Route of entry

Hazardous and dangerous substances are able to enter the body by a number of different routes  

In order for any substance to cause injury to an individual, it must first be taken up by the body. Knowing the way in which substances are taken up is critical in order to understand and prevent toxicity. The body may be exposed to toxic substances through any one or a combination of four routes  

Occupationally, inhalation is the most common route of entry by toxic substances. It is fairly common for substances to have more than one route of entry, and some may cause injury through all four routes. 

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When sulfonic acids are neutralized to sulfonic acid salts, the materials become relatively innocuous and low in toxicity, as compared to the parent sulfonic acid (see Table 4). The neutralized materials cause considerably less eye and skin irritation. The most toxic route of entry for sulfonic acid salts is ingestion (39). The toxicity of neutralized sulfonic acids, especially detergent sulfonates, has been directiy related to the foaming capabiUty of the material. 

Some of the criteria used in the selection of a suitable agent are effectiveness in extremely small concentrations time to onset of action effectiveness through various routes of entry into the body, such as the respiratory tract, eyes, and skin stability in long-term storage and ease of dissernination in feasible munitions. 

The primary routes of entry for animal exposure to chromium compounds are inhalation, ingestion, and, for hexavalent compounds, skin penetration. This last route is more important in industrial exposures. Most hexavalent chromium compounds are readily absorbed, are more soluble than trivalent chromium in the pH range 5 to 7, and react with cell membranes. Although hexavalent compounds are more toxic than those of Cr(III), an overexposure to compounds of either oxidation state may lead to inflammation and irritation of the eyes, skin, and the mucous membranes associated with the respiratory and gastrointestinal tracts. Skin ulcers and perforations of nasal septa have been observed in some industrial workers after prolonged exposure to certain hexavalent chromium compounds (108—110), ie, to chromic acid mist or sodium and potassium dichromate. 

Air pollution principally affects the respiratory, circulatory, and olfactory systems. The respiratory system is the principal route of entry for air pollutants, some of which may alter the function of the lungs. 

For most ehemieals, inhalation is the main route of entry into the body. Penetration via damaged skin (e.g. euts, abrasions) should, however, be avoided. Certain ehemieals (e.g. phenol, aniline, eertain pestieides) ean penetrate intaet skin and so beeome absorbed into the body. This may oeeur through loeal eontamination, e.g. from a liquid splash, or through exposure to high vapour eoneentrations. Speeial preeautions to avoid skin eontaet are required with these ehemieals and potential exposure via skin absorption has to be taken into aeeount when assessing the adequaey of eontrol measures. 

However, there are multiple routes of entry to the body for some materials. When a toxic chemical acts on the body or system, the nature and extent of the injurious response depends upon the dose received, that is, the amount of the chemical actually entering the body or system. This relationship of dose and response is shown in Figure 3. The dose-response curve varies with the type of material and the response. 

Scientific information for the process of establishing OELs may come from human or animal data obtained using different methods, from studies of acute, subacute, and chronic toxicity through various routes of entry. Human data, which is usually the best source, is not easily available, and frequently it is incomplete or inadequate due to poor characterization of exposure and clear dose-response relationships. Human data falls into one of the following categories ... 

Another difficulty comes from the consideration of the route of entry (sf the contaminant, as chemicals can enter the body by various routes and the human body responds to the action of a toxic agent primarily on the basis of the rate and route of exposure. Without any doubt, the most important route of exposure at the workplace is inhalation, and this should be the route used to set OELs. However, if there is a threat of significant exposure by other routes, such as cutaneously (including mucous membranes and the eyes), either by contact with vapors or by direct skin contact w ith the substance, additional recommendations may be necessary. 

Route of entry Path by which toxins and other substances may enter the human body. These include inhalation, ingestion, and absorption through the skin. Less common routes include injection and absorption through moist surfaces surrounding the eyes and ear canal. 

Skin notation The word skin included as part of an exposure limit. It is used for those substances for which absorption through the skin is considered to be a significant route of entry into the body. 

The route of entiy section describes the primary patluvay by which the chemical enters the body. There are tlu-ee principal routes of entry inlialation, skin, and ingestion. This section of the MSDS supplies the PEL. the TLV, and other e.xposure levels used or recommended by the chemical manufacturer. 

Where sufficient toxicologic information is available, we have derived minimal risk levels (MRLs) for inhalation and oral routes of entry at each duration of exposure (acute, intermediate, and chronic). These MRLs are not meant to support regulatory action but to acquaint health professionals with exposure levels at which adverse health effects are not expected to occur in humans. They should help physicians and public health officials determine the safety of a community living near a chemical emission, given the concentration of a contaminant in air or the estimated daily dose in water. MRLs are based largely on toxicological studies in animals and on reports of human occupational exposure. 

Information on dioxins in the environment was acquired rapidly by using some simple, but safe and reliable techniques developed for chlorinated pesticdes. Based on results of these tests, one should be able to predict whether routes of entry into aquatic and terrestrial food chains are significant, the rate and products of decomposition mechanism, and their general longevity in the environment. 

Gram-negative baeteria possess an outer membrane which can act as a barrier to the penetration of antibiotics. The main route of entry of hydrophilic molecules is via the porins, whieh form pores in the outer membrane. Qualitative or quantitative alterations in these porins can result in the decreased accumulation of antibiotic. 

Route Dependent Toxicity. The toxicity of trichloroethylene does not seem to be heavily dependent upon its route of entry. Inhalation and ingestion are the primary exposure routes, and the liver, heart, and central nervous system are the primary targets for both routes (Candura and Faustman 1991). Renal toxicity results principally from oral exposure, and dermal exposure generally confines its toxic effects to the skin, although broad systemic effects can be induced imder conditions of high exposure (Bauer and Rabens 1974). Attributing such effects solely to dermal exposure, however, is difficult because inhalation exposure is often a factor in these cases as well. 

Exposure of women to cosmetic talcum powder, has been related to the observed presence of the characteristic phyUosilicate talc particles in normal and in malignant ovary tissue (Henderson etal., 1979). The experimental demonstration in rats of migration of talc particles from the vagina to the ovary, illustrates the potential route of entry into the body (Henderson etal., 1986). 

Several procedures have been reported for extraction of the suspected allelopathic agents from donor plants. Essentially all the procedures that were employed attempted to simulate the routes of entry of toxic substances into the natural environment. As shown previously, the allelopathic agents are released through leaves and roots, or escape into the environment as volatile materials. Table 3 suratBrizes the different extraction and bioassay procedures employed to isolate and detect the toxic chemicals (17). For extraction, the investigators used either the plant parts from the donor plants or the intact donor plants from which the suspected chemicals were leached through leaves, stems or roots. 

L-l is a vesicant (blister agent) also, it acts as a systemic poison, causing pulmonary edema, diarrhea, restlessness, weakness, subnormal temperature, and low blood pressure. In order of severity and appearance of symptoms, it is a blister agent, a toxic lung irritant, absorbed in tissues, and a systemic poison. When inhaled in high concentrations, it may be fatal in as short a time as 10 min. L-1 is not detoxified by the body. Common routes of entry into the body include ocular, percutaneous, and inhalation. 

BZ is usually disseminated as an aerosol with the primary route of entry into the body through the respiratory system the secondary route is through the digestive tract. BZ blocks the action of acetylcholine in both the peripheral and central nervous systems. As such, it lessens the degree and extent of the transmission of impulses from one nerve fiber to another through their connecting synaptic junctions. It stimulates the action of noradrenaline (norepinephrine) in the brain, much as do amphetamines and cocaine. Thus, it may induce vivid hallucinations as it sedates the victim. Toxic delirium is very common. 

Field protection The principles applied to the nerve agents apply equally as well to the incapacitating agents. It is possible that such agents will be disseminated by smoke-producing munitions or aerosols, using the respiratory tract as a route of entry. The use of protective mask, therefore, is essential. The skin is usually a much less effective route. 

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