is unusable, and it is difficult to predict the environmental impact of 

 energy development and the associated inorganic contaminants. There is a 

 rapidly increasing trend toward use of larger quantities and greater vari- 

 eties of herbicides in agriculture. New forest management techniques call 

 for control of scrub and hardwood vegetation over vast acreages; no-till 

 farming practices require greater uses of herbicides and herbicide mix- 

 tures; and conversion of riparian vegetation into agricultural uses results 

 in herbicide and insecticide run-off. All of the problems with persistent 

 organochlorine pesticides are not gone, however. Decisions concerning some 

 of them still await a stronger factual base; others merely require monitor- 

 ing and surveillance to pinpoint problem areas and insure that the residue 

 trends continue downward. 



Specific research advances and developments in aquatic toxicology in the 

 United States are presented here. 



TOXICITY TESTING 



Acute Toxicity 



Toxicologists are well aware of the virtues and limitations of the acute 

 toxicity measure; yet, there are probably few measurements that have been as 

 misunderstood in evaluating hazard or safety of a chemical to aquatic life 

 as the LC50 (concentration lethal to 50 percent of the organisms within a 

 given period--usually £96 h). Users of any acute toxicity data must bear in 

 mind that the LC50 measures only one biological response — a lethal one. 

 Its main value is to provide a relative starting point for the evaluation, 

 along with other measurements (e.g., water solubility of the chemical, its 

 partition coefficient, its degradation rate), of environmental hazard. In 

 addition, the acute toxicity test provides a rapid, cost efficient way to 

 measure relative toxicity of different forms and formulations of a chemical, 

 its toxicity in different types of water (acidic, basic, hard, cold, warm), 

 and its toxicity to organisms representing different trophic levels. Until 

 other techniques can be shown to be equal or more meaningful to aquatic 

 toxicologists, the acute toxicity test is here to stay. 



Chronic Toxicity 



Partial and complete life-cycle toxicity tests with fish have become 

 commonplace, and provide data on survival, growth, reproduction, and other 

 sublethal responses. However, these tests can be expensive, high-risk in- 

 vestigations that may require up to a year to conduct. Recent evaluations 

 (Eaton 1974; Macek and Sleight 1977; McKim 1977) have shown that 30- to 60- 

 day toxicity tests on embryos and larvae may provide data as sensitive as 

 that observed in partial and complete life-cycle tests. The maximum accept- 

 able toxicant concentrations (MATC) derived from tests with embryos and lar- 

 vae, or juveniles were usually equal to, but never exceeded a factor of 3 

 times the MATC values derived with partial or complete life-cyle tests 

 (Table 1). 



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