in the plant tissues. Those retained in 

 plant tissues may be physically trans- 

 ferred with dead plant material. Trans- 

 fer to other organisms, sediments, or 

 the water occurs when the plant residue 

 is eaten or decomposed. 



Studies by Dunstan and Windom 

 (1975) suggest that metals are not taken 

 up and retained by plants in the marsh 

 to the extent that they occur in the 

 sediments. Concentrations of most heavy 

 metals (Fe, Mn, Zn, Pb, Cu, and Cd) were 

 lower in tissues of saltmarsh cordgrass 

 ( Spartina alterniflora ) than in the sed- 

 iments supporting the plant's growth. 

 An exception was Hg which occurred at 

 higher levels in the plants than in the 

 sediments. 



Unlike most other heavy metals, Hg 

 can exist chemically in different states 

 (solid, liquid, or gas)and can be micro- 

 biologically converted into several 

 forms of varying toxicity in sediment- 

 water systems (Wood 1974). Methyl Hg is 

 of particular interest because (1) it is 

 highly toxic to higher organisms, (2) it 

 can be formed from other forms of Hg in 

 the sediments, and (3) it is retained by 

 muscle tissue and tends to be concen- 

 trated by food chain amplification. Al- 

 though methyl is the prominent form of 

 Hg in most fish and higher animals in 

 coastal areas (Gardner et al. 1975a, 

 Gardner et al. 1978), it is not so in 

 marsh sediments and plants (Windom et 

 al. 1976). If formed in the sediments, 

 its residence time must be short. 



Laboratory and field studies of Hg 

 in Spartina alterniflora (Gardner et al. 

 1975a] showed that plants exposed to 

 high levels of Hg can take up and dis- 

 tribute the metal in their tissues. 

 Methyl Hg tends to concentrate in the 

 upper portions of the plant (leaves and 

 seeds), whereas inorganic Hg generally 

 accumulates in the roots. The very low 

 (below detection) levels of methyl Hg 

 found in natural growths of Spartina 

 suggest that this compound is not re- 

 tained by the plant. The plant, how- 

 ever, could be a potential mechanism for 

 transporting the compound across the 

 sediment water interface (Gardner et al. 

 1975b). 



Studies of a salt marsh ecosystem 

 which had been industrially contaminated 

 with inorganic Hg (chlor-alkal i plant) 

 indicated that methyl Hg can be formed 



in the salt marsh and can accumulate to 

 high levels (1-60 ppm) in tissues of 

 fish, mammals, and birds living in the 

 region (Windom et al. 1976; Gardner et 

 al. 1978). Sediments and plant roots 

 from the immediate area contained high 

 (0.2-1.7 ppm) levels of total Hg, but 

 negligible quantities of methyl Hg. The 

 primary consumers, Littorina irrorata 

 and Ilea sp., contained elevated levels 

 of total Hg and methyl Hg as did their 

 predators. In contrast, lower concen- 

 trations of Hg and methyl Hg were found 

 in herbivorous fish and mammals. 



LITERATURE CITED 



Buhler, D.R. 1973. Environmental con- 

 tamination by toxic metals. hn 

 Heavy metals in the environment. 

 Oregon State University, Water Re- 

 search Institute, Corvallis. 



Dunstan, W.M., and H.L. Windom. 1975. 

 The influence of environmental 

 changes in heavy metal concentra- 

 tions on Spartina alterniflora . 

 Pages 393-404 TR L- E. Cronin, ed. 

 Estuarine research. Vol. 2. Aca- 

 demic Press, New York. 



Gardner, W. S., W. M. Dunstan, and H. L. 

 Windom. 1975a. Flux of mercury 

 through Spartina alterniflora . 38th 

 Annual Meeting American Society of 

 Limnology and Oceanography. Hali- 

 fax, Nova Scotia. 



Gardner, W.S., D.R. Kendall, R.R. Odum, 

 H.L. Windom, and J. A. Stephens. 

 1978. The distribution of methyl 

 mercury in a contaminated salt 

 marsh ecosystem. Environ. Pollut. 

 15:243-251. 



Gardner, W. S., H. L. Windom, J. A. 

 Stephens, F. E. Taylor, and R. R. 

 Stickney. 1975b. Concentrations 

 and forms of mercury in fish and 

 other coastal organisms: implica- 

 tions to mercury cycling. Pages 

 268-278 j_n Proceedings of Mineral 

 Cycling Symposium. U.S. Energy Re- 

 search and Development Administra- 

 tion, Washington, D.C. 



Garrels, R.M., and C.L. Christ. 1965. 

 Solutions, minerals and equilibria. 

 Harper and Row, New York. 



Gibbs, R.J. 1973. Mechanisms of trace 

 metal transport to the sea. Science 

 180:71-73. 



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