Degradation of Methylmercury and Its Effects on Mercury Distribution and Cycling in the Florida Everglades

Abstract

Methylmercury (MeHg) is recognized as one of the major water quality concerns in the Florida Everglades. Degradation of MeHg in the water is thought to be one of the most important processes to the cycling of MeHg, but there is a lack of quantitative estimations of its effect on the distribution and cycling of MeHg in this ecosystem. Stable isotope (Me201Hg) addition method was implemented to investigate the degradation of MeHg in the Everglades. By combining these results with the field monitoring data, effects of photodegradation on MeHg distribution and its contribution to MeHg cycling were estimated. The results indicate that degradation of MeHg in Everglades water is mediated by sunlight and that UV-A and UV-B radiations are the principal driver. The spatial pattern of MeHg photodegradation potential (PPD) generally illustrated an increasing trend from north to south in the Everglades, which was opposite to the distribution of MeHg in water column. Correlation analysis shows that MeHg concentration in the water had a significant negative relation to PPD, suggesting that photodegradation could play an important role in controlling the distribution of MeHg in Everglades water. Furthermore, about 31.4% of MeHg input into the water body was removed by photodegradation, indicating its importance in the biogeochemical cycling of MeHg in the Everglades. This percent reduction is much lower than that reported for other ecosystems, which could be caused by the higher concentration of DOC in the Everglades. The relatively slower degradation of MeHg could be one of the main reasons for the high ratio of MeHg to total mercury (THg) in this ecosystem.

Estimation of the Major Source and Sink of Methylmercury in the Florida Everglades

“…However, its rate was much slower than that of MeHg photodemethylation (k d = 0.26 ± 0.04 day −1 ), 9 indicating that methylation in water plays a minor role in the cycling of MeHg in the Everglades. The changes in Me 202 Hg concentration were taken into account in 9,12 However, MeHg present in a particular compartment (e.g., water) could be determined by the methylation/demethylation that occurred both in that compartment and in other compartments (e.g., floc, periphyton, or soil). Thus, the relationships of MeHg in one compartment to the methylation/demethylation in that compartment and other compartments were evaluated in this study.…”

“…Methylation of Hg in sediment by anaerobic bacteria (sulfate-reducing bacteria 1 or iron-reducing bacteria 2 ) was deemed to be the major pathway for MeHg production 2−7 in most aquatic systems, while photodemethylation in water was widely proposed to be the major process of MeHg elimination. 8,9 Methylation of inorganic mercury in the water column was reported to be another significant pathway of MeHg formation in some ocean (e.g., the Arctic 10 ) and freshwater 11 systems. The double stable isotope addition technique is a useful tool for measuring Hg methylation/demethylation rates owing to its high accuracy, precision, and simultaneous determination of the methylation and demethylation rates.…”

“…21 Hg methylation and/or MeHg demethylation were found to occur in various compartments of the Everglades, including soil, 12,20 floc (flocculent materials on top of soil), 19 periphyton, 18 and water. 9 Despite these findings, it is still unclear which compartment is the major source or sink of MeHg due to the lack of estimation and comparison of the net MeHg production in these compartments. A few previous studies have investigated the relationship of MeHg distribution in a certain compartment of the Everglades to its in situ methylation or demethylation.…”

Identification of mercury methylation product by tert-butyl compounds in aqueous solution under light irradiation

“…Photoreactions under solar or ultraviolet (UV) irradiation can contribute to both the production and degradation of MeHg in aquatic environments (Lehnherr and Louis, 2009;Li et al, 2010;Siciliano et al, 2005). In the presence of various LMWOCs, such as acetic acid, aldehydes, ketones, propionic acid, and ethanol, Hg photo-methylation was observed in aqueous solution under solar or UV irradiation .…”

A Method for the Highly Selective, Colorimetric and Ratiometric Detection of Hg2+ in a 100% Aqueous Solution

“…[5][6][7] It can not be denied that a number of health problems are caused by mercury, such as kidney failure, brain damage, and various cognitive and motion disorders. [8][9][10][11] Thus, it is of great significance to develop an effective method for the detection of Hg 2+ in the environment. Recently, many methods for the detection of Hg 2+ have been developed, such as inductively coupled plasma mass spectrometry, electrochemical sensing, atomic absorption spectroscopy, and fluorescence sensing.…”