exposed to asbestos and even others less directly exposed, such as their 

 families. These toxic properties have only recently been recognized, 

 even though asbestos as a natural mineral has been used for centuries. 



A second general set of problems concerns the determination of 

 acceptable levels of pollutants in our surroundings. Most pollutants 

 are naturally dispersed or removed, ultimately, from the environment. 

 But they can reach local concentrations which endanger health, either 

 because of accompanying unusual conditions (such as atmospheric 

 inversions) or through long-term, low-level exposure. Pollutants 

 occurring in this latter, more subtle, form may also produce 

 undesirable alterations in the chemistry of the planet, its climate, and 

 its complex ecologies. Compounding the problem is the possibility that 

 new pollutants may grow to a dangerous level before their deleterious 

 effects are detected. This is especially true when there is a long time lag 

 between exposure and the subsequent appearance of a deleterious 

 impact, e.g., in the case of aromatic amines and bladder cancer, a 

 decade or more intervenes between exposure and appearance of 

 lesions. 



The rational determination of acceptable concentration levels of 

 pollutants is a vexing problem — for society and science. "Safe" limits 

 may be set which are more stringent than necessary, thus imposing 

 excessive economic and social costs; on the other hand, if limits are set 

 too liberally, the resulting damage — seen only in retrospect — to the 

 environment and health may be great. 



The current stock of knowledge regarding the environment is 

 more descriptive than explanatory and predictive. Base line 

 measurements are needed to gauge changes in the state of the 

 environment, and improved analysis of ecological structure and 

 process is required to forecast the environmental consequences of 

 alternative policies and technologies. Two general approaches are 

 available for expanding the stock of knowledge. The first consists of 

 tracing pollutants through the environment in an effort to determine 

 their sources, routes, rates, and fates, which helps to reveal the 

 environmental interactions as well as the opportunities to prevent, 

 control, or repair ecological damage. The second approach involves the 

 response of ecosystems — their organisms, productivity, and 

 structure — to perturbations that exceed the normal range of 

 environmental change. 



New approaches and improved research strategies are needed, 

 especially for setting acceptable limits on pollutant levels associated 

 with long-term, low-level exposure. One such approach is based on 

 the possibility that changes in the community structure of land or 

 marine organisms may yield clear and timely signals of harmful levels 

 of pollutants in advance of chemical detection. The detection of 

 chromosome aberration or changes in physiology in both higher and 

 lower organisms may also be a useful approach. Several 



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