Bio-Contaminants & Food Webs

By: Patuxent Wildlife Research Center

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

Positive Aspects DDT

•Insecticide used to kill pests and damaging insects in Agriculture

•Commonly kills off mosquitoes, and has been used to help fight malaria.

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 webDDE 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

•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.

•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?

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

eggshell thickness?

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?

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?