Module Four - Lecture Notes
Introduction - Survey of Toxic Substances (1)
- Outdoor Air Pollutants
While this module deals with specific substances, this section has the flexibility to include or substitute other chemicals, depending on the interest and concern of the particular community. For that reason, this section should be presented by an environmental health professional (toxicologist, an environmental health scientist, a health educator). In addition, one or two toxic substances may be the focus of the module. This particular module will require additional research by the trainer.
EPA has focused its attention on the following outdoor pollutants, which may pose a health hazard from exposure (1): carbon monoxide, sulfur oxides, ozone, nitrogen oxides, and particulates. Other chemicals not listed, here, also have the potential to be toxic, however the focus is on the above listed chemicals because they are produced in the largest amount and/or have the greatest chance of producing a toxic effect.
Levels of air pollutants are different at different times of the day, and are usually highest around midday, decreasing in the evening. An accidental release of a chemical could also increase levels.
- Carbon Monoxide (CO) is a colorless, odorless, and
tasteless gas produced by the burning of carbon or materials
containing carbon. It is lighter than air and dissolves
slightly in water. Some common sources of exposure to
carbon monoxide include automobile exhaust and faulty
or poorly ventilated charcoal, kerosene, or gas stoves.
Foundries, coke ovens, and refineries are also sources,
as are smoking tobacco products (2,11). Carbon monoxide
decreases the amount of oxygen available to cells, resulting
in problems with cell function.
Short term (acute) exposure to CO at certain levels could cause a slight headache and shortness of breath. Exposure for longer periods (chronic) may cause headache, nausea, irritability, increased respiration, chest pain, impaired judgement, and fainting.
- Sulfur oxides are a major source of air pollutants. They are produced from automobile exhaust, petroleum refineries, paper manufacturing, and chemical industries. The two types of sulfur oxides are sulfur dioxide (SO2) and sulfur trioxide (SO3). Sulfur dioxide is the main air pollutant of concern. It is an irritant colorless gas with a bitter taste, that dissolves in water to form sulfurous acid. It is a liquid under pressure and cannot catch fire. It affects the eyes and the skin as well as the upper respiratory system, and is able to penetrate the lungs during mouth breathing as opposed to nose breathing. Sulfur dioxide in the air results mainly from activities associated with burning of coal or oil, such as power plants or copper smelting (12). The people most often affected by exposure are workers in plants where sulfur dioxide occurs as a by-product, such as in the copper smelting industry (12). Sulfur dioxide in the body is biotransformed (changed) into a breakdown product which can be measured in blood and urine. That way, exposure can possibly be determined (12).
- Ozone (O3) is a colorless gas and its
odor can be detected at very low levels. It is formed
as a result of the interaction between organic compounds,
like ketones, aldehydes, and unsaturated hydrocarbons,
and nitrogen oxides in the presence of sunlight. It
is also formed by any other high-energy source, such
as lightning, high voltage electrical equipment, and
air- and water-purifying devices (1).
Ozone is one of the major air pollutants in heavily industrialized areas and in cities with a large number of automobiles. More than half of the ingredients needed to produce ozone come from automobile exhaust. Ozone formation occurs most often during the early midday, and begins to decrease during late afternoon and evening.
Symptoms from exposure to low concentrations of ozone include eye, nose, throat, and lung irritation. These symptoms can be seen after only about 10 to 30 minutes of exposure. At higher concentrations, coughing and breathing problems occur. Even higher concentrations result in chest pain and pneumonia. People who suffer from lung diseases such as asthma and emphysema are more sensitive to lower levels of ozone.
- Nitrogen Oxides (Nox) come in the following
forms: nitric oxide (NO), which is a colorless gas;
nitrogen dioxide (NO2), a reddish-brown or
dark orange gas; nitrogen trioxide (N2O3),
a colorless gas; nitrogen tetroxide (N2O4),
a colorless gas; nitrogen pentoxide (N2O5),
and nitrous oxide (N2O), which is colorless
and often referred to as "laughing gas"(1,2)
Reports estimate that about 300,000 tons of NOx are produced each year from industrial processes; combustion of fossil fuels (coal, oil) adds 10 million tons to that number (1). Nitrogen oxides are produced from many sources, such as burning of fuels in furnaces and internal combustion engines, detonation of explosives, welding, and tobacco smoke. Diesel exhaust may contain nitric oxide, while cigarette smoke also contains nitrogen oxides. The most common forms of nitrogen oxides in the air are nitric oxide and nitrogen dioxide. Nitrogen dioxide, which gives smog its brown color, can be detected by its odor or taste at low concentrations. Symptoms of exposure include coughing, difficulty in breathing, chest pain, fluid build-up in the lung, irregular heartbeat, and eye irritation (2).
In some people, only labored breathing and coughing may develop at first, and then the symptoms subside. A few weeks later, people may enter a second stage, characterized by fever, chills, and fluid in the lungs. Death may occur in either of the two stages, depending on the severity of the effects and the health of the individual.
- Particulates come from a number of sources, including automobile emissions, smokestacks, or blowing dust. The particles may be large enough to be seen by the naked eye, or they may be extremely small. The size is important in determining the effect of the particle on the respiratory system. Smaller particles may pose the greatest threat. For example, asbestos fibers are capable of causing cancer, silica particles may cause a disease called silicosis, and coal dust may cause pneumoconiosis. The composition of the particulates is also important. Heavy metals, such as lead, cadmium, and others are often found in the particulate material (1).
Heavy metals are everywhere in nature as components of the earth's crust. Plants can absorb and accumulate metals, which may be toxic. Industrial development has resulted in exposure to heavy metals in people because of increased production of by-products such as cadmium, mercury, chromium, and zinc.
Due to both the prevalence, relative toxicity, and the disproportionate exposure impact on poor and undeserved communities, this module will describe the relative toxicity and health impacts from four of the most toxic heavy metals: arsenic, cadmium, lead, and mercury.
- Arsenic, one of the most toxic metals, is produced
at a rate of about 60,000 tons per year. It is found
primarily in a trivalent form or a pentavalent form
(2). The pentavalent form is not as toxic as the trivalent
form, and will not be discussed further here. The
trivalent form of arsenic is the most toxic and it
is deposited primarily in the respiratory tract. Excretion
is primarily via the urine, although excretion may
also occur by the natural shedding of the skin and
Potable water usually has a very small arsenic concentration. It is also present in very small amounts in such things as wine and seafood. This is why the diet should be taken into account when determining arsenic exposure. The primary routes of exposure to arsenic are ingestion and inhalation. Arsenic tends to collect in skin, hair, and nails. It is removed mainly through the urine, a few days after it is ingested. This can result in some upset stomach. Measuring arsenic in the urine is the main way to detect arsenic exposure.
Acute exposure to arsenic may result in death, fever, anorexia, and liver enlargement (2). Chronic exposure may result in poisoning of the nervous system, liver damage, and peripheral vascular disease, which could result in gangrene of the lower limbs. This condition is more commonly known as "black foot disease" and was a phenomenon that occurred in Taiwan from arsenic contamination of the drinking water supply. In addition, skin cancer and lung cancer may result from chronic arsenic exposure. Chronic arsenic exposure has also been associated with leukemia, kidney, and bladder cancers, dermatitis, hyper pigmentation, and keratosis (or arsenical keratosis).
Approximately 900,000 workers in the United States may be occupationally exposed to arsenic fumes and dust such as in smelting industries. The major source of occupational exposures to arsenic in the United States is in industries involved in the manufacture of pesticides, herbicides, and other agricultural products.
- Cadmium is a byproduct of the mining and smelting
of lead and zinc.(2). It does not corrode and is primarily
used for electroplating activities. Cadmium can gather
and concentrate in plants. It has also contaminated
irrigation waters and is found in fertilizers. Shellfish
represent a major source of cadmium in the diet (100-1,000
microgram per kilogram [ µg/kg]). Cadmium is
also found in tobacco, each cigarette has approximately
1-2 µg of cadmium. Approximately 1 µg
of cadmium may be found in one liter of breast milk.
Very little cadmium is absorbed through the ingestion
route, and it is not easily absorbed.
Acute toxicity from cadmium exposure occurs primarily through ingestion of contaminated beverages or food. This could result in nausea, vomiting, and abdominal pain. Acute toxicity through inhalation may result in chemical pneumonia and fluid in the lung. Irritation of the nose and throat, coughing, dizziness, weakness, chills, fever, chest pains, and labored breathing are also symptoms. Acute cadmium toxicity through inhalation may result in a condition known as metal fume fever. Chronic toxicity may result in chronic obstructive pulmonary disease, emphysema, and kidney disease. It may also result in adverse affects to the cardiovascular system and the skeleton (1,2).
- Lead is primarily used in the manufacture of batteries,
plastics, china, ceramic glass, and paint products.
It is the most widespread toxic metal on earth and
is the second most hazardous substance found at sites
listed on the National Priorities List (NPL). Scientific
evidence links exposure to lead and adverse health
effects due to acute and chronic exposure to lead.
The primary route of lead exposure is ingestion. This could occur through eating lead-based paint flakes and chips (e.g., pica-like behavior), breathing contaminated dust, drinking contaminated water, and absorbing lead from lead-contaminated glaze in pottery. Children are particularly at risk. Approximately 35% of U.S. black children have blood lead levels greater than 10 µg/L (13). Blood lead levels are consistently higher for poor and minority children and for residents of largely urban areas. The fetal brain may be particularly sensitive to the toxic effects of lead because of the immaturity of the blood-brain barrier in the fetus.
The toxic effects of lead include lead encephalopathy (brain disease) in children, resulting in lethargy, vomiting, irritability, loss of appetite, and dizziness (1,2). In adults, lead causes high blood pressure, and adverse reproductive effects (lowered sperm count and sperm motility). One classic symptom of lead toxicity are the Burton's lines, which are purple-blue discolorations of the gums (1,2). The primary measure for treating lead toxicity is through chelation therapy (binding of lead with other metals to remove it from the body).
- Mercury is the third most toxic substance in the
environment (1,2). Approximately half of all mercury
is used to produce vapor lamps, fluorescent tubes,
thermometers, and electrical products. It exists in
a number of forms, which may affect different parts
of the body. Organic mercury primarily affects the
brain. Methyl mercury is the most toxicological form
of the element and, by its accumulation in the central
nervous system (CNS), may result in neurotoxic effects
in adults and toxicity in the fetuses of mothers exposed
to methyl mercury during pregnancy. Metallic mercury
is slowly absorbed by the gastrointestinal system
and is not as toxic as methyl mercury (14). Inorganic
mercury (mercury salts) primarily affects the kidneys.
Exposure to mercuric salts may lead to abdominal cramps
and bloody diarrhea.
Chronic mercury exposure may lead to tremor and personality disturbances and permanent CNS damage may result from methyl mercury exposure. Acute mercury exposure can be assessed by measuring the level of mercury in blood. Chronic exposure is best assessed by measuring the amount of mercury in urine (1,2). Chelation therapy is typically used in acute mercury poisoning.
A classic epidemiological study of mercury exposure involves the occurrence of Minamata disease. Minamata disease results from methyl mercury poisoning and leads to a neurological disorder. Methyl mercury bioaccumulates in fish and shellfish. Thus, exposure to humans primarily occurred through consumption of methyl mercury-contaminated shellfish and fish from Minamata Bay.
Benzene is a component and a by-product of gasoline. Benzene is widespread in the environment, and is one of the most prevalent solvents. In addition, it has been used as a solvent in rubber, inks, adhesives, and transformer fluids (1,2). Benzene dissolves easily in the bloodstream and quickly diffuses from the lungs to the blood and is metabolized in the liver to compounds that interact with cellular DNA. In addition, it is lipid-soluble and is easily absorbed by the skin and by cells lining the digestive tract.
Inhalation is the predominant route of exposure to the toxic effects of benzene, particularly in the workplace. Acute exposure to benzene may result in CNS effects, which may lead to unconsciousness and death. There is no antidote for acute benzene poisoning. Chronic benzene exposure may result in bone marrow damage, resulting in anemia. Symptoms of chronic benzene exposure may include fatigue and anorexia. Leukemia is a classic outcome from chronic low-level exposure to benzene with a latency period of about 15 years.
Polychlorinated Biphenyls (PCBs)
PCBs are another major contaminant of concern in communities (13). They were used in plasticizers, adhesives, and as dielectric fluids in capacitors. In humans, they accumulate in fat tissue and milk, which is a major route of excretion (1,2). PCBs cause liver cancer in rats and mice and is classified as a probable carcinogen in humans by EPA. PCBs are persistent in the environment and bioaccumulate upward in the food chain. A non-occupational source of PCBs is in fish from contaminated water. Cultures where subsistence fishing is a primary source of food would subsequently represent populations of concern regarding PCB-contaminated fish (15).
High-level exposure to PCBs may cause a classic dermatological condition called chloracne. Developmental and fetotoxic effects may also be observed in humans. Occupational exposures to PCBs primarily occurs in the production of electrical equipment. Since 1977, PCBs have been banned from further production as a material for the production of electrical equipment and chronic workplace exposure is now uncommon.
Several classes of pesticides cause adverse human health effects in humans. These major classes of pesticides include insecticides, herbicides, fungicides, fumigants, and rodenticides. Seasonal agricultural workers have an increased risk of harmful human health effects due to pesticide exposure (16).
- Insecticides include the organochlorides, organophosphates,
and the carbamates. Organochloride insecticides affect
the peripheral nervous system (PNS) through dermal absorption,
inhalation, and ingestion. Organochloride compounds
also decrease antibody production, placing a person
at risk for infection (1,2). DDT is a organochloride
insecticide that persists and bioaccumulates in the
environment, which is why it is no longer manufactured
as a pesticide. Organophosphorous exposure may result
in headache, anxiety, chest tightness, seizures, loss
of consciousness, abnormal heart beat, and liver dysfunction
(1,2). In addition, Organophosphorous pesticides, like
malathion, seem to enhance the immune response in some
circumstances. Parathion has been known to decrease
Trainers may want to discuss the use of insecticides. Ask participants about their insecticide use, listing types and determining their knowledge of the contents of these substances.
- Herbicides such as 2,4,5-T, 2,4,-D, and the classic contaminant, 2,3,7,8 - TCDD (dioxin) are toxic to both animals and humans (1,4). Liver problems and nerve damage may result from chronic herbicide exposure, while chloracne is a classic symptom of herbicide dermal exposure.
- Fungicides are used in the treatment of fruit trees and vegetables and have a relatively low toxicity (2). Skin irritation, headache, nausea, vomiting, lethargy, and dermatitis are classic symptoms of some fungicides, such as creosote and hexachlorobenzene.
- Fumigants are used to eradicate insects, bacteria,
and rodents. Fumigants are typically used on fruits,
vegetables, ships, and buildings (1). Methyl bromide
is a classic fumigant that may result in dermatitis,
pulmonary irritation, headache, nausea, vomiting, dizziness,
and dementia from exposure via inhalation and dermal
The trainer may want to discuss the use of fungicides and fumigants in the home (home gardens, etc.).
Rodenticides are used primarily to eradicate rats, mice, rabbits, and gophers (1,2). Warfarin is a rodenticide that causes severe adverse health effects.
Participants may list the types of chemicals they use in the removal of pests. Determine through discussion, whether any adverse health effects have been seen.
Radiation and Radioactive Materials
The two major classes of radiation are ionizing radiation and non-ionizing radiation. Ionizing radiation affects the bone marrow, resulting in a decrease in red blood cell production, reddening of the skin, gastrointestinal and reproductive effects, cataracts, birth defects, and respiratory illness (1,2). Non-ionizing radiation is associated with mutagenic and carcinogenic effects, primarily by UV radiation, which can alter the repair mechanisms for DNA and potentially lead to skin cancer.
The exposure of radium dial workers in the United States is the most classic epidemiological case of occupational radiation exposure. Ingestion of radium may result in bone cancer. Atom bomb survivors were also the victims of radiation exposure, as well as underground miners exposed to radon, patients irradiated with x-rays for ankylosing spondylitis, and children irradiated with x-rays for ringworm (1,2). In addition, radiation is associated with skin, thyroid, and lung cancers, particularly among uranium mine workers.