Exposure, chronic

Chronic exposure refers to repeated or continuous exposure over long periods of time. Amine-based materials, such as amine curatives and catalysts, have a potential for problems to occur after a number of years. The highest-profile potential problem material is MOCA, which has been subject to numerous studies. There have been very few cases of fatalities due to exposure to MOCA. The initial casualties also had exposure to precursor materials that were known carcinogens. Further details are very scant. 

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The third of the major hazards and the one with the greatest disaster potential is the release of toxic chemicals. The hazard posed by toxic release depends not only on the chemical species but also on the conditions of exposure. The high disaster potential from toxic release arises in situations where large numbers of people are briefly exposed to high concentrations of toxic material, i.e., acute exposure. However, the long-term health risks associated with prolonged exposure at low concentrations, i.e., chronic exposure, also present serious hazards. 

Exposure to excessive amounts of lead over a long period of time (chronic exposure) increases the risk of developing certain diseases. The parts of the body which may be affected include the blood, nervous system, digestive system, reproductive system, and kidneys. These effects include anemia, muscular weakness, kidney damage, and reproductive effects, such as reduced fertiHty in both men and women, and damage to the fetus of exposed pregnant women. 

Toxicology. The acute oral and dermal toxicity of naphthalene is low with LD q values for rats from 1780—2500 mg/kg orally (41) and greater than 2000 mg/kg dermally. The inhalation of naphthalene vapors may cause headache, nausea, confusion, and profuse perspiration, and if exposure is severe, vomiting, optic neuritis, and hematuria may occur (28). Chronic exposure studies conducted by the NTP ia mice for two years showed that naphthalene caused irritation to the nasal passages, but no other overt toxicity was noted. Rabbits that received 1—2 g/d of naphthalene either orally or hypodermically developed changes ia the lens of the eye after a few days, foUowed by definite opacity of the lens after several days (41). Rare cases of such corneal epithelium damage ia humans have been reported (28). Naphthalene can be irritating to the skin, and hypersensitivity does occur. 

Chemical Toxicity. Radiopharmaceuticals are subject to the same requirements for safety as are other pharmaceuticals, and are tested for chemical toxicity in much the same manner. It is generally understood, however, that patients are likely to receive relatively few doses of any given radiopharmaceutical so that the effects of long-term chronic exposure to the compound rarely need be assessed. Safety margins, that is, the ratio of the adininistered dose to the lowest dose that produces an observable effect, are usually on the order of 100 or more. 

Health and Safety Factors. Carbonyl sulfide is dangerously poisonous, more so because it is practically odorless when pure. It is lethal to rats at 2900 ppm. Studies show an LD q (rat, ip) of 22.5 mg/kg. The mechanism of toxic action appears to iavolve breakdowa to hydrogea sulfide (36). It acts principally on the central nervous system with death resulting mainly from respiratory paralysis. Little is known regarding the health effects of subacute or chronic exposure to carbonyl sulfide a 400-p.g/m max level has been suggested until more data are available (37). Carbon oxysulfide has a reported inhalation toxicity in mice LD q (mouse) = 2900 ppm (37). 

Fig. 7. Toxicity of chlorine to aquatic organisms, (a) Time-dependent mortaUty (50%) of four example species in various levels of total residual chlorine in the laboratory, where for A, A.losa aestivalis and B, Salmogairdnerii r (correlation coefficient of the curve) = —0.96 and for C, P/euroneetesplatessa and D, Salmo trutta r = —0.98. (b) A summary of chlorine toxicity to freshwater species, indicating overall no-effect thresholds for acute and chronic exposures. Numbers indicate where more than one test yielded the same result. A different summary figure appHes to marine organisms because of differences in the...

Chronic exposures involve consecutive daily exposure to the test material over the lifespan of the test species, or a great portion of it. 

Chronic Toxicity Studies. With the exception of tumorigenesis, most types of repeated exposure toxicity are detected by subchronic exposure conditions. Therefore, chronic exposure conditions are usually conducted for the following reasons if there is a need to investigate the tumorigenic potential of a material if it is necessary to determine a no-effects or threshold level of toxicity for lifetime exposure to a material and if there is reason to suspect that particular forms of toxicity are exhibited only under chronic exposure conditions. 

For the above reasons, chronic exposure studies are frequently designed in such a way that it is possible to combine observations for tumorigenesis and noimeoplastic tissue injury. Chronic studies are usually extensively monitored. It is common practice to sacrifice animals at intervals during the study in order to detect the onset of any tissue injury. For two-year exposure studies, it is most meaningful to have interim sacrifices at 12 and 18 months. 

Dichloroethane is one of the more toxic chlorinated solvents by inhalation (49). The highest nontoxic vapor concentrations in chronic exposure studies with various animals range from 100 to 200 ppm (50,51). 1,2-Dichloroethane exhibits a low single-dose oral toxicity in rats LD q is 680 mg/kg (49). Repeated skin contact should be avoided since the solvent can cause defatting of the skin, severe irritation, and moderate edema. Eye contact may have slight to severe effects. 

The vapors of aHyl chloride are very irritating to the eyes, nose, and throat. Lung injury may be delayed in onset. Liver and kidney injury can result from exposure to vapors kidney injury is expected to be most severe in acute exposures. High concentrations of vapor can be lethal. FoHowing chronic exposures to the vapors, Hver injury would be expected to occur first (23). 

These markings provide a general idea of the hazards of a material and the severity of these hazards as they relate to handling, fire protection, exposure, and control. This standard is not applicable to transportation or to use by the general public. It is also not applicable to chronic exposure. For a full description of this standard, refer to NFPA 704. The system identifies the hazards of a material in four principal categories health, flammability, reactivity, and unusual hazards such as reactivity with water. 

Materials that on intense or continued hut not chronic exposure could cause temporary incapacitation or possible residual injury 2 Materials that must he moderately heated or exposed to relatively high ambient temperatures before ignition can occur 2 Materials that readily undergo violent chemical change at elevated temper atiires and pressures or which react violently with water or which may form explosive mixtures with water... 

Estimating the long-term risk to workers or the public from chronic exposure to potentially harmful substances or activities... 

The nonvisual or subtle effects of air pollutants involve reduced plant growth and alteration of physiological and biochemical processes, as well as changes in the reproductive cycle. Reduction in crop yield can occur without the presence of visible symptoms. This type of injury is often related to low-level, long-term chronic exposure to air pollution. Studies have shown that field plantings exposed to filtered and unfiltered ambient air have produced different yields when no visible symptoms were present (5). Reduction in total biomass can lead to economic loss for forage crops or hay. 

Beeause the diisoeyanate is used in exeess, there is usually free monomer present. Isoeyanates are hazardous materials particularly upon inhalation and skin contact. Chronic exposure ean lead to sensitization. The adhesives must therefore be used with proper ventilation and should not come in eontact with the skin in the unreaeted state. Vapor monitoring badges for employees and periodie real time vapor monitoring around process equipment is reeommended. 

Alopecia Alopecia is the loss of hair. Acute or chronic exposure to some chemicals may result in the temporary or permanent loss of hair. 

Anorexia Anorexia is loss of appetite. You may be familiar with the eating disorder, anorexia nervosa, in which the victim restricts dietary intake to starvation levels. Anorexia may be a symptom of acute or chronic exposure to certain chemicals. If you have suffered an unexplained loss of appetite in conjunction with other unusual symptoms, you may want to explore the MSDSs for chemicals that... 

Hepatic Hepatic means "pertaining to the liver." For example, hepatitis is inflammation of the liver. Liver disorders are sometimes marked by jaundice, a yellowish coloration to the whites of the eyes and skin. Certain chemicals are hepatotoxins (toxic to the liver), usually as a result of chronic exposure. One example is carbon tetrachloride (CCI4). 

Doses from several small exposures over a pjcriod of time (chronic exposure) causing no immediate effect, may also result in a delayed effect. This cumulative effect may be serious or minor. 

Heavy Metals - Heavy metals represent problems in terms of groundwater pollution. The best way to identify their presence is by a lab test of the water or by contacting county health departments. There are concerns of chronic exposure to low levels of heavy metals in drinking water. 

The toxic action of bromine is similar to that of chlorine and can cause physiological damage to humans through inhalation and oral routes. It is an irritant to the mucous membranes of the eyes and upper respiratory tract. Severe exposures may result in pulmonary edema. Chronic exposure is similar to therapeutic ingestion of excessive bromides. 

NUCRAC improves on the health effects model by a reexamination of Hiroshima and Nagasaki data. The dry deposition model was much improved by the inclusion of a particle-si/e distribution, a detailed settling model, and a detailed chronic exposure model via the food pathway. However, it does not include a rainout model. 

Chronic exposure Long-term repeated exposure to low levels of pollutants, which may cause damage to the health of occupants. 

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