Kids Research Express

Carcinogen, any chemical, biological, or physical agent that can potentially be a cause of cancer. The term is most commonly applied to chemicals introduced into the environment by human activity. Researchers label a substance a carcinogen if it causes a statistically significant increase in some form of neoplasm, or anomalous cell growth, when applied to a population of previously unexposed organisms. The modes of cancer initiation are still little understood, however, and efforts to establish the carcinogenic hazards of substances have aroused great controversy. The question of the usefulness of laboratory tests on animals in assessing human risks is particularly complex. The more recent development of short-term tests using cell cultures of microorganisms, however, is considered a major advance in carcinogen research. Substances indicted as carcinogenic over the past few decades include the pesticides DDT, Kepone, and EDB; the synthetic hormone DES; the artificial sweetener cyclamat

About 5 percent of the oxygen humans breathe is converted into free radicals. The presence of free radicals in the body is not always detrimental. Free radicals produced in normal cellular metabolism are vital to certain body functions, such as fighting disease or injury. When tissue is diseased or damaged, the body’s immune system sends disease fighting cells to the site, where they produce free radicals in an effort to destroy foreign invaders. But as the body ages or is subjected to environmental pollutants, such as cigarette smoke, overexposure to sunlight, or smog, the body becomes overwhelmed by free radicals. An excessive number of free radicals causes damage by taking electrons from key cellular components of the body, such as protein , lipids , and deoxyribonucleic acid (DNA), the molecule that carries genetic information in every living cell. These reactions make cells more vulnerable to cancer-causing chemicals, called carcinogens . Free radicals may lead to heart disease

Sulfuric Acid, corrosive, oily, colorless liquid, with a specific gravity of 1.85. It melts at 10.36° C (50.6° F), boils at 340° C (644° F), and is soluble in all proportions in water. When sulfuric acid is mixed with water, considerable heat is released. Unless the mixture is well stirred, the added water may be heated beyond its boiling point and the sudden formation of steam may blow the acid out of its container (see Acids and Bases). The concentrated acid destroys skin and flesh, and can cause blindness if it gets into the eyes. The best treatment is to flush away the acid with large amounts of water. Despite the dangers created by careless handling, sulfuric acid has been commercially important for many years. The early alchemists prepared it in large quantities by heating naturally occurring sulfates to a high temperature and dissolving in water the sulfur trioxide thus formed. About the 15th century a method was developed for obtaining the acid by distilling hydrated ferrous su

Smog, mixture of solid and liquid fog and smoke particles formed when humidity is high and the air so calm that smoke and fumes accumulate near their source. Smog reduces natural visibility and often irritates the eyes and respiratory tract. In dense urban areas, the death rate usually goes up considerably during prolonged periods of smog, particularly when a process of heat inversion creates a smog-trapping ceiling over a city. Smog prevention requires control of smoke from furnaces; reduction of fumes from metal-working and other industrial plants; and control of noxious emissions from automobiles, trucks, and incinerators. In the U.S. internal-combustion engines are regarded as the largest contributors to the smog problem, emitting large amounts of contaminants, including unburned hydrocarbons and oxides of nitrogen. The number of undesirable components in smog, however, is considerable, and the proportions highly variable. They include ozone, sulfur dioxide, hydrogen cyanide, and h

Camphor, volatile, white, crystalline compound,with a characteristic aromatic odor. Ordinary camphor is obtained from the camphor tree, Cinnamomum camphora, which grows in Asia and Brazil. The camphor is distilled by steaming chips of the root, stem , or bark . The leaves of certain plants, such as tansy and feverfew, contain a second form of camphor, which is not used commercially. A racemic form is present in the oil of an Asian chrysanthemum and is also produced synthetically for most commercial uses. Camphor is used in the manufacture of celluloid and explosives and medicinally in liniments and other preparations for its mild antiseptic and anesthetic qualities. It is poisonous if ingested in large amounts. Camphor is insoluble in water, soluble in organic solvents, and melts at 176° C (349° F) and boils at 209° C (405° F).

Ozone (Greek ozein, “to smell”), pale blue, highly poisonous gas with a strong odor. Ozone is considered a pollutant at ground level, but the ozone layer of the upper atmosphere protects life on Earth from the Sun’s harmful ultraviolet radiation. Ozone is one of three forms, called allotropes, of the element oxygen. Ozone is triatomic, meaning that it has three atoms in each molecule (formula O3). Ordinary, or diatomic, oxygen (O2) is more stable than ozone and accounts for the bulk of oxygen in the atmosphere. Electrical sparks and ultraviolet light can cause ordinary oxygen to form ozone. The presence of ozone sometimes causes a detectable odor near electrical outlets. PROPERTIES At normal temperatures and pressures ozone is a gas with a specific gravity of 2.144 (about 1.5 times the density of ordinary oxygen gas). Ozone accounts for only a tiny fraction of the atmosphere and is normally invisible, but high concentrations of ozone gas are pale blue. The gas condenses to a liquid at

Chlorofluorocarbons (CFCs), family of synthetic chemicals that are compounds of the elements chlorine, fluorine, and carbon. CFCs are stable, nonflammable, noncorrosive, relatively nontoxic chemicals and are easy and inexpensive to produce. During the 1970s, scientists linked CFCs to the destruction of Earth’s ozone layer. The manufacture of CFCs has since been banned in most countries. USES Scientists developed the first CFCs during the late 1920s. The compounds subsequently became used in a wide range of industrial products in the United States, Europe, and Japan. Manufacturers used CFCs as refrigerants in refrigerators, freezers, air conditioners, and heat pumps, and as propellants in aerosols and medical inhalers. CFCs also served as insulating foams in packaging materials, furniture, bedding, and car seats. Cleaning agents for electronic circuit boards, metal parts, and dry cleaning processes also used CFCs. Learn more: Harmful Effects of CFCs Regulation Extended Impact