Sunday, September 24, 2006

Dose - Response Relationship

All toxicology considerations are based on the dose-response relationship. A dose is administeed to test animals, and, depending on the outcome, is increased or decreased until a range is found where at the upper end all animals die and, at the lower end, all animals survived. The data collected are used to prepare a dose-response curve relating percent mortality to dose administered. The doses given are expressed as the quantity administered per unit body weight, quantity per skin surface area, or quantity per unit volume of the respired air. In addition, the length of time during which the dose administered should also be listed.

The dose-response relationship can also be expressed as the product of a concentration multiplied by the time duration approximation of other combination of concentration of a chemical and time that would produce similar effects. Although this concept must be used very cautiously and cannot be applied at extreme conditions of either concentration or time, it can be useful in predicting safe limits for airborne contaminants in respect to environmental exposures. Safe limits are set so that the combination of concentrations and time durations are below the levels that will produce injury to exposed individuals.

Exposure to low levels of some chemicals, such as ammonia, causes so much physical irritation that workers will not voluntarily tolerate harmful concentrations. If a person became trapped, however, he would be injured by the excessive exposure.

Thursday, September 21, 2006

Toxicology In The Occupational Setting

All of us have probably experienced at least one episode of toxicity in our lifetime or know of someone who has, wheter a friend, a coworker, or an incident reported in the news. Injuries and deaths occur each year as a result of accidental poisonings, smoke inhalation, entry into confined spaces, and many other situations.These events occur at construction sites, in factories and hospital, and even in homes. Sometimes the events pass without being recognized for what they are, since exposure to some hazardous materials may cause symptoms similar to other illnesses, like cold or the flu. In other cases, the symptoms are mild and pass without concern, or they are non-specific, like nausea or a headache, and are attributed to other causes.

The Malaysian OSHA Hazard Communication Standard went into effect in 1986; it requires employers to inform employee about health hazards specific to the materials they handle or use at work and about ways to protect themselves against those hazards. As a result, workers are now better informed about the hazardous materials present in theirworkplaces. Workers receive specific training about the kinds of health problems that can result from exposure to the hazardous materials; they know what steps to take to protect themselves from these hazards, such as the use of protective respirators or gloves.

However, each year overexposures or accidental releases of hazardous materials occur and cause injury, despite the training and information available to workers. The industrial hygiene professional plays a key role in recognizing potential hazards and implementing controls to protect worker health.

Tuesday, September 19, 2006

Poison Defined: Acute versus Chronic

Poison are chemical which cause illness,injury or death when taken in very small quantities. The legal definition of a poison is a chemical that takes less the 50mg per kilogram of body weight to kill 50% of the victims exposed. This is really a very small amount of material - about 3/4 of a teaspoon for the average adult and about 1/8 a teaspoon for a 2 year old child. There are very few chemicals that are lethal at these doses, but those that are must be classified as poisons. These materials will be classified as "acute poison" because their effect is immediate.

Chronic toxicity, on the other hand, refers to the systemic damage that is done after repeated exposure of low concentrations over long periods of time. Materials most often associated with chronic toxicity are those that have been labeled as carcinogens, though there are other classes of chronic toxins which must be used with equal care. All chronically toxic materials are problematic because we do not know when or if the effect of the exposure will be felt. Workers in research laboratories and in other chemical settings should not discount any chemical exposure - materials not thought to be hazardous in the recent past are often found to be carcinogenic at a later time.

Most chemicals exhibit some degree of both acute toxicity and chronic toxicity. The symptoms displayed and the systemic effect will, however, differ. In addition, some materials may act as chronically toxic, but show no chronic ill effects. The same is true for materials labeled as chronically toxic, which have no adverse single dose effect. Despite this lack of correlation, the effects of both forms of toxicity are definitely dose related, that is, the greated the dose, the greater the effect.

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