Table l. — Average' heavy metal concentrations (parts per million, wet weight) found in surf clams 



and ocean quahogs by latitude. 



'Average of n samples with 4-6 clams per sample 



Table 2. — Average' heavy metal concentrations ipartsper mil- 

 lion, wet weight) found in surf clams and ocean quahogs by 

 latitude. 



'Average of n samples with 4-6 clams per sample 



has not set standards for heavy metals in U.S. 

 fishery products (except mercury), the National 

 Health and Medical Research Council (NHMRC) 

 of Australia has recommended maximum con- 

 centrations for a number of metals in seafoods 

 (Mackay et al. 1975). Concentrations of cadmium, 

 copper, lead, and zinc found in surf clams and 

 ocean quahogs were well under these limits (2.0, 

 30, 2.0, 1,000 ppm, wet weight, respectively) and 

 far below levels found in American oysters har- 

 vested from Atlantic coastal waters (Pringleet al. 

 1968). The NHMRC recommendation of 1.14 ppm 

 (wet weight) arsenic! 1.5 ppm as ASjOg). however, 

 was exceeded at all but a few sampling stations. 



Mean arsenic concentrations for all stations were 

 2.1 ppm in surf clams and 3.0 ppm in ocean 

 quahogs. The distribution of arsenic concentra- 

 tions did not vary greatly with latitude and may 

 indicate that background levels along the mid- 

 Atlantic coast are higher than those in Australian 

 waters. Concentrations of mercury were found to 

 be well below the action limitset by the FDA (0.50 

 ppm, wet weight). 



Major fishing grounds for the surf clam industry 

 are located off the New Jersey and Virginia coasts. 

 Since data for mercury presented in this study are 

 well within the existing guideline set by the FDA 

 for U.S. fishery products and, with a single excep- 

 tion, within the more extensive NHMRC recom- 

 mendations for Australia, there should be little 

 concern to consumers for surf clams or ocean 

 quahogs harvested from these areas at present. 



The latitudinal cline demonstrated in this study 

 should, however, stimulate further interest in 

 heavy metal inputs along the mid-Atlantic coast of 

 the United States. Data indicate that a large area 

 of our eastern coast may be affected by the pres- 

 ence of heavy metals. The effect on clams is impor- 

 tant, particularly since surf clams and ocean 

 quahogs are representative of the important 

 shellfisheries located in this area. 



Literature Cited 



ANONYMOU.S. 



1971. Ocean quahog becomes more important as surf and 

 bay clams dwindle, Commer, Fish. Rev. 33l4):17-19. 



284 



