Chronic effects, definition

The Committee analyzed published studies describing the In vivo and in vitro properties of the agents used and reviewed short-term data collected by the U.S. Army on volunteers. The ability to provide definitive answers to the questions raised by the charge to the Committee was limited by the absence of long-term followup studies of the soldiers and by the sparseness of chronic effects studies of these compounds In animals or In humans after industrial exposure. 

In the proposed Health Effects Test Standards for Toxic Substances Control Act Test Rules by the EPA (6), "chronic effects" was defined as ...disease processes which have a long latency period for development, result from long-term exposure, are long-term illnesses, or combinations of these factors." But ambiguity still exists for instance, how long is "long-term" The reason for the absence of a clear-cut definition for chronic toxicity is the complexity of events... 

Until definitions and test protocols for chronic effects are established, precautionary label texts for serious chronic effects should be used when there is generally accepted, well-established evidence that such serious chronic effects exist or when required by law. 

A major departure occurs in the NIOSH definition of health class . NIOSH is concerned with both acute and low level long term exposure, perhaps for a lifetime, that a worker may experience, primarily occurring under normal work conditions. NIOSH is not directly concerned with the decomposition or combustion products (as NFPA is) of chemicals unless they constitute the normal exposure of a worker. There is greater concern with chronic effects. 

The definitions which form the basis for assigning numerical ratings for reactivity and flammability are similar to the NIOSH and NFPA concepts. A significant difference occurs, however, in the health definitions. NPCA uses the Health Hazard Ratings System developed by Henry F. Smyth in cooperation with the Medical Department, Union Carbide Corporation. This system enlarges previous concepts to specifically include chronic exposure and chronic effects. So called supplemental effects such as photosensitization, acne-like eruptions, eye bum without pain, and metal fume fever among others are also identified. 

Safety hazards related to the physical characteristics of a chemical can be defined in terms of testing requirements, such as ignitability however, health hazard definitions are less precise and more subjective. There have been many attempts to categorize effects and to define them in various ways. Generally, the terms acute and chronic are used to delineate between effects on the basis of severity or duration. Acute effects occur rapidly as a result of short-term exposures. Chronic effects occur as a result of long-term exposures. 

Results of chronic studies permit substantiation of thresholds for chronic effects from oral and inhalation pesticide entry and definition of doses and concentrations that produce no effects. These data are required for determining the... 

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