Heavy metals are a major concern from the point of view of human health. 



Since heavy metals may concentrate in the tissues of marine food organisms, a 



person eating enough contaminated seafood or fish over a period of time could 



develop heavy metal poisoning. For example, organic mercury has been cited as 

 the cause of minamata disease in Japan (Clark 1977). 



The effects of heavy metals on marine and estuarine invertebrates are modified 

 by salinity, dissolved oxygen, temperature, pH, the presence of other 

 toxicants, the form of the metal, and the age and condition of the organism. 

 Laboratory experiments indicate that these factors owe their influence to the 

 variable rates at which metals are absorbed (Bryan 1971). No evidence of 

 damage to macroalgal communities by heavy metals has been documented. 



Little information appears to exist on the accumulation effects of heavy 

 metals in sea grasses (Thayer et al. 1975). Barsclate and coworkers (1975) 

 found that dissolved copper may be removed from overlying water by eelgrass. 



Mercury in North Atlantic zooplankton collections has been studied by Windom 

 and coworkers (1973), who collected samples from the New York Bight south to 

 Cape Hatteras. The species composition of the plankton varied considerably, 

 although most samples were composed of copepods and chaetognaths . The 

 concentration of mercury appeared to bear little relation to species 

 composition, but it was determined that nearshore zooplankton were higher in 

 mercury content than those offshore. Concentrations reached as high as 5.3 

 ppm in the New York Bight in contrast to values of 0.1 to 0.3 ppm in offshore 

 areas. Mercury appears to be concentrated to a similar degree by different 

 organisms in the plankton community. This may be due to passive rather than 

 active uptake. 



Sublethal effects of heavy metals can be grouped into morphological changes, 

 inhibitory effects, and behavioral changes. Some effects of metals, such as 

 the bright green color of oysters that results from accumulated copper in the 

 tissues (personal communication from P. F. Larsen, Bigelow Laboratories, W. 

 Boothbay Harbor, ME; February, 1980), may be recognized visually. Zinc and 

 copper are metals necessary for normal growth but elevated levels can lead to 

 inhibition of growth. Abnormal structural morphology has been observed in the 

 larvae of sea urchins having slightly elevated concentrations of copper and 

 zinc (Bryan 1971). In addition to inhibiting growth, heavy metals may prevent 

 the settlement of larvae, delay or prevent sexual development, and inhibit 

 feeding. Although laboratory experiments usually are performed on hardy 

 species, abnormal behavior has been observed in invertebrates exposed to 

 concentrations of copper, silver, or zinc that are only one order of magnitude 

 higher than those of sea water. Larval forms may be affected at even lower 

 concentrations (Bryan 1971). 



Although little is known about the effects of heavy metals on ecosystems, it 

 has been estimated that when metals such as copper, silver, and zinc reach a 

 concentration ten times that of sea water, serious detrimental effects may 

 occur (Bryan 1971). Suspension-feeding animals, such as clams, mussels, and 

 oysters, are extremely susceptible to accumulation of metals and, thus, are 

 valuable for monitoring ecosystems (Fink et al. 1976). Sediments retain high 

 levels of metals. These metals then may be taken up by organisms and passed 

 to higher trophic levels (Bryan 1971). For example, the Penobscot River has 

 been cited as having high levels of mercury. Also, eels from the Penobscot 



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