What Is Bronchitis?

            Bronchitis (bron-KI-tis) is a condition in which the bronchial tubes, the tubes that carry air to your lungs, become inflamed. Also, bronchitis is a respiratory disease in which the mucous membrane in the lungs’ bronchial passages becomes inflamed. As the irritated membrane swells and grows thicker, it narrows or shuts off the tiny airways in the lungs, resulting in coughing spells accompanied by thick phlegm and breathlessness. The disease comes in two forms: acute (lasting less than 6 weeks) and chronic (reoccurring frequently for more than two years). In addition, people with asthma also experience an inflammation of the lining of the bronchial tubes called asthmatic bronchitis.

            Acute bronchitis is more common and usually is caused by a viral infection. Acute bronchitis may also be called a chest cold. Episodes of acute bronchitis can be related to and made worse by smoking. This type of bronchitis is often described as being worse than a regular cold but not as bad as pneumonia.

            Acute bronchitis is responsible for the hacking cough and phlegm production that sometimes accompany an upper respiratory infection. In most cases the infection is viral in origin, but sometimes it’s caused by bacteria. If you are otherwise in good health, the mucous membrane will return to normal after you’ve recovered from the initial lung infection, which usually lasts for several days. On the other hand, chronic bronchitis is a serious long-term disorder that often requires regular medical treatment. Chronic bronchitis is a cough that persists for two to three months each year for at least two years. Smoking is the most common cause of chronic bronchitis

            If you are a smoker and come down with acute bronchitis, it will be much harder for you to recover. Even one puff on a cigarette is enough to cause temporary paralysis of the tiny hair like structures in your lungs, called cilia, that are responsible for brushing out debris, irritants, and excess mucus.

            If you continue smoking, you may do sufficient damage to these cilia to prevent them from functioning properly, thus increasing your chances of developing chronic bronchitis. In some heavy smokers, the membrane stays inflamed and the cilia eventually stop functioning altogether. Clogged with mucus, the lungs are then vulnerable to viral and bacterial infections, which over time distort and permanently damage the lungs’ airways. This permanent condition is called COPD (chronic obstructive pulmonary disease). Your doctor can perform a breathing test, called spirometry, to see if you have developed COPD.

            Acute bronchitis is very common among both children and adults. The disorder often can be treated effectively without professional medical assistance. However, if you have severe or persistent symptoms or if you cough up blood, you should see your doctor. If you suffer from chronic bronchitis, you are at risk for developing cardiovascular problems as well as more serious lung diseases and infections, you should be monitored by a doctor.

            People who have bronchitis often have a cough that brings up mucus. Mucus is a slimy substance made by the lining of the bronchial tubes. Bronchitis also may cause wheezing (a whistling or squeaky sound when you breathe), chest pain or discomfort, a low fever, and shortness of breath.

Causes

            Acute bronchitis is generally caused by lung infections; approximately 90% of these infections are viral in origin, 10% bacterial. Chronic bronchitis may be caused by one or several factors. Repeated attacks of acute bronchitis, which weaken and irritate bronchial airways over time, can result in chronic bronchitis.

            Industrial pollution is another culprit. Chronic bronchitis is found in higher-than-normal rates among coal miners, grain handlers, metal molders, and other people who are continually exposed to dust. But the chief cause is heavy, long-term cigarette smoking, which irritates the bronchial tubes and causes them to produce excess mucus. The symptoms of chronic bronchitis are also worsened by high concentrations of sulfur dioxide and other pollutants in the atmosphere.

Symptoms of Bronchitis

Symptoms of bronchitis include the following:

• A cough that is frequent and produces mucus
• A lack of energy
• A wheezing sound when breathing, which may or may not be present
• A fever, which may or may not be present

What You Should Do

See your health care provider if you have any of these symptoms:

• A chest cold that lasts for more than two weeks
• A fever greater than 102°F
• A cough that produced blood
• A shortness of breath or wheezing
• Drink fluids every one to two hours unless your doctor has restricted your fluid intake
• Rest
• Don’t smoke
• Relieve body aches by taking aspirin or acetaminophen. (If you are taking any other drugs, talk to your doctor to make sure aspirin or acetaminophen doesn’t interfere with them. Children should NOT take aspirin.)
• Follow your doctor’s instructions on ways to help clear your mucus.
• If you are coughing up mucus, note how often you cough as well as the color and amount of the mucus. Report this to your doctor.
• If you have a dry cough and cough up little to no mucus, your doctor may prescribe a cough medicine to suppress your cough. He or she may also prescribe an expectorant to help loosen mucus so it can be more easily coughed up.
• Because most episodes of bronchitis are caused by viruses, antibiotics will not be useful or necessary. Exceptions would be bronchitis caused by a bacterial infection or bronchitis in a person who has impaired lung function.

How to Reduce the Risk of Getting Bronchitis (chest cold)?

• Don’t smoke.
• Don’t allow others to smoke in your home.
• Stay away from or reduce your time around things that irritate your nose, throat, and lungs, such as dust or pets.
• If you catch a cold, get plenty of rest.
• Take your medicine exactly the way your doctor tells you.
• Eat a healthy diet.
• Wash your hands often.
• Do not share food, cups, glasses, or eating utensils.

Diagnosis

            Tests are usually unnecessary in the case of acute bronchitis, as the disease is easy to detect from your medical history and on examination. Your doctor will simply use a stethoscope to listen for the rattling sound in your lungs’ upper airways that typically accompanies the problem.

            In cases of chronic bronchitis, the doctor will almost certainly augment these procedures with an X-ray of your chest to check the extent of the lung damage, as well as with pulmonary function tests to measure how well your lungs are working.

Treatments

            Conventional treatment for acute bronchitis may consist of simple measures such as getting plenty of rest, drinking lots of fluids, avoiding smoke and fumes, and possibly getting a prescription for an inhaled bronchodilator and/or cough syrup. In severe cases of chronic bronchitis, inhaled or oral steroids to reduce inflammation and/or supplemental oxygen may be necessary. Alternative choices, by and large, help relieve the accompanying discomfort but do not treat infections.

Conventional Medicine

            In healthy people who have normal lungs and no chronic health problems, antibiotics are not necessary, even when the infection is bacterial. The productive (phlegm-producing) coughing that comes with acute bronchitis is to be expected and, in most cases, encouraged; coughing is your body’s way of getting rid of excess mucus. However, if your cough is truly disruptive — that is, it keeps you from sleeping or is so violent it becomes painful — or nonproductive (dry and raspy sounding), your doctor may prescribe a cough suppressant. In most cases, you should simply do all the things you usually would do for a cold: Take or acetaminophen for discomfort and drink lots of liquids.

            If you have chronic bronchitis, your lungs are vulnerable to infections. Unless your doctor counsels against it, get a yearly flu shot as well as a vaccination against pneumonia. The pneumonia vaccine is typically a one-shot procedure: One vaccination will protect many for life against the common strains of the disease. Occasionally a second or booster shot is required.

            Do not take an over-the-counter cough suppressant to treat chronic bronchitis unless your doctor directs you to do so. As with acute bronchitis, the productive coughing associated with chronic bronchitis is helpful in ridding the lungs of excess mucus. In fact, your doctor may even prescribe an expectorant if your cough is relatively dry. However, if you notice any changes in the color, volume, or thickness of the phlegm, you may be coming down with an infection. In that case, your physician may prescribe a 5 to 10-day course of broad-spectrum antibiotics, which fight a range of bacteria. If you are overweight, your doctor may insist that you diet to avoid putting excessive strain on your heart. If you have COPD (as demonstrated by an abnormal spirometry breathing test), many doctors also prescribe an anticholinergic bronchodilator, drugs that temporarily help dilate the lungs’ constricted airways. However, the most important and most successful treatment for chronic bronchitis and COPD is smoking cessation. Your doctor may also prescribe steroids to reduce inflammation in the airways.

            In severe cases of chronic bronchitis with COPD, if your body’s ability to transfer oxygen from your lungs into the bloodstream is significantly handicapped, your doctor may prescribe oxygen therapy, either on a continuous or on an as-needed basis. Oxygen-delivering devices are widely available. If you use an oxygen tank at home, be sure to take special care not to expose the apparatus to flammable materials (alcohol and aerosol sprays, for example) or to sources of direct heat, such as hair dryers or radiators.

            If you smoke, your doctor will urge you to quit. Studies show that people who kick the habit even in the advanced stages of chronic bronchitis and COPD not only can reduce the severity of their symptoms but also can increase their life expectancy.

Pleura is a membrane that covers the lungs and the inner wall of the chest; visceral and parietal pleura respectively. In normal breathing, they slide over each other without any friction.

What is pleurisy?

It is a condition where the pleurae are inflamed and cause pain due to friction during breathing.

What are the symptoms of pleurisy?

The main symptom is sudden, intense chest pain usually located over the area of inflammation. Although the pain can be constant, it is usually most severe when the lungs move during breathing, coughing, sneezing, or even talking. The pain is usually described as shooting or stabbing but, in minor cases, it resembles a mild cramp. When pleurisy occurs in certain locations, such as near the diaphragm, the pain may be felt in other areas such as the neck, shoulder, or abdomen (referred pain). Another indication is that holding one’s breath or exerting pressure against the chest causes pain relief.

Do patients have breathing difficulty?

Yes. Pleurisy is also characterized by certain respiratory symptoms. In response to the pain, patients commonly have a rapid, shallow breathing pattern. Sometimes fluid accumulation can occur. This is called pleural effusion.

What happens in pleural effusion?

In pleural effusion fluid accumulates between both pleurae. When this occurs pain disappears but respiratory difficulty on exertion occurs. In early stages it is not noticeable while walking on plains but becomes manifest when they climb stairs and run to catch a bus. Disappearance of chest pain should not make one complacent. Be careful enough to observe if they are getting breathless on slight exertion. This should alert them to see a physician.

What kinds of fluid can accumulate in the pleural cavity?

Fluid accumulation can range from simple fluid, pus, blood, lymph and, sometimes, faecal matter and urine if there is an accident and multiple organs are involved.

Pleural effusion is excess fluid that accumulates in the pleural cavity, the fluid-filled space that surrounds the lungs. Excessive amounts of such fluid can impair breathing by limiting the expansion of the lungs during inhalation.

Four types of fluids can accumulate in the pleural space:

• Serous fluid (hydrothorax)
• Blood (hemothorax)
• Chyle (chylothorax)

Pus (pyothorax or empyema)

Pleural effusion Chest x-ray of a pleural effusion. The arrow A shows fluid layering in the right pleural cavity. The B arrow shows the normal width of the lung in the cavity

Transudate vs. exudate

The third step in the evaluation of pleural fluid is to determine whether the effusion is a transudate or an exudate. Transudative pleural effusions are caused by systemic factors that alter the balance of the formation and absorption of pleural fluid (e.g., left ventricular failure, pulmonary embolism, and cirrhosis), while exudative pleural effusions are caused by alterations in local factors that influence the formation and absorption of pleural fluid (e.g., bacterial pneumonia, cancer, and viral infection).

Transudative and exudative pleural effusions are differentiated by comparing chemistries in the pleural fluid to those in the blood. According to a meta-analysis, exudative pleural effusions meet at least one of the following criteria ^[1]:

1. Pleural fluid protein >2.9 g/dL (29 g/L)
2. Pleural fluid cholesterol >45 mg/dL (1.16 mmol/L)
3. Pleural fluid LDH >60 percent of upper limit for serum

Previously criteria proposed by Light for an exudative effusion are met if at least one of the following exists (Light’s criteria) ^[2]:

1. The ratio of pleural fluid protein to serum protein is greater than 0.5
2. The ratio of pleural fluid LDH and serum LDH is greater than 0.6
3. Pleural fluid LDH is more than two-thirds normal upper limit for serum

Twenty-five percent of patients with transudative pleural effusions are mistakenly identified as having exudative pleural effusions by Light’s criteria. Therefore, additional testing is needed if a patient identified as having an exudative pleural effusion appears clinically to have a condition that produces a transudative effusion. In such cases albumin levels in blood and pleural fluid are measured. If the difference between the albumin levels in the blood and the pleural fluid is greater than 1.2 g/dL (12 g/L), it can be assumed that the patient has a transudative pleural effusion.

If the fluid is definitively identified as exudative, additional testing is necessary to determine the local factors causing the exudate.

Exudative pleural effusions

Once identified as exudative, additional evaluation is needed to determine the cause of the excess fluid, and pleural fluid amylase, glucose, pH and cell counts are obtained. The fluid is also sent for Gram staining and culture, and, if suspicious for tuberculosis, examination for TB markers (adenosine deaminase > 45 IU/L, interferon gamma > 140 pg/mL, or positive polymerase chain reaction (PCR) for tuberculous DNA).

Pleural fluid amylase is elevated in cases of esophageal rupture, pancreatic pleural effusion, or cancer. Glucose is decreased with cancer, bacterial infections, or rheumatoid pleuritis. Pleural fluid pH is low in empyema (<7.2) and may be low in cancer. If cancer is suspected, the pleural fluid is sent for cytology. If cytology is negative, and cancer is still suspected, either a thoracoscopy, or needle biopsy of the pleura may be performed.

Causes

The most common causes of transudative pleural effusions in the United States are left ventricular failure, pulmonary embolism, and cirrhosis (causing hepatic hydrothorax), while the most common causes of exudative pleural effusions are bacterial pneumonia, cancer (with lung cancer, breast cancer, and lymphoma causing approximately 75% of all malignant pleural effusions), viral infection, and pulmonary embolism. Although pulmonary embolism can produce either transudative or exudative pleural effusions, the latter is more common.

Other causes of pleural effusion include tuberculosis (though pleural fluid smears are rarely positive for AFB, this is the most common cause of pleural effusion in some developing countries), autoimmune disease such as systemic lupus erythematosus, bleeding (often due to chest trauma), chylothorax (most commonly caused by trauma), and accidental infusion of fluids. Less common causes include esophageal rupture or pancreatic disease, intraabdominal abscess, rheumatoid arthritis, asbestos pleural effusion, Meigs syndrome (ascites and pleural effusion due to a benign ovarian tumor), and ovarian hyperstimulation syndrome.

Pleural effusions may also occur through medical/surgical interventions, including the use of medications (pleural fluid is usually eosinophilic), coronary artery bypass surgery, abdominal surgery, endoscopic variceal sclerotherapy, radiation therapy, liver or lung transplantation, and intra- or extravascular insertion of central lines.

Diagnosis

How can pleural effusion be diagnosed?

The symptoms of chest pain and respiratory difficulty are too classic to be missed. A chest x-ray can easily diagnose effusion.

What are the causes of pleural effusion?

It could be due to infections like TB, pneumonia or cancers. Pleural effusion can also occur in heart failure, liver diseases and kidney diseases where improper diet and decrease in protein are the causes. In fact they are bigger causes of pleural effusion.

Are there any tests to diagnose the cause of pleural effusion?

The fluid in the chest can be removed by a procedure called aspiration. In this a needle is introduced through the skin under local anaesthesia, fluid is withdrawn and sent for bacteriological and pathological tests. This test can be done under the guidance of a radiologist, as he can guide the needle exactly to the point where fluid is located. The tests and the markers are to be decided by your physician.

Can effusion occur in people who smoke?

People who smoke are prone to lung cancer and when cancer involves pleura, effusion occurs making the cancer slightly advanced.

Which is the best way to confirm the cause of effusion?

The confirmatory test is pleural biopsy, which can be done by a needle or thoracoscopy.These small pieces of pleural tissue is sent for a pathological examination that will confirm the diagnosis.

What is pleuroscopy?

Some times the needle biopsy may not yield the diagnosis. In such cases pleuroscopy can be used. It is a fibre-optic instrument that is passed into the chest and the whole pleural cavity can be visualised in a monitor, biopsies can be taken under vision. In this procedure the diagnosis can be obtained with greater accuracy.

Can all the fluid be removed?

All the fluid is removed only during respiratory difficulty or when it is accumulating rapidly. This occurs more often in cancers. A tube is then kept in the chest cavity to prevent the rapid expansion of the lung. In cancer after complete expansion a chemical or talc powder is introduced to seal the chest cavity to prevent further accumulation.

Treatment

The free end of the Chest Drainage Device is usually attached to an underwater seal, below the level of the chest. This allows the air or fluid to escape from the pleural space, and prevents anything returning to the chest.

Treatment depends on the underlying cause of the pleural effusion. Therapeutic aspiration may be sufficient; larger effusions may require insertion of an intercostal drain (either pigtail or surgical). Repeated effusions may require chemical (talc, bleomycin, tetracycline/doxycycline) or surgical pleurodesis, in which the two pleural surfaces are attached to each other so that no fluid can accumulate between them.

Health Effects from Exposure to Ionizing Radiation
Radiation Exposure
Any release of radioactive material is a potential source of radiation exposure to the population. In addition to exposure from external sources, radiation exposure can occur internally from ingesting, inhaling, injecting, or absorbing radioactive materials. Both external and internal sources may irradiate the whole body or a portion of the body.
The amount of radiation exposure is expressed in a unit called millirem (mrem). In the United States, the average person is exposed to an effective dose equivalent of approximatly 360 mrem (whole-body exposure) per year from all sources (NCRP
Report No. 93).

Results of Exposure
Radiation affects people by depositing energy in body tissue, which can cause cell damage or cell death. In some cases there may be no noticeable effect. In other cases, the cell may survive but become abnormal, either temporarily or permanently. Additionally, an abnormal cell may become malignant. Both large and small doses of radiation can cause cellular damage. The extent of the damage depends upon the total amount of energy absorbed, the time period and dose rate of the exposure, and the particular organs exposed.
By damaging the genetic material (DNA) contained in the body’s cells, radiation can cause cancer. Damage to genetic material in reproductive cells can cause genetic mutations that can be passed on to future generations. In rare occurrences where there is a large amount of radiation exposure, sickness or even death can occur in a limited amount of hours or days.

Chronic Exposure
Chronic exposure is continuous or intermittent exposure to low doses of radiation over a long period of time. With chronic exposure, there is a delay between the exposure and the observed health effect. These effects can include cancer and other health outcomes such as benign tumors, cataracts, and potentially harmful genetic effects.

Acute Exposure
Acute exposure is exposure to a large, single dose of radiation, or a series of moderate doses received during a short period of time. Large acute doses can result from accidental or emergency exposures or from specific medical procedures (radiation therapy). For approved medical exposures, the benefit of the procedure may outweigh the risk from exposure.
In most cases, a large acute exposure to radiation causes both immediate and delayed effects. Delayed biological effects can include cataracts, temporary or permanent sterility, cancer, and harmful genetic effects. For humans and other mammals, acute exposure to the whole body, if large enough, can cause rapid development of radiation sickness, evidenced by gastrointestinal disorders, bacterial infections, hemorrhaging, anemia, loss of body fluids, and electrolyte imbalance. Extremely high dose of acute radiation exposure can result in death within a few hours, days, or weeks.

Risks of Health Effects
All people receive chronic exposure to background levels of radiation present in the environment. Many people also receive additional chronic exposures and relatively small acute exposures. For populations receiving such exposures, the primary concern is that radiation could increase the risk of cancer or harmful genetic effects.
The probability of a radiation-induced cancer or harmful genetic effects is related to the total amount of radiation accumulated by an individual. Based on current scientific evidence, any exposure to radiation can be harmful (e.g., can increase the risk of cancer); however, at very low exposures, the estimated increases in risk are very small. For this reason, cancer rates in populations receiving very low doses of excess radiation (doses of radiation above background) may be similar to the rates for average populations.
Evidence of injury from low or moderate doses of radiation may not show up for months or even years. For example, the minimum time period between the radiation exposure and the appearance of leukemia (latency period) is 2 years. For solid tumors, the latency period is more than 5 years. The types of effects and their probability of occurrence can depend on whether the exposure was chronic or acute. It should be noted that all of the long-term health effects associated with exposure to radiation can also be caused by other factors.

Estimating Health Risk
The most complete data available to scientists are on the survivors of the atomic bomb explosions in Japan, on radiation industry workers, and on people receiving large doses of medical radiation. These data demonstrate a higher incidence of cancer among exposed individuals and a greater probability of cancer as the level of exposure increases. In the absence of more direct information, the data also are used to estimate what the effects might be at lower exposures. Where questions arise, scientists try to come to conclusions based on information obtained from laboratory experiments, but these determinations are acknowledged to be uncertain. For radon, scientists largely depend on data collected on underground miners. Professionals in the radiation protection field prudently assume that the chance of a fatal cancer from radiation exposure increases in proportion to the magnitude of the exposure. In other words, it is assumed that no radiation exposure is completely risk free.

What Are the Health Effects of Ionizing Radiation?
Radiation may affect living things by affecting the cells that make up the living organism. Radiation effects on a cell are random. That is, the same type and amount of radiation could strike the same cell many times and have a different effect, including no effect, each time. However, in general, the more radiation that strikes the cell, the greater the chances of an effect occurring. If a significant number of cells are affected, the organism may be damaged or even die.
All living things are constantly exposed to background radiation. Most cells have the ability to repair some damage done by this level of radiation. As a result, the effects of doses similar to background levels are impossible to measure in a single individual. Effects of these low levels of radiation are often predicted for populations rather than for individuals.
This fact sheet describes how low levels of radiation affect cells, how cell damage affects the health of individuals, and how the health effects on populations are estimated. Effects of high levels of radiation will be discussed briefly.
Radiation Effects on a Cell
When a cell absorbs radiation, there are four possible effects on the cell. First, the cell may suffer enough damage to cause loss of proper function, and the cell will die. Second, the cell may lose its ability to reproduce. Third, the cell’s genetic code (i.e., the DNA) may be damaged such that future copies of the cell are altered, which may result in cancerous growth. Finally, the absorption of radiation by a cell may have no adverse effect.
Cells are made up of molecules. Cell damage may be caused by interaction of radiation with these molecules. If radiation strikes a molecule crucial to the cell’s function, such as DNA, damage to the cell is likely to be greater than if the radiation strikes a less crucial molecule such as water.
Some cells are more likely to be affected by radiation than others. Cells that multiply rapidly are the most susceptible. Cells can often repair radiation damage, but if the cell multiplies (splits into two identical cells) before it has had time to repair the most recent radiation damage, the new cells might not be accurate copies of the old one. Some examples of rapidly multiplying cells are those in a fetus and cancer cells.
Health Effects of Radiation
Health effects of radiation are divided into two categories: threshold effects and non-threshold effects. Threshold effects appear after a certain level of radiation exposure is reached and enough cells have been damaged to make the effect apparent. Non-threshold effects can occur at lower levels of radiation exposure.
Threshold effects occur when levels of radiation exposure are tens, hundreds, or thousands of times higher than background, and usually when the exposure is over a very short time, such as a few minutes. Some examples of observed threshold effects and the doses which cause them are presented in Table 1. Dose is measured in rem or millirem. (1,000 millirem = 1 rem)
Table 1. Threshold Effects
Dose (in rem) Effects
5 to 20 Possible latent effects (cancer), possible chromosomal abberations
25 to 100 Blood changes
More than 50 Temporary sterility in males
100 Double the normal incidents of genetic defects
100 to 200 Vomiting, diarrhea, reduction in infection resistance, possible bone growth retardation in children
200 to 300 Serious radiation sickness, nausea
More than 300 Permanent sterility in females
300 to 400 Bone marrow and intestine destruction
400 to 1000 Acute illness and early death (usually within days)

Non-threshold effects can occur at any level of radiation exposure, but the risk of harmful health effects generally increases with the amount of radiation absorbed. The most studied non-threshold effect is cancer. These studies are somewhat complicated by the facts that (1) not all cancers are caused by radiation, (2) exposure to a particular dose may cause cancer in one person but not another, and (3) the cancer often doesn’t appear until many years after the exposure to radiation. It is currently impossible to determine which cancers are caused by radiation and which are caused by other carcinogens in our environment.
Susceptibility to radiation-induced cancer depends on a number of factors such as the site of exposure in the body, sex, and age. Sites in the body where cells rapidly grow and multiply, and those where radioactive materials tend to concentrate, are more susceptible to cancer than others. For example, the breast and thyroid gland have relatively high susceptibilities to radiation-induced cancer, while the kidney and nerve cells have lower susceptibilities.
Many studies have been done on other possible effects of radiation on human health. The detail necessary to present accurate information on these studies is beyond the scope of this fact sheet. Health effects are thoroughly discussed in a book entitled Medical Effects of Ionizing Radiation by Fred A. Mettler, Jr., M.D. and Robert D. Moseley, Jr., M.D. This book is fairly technical, but it has an extensive glossary of terms and contains hundreds of references to studies done on the health effects of radiation.
Radiation Effects on Populations
Because it is impossible to predict the effect of low levels of radiation on any one person, studies of the human health effects of radiation are usually done by trying to predict how many people in a large population might be affected. The result of such a study is usually a prediction of how many people in a population of 100,000 or a million may get cancer due to a specific radiation exposure. The predicted cancers due to this specific radiation exposure are in addition to cancers that would normally be expected in the selected population.
The number of additional cancers expected in a population is calculated in two steps. First, the dose (in rems) to an average person in a population is multiplied by the number of persons in that population. The answer is given in person-rems. Then that answer is divided by the number of person-rems that produce one cancer in the population. The final result is the number of additional cancers expected.
Biological Effects
Mechanisms of Damage
Injury to living tissue results from the transfer of energy to atoms and molecules in the cellular structure. Ionizing radiation causes atoms and molecules to become ionized or excited. These excitations and ionizations can:

• Produce free radicals.
• Break chemical bonds.
• Produce new chemical bonds and cross-linkage between macromolecules.
• Damage molecules that regulate vital cell processes (e.g. DNA, RNA, proteins).
The cell can repair certain levels of cell damage. At low doses, such as that received every day from background radiation, cellular damage is rapidly repaired.
At higher levels, cell death results. At extremely high doses, cells cannot be replaced quickly enough, and tissues fail to function.

Chapter III
Conclusion
Exposure to ionizing radiation can come from many sources. You can learn when and where you may be exposed to sources of ionizing radiation in the exposure section below. One source of exposure is from hazardous waste sites that contain radioactive waste. The Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in the nation. These sites make up the National Priorities List (NPL) and are the sites targeted for federal cleanup. However, it’s unknown how many of the 1,467 current or former NPL sites have been evaluated for the presence of ionizing radiation sources. As more sites are evaluated, the sites with ionizing radiation may increase. This information is important because exposure to ionizing radiation may harm you and because these sites may be sources of exposure.
When a substance is released from a large area, such as an industrial plant, or from a container, such as a drum or bottle, it enters the environment. This release does not always lead to exposure. Even in the event that you are exposed, it does not necessarily mean you will be harmed or suffer long-term health effects from exposure to ionizing radiation.
If you are exposed to ionizing radiation, many factors determine whether you’ll be harmed. These factors include the dose (how much), the duration (how long), and the type of radiation. You must also consider the chemicals you’re exposed to and your age, sex, diet, family traits, lifestyle, and state of health.

Three basic concepts apply to all types of ionizing radiation. When we develop regulations or standards that limit how much radiation a person can receive in a particular situation, we consider how these concepts might affect a person’s exposure.
Time
The amount of radiation exposure increases and decreases with the time people spend near the source of radiation.
In general, we think of the exposure time as how long a person is near radioactive material. It’s easy to understand how to minimize the time for external (direct) exposure. Gamma and x-rays are the primary concern for external exposure.
However, if radioactive material gets inside your body, you can’t move away from it. You have to wait until it decays or until your body can eliminate it. When this happens, the biological half-life of the radionuclide controls the time of exposure. Biological half-life is the amount of time it takes the body to eliminate one half of the radionuclide initially present. Alpha and beta particles are the main concern for internal exposure.
Distance
The farther away people are from a radiation source, the less their exposure.
How close to a source of radiation can you be without getting a high exposure? It depends on the energy of the radiation and the size (or activity) of the source. Distance is a prime concern when dealing with gamma rays, because they can travel long distances. Alpha and beta particles don’t have enough energy to travel very far.
As a rule, if you double the distance, you reduce the exposure by a factor of four. Halving the distance, increases the exposure by a factor of four.
Why does exposure change more rapidly than the distance?
The area of the circle depends on the distance from the center to the edge of the circle (radius). It is proportional to the square of the radius. As a result, if the radius doubles, the area increases four times.
Think of the radiation source as a bare light bulb. The bulb gives off light equally in every direction, in a circle. The energy from the light is distributed evenly over the whole area of the circle. When the radius doubles, the radiation is spread out over four times as much area, so the dose is only one fourth as much. (In addition, as the distance from the source increases so does the likelihood that some gamma rays will lose their energy.
The exposure of an individual sitting 4 feet from a radiation source will be 1/4 the exposure of an individual sitting 2 feet from the same source
Shielding
The greater the shielding around a radiation source, the smaller the exposure.
Shielding simply means having something that will absorb radiation between you and the source of the radiation (but using another person to absorb the radiation doesn’t count as shielding). The amount of shielding required to protect against different kinds of radiation depends on how much energy they have.

(Alpha) A thin piece of light material, such as paper, or even the dead cells in the outer layer of human skin provides adequate shielding because alpha particles can’t penetrate it. However, living tissue inside body, offers no protection against inhaled or ingested alpha emitters.

(Beta) Additional covering, for example heavy clothing, is necessary to protect against beta-emitters. Some beta particles can penetrate and burn the skin.

(Gamma) Thick, dense shielding, such as lead, is necessary to protect against gamma rays. The higher the energy of the gamma ray, the thicker the lead must be. X-rays pose a similar challenge, so x-ray technicians often give patients receiving medical or dental X-rays a lead apron to cover other parts of their body.

At high radiation doses, significant effects can occur in exposed individuals within a short time of exposure, and in severe cases this can lead to early death. At low radiation doses, the principal concern is the risk of radiation-induced cancer in exposed individuals and hereditary disease in their descendants. The risks of these late effects have been quantified and this provides the basis for recommendations on limits for exposure.