THE IMPACT OF WATER HYACINTH (EICHHORNIA CRASSIPES) ON MERCURY LEVELS AND OTHER WATER QUALITY PARAMETERS IN A SOUTH CAROLINA COASTAL PLAIN RIVER

The most common route of exposure to methyl mercury in humans is through the consumption of fish, shellfish, and sea mammals (NAS, 2000; Clarkson et al., 2003). Human health risks associated with methyl mercury poisoning and the occurrence of elevated (>0.3 ppm) levels of methyl mercury in freshwater fish have resulted in the promulgation of greater than 60 fish consumption advisories for South Carolina. Approximately 86% of these advisories located in SC coastal plain rivers (Guentzel, 2009) and the concentrations of methyl mercury in largemouth bass from SC coastal plain rivers are some of the highest in the nation (Scudder et al., 2009). In addition to the elevated fish concentrations, the percentages of methyl mercury in the water column of SC coastal plain rivers are also higher than the national average. Typically methyl mercury represents 1-5% of the total mercury in the water column. Water samples taken from one SC coastal plain river (Waccamaw River) contain 3-23% methyl mercury relative to the total mercury (Guentzel 2009). Large areas of the shoreline within this river contain solid masses of water hyacinths (Eichhornia crassipes). When hyacinths grow they form dense floating mats on the surface which can alter the water chemistry and microbial populations directly below the mats. These dense mats can block light and oxygen from penetrating the surface waters below the mats, thus creating low to no oxygen environments in the surface waters that are conducive to the transformation of inorganic mercury to methyl mercury. This project will investigate changes in water quality parameters (dissolved oxygen, nutrients, chlorophyll, pH, redox potential, total mercury, methyl mercury) and the presence of sulfate reducers living on the root zones while these floating mats grow and increase in size during the spring and summer months. The roots and shoots of the water hyacinths will be analyzed for total and methyl mercury.