RADIOISOTOPIC STUDY OF MERCURY UPTAKE 



281 



(28 df, P < 0.05). Uptake of methyl mercury was greater than 

 uptake of mercuric nitrate. There were no uptake differences 

 between mercuric nitrate and mercuric chloride or between methyl 

 mercury and phenyl mercury. Combining uptake of the two 

 inorganic forms and the two organic forms after a 1-day exposure 

 showed that mean uptake of inorganic compounds was less than that 

 of organic compounds, but this was not statistically significant. 

 Organic mercury uptake was three times greater than inorganic 

 uptake after 1 week (P < 0.007; Table 4). 



TABLE 4 



MEAN MERCURY CONCENTRATION FACTORS AND 95% 

 CONFIDENCE LIMITS (Lj L2 ) FOR Gammarus sp. 



Rates of uptake over time were rapid for both methyl mercury 

 and mercuric chloride (Figs. 1 and 2). Of the total mercury taken up 

 by Gammarus after 1 week, almost one-half the radioactivity of 

 organic mercury and one-third the radioactivity of inorganic mer- 

 cury were taken up during the first day. Studies of mercury uptake 

 over periods longer than a week show a decline in mercury per gram 

 of organism between days 10 and 19 (Fig. 3). 



Further studies were undertaken with Gammarus sp. to deter- 

 mine what changing conditions might explain the variations in 

 concentration factors shown by one species. Studies of mercury 

 uptake in conjunction with seasonally changing estuarine variables 

 show that the difference between inorganic and organic uptake is 

 increased during the summer months (Fig. 4). There was a strong 

 positive correlation between uptake and temperature for both types 

 of mercury compounds and an inverse correlation of mercury uptake 

 with total organic carbon. Positive correlations existed with phos- 

 phates and algal cell concentration, but there were peaks in these 

 values when there were no peaks in mercury uptake. No single 

 environmental parameter adequately explains the seasonal fluctua- 

 tions in mercury uptake (Fig. 4). 



