276 ZUBARIK AND O'CONNOR 



Eppendorf pipettor directly into Hudson River water containing the 

 test organisms. The four mercury compounds used [mercuric nitrate, 

 ^^•^Hg(N03 )2 ; mercuric chloride, ■^°^HgCl2; methyl mercury 

 chloride, ^^^HgCHaCl; and phenyl mercuric acetate, 

 ^ ^^HgCOOCH3 ] were purchased from New England Nuclear, 

 Dilutions to appropriate radioactive concentrations (0.1 to 1 /iCi) 

 were made in deionized water. The final concentrations of stable 

 mercury added with the radioisotope was always less than mercury 

 concentrations reported for Hudson River water (0.1 ppb). 



At predetermined intervals organisms were removed from the 

 water by collection in netted cages, killed in hot water, and rinsed 

 with clean Hudson River water. There was no evidence that the 

 technique caused breakage of cells of the organisms used. They were 

 then air dried overnight and placed in scintillation vials filled with 



15 ml of phase combining system solubilizer (PCS) (Amersham/ 

 Searle Corp.) and 5 ml of water. 



The test water was filtered immediately through 0.45-/J Millipore 

 filters when an experiment was terminated. Five milliliters of the 

 filtered river water and the filter paper containing the suspended 

 particulate matter from the test water were placed in separate liquid 

 scintillation vials containing 15 ml of PCS. The filter paper was air 

 dried overnight and then weighed. To avoid yellowing of the sample, 

 we added the cocktail to the filter paper just before counting. The 

 samples were counted on Nuclear Chicago Mark I or Isocap/300 

 liquid scintillation counters. Both instruments were calibrated with a 

 primary standard from Amersham /Searle Corp. (126 mCi/g ± 2.9%). 

 Quenching was corrected for by the channels ratio technique on the 

 Mark I and by an external standard on the Isocap (Wang and Willis, 

 1965; Chase and Rabinowitz, 1967). Samples were counted for 10 

 min or longer (if necessary) to give a counting error of less than 3%. 

 Experiments generally consisted of three replicates. 



All counts were corrected for decay and background, and the 

 counts were converted to disintegrations per minute. Concentration 

 factors were obtained by dividing the disintegrations per minute per 

 gram of organism by the disintegrations per minute per gram of 

 filtered test water. 



Food organisms were labeled as if they were being tested for 

 uptake from water except that, instead of being killed at the end of 

 the experiment, they were washed in filtered Hudson River water, 

 recollected, and added to the test culture. Food organisms were 

 always supplied to test cultures in excess amounts. 



During each experiment, salinity, dissolved oxygen, conductivity, 

 alkalinity, and temperature were measured according to procedures 



