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. Chemicals that are soluble in fat, like DDE, particularly tend to bioaccumulate compared to those soluble in water. Chemicals that are soluble water are removed from the body in urine, whereas those soluble in fat, do not have a means to leave the body and remain in tissue.

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

In the body of an animal, DDT is changed (metabolized) to DDE 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.

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. After DDT is applied, some DDT residue remains on the plant material and some washes off the plant into the soil eventually making its way to a body of water. The DDT that remains on the leaves of plants is taken up by primary consumers such as insects and rodents. As for the DDT that has washed into a stream, river or lake, it enters the food chain through consumption by bottom-feeding fish or through absorption by fish gills and skin.

Is DDT still used today?

DDT is still used in some countries for insect control on crops. 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. In some countries, DDT is still applied to crops or to wetlands for general insect and mosquito control. After DDT is applied, some DDT residue remains on the plant material and some washes off the plant into the soil eventually making its way to a body of water. The DDT that remains on the leaves of plants is taken up by primary consumers such as insects and rodents. As for the DDT that has washed into a stream, river or lake, it enters the food chain through consumption by bottom-feeding fish or through absorption by fish gills and skin.

Biomagnification of DDE in Aquatic Environment Level Amount of DDE in Tissue Tertiary Consumer 3-76 µg/g ww (fish eating birds) Secondary Consumers 1-2 µg/g ww (large fish) This is an example of actual concentrations of DDT as it passes through the heron food chain. It is important that the students notice the units in which DDT is measured and to become familiar with the relative amount of DDT that accumulates in organisms of different trophic levels. Students will also be given another example using osprey to demonstrate this point. There are several factors that contribute to the problem of bioaccumulation and biomagnification in aquatic environments. When DDT is applied it runs off into water and collects in lakes, streams, wetlands and other bodies of water. Fish are then exposed to DDT through consumption of organic debris on the floor of a water body and/or through their gills when it is suspended in water. Thus, water dwelling creatures are at higher risk of bioaccumulating DDE. Primary Consumers (small fish) 0.2-1.2 µg/g ww Primary Producers (algae and aquatic plants) 0.04 µg/g ww

What kind of damage can DDT cause to birds?

DDE: Kinds of Damage Reproductive failure (in birds- eggshell thinning) Immune system problems Nervous system damage Death  Students will be asked to list some of the damage caused by DDE on their worksheets.

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.  Students have fill-in-the-blank questions to answer questions about this slide. It is important that students understand that high levels of DDE result in female osprey to lay thin eggs with thin eggshells.

How is the impact of DDE on osprey and eagle reproduction measured? In Lesson 3 and Lesson 4 students will be working with real data. In order for students to have a clear picture of how and why data was collected, the next slide introduces the data collection method.

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 The last part of the lecture focuses on data visualization. This exercise is included to encourage students to start thinking about how graphs of different types of datasets may appear. For advanced students,teachers can first put up the question and then let students draw out the graph on their worksheets. For students less comfortable with graphing, teachers may want to guide students through the graphing process using the following steps: Drawing the axes on the board. As a class, determine the labels of the axes. As a class, work out the first graph.

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

The above graph depicts data where eggshells with higher levels of DDE concentration are thinner.

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

This graph depicts data where regardless of the concentration of DDE, eggshells have the same thickness.