1. Module 42 Heavy Metals and Other Chemicals
After reading this module you should be able to
explain the sources of heavy metals and their effect on organisms.
discuss the sources and effects of acid deposition and acid mine drainage.
explain how synthetic organic compounds can affect aquatic organisms.

2. Heavy metals are highly toxic to organisms
 Three heavy metals are of particular concern: 
Lead: found in pipes and other materials in older construction.
Arsenic: occurs naturally and through human activity such as mining and industry.
Mercury: occurs naturally and through human activity, primarily burning coal.

3. Arsenic
Arsenic in U.S. well water. The highest concentrations of arsenic are generally found in the upper Midwest and the West.

4. Mercury
World mercury emissions. Mercury emissions from human activities vary greatly among regions of the world.

5. Acid deposition and acid mine drainage affect terrestrial and aquatic ecosystems
Acid deposition Acids deposited on Earth as rain and snow or as gases and particles that attach to the surfaces of plants, soil, and water.
Acid deposition occurs when burning coal releases sulfur dioxide and nitrogen dioxide into the air.

6. Acid Pollution Continued
In the atmosphere, these chemicals are converted to sulfuric acid and nitric acid, which fall back to Earth as acid deposition. 
Acid deposition reduces the pH of water bodies to levels that are lethal to many organisms. 
Many coal-burning facilities have installed coal scrubbers to combat this problem.

7. Synthetic organic compounds are human-produced chemicals
Synthetic compounds can enter the water supply from industrial point sources or from nonpoint sources when they are applied over large areas. 
These compounds include pesticides, pharmaceuticals, military compounds, and industrial compounds.
Synthetic organic compounds can be toxic, cause genetic defects, and interfere with growth and sexual development.

8. Pesticides and Inert Ingredients
Pesticides serve an important role in helping to control pest organisms that pose a threat to crop production and human health.
However pesticides can have unintended impacts on other pests as well as on many nonpest species.

9. Pesticides Continued
For example, DDT—designed to kill mosquitoes—can move up an aquatic food chain to birds that consume fish.
Eagles that consumed DDT-contaminated fish produced eggs with thinner shells that broke too easily. After the United States banned DDT in 1972, the bald eagle and other birds of prey increased in numbers.
What about the Honeybees?

10. Pharmaceuticals and Hormones
Contaminants in streams. Streams contain a wide variety of chemicals including pharmaceutical drugs and hormones. These come from a combination of wastewater inputs, agriculture, forestry, and industry.

11. Military Compounds
Perchlorates A group of harmful chemicals used for rocket fuel.
Perchlorates sometimes contaminate the soil in regions of the world where military rockets are manufactured, tested, or dismantled.

12.   Industrial Compounds
Industrial compounds: chemicals used in manufacturing. 
It used to be common for manufacturers in the United States to dump industrial compounds directly into bodies of water.
Polychlorinated biphenyls (PCBs) A group of industrial compounds used to manufacture plastics and insulate electrical transformers, and responsible for many environmental problems.