Class Session 15>
Chemicals are everywhere, in the air you breathe, in the food you eat, and in the chair you’re sitting on. Moreover, you’re mostly chemicals. Ninety nine percent of the human body is composed of just 6 chemical elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. After you die, you’ll decompose into hydrogen, nitrogen, water, ammonia, carbon dioxide, phosphoric acid, and sulfuric acid. So, from chemicals we come and to chemicals we go.
Chemical elements are substances that contain one kind of atom and cannot be separated into simpler substances. There are 116 known chemical elements, of which 91 occur naturally. The other 25 are man-made. These elements are listed in the periodic table. Go to http://www.iupac.org/reports/periodic_table/. Scroll down below the table and you’ll see the elements listed. Many of them will be familiar to you.
Chemical compounds are formed by the combination of two or more elements. The one you’re probably most familiar with is H20, two parts hydrogen and one part oxygen, also known as water. Other common compounds include sodium chloride (NaCl) or salt, glucose (C12H22O11) or sugar, and CH3COOC6H4COOH or aspirin. Chemicals are used in a wide range of industrial and commercial applications including plastics, adhesives, absorbents, fertilizers, detergents, dyes, explosives, oils, inks, lubricants, metals, paper, insecticides, pharmaceuticals, solvents, waxes, photography, food additives and on and on. So you see, chemicals are everywhere.
There are several ways to classify chemicals. Organic chemicals are those chemicals that contain the element carbon, C. Organic chemicals can be broken down by micro-organisms and reactions with other chemicals, as well as photo chemically by ultraviolet or visible light. The rate at which a chemical degrades is expressed as half-life, the amount of time it takes for half of the chemical to be converted into some other chemical or element. Generally, organic chemicals biodegrade or decompose more rapidly than inorganic chemicals, which do not contain carbon. Inorganic chemicals include salt, asbestos, and silicates as well as minerals such as iron, aluminum, and phosphorus, among others.
Chemicals can also be either natural or synthetic. Natural chemicals are those which are found occurring in the environment which are not introduced by humans. Synthetic chemicals are those which are developed by humans and do not exist in nature. It might be easy to assume that natural, organic chemicals are less harmful to humans. This is not the case as many poisons come from plants and animals.
II. Chemical Use and Safety
Humans have used chemicals for a long time. The ancient Egyptians used chemicals for dyeing, soldering and coloring metal, and making jewelry. The Industrial Revolution, which began in the middle of the 18th century, spawned the development of many new chemicals and chemical processes. Since World War II, the global chemical industry has boomed. Global production of chemicals was 1 million tons in 1930 and is now over 400 million tons.
Environmental scientists study chemicals to determine if they are harmful to human health and the environment. Pretty much every chemical can harm you if you ingest too much of it. Take in too much water, for example, and you’ll drown. Inhaling too much oxygen can lead to oxygen toxicity, a condition that can damage lung tissue as well as death. At the other end of the harmful spectrum is botulinum toxin, a single gram of which could kill upwards of a million people. Needless to say, it’s classified as a bioweapon. In between oxygen and botulinum toxin are thousands of chemicals used every day to wash your hair, keep insects off your vegetables, and make you smell good.
The amount of harm a chemical can cause is known as toxicity. The word toxic comes from the Greek word “toxon” meaning a bow. Arrows were sometimes tipped with poison and the association between bows, arrows and poisons became our word “toxic”. Harm from chemicals can be acute or chronic, or a combination. Acute effects are those that happen immediately. Chronic effects are those that are generally less harmful but over a longer time period. A severe cold, for example with a high fever, would be considered acute. A less bothersome one that you can’t get rid of would be considered chronic. Some chemicals can kill you in a very short period of time. Others can affect you in ways which may not be detectable for decades.
There is the increasing concern about the risks through which humans are exposed by toxic substances in the environment. Toxic substances can cause cancer which may appear decades after exposure and be indistinguishable from cancer caused by other means. Exposure to toxic substances can also result in effects on reproductive systems and immune system degradation. Plants and wildlife can also be affected by toxic substances.
A number of factors can affect the potential for a chemical to be harmful to public health or the environment. These include persistence, bioaccumulation and toxicity. Persistence refers to how long a chemical remains in air, water, soil or sediment in an unchanged form. Bioaccumulation refers to the ability of a chemical to increase in concentration as it makes its way through living organisms. Some chemicals, mainly organic chemicals, breakdown and are released as waste in living organisms. Inorganic chemicals tend not to break down but rather stay within living organisms and accumulate. Toxicity is a function of the chemical nature of a chemical, as well as its concentration.
Environmental Protection Agency (EPA) and the Food and Drug Administration
(FDA) have the authority to regulate chemicals in the
has the authority to both regulate existing chemicals as well screen new chemicals before they are used commercially. There are some 75,000 chemicals in EPA’s TSCA inventory, though a proportion of these may not be currently manufactured or are produced in small volumes. Chemical companies claim that EPA requires too much testing, while environmental and health organizations maintain that EPA does not go far enough to protect public health and the environment. Most Americans assume that basic toxicity testing data is readily available and that all chemicals used in commerce today are safe.
III. Chemical Use – Pesticides
Pests refer to any organism - plant, animal, or insect - that compete with the desired crop or plant. Pesticides fall into four major categories:
1. Herbicides are used to kill weeds, which are unwanted plants that compete with crops for soil nutrients.
2. Insecticides kill insects that consume crops and transmit diseases.
3. Fungicides kill fungi that damage crops.
4. Rodenticides kill rodents such as rats & mice.
In total, some 80,000 chemical
compounds are used as pesticides in the
1. commercial cropland - 77%
2. government and industrial land - 11%
3. households - 11%
4. forests - 1%
By type herbicides account for 85
percent of pesticides used in the
Some 20 percent of the pesticide used each year in
Pesticides can cause cancer,
reproductive, immunological, and neurological effects on human health. The
World Health Organization estimates that 1 million people worldwide are
poisoned by pesticides. Most of those who are poisoned are farm workers in
developing countries. In the
In 1972, Congress pass the Federal Insecticide, Fungicide, and Rodenticide Act. This legislation requires that all commercial pesticides be approved for general or restricted use. In addition, alternatives to pesticides are being developed. These include integrated pest management practices, crop rotation, planting rows of hedges or trees around crop fields, selective planting timing as well as location, and biological pest control.