Odors can warn of potentially dangerous materials. The warning property of odor has long been recognized. In the Middle Ages, odors were held responsible for disease, rather than being the result of disease and poor hygiene. Physicians protected themselves by theoretically purifying the air in a sick room with perfumed water. In this century, the property of odor as a warning agent has been used on a worldwide scale through the addition of pungent odorants such as ethyl mercaptan to odorless natural gas. The perceived connection between odors and disease persists. With national attention focused on waste and chemical spills, in the absence of specific information to the contrary, the average person concludes that a bad smell is unhealthy.
The relationship between odor and health effects should be clarified. Many odorants are perceptible at concentrations far below harmful concentration levels. For example, hydrogen sulfide (H2S) has been detected at concentrations as low as 0.15 ppb, whereas the acceptable exposure limit or the threshold limit value-time-weighted average (TLV-TWA) recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) for this compound is 10 ppm, 6 orders of magnitude greater. Thus, the detection of the "rotten egg" character of H2S is not necessarily an indicator of a potential health effect. Indeed, at concentrations near the TLV, the odor intensity of H2S is unbearable. Similarly, the TLVs for creosol and ethyl acrylate are 4 orders of magnitude greater than their threshold values.
The nose is not a suitable screening device to determine the presence or the absence of a health risk. Although detecting an odor indicates that a chemical exposure has occurred, a more detailed sampling investigation should be conducted.
Studies that have reviewed community odor and health problems reveal that a variety of common ailments are related to chemical exposure. However, in most cases, the identified chemicals were well below the thresholds for toxicity. This evidence suggests that detecting unpleasant odors can cause adverse physiological and neurogenic responses such as nausea, stress, and low concentration levels and that these effects are a result of chemical exposure. Therefore, further studies are necessary to define allowable exposures and how they relate to odor detection.
By definition, chemicals that are hazardous to health are considered toxic whether odorous or not. They are therefore controlled under existing laws such as the Toxic Substances Act and the CAA and their related regulations.
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