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 the 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 (119 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. 
Mercanaria mercenaria is a molluscan species indigenous to all areas of the 
Bay. Phelps and Myers (5) 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 Mercenaria collected from 
the “polluted’ upper Bay and the “clean” lower Bay. Of particular interest is 
the tact that alter a thirty-day period of depuration, Mercenaria from the 
upper polluted part of the Bay retained significantly higher levels of Cd, Cu, 
Ni, Pb, and Ti compared to Mercenaria collected from the lower “clean” part 
of the Bay (Figure 3-2). 
This paper reports on the use ot Mytilus ednlis as an introduced biological 
monitor for trace metals. The specific goals of the study were: 
1. To observe whether or not introduced Mytilus bioaccumulation would 
reflect the spatial differences in trace metal levels previously observed 
in sediments and indigenous Mercenaria. 
2. It such differences were reflected by Mytilus , over what time frame 
were differences observable. 
3. If quantitative difterences were reflected, how do metals accumulated 
by introduced Mytilus , compare qualitatively to metals accumulated by 
indigenous Mercenaria. 
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