would be only 20 percent of normal, shrimp popu- 

 lations would suffer a 20-percent mortality, and 

 menhaden would suffer a disastrous mortality. 

 Some insecticides are toxic enough to kill 50 per- 

 cent or more of shrimp populations after 48 hours 

 exposure to concentrations of only 30 to 50 nano- 

 grams per liter of the compound. 



Pesticides may be classified by their chemical 

 affinities and a large number of economically im- 

 portant insecticides are chlorinated hydrocarbon 

 compounds. These include the well-known DDT 

 and aldrin-toxaphene group. Typically, these are 

 persistent compounds, but they may be degraded 

 by living systems into less toxic metabolites. As 

 residues in soil and marine sediments, they may 

 persist unchanged for many years and conse- 

 quently present a continuing threat to animal 

 communities. As a general rule, the acute toxicity 

 of this group of pesticides increases with the level 

 of metabolic activity so that their presence may 

 cause two or three times more damage in summer 

 than in winter months. 



The organophosphorous pesticides are also pri- 

 marily insecticides. Typically, they hydrolyze or 

 break down into less toxic products much more 

 readily than the organochloride compounds. Prac- 

 tically all persist for less than a year, while some 

 last only a few days in the environment. Most of 

 them are degraded rather quickly in warm water 

 and consequently are more hazardous to aquatic 

 animals at winter rather than summer tempera- 

 tures. They exhibit a wide range of toxicity, both 

 more and less damaging to marine fauna than the 

 organochlorides. They are usually preferable as 

 control agents because of their relatively short life. 



Other major chemical categories including the 

 carbamates, arsenicals, and 2,4-D and 2,4,5-T 

 compounds are generally, but not necessarily, less 

 toxic to marine biota. 



Pesticides registered for uses which might per- 

 mit their dispersal into the marine environment 

 must be evaluated for their toxic effect on oysters, 

 fish, and shrimp. Consequendy, there is a con- 

 siderable amount of information on the 48 or 96- 

 hour TLni values of these compounds. Unfortu- 

 nately, information is still lacking on their long- 

 term effects at sublethal levels on the productivity 

 of economically important marine species. 



The extreme sensitivity of marine crustaceans, 

 such as crabs, lobsters, and shrimp, to the array of 

 insecticides is to be expected because of their phy- 

 logenetic relationship with terrestrial arthropods. 

 In general, shrimp are also much more sensitive 

 than fish or oysters to the other pesticides. This fact 

 and their economic importance make shrimp a 

 valuable yardstick for establishing safe levels of 



pesticides that might be expected as toxicants in 

 the marine environment. 



A much broader spectrum of pesticide pollutants 

 can be anticipated in the fresh water (salinity 

 <0.5 %o) zones of tidal estuaries. Fresh water 

 criteria listed in another section will apply under 

 these circumstances. 



Recommendation: The pesticides are grouped accord- 

 ing to their relative toxicity to shrimp, one of the most 

 sensitive groups of marine organisms. Criteria are based 

 on the best estimates in the light of present knowledge 

 and it is expected that acceptable levels of toxic ma- 

 terials may be changed as the result of future research. 



Pesticide group A. — ^The following chemicals are 

 acutely toxic at concentrations of 5 /ig/1 and less. On 

 the assumption that Hoo of this level represents a rea- 

 sonable application factor, it is recommended that en- 

 vironmental levels of these substances not be permitted 

 to rise above 50 nanograms/ 1. This criterion is so low 

 that these pesticides could not be applied directly in 

 or near the marine habitat without danger of causing 

 damage. The 48-hour TL„ is listed for each chemical 

 in parts per billion (Mg/1). 



Organochloride pesticides 

 Aldrin ^ 0.04 DDT 0.6 



BHC 2.0 



Chlordane 2.0 



Endrin 0.2 



Heptachlor 0.2 



Lindane 0.2 



Dieldrin 0.3 



Endosulfan 0.2 



Methoxychlor 4.0 



Perthane 3.0 



TDE 3.0 



Toxaphene 3.0 



Organophosphorous pesticides 



Coumaphos 2.0 Naled 3.0 



Dursban 3.0 Parathion 1.0 



Fenthion 0.03 Ronnel 5.0 



Pesticide group B. — The following types of pesticide 

 compounds generally are not acutely toxic at concen- 

 trations of 1 mg/1 or less. It is recommended that an 

 application factor of Hoo be used and, in the absence of 

 acute toxicity data that environmental levels of not 

 more than 10 Mg/1 be permitted. 



Arsenicals 

 Botanicals 

 Carbamates 

 2,4-D compounds 



2,4,5-T compounds. 

 Phthalic acid compounds. 

 Triazine compounds. 

 Substituted urea compounds. 



Other pesticides. — Acute toxicity data are available 

 for approximately one hundred technical grade pesti- 

 cides in general use not listed in the above groups. These 

 chemicals either are not likely to reach the marine en- 

 vironment, or, if used as directed by the registered 

 label, probably would not occur at levels toxic to marine 

 biota. It is presumed that criteria established for these 

 chemicals in fresh water will protect adequately the 

 marine habitat. It should be emphasized that no un- 

 listed chemical should be discharged into the estuary or 

 coastal water without preliminary biossay tests and the 

 establishment of an adequate application factor. 



83 



