = one millionth of a gram
To describe concentrations: µg/g = number of micrograms
(of toxin) per gram (of tissue)
2 µg/g DDE in egg content means there is 2 parts of DDE in
1,000,000 parts of an egg contents
ww or wet weight refers to the fresh weight of animal tissue.
dw or dry weight refers to the weight of animal tissue after it has
been dried in an 65°C oven to remove all the water.

The Effects of DDE on Reproduction
Species Effect on
Reproduction
DDE: Critical
Concentration
(measured in egg contents)
Bald Eagle None < 3µg/g 1
Bald Eagle Failure 16 µg/g 1
Osprey Failure 17.6 µg/g 2
1. Wiemeyer, S.N. et al., 1984. Organochlorine pesticide, polychlorobiphenyl, and mercury residues in bald eagles,
1969-1979, and their relationship to shell thinning and reproduction. Arch. Environ. Contam. Toxicol., 13, 529.
2. Johnson, D.R. et al., 1975. DDT and PCB levels in Lake Coeur d’Alene, Idaho osprey eggs, Bull. Environ. Contam.
Toxicol., 13, 401.

High levels of DDE cause the female ospreys to
lay eggs with thin eggshells.
Thin eggshells have a greater chance of
breaking, leading to embryo death.
With high levels of DDE, female ospreys can
also lay eggs that contain high enough
concentration of DDE to prevent embryo
development.

How is the impact of
DDE on osprey and
eagle reproduction
measured?

One Method for Measuring the Impact of
DDE on Osprey Reproduction
• Collect eggs from abandoned osprey nests.
• Measure the thickness of the eggshells.
• Measure the amount of DDE in the egg.
• Determine the association between eggshell
thickness and DDE residue.

Visualizing the Data

If increased DDE concentrations causes
increased eggshell thinning, how would
you draw a graph showing the
relationship between eggshell thinning
and DDE concentration?

Relationship Between DDE Concentrations and Eggshell
Thickness
0.44
0.45
0.46
0.47
0.48
0.49
0.5
0.51
0.52
0 1 2 3 4 5 6
DDE Concentration
Eggshell
Thickness
low concentrations high concentration
normal
thin

If DDE has no impact on eggshell
thickness, what relationship would you
expect to see between DDE levels and
eggshell thickness?

Relationship Between DDE Concentrations and Eggshell
Thickness
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12
DDE Concentration
Eggshell
Thickness
high concentration
low concentration
normal
thin

If increased levels of DDE are
associated with increased eggshell
thickness, how would you make a graph
showing the relationship between
eggshell thickness and DDE
concentration?

Relationship Between DDE Concentrations and
Eggshell Thickness
0.4
0.45
0.5
0.55
0.6
0.65
0 1 2 3 4 5 6 7 8
DDE Concentration
Eggshell
Thickness
high concentration
low concentration
normal
thin

DDE reduces reproductive rates at
moderate concentrations. At high
concentrations it causes total
reproductive failure.
How would you make a graph
showing the relationship between
DDE concentration and reproductive
success?

Relationship Between DDE Concentrations and Eggshell
Thickness
0
20
40
60
80
100
0 2 4 6 8 10 12
DDE Concentration
Reproductive
Success
high concentration
low concentration
high
low