only possible road block is that stability conditions must often be found by trial and error with no prior theoretical assurance that any can, in fact, be found. So far, however, this has not been a serious hindrance although some care is necessary to ensure that the solutions obtained utilize values of h and g that are small enough [and in the proper ratio (811 so that further decreasing does not (materially) change the results. On the other hand, our program took about twelve hours for each run. By the time one includes
stability and accuracy tests (which have to be carried out separately for each case), the time becomes considerably greater than this. In the absence of cheap computer time, this may become a determining disadvantage. RECEIVEDfor review December 17, 1973. Accepted April 15, 1974. Funds for this research from the National Science Foundation's Undergraduate Research Program and Juniata College are gratefully acknowledged. f
CORRESPONDENCE
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Loss of Methylmercury-203 from Water Sir: The recent paper of Feldman ( I ) concerning loss of mercury(I1) from water has prompted us to recount our experience with loss of methylmercury chloride from submicromolar solutions. In the course of examining the uptake of methylmercury-203 from water by fish, it was found that the loss of activity from an unaerated 30-liter aquarium exceeded 10%per day (after correction for decay) for the first few days (2). In an effort to assess the importance of the source of water, samples containing 1 &i/l. of methylmercury-203 chloride of 90-95% purity (0.5 ng/ml total mercury) in 1.5-1. Pyrex beakers were aerated for 20 hours by means of an aquarium pump. Deionized water thereby lost 91% of its activity. Nashville tap water treated similarly lost less than 5% of its activity, while tap water filtered through coarse charcoal and preaerated lost 35%. Settled, untreated winter water from the shallows of Percy Priest Reservoir, containing visible turbidity, lost slightly more than 15% under the same conditions. Adsorption of mercury on the glass (which had been cleaned before use with aqua regia) was a constant 1-2% of the total activity originally present in the water. We conclude from these observations that very little methylmercury is present in dissolved form in most natural waters, and that experiments involving uptake of methylmercury by aquatic organisms may be influenced by the origin of the water. Toribara e t al. have argued that the loss of radioactivity from solutions of labeled mercury(I1) salts is due to adventitious reduction to mercury(1) followed by disproportional
To whom correspondence should be addressed.
(1) C. Feldman. Anal. Chem., 46, 99 (1974). (2) W. D.Burrows and P. A . Krenkel. Environ. Sci. Techno/.,7, 1127 (1973).
tion of mercury(1) and loss of metallic mercury in the gas phase ( 3 ) .They noted, as have Feldman and others, that aqueous mercury(I1) solutions are stabilized by strong oxidizing agents. The mechanism for loss of methylmercury derivatives from water has not been demonstrated, but probably involves vaporization of the intact molecule. A significant loss of methylmercury-203 has been reported for certain biological samples which have been heated ( 4 ) or freeze-dried ( 5 ) .For reasons of safety as well as analytical accuracy, it would seem prudent to assume that mercury in any form can be lost from any substrate unless proved otherwise. W. Dickinson Burrows' Associated Water and Air Resources Engineers, Inc. Nashville, Tenn. 37204 Peter A. Krenkel Environmental and Water Resources Engineering Program Vanderbilt University Nashville, Tenn. 37235 RECEIVEDfor review March 7, 1974. Accepted May 14, 1974. The authors gratefully acknowledge the support of t,he Sport Fishery Research Foundation with cooperative funding from the American Fishing Tackle Manufacturers Association, the John M. Olin Foundation, and the Tennessee Valley Authority, through the auspices of the Sport Fishing Institute, and the Tennessee Game and Fish Commission. (3) T. Y. Toribara, C. P. Sields, and L. Koval. Talanta, 17, 1025 (1970). (4) T. Jarvenpaa, M. Tillander, and J. K. Miettinen, Suorn. Kemistilehti, 843, 439 (1970). (5) K. R. Olson and P. 0. Frornrn. J. Fish. Res. Bd. Can., 30, 1575 (1973).
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 11, SEPTEMBER 1974
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