Biomagnification

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Chemistry

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Nov 24, 2024

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Section Objectives: • Students will be able to define biomagnification and describe its impact on living things. Introduction The Bald Eagle is the national bird of the United States. In the early 1700s, it was estimated that over 300,000 were in the United States, not counting Alaska 1 . By the 1960s, however, there were less than 500 pairs of males and females. What happened? By doing some care - ful detective work on the food chain of eagles, biologists discovered a phenomenon called biomagnification that was causing the eagles to die. In this chapter, we’ll explore the case of the eagles and other examples of biomagnificaiton. Biomagnification of DDT During the 1940s, many farmers began using chemicals called pesticides to kill the pes - ky insects that harmed their crops 2 (Figure 1). Many people became concerned that these chemicals could also harm humans and other animals. In 1962, the writer Rachel Carson published the famous book, Silent Spring 3 . She presented the different types of evidence showing that the commonly used pesticide DDT was harming birds 4 . Figure 1: DDT was used both in farms and in homes to kill insects, including mosquitos. Eagles, however, are not known for spending much time around farms. While DDT does not actually poison eagles, it does prevent them from laying healthy eggs 5 . Eagles weren’t being killed by DDT, but no new eagles were being born. Biologists eventually discovered that DDT was being washed by rain into rivers. It was then being absorbed into the bodies of plankton, which are small animals that live in the water 6 . Plankton are eaten by many small fish such as minnows. Small fish are the prey of larger fish, such as bass. Eagles and other birds of prey such as osprey are excellent fisher - men and live off of catching large fish. As we learned in the last chapter, these species are organized into a food chain .

By studying each part of this food chain, biologists discovered that each level contained more DDT in its cells than the previous one. For example, in the Carmans River near Long Island, New York, biologists found that found that there was only 0.00005 ppm of DDT in the water. PPM stands for parts per million and is a way of showing the concentration of chemicals when they are very rare. One ppm would mean there is one milliliter of DDT for every one million milliliters of water in the river. 0.00005 is therefore a very small amount 7 . In the plankton living the river, however, there was 0.04 ppm of DDT 8 . Small fish like the Atlantic Silverside had 0.23 ppm in their cells. Larger fish like the Atlantic Needlefish had 2.07 ppm. Osprey, a fish-eating raptor, had 13.8 ppm of DDT 9 . Another fish-eating bird, a Cormorant, had 26.4 ppm 10 . This high concentration of DDT was causing eagles, osprey, and other birds to lay eggs with weak shells that did not develop normally. This phenomenon became known as biomagnficiation because at each level of the food web the amount of DDT increased or was magnified. In the water, it was not concentrated enough to cause any harm. Even in fish, it may not have been dangerous. It was too con - centrated, however, in birds and was causing serious harm. In the last chapter, we saw that food webs often have a pyramid shape, with many plants at the bottom and few predators at the top. The concentrations of DDT are like a pyramid that has been flipped. The lowest concentration of DDT is in the water, and the highest in the top predators. How Does Biomanfication Happen? There are two reasons why biomagnification happens. First, DDT is very slow to break down in the environment. Unlike other chemicals, it is not easily broken down by de - composers. It is estimated that DDT can take 15 years to disappear from soil or water that contains it 11 . Eagles can live for up to 40 years 1 . DDT can therefore build up slowly in their bodies until it reaches level where it causes problems. Biomagnification also occurs because eagles eat a lot of fish. Needle fish in the river may have only 2 ppm of DDT in their bodies, but an eagle may eat hundreds of eagle fish dur - ing its life. The DDT from each fish it eats slowly adds up until it causes problems. This happens at each level of the foot chain. Each small fish eats thousands of zooplankton with DDT in them. Therefore, it builds up bit by bit. Needlefish eat hundreds of small fish and DDT builds up even more in their bodies. Small single fish eats thousands of plankton during its life, and accumulates a lot of DDT over time. The plankton of the river spent their entire lives swimming in water with DDT, so they absorbed it into their cells, getting a higher concentration of it than was in the water. Other Toxic Chemicals Scientists have found other toxic chemicals that can go through the process of bioam - plification. Sometimes chemicals that occur naturally in the environment such as arsenic and mercury can reach toxic levels in herbivores and predators 12 . PCBs, a chemical used in pesticides and many other things, can also be biomagnified. Other pesticides have also been found to biomagnify 13 .

Saving the Eagles Figure 1: Bald eagles were listed as an endangered species in 1967. Many other birds were also suffering from problems that scientists thought were from DDT. In 1967, Bald Eagles were listed as an endangered species (cite). This required that bald eagles and their habitat be given special attention to prevent them from going extinct in the USA (Figure 1). It was finally proven that DDT was harming the environment and humans. DDT was banned from being used in the USA in 1972 16 . Bald Eagles quickly began recovering. The population around the country increased to about 110,000 birds by the year 1992 (cite). That year, eagles were changed from being endangered to threatened, a sign that they were recovering. In 2007, Bald Eagles were finally considered safe and removed from the threatened list. It took many years for eagles to fully recover because the population was so small in the 1960s. Also, since DDT stays in the environment for so long, it continued to harm eagles long after it was banned. Biologists are now always monitoring birds and other animals to make sure they are not being poisoned by new pesticides and chemicals. Summary Biomagnification is the process that causes poisonous chemicals to become more concen - trated at higher levels of a food chain. For example, the concentrations of DDT can be very low in plankton and small fish, but very high in birds. The most famous case of biomagnifi - cation is the bald eagle. When high concentration of DDT accumulated in the cells of bald eagles, they could not lay healthy eggs. Bald eagles were declared an endangered species but have now recovered. Other chemicals that can become biomagnified include mercury, arsenic, and PCBs. Concept Reinforcement 1. Explain why a hawk would be more likely to suffer because of biomagnification than a minnow. 2. Explain why it is significant that DDT takes 15 years to break down in the environ - ment. 3. Explain how biomagnification could happen in the bodies of human beings. Extinction and Exitirpation Extinction is when all members of a species have died. Extirpa- tion is when they have all been killed within a certain country. Bald eagles were not in danger of going extinct since they are also found in Mexico and Canada. They would have been extirpated from the USA.

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Notes 1. http://www.eagles.org/moreabout.html 2. Silent Spring. 1962. Rachel Carson. Houghten Miflin, Boston. 3. The Gentle Subversive: Rachel Carson, Silent Spring, and the Rise of the Environ - mental Movement. 2007. Mark H. Lytle. Oxford University Press, New York. 4. The Gentle Subversive: Rachel Carson, Silent Spring, and the Rise of the Environ - mental Movement. 2007. Mark H. Lytle. Oxford University Press, New York. 5. Silent Spring. 1962. Rachel Carson. Houghten Miflin, Boston. 6. Silent Spring. 1962. Rachel Carson. Houghten Miflin, Boston. 7. DDT Residues in an East Coast Estuary: A Case of Biological Concentration of a Persistent Insecticide. George M. Woodwell, Charles F. Wurster, Jr., Peter A. Isaa - son. Science, Vol. 156, No. 3776, (May 12, 1967), pp. 821-824. 8. “DDT Residues in an East Coast Estuary: A Case of Biological Concentration of a Persistent Insecticide.” May 1967. George M. Woodwell, Charles F. Wurster Jr., and Peter A. Isaacson. Science, Volume 156. Pages 821 - 824. 9. “DDT Residues in an East Coast Estuary: A Case of Biological Concentration of a Persistent Insecticide.” May 1967. George M. Woodwell, Charles F. Wurster Jr., and Peter A. Isaacson. Science, Volume 156. Pages 822. 10. “DDT Residues in an East Coast Estuary: A Case of Biological Concentration of a Persistent Insecticide.” May 1967. George M. Woodwell, Charles F. Wurster Jr., and Peter A. Isaacson. Science, Volume 156. Pages 822. 11. http://www.epa.gov/pbt/pubs/ddt.htm 12. “DDT Residues in an East Coast Estuary: A Case of Biological Concentration of a Persistent Insecticide.” May 1967. George M. Woodwell, Charles F. Wurster Jr., and Peter A. Isaacson. Science, Volume 156. Pages 822. 13. http://deepblue.lib.umich.edu/bitstream/2027.42/48075/1/244_2005_Article_ BF01065333.pdf 14. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V74- 4BS0CD8-3&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_ acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=90b14c9ba78 8151e921d2cc6e3979e48 15. http://www.pwrc.usgs.gov/infobase/eisler/chr_4_toxaphene.pdf 16. 1967 - http://www.fws.gov/endangered/pdfs/Posters/eagle_back.pdf