Gastrointestinal tract occupational exposures

D may be encountered as a vapor, liquid, or as a component of mixtures. It may cause damage at the point of contact (skin, eyes, lungs, and gastrointestinal tract). Occupational exposure may occur through inhalation and dermal contact when 2,4-D is produced or used. 

During occupational exposure, respiratory absorption of soluble and insoluble nickel compounds is the major route of entry, with gastrointestinal absorption secondary (WHO 1991). Inhalation exposure studies of nickel in humans and test animals show that nickel localizes in the lungs, with much lower levels in liver and kidneys (USPHS 1993). About half the inhaled nickel is deposited on bronchial mucosa and swept upward in mucous to be swallowed about 25% of the inhaled nickel is deposited in the pulmonary parenchyma (NAS 1975). The relative amount of inhaled nickel absorbed from the pulmonary tract is dependent on the chemical and physical properties of the nickel compound (USEPA 1986). Pulmonary absorption into the blood is greatest for nickel carbonyl vapor about half the inhaled amount is absorbed (USEPA 1980). Nickel in particulate matter is absorbed from the pulmonary tract to a lesser degree than nickel carbonyl however, smaller particles are absorbed more readily than larger ones (USEPA 1980). Large nickel particles (>2 pm in diameter) are deposited in the upper respiratory tract smaller particles tend to enter the lower respiratory tract. In humans, 35% of the inhaled nickel is absorbed into the blood from the respiratory tract the remainder is either swallowed or expectorated. Soluble nickel compounds... 

In 1971 the National Academy of Science published a 40-page report, Asbestos The Need for and Feasibility of Air Pollution Controls, (Cooper, 1971) summarizing the illnesses associated with occupational exposure to asbestos and the risks of developing asbestosis, pleural calcifications, and cancers of the pulmonary and gastrointestinal tracts and thoracic cavity. Based on the evidence, the committee recommended control and reduction of dust containing fibrous inorganic materials in the workplace it also discussed nonoccupational exposure to asbestos. 

Occupationally, liver injury is most likely to occur following exposure to vapors of volatile halogenated hydrocarbons (such as chloroform, carbon tetrachloride, and bromobenzene), which may enter the bloodstream via the pulmonary route. However, hepatotoxins may enter the gastrointestinal tract, and hence the liver, in the form of fine particles. They are inhaled, then expelled from the bronchi or trachea into the oral cavity, and swallowed with saliva. 

There is considerably less information available on the toxicology of HDl after oral exposure compared to the data available on the inhalation toxicology of HDl discussed in the previous section of this profile. Clearly, inhalation is the major route of occupational exposure to HDl however, given exposure routes such as the lung mucocilliary clearance pathways, a very small amoimt of HDl could eventually enter the gastrointestinal tract and be presented for absorption, with possible systemic effects. Most of the information available on the oral absorption of HDl is about relatively large doses of HDl administered to laboratory animals, with no information located on the health effects of HDl in humans after oral exposure. 

NA is well absorbed through the skin, as well as via the gastrointestinal and respiratory tracts. With this and other aromatic amines, the skin appears to be a significant, if not the major occupational exposure pathway. Workers tolerate skin contamination since the acute effects of exposure are minimal. Inhalation... 

In studies of human occupational exposures, it appears that the respiratory tract is the primary site of injury after inhalation of selenium dust or selenium compounds, but gastrointestinal (possibly due to swallowed selenium) and cardiovascular effects, as well as irritation of the skin and eyes, also occur. Little of the available information for humans, however, relates health effects exclusively to measured concentrations of the selenium dust or compounds because of the possibility of concurrent exposures to multiple substances in the workplace. In animals, the respiratory tract is also the primary site of injury following inhalation exposure to selenium dust and hydrogen selenide. Hematological and hepatic effects have also been noted in animals. Inhalation data from laboratory animal studies are available only for acute exposures. 

The selectivity of oral exposure for suppressing humoral rather than cell-mediated immune function is the opposite of what was observed after dermal exposure to JP-8. Because JP-8 is irritating to the gastrointestinal tract and because the oral route is not considered to be relevant to routine occupational exposures, those data were not considered relevant to the subcommittee s charge. 

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