Summer Research Program for Science Teachers

Jennifer N. Girard

Edward R. Morrow High School, Brooklyn

2000

Arsenic Contamination Research

BACKGROUND:

Arsenic poisoning is more often thought of as a topic for a mystery novel, but it is a grim part of our global reality.  All across the world there are over one hundred million people slowly being poisoned by their only available water source.  Most recent and devastating problems with contaminated well water were identified in India.  Arsenic tainted water can be found in as far reaching places as Thailand, Japan, Australia, The United Kingdom, Inner Mongolia, Hungary, Chile, China, Argentina, Taiwan, Ghana, Mexico, Philippines, New Zealand, and Canada.  This is not only a problem for distant lands, contaminated water occurs in the United States as well, in areas such as California, Washington, and Oregon. [9-12 Content Standard F- Natural and human induced hazards]

These events, though catastrophic, can make for a great learning experience in a classroom setting.  It can obviously apply to a Social Studies lesson where you can discuss geography and the socioeconomic classes in the country that have been stricken.  [Teaching Standard A- Work across disciplines]This topic can easily fit into an environmental science classroom where a discussion could develop based on how the surrounding biome is affected by the contaminated water.  Also the fact that the arsenic is believed to occur in ground water from the use of outdated pesticides and mine leeching is also a hot topic for debate.  A biology teacher could parlay arsenic into his or her lesson simply by discussing its carcinogenic properties.  A forensic lesson can be enhanced as well, due to the fact that arsenic remains as part of hair and nail samples even after a person has died.  The final class that can draw from this tragedy is a chemistry class.

Arsenic exists in the water supply as dissolved particles. This is an example of solubility.  [9-12 Content Standard B- Properties of matter] The question of why it dissolves can be answered by taking a look at how an electrolyte interacts with water.  There are multiple oxidation states for arsenic, and, interestingly enough, the +3 state will form more toxic compounds than the +5 state.  Changing the oxidation state of the arsenic can be achieved by a simple oxidation and reduction reaction, yet another topic tackled by the chemistry teacher.  [9-12 Content Standard B- Chemical reactions] The remediation techniques that are being used to "filter" the contaminated water also depend on chemistry to work.  Other substances, such as iron, are added to the water, which causes an iron/arsenic compound to precipitate out of the solution.  The precipitate is not soluble in the water, which is why it can than be passed through a fine mesh filtering apparatus.  Arsenic is one of the few elements that are known as a semi metal.  So this means it will have the characteristics of both a metal and nonmetal.  This makes arsenic an even scarier foe, because it can form a countless number of both organic and inorganic compounds.  The following are some ideas for how a chemistry lesson/lab can be developed based on this real life problem.

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WHERE TO BEGIN?

THE INTERNET: 

Many students (and some teachers) find using the Internet for research to be a frustrating experience.  However there is a fantastic website devoted to arsenic contamination around the world.  It is hosted by Harvard University and is quite user friendly.  The resources it contains are written at many different levels from scientific journal to local newspaper clippings.  This is where to begin with your students.

Assignment:

Go to this website http://phys4.harvard.edu/~wilson/arsenic_project_introduction.html [Teaching Standard D- Make accessible science media]

Navigate this website, explore different links that interest you.  Familiarize yourself with the tragedy of arsenic contamination around the world.

Directions

Look through the different techniques being used to remove arsenic from the drinking water.  Choose one of the techniques and defend why it is the best method for the job.  Include such arguments as the cost for the clean up and its effectiveness.  Then discuss how this method relies on topics we discussed in class. [9-12 Content Standard F- Science and technology in local, national, and global challenges]

SUGGESTED FOLLOW UP

• This project can also be expanded to include the following

• Contact one of the scientists working on an arsenic remediation project.  [Teaching Standard D- Identify/use resources outside the school] Interview them via e-mail.  If possible the interview could take place live in the classroom via a chat room or a digital camera and microphone.

• Set up a connection between a school that is in an area affected by arsenic water contamination.  Keep in touch via e-mail and letters.

• The test for arsenic in water supplies is a difficult and dangerous test.  However students can collect water samples from various sources (tap water, bottled water, etc) and test for other contaminants via a simple water testing kit that is available from sources such as Carolina.

  EVALUATION

•  EXPERIMENTAL DESIGN:

Based on the methods used in India, design an experiment to remove a dissolved substance from contaminated water.   [9-12 Content Standard A- Design and conduct a scientific investigation]

• Break students into groups of four.
• Each group is given a water solution with a known solid dissolved into solution.
• Students will also have a list of solubilities for the substances being used during this lab when they are dissolved in water.
• Students will be given various solutions to mix with their “tainted water”.  One of the solutions will react with the dissolved contaminant to form a product that is not soluble in water.  This will allow the contaminant to precipitate out from the water.  You can also choose other solutions, which will react with the contaminant to form slightly soluble products so that the students see various degrees of precipitation.  They can than select which substance is most affective in removing the contaminant.

• The students must than design a filtration process, which will separate the "clean" water from the unwanted waste.  They must remember the simpler the better so that the general population can use this system. [9-12 Content Standard E- Abilities of technological design] 
• All observations and data should be organized in tables and graphs either provided by the teachers or formulated by the students [9-12 Content Standard A- Use mathematics to improve scientific communication]

•  If the substance dissolved in water was arsenic what safety protocols would you be required to use?

•  If it is a more advanced group they can be asked to write out the balanced equation and reaction mechanism for the final reaction they felt worked the best. [9-12 Content Standard B- Chemical reactions]

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