Levels of exposure

Regulatory levels of exposure to various chemicals, among them solvents and benzene, have been a subject for constant pressure from industry manufacturers on one hand, regulatory agencies, health care, and patients on the other hand. The most common question asked is Is there a safe level of exposure to benzene The answer to that question has been given by the American Petroleum Institute in their paper on benzene, 1948, and their statement 

Indeed, in its most recent pubhcation the U.S. EPA, 10/14/98, further supports that approach and the panel members who evaluated the data felt that for the leukemogenic effects of benzene the linear model is consistent with the spirit of the proposed cancer risk assessment guidelines. 

---

Interest ia the toxicity of aldehydes has focused primarily on specific compounds, particularly formaldehyde, acetaldehyde, and acroleia (13). Litde evidence exists to suggest that occupational levels of exposure to aldehydes would result ia mutations, although some aldehydes are clearly mutagenic ia some test systems. There are, however, acute effects of aldehydes. 

Rats exposed to 500 ppm of bromotrifluoroethylene died following a 4-h exposure. Since the monomer decomposes in air, the level of exposure to it was actually lower. The effects in rats of repeated exposure over a two-week period have been studied. At 50 ppm, the animals lost weight and renal damage was noted although the effect was reversible. Very mild testicular damage was seen at 50 but not 10 ppm. The amount of urinary duotide excreted suggested that extensive metaboHsm was occurring (34). 

One of the most significant laser safety standards is that developed by the Z-136 committee of the American National Standards Institute (ANSI) (55). Although it is voluntary, many organi2ations use the ANSI standard. It contains a number of items including a recommendation for maximum permissible levels of exposure to laser radiation for various wavelengths, exposure durations, and different parts of the body separation of lasers into four different classes according to the level of ha2ard they present and recommendation of safety practices for lasers in each of the classes. 

Pyridine Acute Toxicology. Pyridine causes gastrointestinal upset and central nervous system (CNS) depression at high levels of exposure. The odor of pyridine can be detected at extremely low concentrations (12 ppb). The LD q (oral, rats) is 891 mg/kg, the LC q (inhalation, rats) is 4000/4 (ppm/h), and the TLV is 15 mg/nP (79,80). 

Inhalation of certain fine dusts may constitute a health hazard. Eor example, exposure to siUca, asbestos, and beryllium oxide dusts over a period of time results ki the potential risk of lung disease. OSHA regulations specify the allowable levels of exposure to kigestible and respkable materials. Material Safety Data Sheets, OSHA form 20, available from manufacturers, provide information about hazards, precautions, and storage pertinent to specific refractory products. 

Chromium Exposure Levels and U.S. Government Regulations. The level of exposure to chromium compounds for employees in industry and for the general population via waste disposal and industrial emissions is the subject of much regulation, research, and controversy. Some U.S. Government regulations, such as the Comprehensive Environmental Response, Compensation, and LiabiUty Act (CERCLA), also known as the Superfund Act, make no distinction as to the oxidation state of chromium (144). However, there is valence distinction in other regulations. 

The results from the consequence analysis step are estimates of the statistically expected exposure of the target population to the hazard of interest and the safety/health effects related to that level of exposure. For example ... 

Arguably, risk assessment from exposure to carcinogens merits special consideration because of the low levels of exposure capable of producing an adverse response in certain individuals coupled with the often long time-lag (latency period) between exposure and onset of disease. 

Eirst-aid measures for people exposed to nitrogen dioxide are mentioned in Chapter 9. In any event, containment, ventilation and/or appropriate respiratory protection should be considered depending upon scale of operation and level of exposure. 

For routine monitoring, frequency will be influenced by the level of exposure. The further the levels depart from the standard, the less the need for routine monitoring. A suggested guide is ... 

Detailed preeautions for handling radioaetive substanees will be dietated by die nature and quantity of isotope and die likely level of exposure. Thus for some materials laboratory eoats and gloves may be adequate for odiers a fully enelosed suit and respirator may be more appropriate. Some general preeautions are listed in Table 11.6. 

Reliability of airflow measurements m assessing ventilation systems performance Cobalt - a review of properties, use and levels of exposure A review of respirable crystalline silica - Exposure and control... 

In nonindustrial settings, MCS substances are the cause of indoor air pollution and are the contaminants in air and water. Many of the chemicals which trigger MCS symptoms are known to be irritants or toxic to the nervous system. As an example, volatile organic compounds readily evaporate into the air at room temperature. Permitted airborne levels of such contaminants can still make ordinary people sick. When the human body is assaulted with levels of toxic chemicals that it cannot safely process, it is likely that at some point an individual will become ill. For some, the outcome could be cancer or reproductive damage. Others may become hypersensitive to these chemicals or develop other chronic disorders, while some people may not experience any noticeable health effects. Even where high levels of exposure occur, generally only a small percentage of people become chemically sensitive. 

Air samples are collected over an 8 hour work shift for MEK. Measurements showed 3 ppm after 2 hours, 24 ppm after 4.5 hours, 12 ppm after 6 hours, and 2 ppm after 8 hours. Caleulate the TWA concentration and compare this value against the OSHA safe level of exposure. 

The links between levels of exposure and inconvenience caused by ventilation noise are described in an investigation carried out on office workers.- Technical measurements and analyses of the ventilation noise at 155 typical office workplaces were in this study combined with assessments by the office workers of the level of disturbance that they experienced, the effect on working performance, fatigue, stress-related pain, and headaches. The average noise level was about 40 dB(A) at two of the workplaces, while it was about 35 dB(A) at two others. It emerged from rhe narrow-band analyses that the sound pressure levels of rhe infrasound were not in any event of an order that this type of sound frequencies (below 20 Hz) could contribute to any disturbance effects. Any steps taken to counter the sound frequencies of the ventilation noise under 50 Hz, i.e., the point of btersection between the threshold curve of auditory perception and the spectral level distribution curve of... 

The office workers involved in the study mentioned above rated the ventilation noise as somewhat disturbing to quite disturbing at the two workplaces where the level of exposure was about 40 dB(A). At the two workplaces... 

The idea behind OELs is to identify the highest level of exposure concentration and the corresponding reference time period for which we can be confident that there will be no adverse effects on health. However, the concentrations and lengths of exposure at which the presence of airborne chemical agents could damage health have not been clear for many years, and even today there are many questions to be answered. 

However, for some type of adverse effects, such as genotoxicity, carcinogenicity, and respiratory sensitization, it may not be possible from present knowledge to define this threshold of activity, so we may conclude that any level of exposure might carry some finite risk. In this case, OELs should be established at levels sufficiently low to avoid risks these are called pragmatic OELs. 

Provides information on how levels of exposure of hazardous chemicals affect human health. Covers levels of exposure to hazardous chemicals below which no adverse health effects are expected to occur in various segments of the human population. The reference dose and carcinogenicity assessments on IRIS can sen>e as guides in e >aluating potential health hazards and selecting response to alleviate a potential risk to human health. Hours 8 00 a.m. to 4 40 p.m. EST, Monday - Friday. 

Molecular structural analysis is a developing method. The objective of a molecuhu structural analysis is to demonstrate a physical, structural, or chemical similarity between tlie chemical in question and a known toxic chemical tliat produces toxic and healtli effects in experimental animals and/or humans. Unfortunately, scientists do not fully understand tlie effects of slight changes in tlie chemical structure and tlieir biological effect on humans. As a result, tills type of analysis is useful in preliminary studies to identify potential health hazards for further e. amination with more established metliods in short-tenii tests or tests in experimental animals, hi its present stage of development, molecular structural analysis caiuiot be used to make absolute decisions about tlie appropriate levels of exposure of humans to chemicals... 

The measure used to describe the potential for noncarcinogenic toxicity to occur in an individual is not expressed as tlie probability of an individual suffering an adverse effect. The EPA does not at tlie present time use a probabilistic approach to estimate tlie potential for noncarcinogenic healtli effects. Instead, tlie potential for non carcinogenic effects is evaluated by comparing an exposure level over a specified time period (e.g., lifetime) witli a reference dose derived for a similar exposure period. Tliis ratio of exposure to toxicity is called a liazard quotient and is described below. (The reader is referred to Chapter 11 for additional details on tlie material tliat follows). The noncancer liazard quotient assumes tliat tliere is a level of exposure (i.e., RfD) below which it is unlikely for even sensitive populations to experience adverse healtli effects. 

Mental disturbances have been reported after organophosphate exposure. Neuropsychiatric symptoms occurred in two aerial applicators, one of whom used methyl parathion as well as other insecticides. One of these pilots had high levels of exposure to a mixture containing methyl parathion, toxaphene, and Dipterex when his clothing became saturated when the tank of his aircraft accidentally overflowed. Several months after the accident, the subject complained of anxiety, dizziness, emotional lability, and frequent and severe disagreements with family members and associates. Similar observations had been... 

The significance of the exposure levels shown in the Levels of Significant Exposure (LSE) tables and figures may differ depending on the user s perspective. Public health officials and others concerned with appropriate actions to take at hazardous waste sites may want information on levels of exposure associated with more subtle effects in humans or animals (LOAELs) or exposure levels below which no adverse effects (NOAELs) have been observed. Estimates of levels posing minimal risk to humans (minimal risk levels or MRLs) may be of interest to health professionals and citizens alike. 

---