Major environmental differences within the system are attributable to a 

 history of pollution effects in the upper reaches of the Bay (Figure 3-1). Major 

 sources of pollution are domestic waste treatment plants, which include 

 industrial effluents from such activities as metal plating and jewelry 

 manufacturing, and urban runoff. 



Fine sediments in the upper area (Stations 1 and 2) are anaerobic, 

 characteristically having the redox boundary at the sediment-water interface, as 

 well as having a strong odor of H^S. In the lower Bay (Stations 3 and 4), fine 

 sediments have a well-defined aerobic layer with a redox boundary defined 

 between 5 and 10 cm below tlie sediment-water interface (2). Metals in upper 

 Bay sediments include typically elevated levels of zinc (337 ppm), lead (167 

 ppm), copper (493 ppm), and chromium (208 ppm) compared to lower Bay 

 levels of zinc (1 19 ppm), lead (40 ppm), copper (48 ppm) and chromium (53 

 ppm) (2). In addition, higher concentrations of hydrocarbons have been 

 reported in upper Bay sediments compared to levels found in the lower Bay 

 (3). Over the past few years, a transect of stations, indicated in Figure 3-1 as 1, 

 2, 3, and 4, has been used to study the effects of pollution from north to south 

 in the Bay. 



M. nienenaria is a molluscan species indigenous to all areas of the Bay. 

 Phelps and Myers (4) compared levels of aluminum (Al), cadmium (Cd). 



cobalt (Co), copper (Cu), lead (Pb). manganese (Mn), nickel (Ni), silver (Ag), 

 titanium (Ti), vanadium (V). and zinc (Zn) between M. mercenaria collected from 

 the "polluted" upper Bay and the "clean" lower Bay. Of particular interest is 

 the fact that after a thirty-day period of depuration, M. mercenaria from the 

 upper polluted part of the Bay retained significantly higher levels of Cd, Cu, 

 Ni, Pb, and Ti compared to M. mercenaria collected from the lower "clean" part 

 of the Bay (Figure 3-2). 



This paper reports on the use of M. edulis as an introduced biological 

 monitor for trace metals. The specific goals of the study were: 



1. To observe whether or not introduced M. edulis bioaccumulation would 

 reflect the spatial differences in trace metal levels previously observed 

 in sediments and indigenous M. mercenaria. 



2. if such differences were reflected by M. edulis. over what time frame 

 ucre differences observable? 



3. If quantitative differences were reflected, how do metals accumulated 

 by introduced M. edulis, compare qualitatively to metals accumulated by 

 indigenous M. mercenaria'} 



28 



