focused on the effects of single pollutants rather than on how combinations of pollu- 

 tants alter toxic effects. Livingston et al. (1974) considered these interactions, but 

 Bahner and Nimmo (1976) first examined how combinations of heavy metals and 

 pesticides (cadmium-malathion; cadmium-methoxychlor; and cadmium-methoxy- 

 chlor-Aroclor® 1254) might affect the pink shrimp, Penaeus duorarum. They con- 

 cluded that the absence of cumulative toxicity indicated that toxicity is independent 

 and that no synergistic activity occurred. 



Koenig ( 1977) developed experiments to determine the relative toxicity of DDT 

 and mirex, alone as well as in combination, during the early life stages of the salt 

 marsh cyprinodont fish, Adinia xenica. He identified a synergistic interaction be- 

 tween DDT and mirex that affected larval mortality. The addition of mirex to the 

 DDT dosages increased the toxicity by a factor of approximately 1 .5. There was no 

 apparent synergistic effect on embryos, embryo developmental rate, or hatching 

 time. Secondary effects of DDT intoxication, as opposed to the effects of mirex 

 alone, included lack of coordination, cessation in feeding, and increased darkening 

 in overall appearance. The larvae soon became emaciated and died. Larvae exposed 

 to mirex, however, fed normally and initially appeared normal. After a loss of equi- 

 librium, which caused the larvae to drift in a disoriented manner, death occurred. 



In more recent studies (Costlow, unpublished) four pesticides, Dimilin®, Altosid®, 

 mirex, and Kepone, were combined at levels previously determined to be sublethal. 

 Developing stages of the mud crab Rhithropanopeus harrisii were exposed to sub- 

 lethal levels both of the individual pesticide and a composite of the four. At the sub- 

 lethal levels of the individual compounds, survival was similar to that observed for 

 the controls, whereas for the composites, toxic effects increased considerably. 

 Although the previous studies were conducted under conditions approaching opti- 

 mum salinity and temperature, further experiments are necessary to determine the 

 effects of composites of pollutants in those suboptimal conditions of salinity and 

 temperature known to occur in estuarine systems. 



Virtually all of the research of the seventies was directed to acute effects. A few 

 studies sought to evaluate chronic effects, primarily as they apply to assemblages of 

 organisms. Livingston et al. (1978) described a significant decline in organochlorine 

 residues in Apalachicola Bay, Florida. They attributed this decline to a decrease in 

 use of pollutants, a major natural flushing of the area, and the deterioration of the 

 compounds themselves. A major problem in this study was the difficulty in corre- 

 lating trends in the various assemblages with the decline of the pesticides. The need 

 for studies that relate long-term changes and physical-chemical changes, be they 

 natural or artificial, is therefore emphasized. This same difficulty is apparent in 

 other efforts to relate the decline in species abundance to the observed increase of 

 pesticides in specific estuarine waters. For example, the recorded commercial catch 

 of blue crabs in the James River from 1968 to 1972 averaged 899,000 kg (1,977,800 

 lb) and declined from 1972 to 1975 by more than 90 percent. In noting this decline 

 Bookhout et al. (1980) indicates that Kepone, shown to be highly toxic to the larvae 

 of Callinectes sapidus, may be responsible for the decline of the blue crab catch in the 

 James River. There is, however, no way to specifically attribute this decline to 

 Kepone poisoning alone. 



Virtually nothing is known of the mutagenic effects of organic compounds over 

 several generations of estuarine and marine organisms. Techniques are now avail- 

 able to permit the culture of many invertebrates, including certain harpacticoid 

 copepods and polychaetes that have relatively short life spans (10 to 20 days). For a 

 more complete understanding of the long-term effects of pollutants in estuarine 

 ecosystems, studies must be designed to determine how sublethal levels of the more 

 commonly utilized organic compounds affect successive generations of several 

 species. 



Although many studies have been conducted on the extent to which individual 

 species accumulate organic compounds, nothing is known about the mechanism of 



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