and one is lost, the system suffers less than if only one organism is perform- 

 ing a job and is lost. This is discussed at length in Cairns et al . (1979). 

 Chemical characteristics are important in estimating inertia. In aquatic 

 systems, hard water antagonizes heavy metals. For example, the Guadalupe 

 River in Texas will tolerate roughly four times as much zinc as an eastern 

 coastal stream before reaching a toxic threshold. The Texas stream has ap- 

 proximately 300 parts per million (ppm) of calcium whereas the eastern stream 

 has about 30 ppm of calcium. Another characteristic important in estimates 

 of inertia is the proximity to an ecological threshold. This is easy to des- 

 cribe but difficult to document. It is known that ecological thresholds 

 exist for temperature,- pH, and so forth, but these limits are hard to estab- 

 lish. However, an attempt must be made to do so. I believe we can calculate 

 an ecosystem's inertia as well as its elasticity, and substantial evidence 

 exists to make these estimations (Cairns et al . 1979). 



HAZARD ASSESSMENT 



With 6,000 new chemicals being developed each year, it is impossible to 

 conduct hazard assessment tests on every chemical. Further, it is known that 

 certain environmental situations require more assessment information than 

 others. So, the problem is how do we know when we have enough information 

 to make a management decision? 



The process of hazard assessment is shown graphically in Figure 1. Tier 

 1 is a "dropdead" batch bioassay that is crude, simple, and costs, approxi- 

 mately $300 to $1,000. Tier 2 is a continuous-flow, more sophisticated and 

 expensive bioassay, and Tier 3 even more so, perhaps a life cycle bioassay 

 that might cost as much as a hundred thousand dollars. Two important pieces 

 of information are to be determined for the evaluation. The first is the 

 environmental concentration of the chemical in question, which depends on the 

 amount of the release, on the dispersion, and on the properties of the speci- 

 fic chemical, such as how it partitions, its volatility, and its stability. 

 For instance, a linear alkyl sulfonate degrades rapidly; a chlorinated hydro- 

 carbon does not. The second type of information is the concentration of the 

 chemical that does not cause adverse biological effects. There is great un- 

 certainty about this concentration for most chemicals. However, methods are 

 available for making these determinations. 



In Figure 1 the horizontal solid lines are the concentration of a chemi- 

 cal that produces no adverse biological effects and the actual environmental 

 concentration of the chemical. The dotted lines around the solid lines in 

 the figure indicate the uncertainty associated with these numbers at each 

 level of testing. Uncertainty decreases with more testing, but it is never 

 reduced to zero, because testing can only involve a few of the many organisms 

 that are being protected. As a consequence, results are being projected from 

 a few organisms to a large community. 



165 



