pentachlorobenzene, and having a last crystal point 

 of 18° C. ± 3° C), a less expensive product than 

 oithodichlorobenzene, was used for the first time on 

 experimental beds in New Haven Harbor, Conn., 

 in the summer of 1961. I made field tests to com- 

 pare the effectiveness of orthodichlorobenzene and 

 Polystrcam and to determine the minimum quan- 

 tity of chemically treated sand needed to control 

 oyster drills. Sevin was added to both types of 

 polychlorinated benzenes at the rate of 2 percent 

 by weight, and a total of 1.9 hi. of either ortho- 

 dichlorobenzene or Polystream was mixed with 

 each 9.5 kl. of sand. The two chemical-sand mix- 

 tures were spread over eight 0.4-ha. beds at rates 

 of 1.9, 5.1, 9.5, and 19 kl. per hectare. Drill traps 

 were used to estimate the effects of treatments on 

 populations of oyster drills and mud crabs. 



SCUBA divers studied the effects of these 

 treatments. Their observations indicated that 

 treatments of 9.5 and 19.0 kl. per hectare of either 

 orthodichloi'obenzene and Sevin or Polystream and 

 Sevin caused all visible gastropods, including 

 thick-lipped drills, northern moon shells, knobbed 

 whelks, Biisycon carica^ channeled whelks, Busy- 

 con ccmalietdatum, and New England nassas, Nas- 

 sarius trivittatvs, to become swollen (snails listed 

 in order of importance as shellfish predators; the 

 New England nassa is not a predator). Appar- 

 ently, the latter three species of predators were 

 compelled to emerge from their usual position 

 buried in the bottom. A number of pipefish, 

 Syngnathus fusc^is, mud crabs, and shrimp were 

 either partially paralyzed or behaved abnormally. 

 Small flounders, Pseudopleuronectes americanus, 

 however, swam around apparently unliarmed. 

 Three days later these effects wei'e more evident; 

 all visible gastropods were either swollen and being 

 eaten alive by starfish or they had already died. 

 The pipefish, mud crabs, and shrimp, nevertheless, 

 had either recovered or had been replaced by otiiers 

 from surrounding areas. Subsequent observations 

 revealed that starfish were gradually consuming 

 the remaining swollen gastropods. Thus, the area 

 was left with a large number of empty gastropod 

 shells which gradually disappeared ; a lot with 42 

 shells of the northern moon shell per 50 m.^ of 

 bottom on July 3, for example, had none by July 

 18. Presumably, the shells had been occupied by 

 hermit crabs and carried away. 



Catches of oyster drills on traps indicated that 



CONTROL OF OYSTER DRILLS WITH POLYSTREAM 



applications of 9.5 and 19.0 kl. of treated sand 

 per hectare had killed nearly all drills and that 

 the mixture of Polystream and Sevin was more 

 effective than the mixture of orthodichlorobenzene 

 and Sevin. The numbers of mud crabs on traps 

 before and after treatments indicated that they 

 were not harmed by the treatments. As a result, 

 we thereafter used Polystream exclusively, aban- 

 doned orthodichlorobenzene, and standardized the 

 treatment rate at 9.5 kl. per hectai'e. 



Increased catches of drills, along the borders of 

 lots several weeks after the treatment, indicated 

 that drills were migrating into the lots from sur- 

 rounding areas. This observation suggested that 

 to ensure protection of an oyster bed from oyster 

 drills, a zone perhaps 25 or more meters wide out- 

 side the bed, as well as the bed itself, should be 

 treated, and that treatment of a single large bed 

 would be more efficient than treatment of a number 

 of small beds. 



Polystream was used to treat beds inhabited by 

 oysters and clams that are later consumed by 

 humans. It was necessary, therefore, to determine 

 whether these shellfish retained any residues of this 

 chemical. In practice, however, only those beds 

 with seed oysters on them are treated with Poly- 

 stream. These oystei-s are transplanted to untreated 

 beds at least 4 months before harvest. It was also 

 desirable to know whether other organisms inhab- 

 iting treated beds, particularly those that might 

 be taken by sport or commercial fishermen, retain 

 residues of Polystream. 



To determine whether oysters, clams, or other 

 animals or plants accumulated and then lost resi- 

 dues of Polystream, I studied specimens that were 

 collected from treated beds by divers or by dredg- 

 ing. I also studied northern lobsters, Homurus 

 americanus, in cages to determine whether residues 

 would be lost after a period of time in water free 

 of Polystream. The U.S. Testing Company of 

 Hoboken, N.J., determined the quantity of Poly- 

 stream in tissues of the plants and animals through 

 use of a technique developed by Schwartz, Gaffney, 

 Schmutzer, and Stefano (1963). 



In 1961 and 1962, 1 determined the quantities of 

 Polystream in oysters and clams from a 0.4-ha. lot, 

 treated with 1.9 hi. of this chemical. In oysters the 

 residue was 1.8 p.p.m. (parts i^er million) 8 days 

 after the treatment. It diminished slowly until 

 none was detected 119 days later. Residues in clams 



287 



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