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A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.
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When external circumstances (like extreme heat or cold) or internal conditions (disease or poisoning) cannot be adjusted by normal mechanisms, the signs of discomfort and disease appear. The types of physical effects seen or felt (signs and symptoms) depend on the type of stress to which the body has been exposed. Because there are so many complex interrelationships between the systems within the body, a single change in any one system may result in numerous effects in other systems. In addition, the types of response to disease are limited, thus signs and symptoms of disease are often quite similar for different diseases. For example, headache, fever, nausea, vomiting and diarrhea are very common non-specific symptoms of disease, produced by many, many conditions. Because of the generality of most physiological responses to disease, many other methods have been developed to help diagnose the actual causes of disease. These methods include physical, biochemical and immunological techniques upon which modern clinical medicine is based.
A body's homeostasis can be upset by physical, chemical and/or biological agents which put stress on the body. The body's reaction to prolonged stress depends on the nature of the agent, the degree of stress, and the duration of stress. When the stress is too strong or too long, and homeostasis cannot be maintained or restored, disease occurs. Poisoning by chemical agents is nothing more than chemically induced disease, and the symptoms of chemical poisoning often are the same as symptoms caused by biological agents such as bacteria or viruses. To better understand how disease is caused by exposure to toxic chemicals, we must first understand how poisons work within the body.
Depending on the specific biochemical mechanism of action, a poison may have very widespread effects throughout the body, or may cause a very limited change in physiological functioning in a particular region or organ. Parathion causes a very simple inactivation of an enzyme which is involved in communication between nerves. The enzyme which parathion inactivates however, is very widespread in the body, and thus many varied effects on many body systems are seen besides sweating.
Toxicity is normally divided into four types, based on the number of exposures to a poison and the time it takes for toxic symptoms to develop. The two types most often referred to are acute and chronic. Acute toxicity is due to short-term exposure and happens within a relatively short period of time, whereas chronic toxicity is due to long-term exposure and happens over a longer period.
Most toxic effects are reversible and do not cause permanent damage, but complete recovery may take a long time. However, some poisons cause irreversible (permanent) damage. Poisons can affect just one particular organ system or they may produce generalized toxicity by affecting a number of systems. Usually the type of toxicity is subdivided into categories based on the major organ systems affected. Some of these are listed in table 1. Individual Toxicological Information Briefs (TIBs) are available which more fully explain skin and reproductive toxicities. Another is available which covers the formation of tumors and cancer.
Because the body only has a certain number of responses to chemical and biological stressors, it is a complicated business sorting out the signs and symptoms and determining the actual cause of human disease or illness. In many cases, it is impossible to determine whether an illness was caused by chemical exposure or by a biological agent (like a flu virus). A history of exposure to a chemical is one important clue in helping to establish the cause of illness, but such a history does not constitute conclusive evidence that the chemical was the cause. To establish this cause/effect relationship, it is important that the chemical be detected in the body (such as in the blood stream), at levels known to cause illness. If the chemical produces a specific and easily detected biochemical effect (like the inhibition of the enzyme acetylcholinesterase), the resulting biochemical change in the body may be used as conclusive evidence.
People who handle chemicals frequently in the course of their jobs and become ill and need medical attention should tell their physicians about their previous exposure to chemicals.
| Category | System affected | Common symptoms |
|---|---|---|
| respiratory | nose, trachea, lungs | irritation, coughing, choking, tight chest |
| gastrointestinal | stomach, intestines | nausea, vomiting, diarrhea |
| renal | kidney | back pain, urinating more or less than usual |
| neurological | brain, spinal cord | headache, dizziness, behavior confusion, depression, coma, convulsions |
| hematological | blood | anemia (tiredness, weakness) |
| dermatological | skin, eyes | rashes, itching, redness, swelling |
| reproductive | ovaries, testes, fetus | infertility, miscarriage |
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