Green Chemistry

Overview

In 1962, Rachel Carson made a very strong statement in her book, "Silent Spring," which says, "Along with the possibility of the extinction of mankind by nuclear war, the central problem of our age has therefore become the contamination of man's total environment with such substances of incredible potential for harm, substances that accumulate in tissues of plants and animals, and even penetrate the germ cells, to shatter or alter the very material of heredity upon which the shape of the future depends." ¹

This is what we are witnessing today. We have seen an alarming increase of incidents that have irrevocably affected man's total environment. From the 1940's to the present, we have observed how chemical agents have resulted in death and serious consequences. We have heard about how the Chernobyl Nuclear Accident in 1986 resulted in approximately 93,000 deaths and predictions were that about 270,000 people would most likely develop cancer. ² In India, we have heard of news reports about the Bhopal Gas Tragedy in 1984 where a leak in a pesticide plant caused thousands of deaths and exposed hundreds of thousands of people to toxic gases. ³ We have read volumes of articles that discussed the usefulness of DDT, (dichloro-diphenyl-trichloro-ethane) as a pesticide, especially during World War II, when there was a great need to protect troops from insect borne-diseases. ⁴ But, using DDT resulted in some serious surprises. The first serious surprise of DDT use, was the rapid evolution of insects' resistance to pesticides that created a continuous demand for new products. Second, scientists discovered that residues often persisted longer and traveled farther in the environment. Third, residues were found accumulating in plant, animal, and human tissues. And fourth, diverse ways that living organisms accumulate, and get adversely affected by pesticide residues from exposures to contaminated food, water, soil, and air, completed the view that pesticides threatened human health, biological diversity, and basic ecological processes.

In food chains, it is the producers, the plants, some forms of algae and bacteria that provide other organisms the food and energy they need to survive. These producers can put together inorganic substances, like water and carbon dioxide from their environments, and form starch and oxygen gas. This is the process of photosynthesis. But while photosynthesis is taking place, chemicals are accumulating in tissues of various living organisms, like the phytoplankton in marine ecosystems. Other marine life forms feed on the phytoplankton. These other life forms are the consumers. These consumers do not have the ability to trap the energy from the sun; therefore, they also cannot perform photosynthesis. They depend on photosynthetic organisms for survival. Those bigger and stronger consumers will feed on smaller organisms, creating a chain. And, as the chain continues, chemicals are also moving and building up among organisms.

Photosynthesis is a complex process, so, I will start with an activity on "Starch Pictures." ⁵ As students develop the "starch pictures," they will acquire a concrete visualization that starch is produced in photosynthesis. I will then show videos and animations that will demonstrate that, as photosynthetic plants manufacture starch, toxins are also absorbed from their environments. I know videos and animations are not sufficient for my students to really "experience" the process of bioaccumulation, so, I created the "Bioaccumulation Game." Using this game as a teaching tool for bioaccumulation, I will show, using colored candies, how a particular toxin-containing candy accumulates at the last person representing the organism in the highest level of the food chain. Learning will be more fun, and the complex concept of bioaccumulation, will be easily understood. After the "visualizing, concretizing, and experiencing" strategies, I will use case-based teaching. I will take advantage of this teachable moment to integrate measurement and solution concentration. As students enter data gathered from their case studies, I will use this engaging activity to introduce units and unit conversion. As they analyze the bioaccumulation cases and establish the toxicity level of chemicals, I will introduce various ways in which solution concentration can be expressed.

As I teach the unit, I intend to cover/review biology content areas like forms and kinds of energy, parts of the cell, populations, and ecosystems. Chemistry content includes states of matter, elements and compounds, symbols and formulas, chemical reactions and equations, and stoichiometry. This unit is limited only to the study of accumulation of heavy metals present in pesticides. Hydrocarbons, plastics, and chlorofluorocarbons are discussed only as they relate to environmental contamination. Their properties and toxicity levels will not be utilized in the teaching of measurement and solution concentration.

My four-week curriculum unit is designed for ninth grade honors biology and tenth grade honors chemistry at Dunbar Vocational Career Academy. All classes, including science courses with laboratory components are taught daily, in 45-minute periods. In biology, I will teach this unit the whole month of October. In chemistry, I plan to use this unit as the culminating activity in the last four weeks of the first semester. This unit is aligned to Goals 11, (Principles and Processes of Scientific Inquiry), 12, (Fundamental Concepts and Principles of the Life, Physical, and Earth/Space Sciences), and 13, (Relationships Among Science, Technology, and Society), of the Illinois State Standards in the teaching of science.