CPH Exam - Environmental Health Sciences

Terms in this set (626)

Lead is a metal with the longest history of use by humans. It has been mined for thousands of years and a medical description of its toxic effects was reported among Roman miners. The use of lead throughout the late nineteenth and twentieth centuries was an important public health hazard mainly due to its use in lead based paint and gasoline. Lead use in paint took advantage of pigment properties of lead compounds. The dusting, or chalking property, of white lead-based paint made painted surfaces continue to appear white, but this characteristic allowed lead contaminated dust to be freely available. Childhood hand-to-mouth behavior resulted in lead exposure from contaminated indoor dust and outdoor soil of painted houses. Lead for use in house paint was banned in 1978. Tetraethyl lead was added to gasoline to enhance the octane rating. The lead was emitted in the automobile exhaust. This significant source of human exposure was phased out to a complete ban in 1995 due to the Clear Air Act Amendments of 1990. Lead used for water pipes could also be found throughout the mid-twentieth century, but the use of leaded pipe has been replaced by copper and plastic pipe. In 1998, the Safe Drinking Water Act prohibited the use of lead piping. Occupational exposures to lead still occur in the steel, manufacturing, smelting, automobile trades, and other sometimes unexpected industries such as rubber manufacturing. Lead is a common contaminant of hazardous waste sites, especially near mining and smelting operations. This source has been a significant human exposure route among some communities.
The volatile organic compounds (VOCs) are so-named because they are short-chain or cyclic hydrocarbon compounds which are easily vaporized at ambient temperatures. These substances have become ubiquitous in the human environment since they are commonly used in many chemical products. VOCs are frequently found in adhesives used in building products such as fiberboard, carpeting, resins of furniture, and home products. Their ubiquitous presence has resulted in being a common waste product that has contaminated drinking water. Trichloroethylene (TCE) has become one of the most common contaminants of drinking water supplies because of its widespread use in industry. VOCs have been a common substance for exposures in the workplace, often as degreasing agents and solvents. Occupational exposures may occur via inhalation or dermal absorption. Skin absorption may be rapid due to the lipophilic nature of the degreasers. Once in the body, solvents affect the central and peripheral nervous system, liver, kidneys and hematopoietic system. Some solvents with exposure of historic public health significance include benzene, n-hexane, and fluorochlorocarbons called freons. Benzene has been strongly associated with bone marrow depression and acute mylogeneous leukemia. N-hexane is a cause of peripheral neuropathy in workers. Several solvents, including the special class of freons, have been associated with cardiac sensitization for arrhythmias. TCE is also considered a probable human carcinogen.
Ionizing radiation results from the release of atomic material or energy due to instability of the atomic structure. Some radiation comes from natural sources, such as that from cosmic rays and radioactive substances in the earth's crust. The gray (Gy) is the current official unit of measure for radiation exposure, but references to rads and rems are still used; a gray is equal to 100 rad. People are exposed to this "background" radiation at a rate of about 1 to 2 mGy per year. There are three types of radiation particulates: alpha particles, which consist of a hydrogen nucleus, a beta particle which consists of an electron or positron, and a neutron. The additional types of radiation are x-rays and gamma rays. The alpha particle is a relatively large mass unit which has, due to its size and lower energy, a low ability to penetrate tissue. External alpha sources cannot penetrate the dead keratin epithelial layer of the skin but are extremely toxic to the susceptible tissue such as occurs when the radioactive substance is taken internally, via ingestion or inhalation. Beta radiation has greater penetration but generate relatively less damage per particle. Likewise, gamma and x-rays have very high penetration, and a high energy level. When the relative biological effect of the individual types of radiation is considered, the biological radiation effective dose is measured as rems (Roentgen Equivalent Man). Since DNA is one of the most sensitive targets of radiation exposure, cancer is an important effect. Cancers of the lung, breast, bone, brain, hematopoietic system (leukemia and lymphoma), skin, and thyroid have all been associated with radiation exposure. Important epidemiologic associations between exposure to radiation and cancer have been identified in Japanese atomic bomb survivors for leukemia and breast cancer, uranium miners and lung cancer, and patients treated with radiation to the thymus and thyroid cancer. In addition to cancers and other conditions due to chronic exposures, acute radiation illnesses may be seen in occupational disasters. Acute radiation illness may begin after an exposure in excess of 1Gy (100 rad) and is always expected with exposures in excess of 4Gy. The three main organ systems affected are the gastrointestinal, hematopoietic and neurological system.