ROUTES OF EXPOSURES TO HAZARDS

Preview This section describes the potential pathways of exposure and explains how blocking these pathways can prevent exposure. 

INCIDENT 3.1.1.2 RESEARCHER BURNED BY SPLASH OF STRONG ACID  

What lessons can be learned from these incidents  

Laboratory Safety for Chemistry Students, Second Edition. Robert H. Hill, Jr. and David C. Finster. 2016 John Wiley Sons, Inc. Published 2016 by John Wiley Sons, Inc. 

Routes of exposure are the pathways by which chemicals may reach or enter the body. To cause toxic effects in a living organism or body, a chemical must find a way to come in contact with and enter the body. To prevent exposure to harmful chemicals, it is only necessary to prevent entry or exposure to the body. If you know the potential routes of exposure and you seek to prevent chemicals from entering by those pathways, you will effectively prevent exposure to those chemicals and will be protecting yourself from harm. There are four routes of entry or exposure ingestion, inhalation, skin and eye exposure, and injection. 

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Probably the most important concern for potential health effects due to engineered nanomaterials is inhalation exposure to ultrafine, respirable particles. In Section 3.1.1 (Routes of Exposure to Hazards),... 

The most important routes of exposure to endosulfan for the general population are ingestion of food and the use of tobacco products with endosulfan residues remaining after treatment. Farmers, pesticide applicators, and individuals living in the vicinity of hazardous waste disposal sites contaminated with endosulfan may receive additional exposure through dermal contact and inhalation. 

People living near hazardous waste sites may be exposed to lead via ingestion of contaminated water or soils or by inhalation of lead particles in the air. For people not living in the vicinity of hazardous waste sites, the major route of exposure to lead is ingestion, particularly of lead-contaminated water, food, soil, lead-based paint chips, or dusts (the latter two are particularly relevant to children in lower-income urbanized populations). For occupationally exposed individuals, the predominant route of exposure is the inhalation of lead particles with oral ingestion also important in many cases. 

Endrin has also been shown to be absorbed after ingestion by humans (Coble et al. 1967 Curley et al. 1970 Kintz et al. 1992 Rowley et al. 1987 Runhaar et al. 1985 Waller et al. 1992 Weeks 1967) however, no studies were located on the rate or extent of absorption that occurs in orally exposed humans or animals. Exposure to endrin through ingestion of contaminated drinking water is not expected to be an important source of concern because the compound has only rarely been detected in drinking water (Schafer et al. 1969 Wnuk et al. 1987). Since endrin is tightly bound to soil particles, ingestion of endrin-contaminated soil, particularly by children, may be an important route of exposure near hazardous waste disposal sites that contain endrin. 

The most important route of exposure to 1,2-dibromoethane for most members of the general population is ingestion of contaminated drinking water. Individuals living in the vicinity of hazardous waste sites contaminated with 1,2-dibromoethane may be exposed to higher concentrations of the compound. 

In the past (prior to 1974), exposure of humans to heptachlor and heptachlor epoxide was directly related to the application of heptachlor as an insecticide. However, because of the persistence and bioaccumulation of heptachlor and heptachlor epoxide, exposure of the general population can occur through ingestion of contaminated food (especially cow s or maternal human milk), inhalation of vapors from contaminated soil and water, or direct contact with residual heptachlor from pesticide application. People whose homes have been treated may continue to be exposed to these chemicals in the air over long periods. Occupational exposure can occur in the manufacture of the chemical or from use of heptachlor to control fire ants. The most likely routes of exposure at hazardous waste sites are unknown. Heptachlor has been found infrequently in soil and groundwater at hazardous waste sites. Children who eat contaminated soil or people who obtain tap water from wells located near hazardous waste sites might be exposed to heptachlor. Also, since both compounds can volatilize from soil, people living near hazardous waste sites may be exposed to the compounds in the air. 

Infants and toddlers are exposed to higher levels (based on their greater dose to surface area [or body weight] ratio) of heptachlor epoxide in the diet (particularly from milk) than are adults. Higher exposure rates in indoor air may occur for at least 1 year in homes that have been treated for termites with heptachlor in the past. Although the most likely routes of exposure at hazardous waste sites are unknown, exposure may result from ingestion of contaminated soil near these sites particularly by children. Since both heptachlor and heptachlor epoxide volatilize from soil, inhalation exposure may also be important for persons living near hazardous waste sites. Exposure via... 

Information on nickel exposure from hazardous waste sites is lacking. The most probable route of exposure from hazardous waste sites would be dermal contact, inhalation of dust, and ingestion of nickel-contaminated soil. Groundwater contamination may occur where the soil has a coarse texture and where acid waste, such as waste from plating industries, is discarded. People using this water may be exposed to high levels of nickel. 

Polybrominated Diphenyl Ethers. Information on the relative importance of different routes of exposure to PBDEs is limited. Data on the concentrations of PBDEs in foods, collected using a market-basket approach, are needed to determine concentrations of PBDEs in foods consumed by the general population. Data on the PBDE concentrations in foods grown in contaminated areas, particularly in the vicinity of hazardous waste sites, are also needed. Data on congener-specific PBDE analysis of food, especially plant products, would be useful. More monitoring data on the concentrations of total PBDEs as well as conquers in air in remote, rural, urban, and areas near hazardous waste sites and incinerators are needed. Data on PBDE concentrations in finished drinking water nationwide would be helpful. 

Although dermal exposure is potentially important as a route of exposure around hazardous waste sites, the limited data on dermal/ocular toxicity do not permit a complete evaluation of the toxic potential of the tin compounds by this route. Skin and eye irritation and dermatitis have been observed in both humans and animals after acute and intermediate exposure to inorganic tin or organotin compounds. None of the compounds appear to cause dermal sensitization in humans or animals. 

Characterize possible mechanisms of exposure to hazardous substances. The pathways by which hazardous substances released from a disposal facility can be transported through the biosphere and the resulting routes of human exposure are specified, often along with their respective probabilities. To estimate exposures of humans at assumed receptor locations, dilution of contaminants by transport in air or water as well as concentration by various means, such as precipitation and uptake by intermediate biological organisms consumed by humans, must be considered. An example of the potentially complex web of exposure pathways is shown in Figure 3.3. 

Oral exposure through consumption of contaminated food is presumed to be the major route of exposure to PCB mixtures for the general population (Duarte-Davidson and Jones 1994 Hansen 1999). Furthermore, oral exposure through ingestion of contaminated water or soil represents a possible additional source of exposure for populations in the vicinity of hazardous waste sites. Duarte-Davidson and Jones (1994) estimated that the average total PCB exposure for the contemporary UK population was... 

In addition to contributing to exposure in occupational settings, the dermal route, through skin contact with contaminated water or soil, represents a potential route of exposure to PCB mixtures for populations in the vicinity of hazardous waste sites. 

In considering the adequacy of specific investigations as a basis to identify hazard in risk assessment, several features of study design are considered including the purity of the compound administered, the size of the study (i.e., numbers of exposed and control animals), whether the study was performed under Good Laboratory Practice standards, the relevance of the route of exposure to that of humans, duration of exposure, the number and suitability of the dose levels administered, the extent of examination of various toxicological endpoints, and the statistical analysis of the data (HC 1994 Meek et al. 1994). Criteria for the technical adequacy of animal carcinogenicity studies have been published (e.g., Chhabra et al. 1990 NTP 1984 OSTP 1986). 

Aerosols of agents are not persistent. However, the solid agents can persist in the environment for extended periods. Since the primary route of exposure to Metal Fume Choking Agents is through inhalation and agents have very little vapor pressure, there is minimal risk once the initial aerosol has settled. However, re-suspension of any dust contaminated with metal oxides can pose a continuing hazard. 

As with chenoical hazards there are several potential routes of exposure to infectious agents in the laboratory—ingestion, dermal exposure, eye exposures, inhalation, and injection. 

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