OYSTBR-CULTUEAL PROBLEMS OF CONNECTICUT. 7 



Tlie chief factor to be corrected in order to bring this about is 

 trade-waste polhition. Domestic sewage pollution is, of course, un- 

 desirable, and when sufficiently great it makes necessary the trans- 

 fer of oysters to pure water for cleansing. "Wliere such pollution 

 is excessive, it may produce such a degree of depletion of dissolved 

 oxygen as to be harmful or even deadly to oysters or other aquatic 

 forms. If rapid sedimentation from contact of the sewage with 

 salt water (" salting out") occurs over an 03'ster bed, much damage 

 may be wrought. Moreover, in these days of the automobile, even 

 if trade wastes in the sense of discarded by-products of manu- 

 facture be kept from the municipal sewers, many poisonous petro- 

 leum products are inevitably present in untreated sewage. There- 

 fore, from the standpoint of oyster production as well as from that 

 of health, municipal sewage discharge into oyster waters should be 

 prevented or properly controlled. However, as before stated, the 

 principal factor to be corrected in this highly industrialized region 

 is trade-waste pollution. Many of these trade wastes are actively 

 poisonous to oysters or other edible forms, or to the organisms on 

 which they feed. The prevention of the discharge of harmful 

 trade wastes is the great problem to be solved in the restoration 

 of the most valuable of Connecticut's oyster waters. 



In order to shed light on some of the specific improvements needed, 

 the bureau's investigators tested the effect of various important in- 

 dustrial pollutants*^ on oyster larvae and spat. Doctor Churchill, in 

 1920, used various solutions of metallic salts, which, in strengths of 

 10 parts of copper, 20 parts of zinc, and 45 parts of lead per million 

 parts of water, were quickly fatal to small oyster larvae. He also 

 found various dyes to be highly poisonous. More recently the author 

 conducted experiments with salts of these heavy metals and with a 

 few other substances to test their effect on embiyos, larvae, and spat. 

 The results of these experiments were tested by means of '' controls," 

 in which embryos, larvae, or spat were kept under the same conditions 

 except that pure water, lacking the chemicals, was used. Where exper- 

 iments were prolonged the water was changed from the same source, 

 both for the controls and for the poisoning experiments, with a 

 renewal of the chemicals for the latter. Except where otherwdse 

 indicated there was approximately 100 per cent survival in the con- 

 trols. This consistent high survival shows that the loss in the poison- 

 ing experiments was due to the addition of the chemicals. 



Although spat, because of their ability to remain tightly closed 

 for hours and probably days at a time, are difficult to poison quickly, 

 yet they are satisfactory subjects for most tests because of the ease 

 with which they may be kept alive. In the tests of the effect of 

 metallic salts upon spat, the copper salts have consistently proved 

 most deadly. A copper-salt solution containing 1 part of metal per 

 million was fatal in 5 days to 70 per cent of the spat exposed to it. 

 A solution of slightly less than 2 parts per million was fatal in four 

 days to all spat exposed to it. Solutions of zinc and lead salts of 

 10 parts of the metal per million exhibited no greater toxicity than 

 did solutions of 1 and 2 parts of the copper per million. With 



« Determined by the investifrations of J. W. SaJ*>, now chemist in charge. Water and 

 Beverage Laboratory, Bureau of Chemistry, U. S. Department of Agricultm-e. 



