Exposure, chemical chronic

The exact mechanism by which chemical exposures cause MCS is unknown. It is believed that a two-step process occurs. First, an initial exposure or chronic exposures interacts with a susceptible individual, leading to loss of that person s prior, natural tolerance for everyday, low-level chemicals, as well as certain foods, drugs, alcohol, and caffeine. In the second stage, symptoms are thereafter triggered by extremely low doses of previously tolerated products and exposures.2 This theory is called toxicant-induced loss of tolerance or TILT. 3... 

Reports of heightened sensitivity to chemicals have been documented since the 1800s. Since World War II, there has been a dramatic rise in the manufacture and use of synthesized chemicals like pesticides, plastics, and artificial fragrances, and the incidence of MCS has steadily grown. One of the first doctors to identify the relationship between low-level chemical exposures and chronic illness was Theron Randolph in the 1950s. 

As an alternative to the assumption of a one-time exposure for 1,000 h at the time of facility closure, permanent occupancy of a disposal site following loss of institutional control could be assumed (see Section 7.1.3.4). The assumption of chronic lifetime exposure would affect the analysis for hazardous chemicals that induce deterministic effects only if estimated intakes due to additional pathways, such as consumption of contaminated vegetables or other foodstuffs produced on the site, were significant. Based on the results for lead in Table 7.8, an intake rate from additional pathways of about 50 percent of the assumed intake rate by soil ingestion, inhalation, and dermal absorption would be sufficient to increase the deterministic risk index above unity. The importance of additional pathways was not investigated in this analysis, but they clearly would warrant consideration. The increase in exposure time during permanent occupancy does not otherwise affect the analysis for chemicals that induce deterministic effects, provided RfDs are appropriate for chronic exposure, because chronic RfDs incorporate an assumption that the levels of contaminants in body organs relative to the intake rate (dose) are at steady state. 

Chronic Occurring over a long period of time freqnently recurring Chronic exposure Exposure to a chemical substance for more than 1 year Chronic toxicity The capacity of a substance to canse adverse or harmful effects in the organism after long-term exposure CIN Chronic interstitial nephritis... 

IRPTC International Register of Potentially Toxic Chemicals Irritant A chemical substance that can cause an inflammatory reaction to the eye, skin, respiratory system. An irritant can cause an acute effect from a single high-level exposure or chronic effects from repeated exposures Itching An uncomfortable sensation in the skin... 

The Environmental Criteria and Assessment Office in Cincinnati (ECAO-Cin) of the U.S. Environmental Protection Agency (EPA) has been preparing health risk assessment documentation and developing methods useful for assessment of health hazards for single chemical chronic exposure for several years (1,2). 

Risk Assessment for Single Chemical Chronic Exposure and Chemical Mixtures... 

Separate from the acute toxicity endpoints described above, one must be concerned about the long-term effects of exposure to chemicals. Chronic toxicity is particularly insidious because effects may not be felt by the individual(s) for years (or even decades) before serious effects such as cancer become apparent, which may by then be too late to treat. Cancer can result from many sources, cigarette smoking and genetic disorders being notable examples, but the public is also very concerned about cancer and other serious health effects which may result from exposure to synthetic chemicals. Repeated or continuous exposure to low levels of chemicals over an extended period ( chronic exposure ) is of primary concern and therefore a focus of the EPA under the TSCA. 

In the Green Screen the hazards of a chemical are defined by its potential to cause acute or chronic adverse effects in humans or wildlife, its fate in the environment, and certain physi-cal/chemical properties of concern to human health. Acute mammalian toxicity (lethality) and irritation of the skin or eye are examples of acute adverse effects that can result from inhalation, ingestion, or dermal contact with a chemical. Chronic effects occur after repeated exposures and include cancer and adverse effects to the reproductive, neurological, endocrine, or immune systems. 

In your work in the laboratory, you will encounter chemicals that have documented or suspected chronic effects—chronic toxicants. While the incident described above illusAates an adverse outcome from exposure to a chronic toxicant, these cases are rare in laboratories. The nature of effects from exposures to chronic toxicants usually requires receiving doses over an extended period, usually many months or years, and this is an unlikely scenario in a laboratory situation. Most laboratories use very small amounts of a wide variety of chemicals over many years of time, and reports of chronic toxic effects from laboratory exposures have been sparse and rare. Nevertheless, a few epidemiologic studies have found that chemists, as a group, were at excess mortality risks for suicide and cancer but the causes of these observaAons are not clear. ... 

In your work in the laboratory, you will encounter chemicals that have documented or suspected toxic effects due to relatively low exposures over longer periods of time. These are chronic toxicants as introduced in Section 4.1.1. While the incident described above illustrates an adverse outcome from exposure to a chronic toxicant, these cases are rare in laboratories. The nature of the effects from exposures to chronic... 

The brain is also affected by chronic exposure. Chemicals such as lead can decrease IQ, decrease the ability to remember things, and make someone more irritable. Many times these changes are small and can only be found with special medical tests. Workers exposed to solvents, such as toluene or xylene in oil-based paints, may develop neurological changes over a period of time. 

The supervisor should at least counsel all female employees about the hazards to a fetus of maternal infection or exposure to chronic doses of low levels of virus or other infectious agent. Exposure to potential chemical teratogens during the first trimester poses an additional hazard. The individual should be given enough information by the supervisor to allow her to make a rational decision according to the doctrine of informed consent. ... 

For extrapolation to humcms, the U.S. EPA has adopted a convention of applying an uncertcunty factor of 10 to the dose tested in cmimals. This is equivalent to assuming that the chemical might be 10 times more toxic if exposure were chronic rather them of shorter duration. The same process and factor is typiccdly used for extrapolation to wildlife species. 

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. 

Workers in the metals treatment industry are exposed to fumes, dusts, and mists containing metals and metal compounds, as well as to various chemicals from sources such as grinding wheels and lubricants. Exposure can be by inhalation, ingestion, or skin contact. Historically, metal toxicology was concerned with overt effects such as abdominal coHc from lead toxicity. Because of the occupational health and safety standards of the 1990s such effects are rare. Subtie, chronic, or long-term effects of metals treatment exposure are under study. An index to safety precautions for various metal treatment processes is available (6). As additional information is gained, standards are adjusted. 

In additional EPA studies, subchronic inhalation was evaluated ia the rat for 4 and 13 weeks, respectively, and no adverse effects other than nasal irritation were noted. In the above-mentioned NTP chronic toxicity study ia mice, no chronic toxic effects other than those resulting from bronchial irritation were noted. There was no treatment-related increase ia tumors ia male mice, but female mice had a slight increase in bronchial tumors. Neither species had an increase in cancer. Naphthalene showed no biological activity in other chemical carcinogen tests, indicating Htde cancer risk (44). No incidents of chronic effects have been reported as a result of industrial exposure to naphthalene (28,41). 

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