Document aJMvoNBQNDmMj322o9j1kO6m9

Lead, when taken into the body, may be deposited in the bones When the intake of lead stops, the stored portion is excreted until it is virtually eliminated from the system In chronic poisoning the excretion rate usually rises until it balances the absorption rate In the case of lead poisoning, biochemical tests performed on the body fluids would indicate the amount that is being circulated in the blood, excreted in the unne, or stored in the bones if an autopsy was made An important difference between inhalation as route of entry and ingestion or skin absorp tion is that through inhalation the material enters the arterial blood directly, whereas with ingestion or skin absorption the material enters the venous blood and is earned through the nght portion of the heart where it is then diluted by the entire venous system and passed through the lungs and then pumped by the left portions of the heart to the brain and other organs Reactive gases and vapors are altered with in the body and are eliminated to a large ex tent in forms other than those in which they are absorbed The toxicological action may be exerted either by the substance in its ongmal form or by its detoxification products Nonreactive gases and vapors are not al tered to any appreciable extent m the body and are eliminated in the same chemical form m which they are absorbed The aliphatic hydrocarbons, such as propane and heptane, are examples of that type Mode of action Industrial poisoning may be classified as one of three types acute, subacute, or chronic The classification is based on the rate of in take of harmful materials, rate of onset of symptoms, and the duration of symptoms Typically, acute poisoning is character ized by rapid absorption of the offending ma terial and the exposure is sudden and severe For example, inhaling high levels of carbon monoxide or swallowing a large quantity of cyanide compound will produce acute poi soning The death or survival of a victim through the critical period occurs suddenly Generally, acute poisoning results from a single dose which is rapidly absorbed and damages one or more of the vital physiologi cal processes The development of cancer long after recovery from acute radiation dam age is called a delayed acute effect Frequently repeated and extended ex posures, over a period of several hours or days, results in subacute effects, depending on the dose rate Chronic poisoning is concerned with the continued absorption over a long period of time of a harmful material in small doses, each dose, if taken alone, would barely be effective Chronic poisoning is character ized by the harmful materials remaining m the tissues, continually injuring some body process The rate of intake exceeds the rate of excretion or detoxification, thus chronic poisoning can also be produced by exposure to a harmful material which produces irrevers ible damage, so the injury accumulates, rather than the poison The symptoms in chronic poisoning are usually different than those seen in acute poisoning by the same toxic agent It is readily apparent that not all individuals react m the same manner to the same amount of a harmful material According to Stokmger (see "References"), "The atypical, or idiosyncratic, response to chemicals has al ways been a cause for unusual concern in those responsible for the control of hazard ous exposures to individuals " Predictive tests can be used in pre-employment place ment examinations to screen out the hypersusceptible individuals against future in jurious exposure to the company's products Type of harmful effects Narcosis, lmtation of the respiratory tract, and asphyxiation characterize the acute effect produced upon exposure to toxic gases, vapors, and fumes All organic solvents, upon extended high level exposures, are capable of producing a gradual conbnuous paralysis of the central nervous system, which is expressed m loss of consciousness, or vol untary movements Death may result from respiratory failure Many symptoms of narcosis and asphyxia tion are quite similar in that the primary effect m each is to impair the functioning of the brain--in narcosis by direct action and in asphyxiation by denying the brain sufficient oxygen Mild exposure to chemical agents producing asphyxiation and narcosis are 1303