is common to many marine invertebrates. Of 

 particular interest is tlie ability of many 

 bivalves to accumulate various heavy metals, 

 such as zinc, copper, iron, manganese, lead, and 

 arsenic. Tlie problem is of importance because 

 in polluted coastal waters shellfish may store 

 substances that may be dangerous to human 

 health. Hunter and Harrison (192s) showed 

 that oysters affected by industrial pollution in 

 certain coastal areas in Connecticut, New York, and 

 New Jersey contained traces of lead (determined 

 as Pb) and arsenic (AsaOs), the concentration of 

 the arsenic varying, depending on locality, from 

 0.6 mg./kg. to 3.0 mg./kg. of dry weight. 



The accumulation of copper causes green dis- 

 coloration of the mantle and gills of oysters and 

 gives them an unpleasant coppery flavor. The 

 problem of greening has attracted many investi- 

 gators, especially since Lankester (1886) demon- 

 strated that green color in some oysters may 

 be due to an excess of copper, while in the green- 

 gilled European oysters of the west coast of France 

 the bluish-green coloration was caused by ab- 

 sorption of a pigment from a diatom, Nitzschia 

 ostrearia, called marenin (Ranson, 1927). Green 

 oysters similar to those of Marennes, France, 

 occur occasionally along the Atlantic coast in 

 Virginia (Mitchell and Barney, 1917) and in 

 North Carolina (personal observation). Accu- 

 mulation of iron, zinc, and manganese does not 

 change the color of oyster meat. . 



The degree of concentration of heavy metals in 

 the oyster body is related to the environment. 

 Oysters from the North Atlantic States are poorer 

 in iron and riclier in copper than oysters of the 

 South Atlantic and Gulf States in which the rela- 

 tion is reversed. This has been shown by Coulson, 

 Levine, and Remington (1932), who analyzed a 

 number of samples collected from various states 

 in April and again in November-December, 1931. 

 Their observations are summarized in table 41. 

 The data show that the iron content of oyster meat 



significantly increases from north to south while 

 the copper content decreases. The samples show 

 no significant variations in the manganese content. 

 The increase in iron content is associated with a 

 greater percentage of iron (as FcoOj) in the river 

 water of the South Atlantic States discharged into 

 the estuaries than is present in the runoff waters 

 of the North Atlantic States. High copper con- 

 tent in the oysters of New Jersey, New York, 

 Connecticut, and Rhode Island is possibly asso- 

 ciated with the discharge of chemical wastes from 

 shore installations of these highly industrialized 

 states. 



OBSERVATIONS ON NEW ENGLAND 

 OYSTERS 



Seasonal changes in the composition of oysters 

 can best be studied by regularly taking samples 

 from a single bed containing a population of 

 oysters of known age. Such an investigation was 

 made by taking samples of oysters from a com- 

 mercial bed in Long Island Sound, off Charles 

 Island, and simultaneously recording the temper- 

 ature, salinity, and pH of the water. The work 

 was conducted from the Bureau of Commercial 

 Fisheries Biological Laboratories at Woods Hole 

 and Milford. For experimental purposes and for 

 checking analytical methods a large number of 

 4- to 5-year-old oysters were kept in the outdoor 

 tanks near the laboratories. Samples of 25 oys- 

 ters were taken once or twice a month for a period 

 of 22 months from July 1933 to August 1935. 

 Ten of the oysters were used for a chemical 

 analysis of ash, 10 for the extraction of glycogen, 

 and 5 for biological studies. 



ANALYTICAL PROCEDURES 



Oyster meats being prepared for chemical 

 analyses are easily contaminated with iron while 

 they are being removed from the shell. We found 

 that the following analytical procedure was most 

 satisfactory. The surface of the shells was cleaned 

 with a stiff nonmetal brush, and the whole oysters 



Table 41. — Iron, copper, and manganese content of oysters from the Atlantic and Gulf coasts 

 [Results are expressed in mg./kg. (wet basis). From Coulson, Levine, and Remington, 1932] 



384 



FISH AND WILDLIFE SERVICE 



