286 ZUBARIK AND O'CONNOR 



exposures. Initigil uptake of both forms was extremely rapid, 

 however; this indicates that perhaps the hypothesized "necessary" 

 conversion of inorganic mercury to a methylated form before uptake 

 by organisms is not required. Mercury methylation by natural 

 bacterial assemblages could not convert mercuric nitrate or mercuric 

 chloride to an organic form rapidly enough to generate the rates of 

 uptake observed in these experiments (Langley, 1973). These results 

 are confirmed by those of Olson, Bergman, and Fromm (1973), who 

 studied the rainbow trout; Prabhu and Hamdy (1977), who studied 

 Lebistes reticulatus (guppy); and Mellinger (1973), who studied 

 Margaritifera margaretifera (freshwater mussel). Kramer and Neidhart 



(1975) found that mercury uptake by fish (Poecilia reticulata) in a 

 methyl mercury chloride solution was about four times as fast as in a 

 mercuric nitrate solution. 



Variations in concentration factors for the same species can be 

 related to the conditions under which bioconcentration of mercury 

 took place. The facts that the presence of sediments decreases uptake 

 by Gammarus sp. and that there is an inverse correlation between 

 mercury uptake and total organic carbon levels indicate that mercury 

 concentration or type of mercury compound are not the only factors 

 controlling mercury uptake by aquatic organisms. Environmental 

 parameters may affect the availability of mercury for uptake and 

 accumulation. Tsai, Boush, and Matsumura (1975) reported that the 

 pH of the ambient water has a great effect on the translocation of 

 inorganic mercury to fish. In the area of the Hudson River studied, 

 pH varies annually by only 0.6 of a unit (7.2 to 7.8). Therefore, it 

 was impossible to assess the effect of pH on mercury uptake in this 

 study. Lindberg, Andrew, and Harriss (1975) reported that transport 

 and deposition of mercury in the estuarine environment is largely 

 controlled by interaction with natural organic matter. Cranston 



(1976) stated that the process controlling accumulation and distribu- 

 tion of mercury in estuarine sediments is related to the amount of 

 fine-grain sediments. 



The experiments reported here address only the effects of 

 relationships among species, environmental parameters, and chemical 

 form on the uptake of mercury from water and food. The impact 

 related to the community and to seasonal differences in mercury 

 uptake was not studied directly. The relationship between tempera- 

 ture and mercury uptake identified in our study, however, justifies 

 some speculation on the stress mercury compounds may cause on 

 aquatic systems. First, since the toxicity of organic mercury 

 compounds is greater than that of inorganic and since organic 

 compounds can be accumulated to greater levels during periods of 



