FISHERY BULLETIN: VOL. 84. NO. 1 



Table 3—Arctica islandica trace metal body burdens (mean and standard deviation, ^glg-6ry weight) 

 in areas of the northwest Atlantic; N = number of individual clams examined at each site. Results of 

 analysis of SRM 1566 are also included; 5-8 NBS (National Bureau of Standards) samples were ex- 

 amined for each metal (nd = nondetectable). 



edge of a baseline PPI value can be important for 

 discerning the source of any change in contaminant 

 levels in benthic animals. 



In a similar manner, the PCB value has been 

 separated, by virtue of the use of capillary GC, into 

 isometric groupings (Table 1). Again, there were dif- 

 ferences in PCB composition between samples. For 

 example, samples from stations 22, 28, 32, and 244 

 were largely comprised of tri-, tetra-, and hexachloro 

 PCB isomers, while those from stations 107 and 27 

 contained significantly greater quantities of the tri- 

 chlorobiphenyls. Aroclor 1016 and 1242 contain pro- 

 portionately more of the C\ l to Cl 4 isomers while 

 Aroclor 1254 contains a greater abundance of Cl 4 

 to Cl 6 isomers. In the future, it may be possible to 

 ascribe the differences in the PCB composition in 

 animals to possible sources through capillary 

 GC/ECD measurements. 



Highest trace metal concentrations in A. islandica 

 varied from metal to metal (Table 3); however, high- 



est mean Ag, Cr, Cu, and Pb concentrations were 

 found in New York Bight (stations 26 and 29), while 

 Ni and Zn were highest in the "Mud Patch" (stations 

 181 and 237) with the highest Cd values off Dela- 

 ware (Table 3). Lowest concentrations, overall, were 

 observed at midshelf stations off New Jersey and 

 Maryland (with the exception of stations 167, 168, 

 and 123 that could have been influenced by dump- 

 ing at a nearby dumpsite) and station 379, on 

 Georges Bank. Comparison of these data with those 

 of Wenzloff et al. (1979), who analyzed metals in 

 ocean quahogs from the New York Bight to an area 

 off Chesapeake Bay, was attempted for temporal 

 trends. Unfortunately, the Wenzloff et al. (1979) data 

 were obtained from only foot muscle composites of 

 5 or 6 quahogs at each station, reported as means 

 of all composites per half degree of latitude; hence, 

 a direct comparison was not possible. The geogra- 

 phic pattern, a decrease in metal concentrations with 

 latitude believed present in the Middle Atlantic Bight 



138 



