274 ZUBARIK AND O'CONNOR 



(Skei, Saunders, and Price, 1976; Williams and Weiss, 1973), and 

 estuarine organisms in the southeastern United States, including blue 

 crabs and many species of fish, have average mercury levels above 0.5 

 ppm. Larger predators, such as lemon and bull sharks, exhibited 

 mercury levels of 4 to 10 ppm (Gardner et al., 1975). 



Despite abundant data on mercury levels in aquatic systems, it is 

 the consensus that insufficient data exist on the mechanisms of 

 mercury accumulation and cycling (Gavis and Ferguson, 1972; D'ltri, 

 1973; Gardner et al., 1975; Lindberg, Andrew, and Harriss, 1975; 

 Matsunaga, 1975; Tsai, 1975; Stickney et al., 1975; Wallace et al., 

 1971; Friberg and Vostal, 1972). Measuring mercury levels in 

 organisms is important in assessing the degree of an environmental 

 problem, but survey and monitoring data frequently cannot be used 

 for msiking predictions about mercury cycling because the conditions 

 under which uptake and accumulation occurred are not known. 



Most uptake and accumulation studies performed to date have 

 been on fish, marine mammals, and larger invertebrates (D'ltri, 1973; 

 Miettinen, 1969; Olson, Bergman, and Fromm, 1973; MacLeod and 

 Pessah, 1972; Guarino and Anderson, 1976; Hannerz, 1968). Often 

 there seems to be no clear reason for the high mercury levels 

 frequently found in fish. Confusion still exists over the relative 

 importance of mercury availability for direct uptake from water vs. 

 biomagnification through food chains. To understand aquatic cycling 

 of mercury, we must determine uptake and accumulation of mercury 

 by forage organisms as well as commercially important fish and 

 shellfish. 



There are few investigations of bioaccumulation by smaller 

 invertebrates, few studies on mercury uptake by any estuarine biota, 

 and no studies on mercury uptake by Hudson River biota. Our study 

 was carried out to evaluate the role of estuarine organisms in 

 mercury dynamics and to determine the accumulation of mercury 

 compounds by Hudson River biota. A broad spectrum of planktonic 

 organisms, from algae to fish larvae, were selected for study of 

 bioconcentration under natural conditions. The organisms were 

 chosen on the basis of their abundance in the river and their 

 importance as forage. The amphipod Gammarus sp. was studied in 

 detail, to acertain if there was a difference in uptake of four mercury 

 compounds (mercury chloride, mercury nitrate, methyl mercury 

 chloride, and phenyl mercuric acetate) and to determine if 

 fluctuations in selected environmental parameters might relate to 

 changes in mercury uptake. 



