Occurrence of Monoethylmercury in the Florida Everglades: Identification and Verification
Total Page：16
File Type：pdf, Size：1020Kb
Environmental Pollution 158 (2010) 3378e3384 Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol Occurrence of monoethylmercury in the Florida Everglades: Identification and verification Yuxiang Mao a,b, Yongguang Yin c, Yanbin Li a, Guangliang Liu a, Xinbin Feng d, Guibin Jiang c, Yong Cai a,* a Department of Chemistry & Biochemistry and Southeast Environmental Research Center, Florida International University, Miami, FL 33199, USA b Henan Polytechnic University, Jiaozuo, 454000 China c State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China d State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Science, 46 Guanshui Road, Guiyang 550002, China A combination of various analytical techniques and stable isotope tracer experiments confirms monoethylmercury is present in Everglades soil. article info abstract þ Article history: A few studies have reported the occurrence of monoethylmercury (CH3CH2Hg ) in the natural envi- Received 28 April 2010 ronment, but further verification is needed due to the lack of direct evidence and/or uncertainty in Received in revised form analytical procedures. Various analytical techniques were employed to verify the occurrence of 19 July 2010 þ þ CH CH Hg in soil of the Florida Everglades. The identity of CH CH Hg in Everglades soil was clarified, Accepted 24 July 2010 3 2 3 2 for the first time, by GC/MS. The employment of the recently developed aqueous phenylation-purge-and- þ trap-GC coupled with ICPMS confirmed that the detected CH3CH2Hg was not a misidentification of Keywords: þ þ CH SHg . Stable isotope-tracer experiments further indicated that the detected CH CH Hg indeed Monoethylmercury 3 3 2 originated from Everglades soil and was not an analytical artifact. All these evidence clearly confirmed Occurrence þ Soil the occurrence of CH3CH2Hg in Everglades soil, presumably as a consequence of ethylation occurring in þ Everglades this wetland. The prevalence of CH3CH2Hg in Everglades soil suggests that ethylation could play an Isotope tracer important role in the biogeochemical cycling of Hg. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction conventional and widely used mercury speciation method, aqueous ethylation followed by purge-and-trap-gas chromatography (GC)- Mercury is a global pollutant that originates from both natural atomic fluorescence spectrometry (AFS) method cannot distinguish þ 2þ and anthropogenic sources. Speciation of mercury determines both CH3CH2Hg from Hg because the ethylation products of both its toxicity and biogeochemistry (Craig et al., 2003). One of the compounds are diethylmercury (Hg(CH3CH2)2)(Cai et al., 2000). þ organomercury species, monomethylmercury (CH3Hg ), has been In the past half-century, a few studies have reported the þ intensively studied due to its prevalence in the environment, high occurrence of CH3CH2Hg in the environment. Using a conven- toxicity, and high enrichment factor through food webs (Mason and tional GC with an electron capture detection (ECD) method, þ Benoit, 2003). It has been widely recognized that microbial activi- CH3CH2Hg was detected in fish collected from the polluted Jinzhu ties play an important role in the formation and degradation of River in Japan (Yamanaka and Ueda,1975) and in the sediment from þ CH3Hg in the environment (Mason and Benoit, 2003; Morel et al., the polluted areas of St. Clair system (Jerneloev and Wennergren, 1998). However, little is known about the occurrence of other 1980). By using various isolation/preconcentration methods þ þ organomercury species, such as monoethylmercury (CH3CH2Hg ), combing with GC-ECD, Horvat detected CH3CH2Hg in different in the natural environment. As a short-chain alkyl mercury species, biological reference materials, such as mussel, copepod, shrimps þ CH3CH2Hg is also highly toxic, although its toxicological mecha- and tuna fish, certified by the International Atomic Energy Agency þ þ nisms and effects may differ from those of CH3Hg (Clarkson, 2002; (IAEA) (Horvat, 1991). In all these cases, the detected CH3CH2Hg þ Gerstner and Huff, 1977; Magos, 2001). The lack of CH3CH2Hg was present at mg/Kg or sub mg/Kg levels. Accompanying with the information could be partially attributed to the fact that sensitive advances in analytical techniques, reports on the finding of þ þ and reliable methods for the analysis of trace level CH3CH2Hg in CH3CH2Hg at lower levels appeared. In 1993, a study (Hintelmann environmental matrices were not available until recently. The and Wilken, 1993), in the course of developing an HPLC-AFS method for organomercury speciation analysis, detected þ CH3CH2Hg at mg/Kg level in sediment of a polluted river in * Corresponding author. Germany. Two years later (Hintelmann et al., 1995), the same group þ E-mail address: cai@fiu.edu (Y. Cai). reported the occurrence of CH3CH2Hg and some other 0269-7491/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2010.07.031 Y. Mao et al. / Environmental Pollution 158 (2010) 3378e3384 3379 organomercury species, such as phenylmercury and methosxye- chloride (CH3CH2HgCl) were prepared by dissolving the standards in methanol. 199 thylmercury compounds, in soils/sediments of some industrially Enriched HgO (atomic percentage 91.09 Æ 0.05) was purchased from Oak Ridge National Laboratory (Oak Ridge, Tennessee) and dissolved in 10% HCl. Other reagents contaminated sites in Germany. In addition to the finding of þ þ used were of reagent grade or higher. All the gases used were passed through CH3CH2Hg in polluted areas, the occurrence of CH3CH2Hg in activated charcoal traps to remove mercury background. some relatively pristine environments was also reported. During the development of a GC-AFS method for mercury speciation 2.2. Instrumentation analysis, a study (Alli et al., 1994) observed the presence of þ Mercury speciation was performed using a modified PerkinElmer AutoSystem CH CH Hg in soil of the Florida Everglades. Preliminary study was 3 2 XL GC (PerkinElmer) coupled with an Elan DRC-e ICPMS (PerkinElmer) following carried out (Cai et al., 1997) using GC-AFS with two GC columns and a procedure reported recently (Mao et al., 2008). Aqueous phenylation reactions different derivatization reactions in an effort to verify the occur- were performed in 200 mL glass bubblers purchased from Brooks Rand LLC (Seattle, þ WA). The traps used for retaining mercury species were deactivated inlet liners rence of CH3CH2Hg in Everglades soil. Using a similar GC-AFS þ (5.8 mm o.d.  9.2 mm length  4.0 mm i.d.) for PerkinElmer AutoSystem XL GC. The method, the presence of CH3CH2Hg in the soils of some Canadian liners were packed with 0.06e0.08 g of Tenax (60/80 mesh, SUPELCO) and plugged wetlands was reported (Siciliano et al., 2003), and the prevalence of with deactivated glass wool on both ends to hold the Tenax grains in place. The þ CH3CH2Hg in Canadian wetlands was revealed in follow-up temperatures of injection port and detector of the GC were set at 200 and 250 C, Ò studies (Holmes and Lean, 2006). In the soil of these wetlands, respectively. A fused-silica capillary column (Rtx -1, 0.53 mm  15 m, 1.5-mm film, Restek Corporation, Bellefonte, PA) was used for mercury species separation, and including the Florida Everglades (Cai et al., 1997) and Canadian Ò þ a Rtx -50 capillary column (0.53 mm  15 m, film 1.0 mm) was used for purposes of wetlands (Holmes and Lean, 2006), CH3CH2Hg was determined at þ verification. The column temperature was programmed as follows: 50 C for 1 min, m g/Kg level, similar to the concentration of CH3Hg in the corre- ramped from 50 to 150 C at a rate of 20 C/min, maintained at 150 C for 1 min, sponding sites. ramped to 250 C at a rate of 20 C/min, and then maintained at 250 C for 3 min. A þ In the aforementioned studies, CH3CH2Hg was determined in split/splitless injection port was used in splitless mode. The carrier gas was argon at either polluted (by industry) or relatively natural environment 4 mL/min. Organomercury species eluting from the GC capillary column were converted to elemental Hg via a pyrolysis oven (800 C). A piece of PFA tubing (without apparent anthropogenic pollution sources). If the occur-  þ (0.635 cm i.d. 150 cm length, NALGENE NUNC, Rochester, NY) operated at room rence of CH3CH2Hg in the environment is confirmed, the corre- temperature was used to transfer elemental Hg to ICPMS. The nebulizer gas flow for sponding environmental implications and risk of exposure should ICPMS was 1.05 L/min and the ICP RF power was1300 W 202Hg and 199Hg were be assessed accordingly. As a consequence, our understanding of monitored with a dwell time of 25 ms and 5 sweeps/reading. GC-AFS system used was a capillary GC (Model GC94, Ai Cambridge, UK) coupled the biogeochemistry of mercury could be altered. However, to mercury AFS (PSA Merlin) via a pyrolysis oven maintained at 800 C. Details of the uncertainty remains in the above mentioned studies where system can be found elsewhere (Mao et al., 2008). Temperature program used was þ þ occurrence of CH3CH2Hg was reported. First, CH3CH2Hg was the same as the one described above. Carrier and makeup gases were argon, at flow identified according to its retention time on either GC or HPLC rates of 4 and 35 mL/min, respectively. fi columns. It is possible that other compounds bearing the same Identi cation of organomercury species was also accomplished on an HPLC-AFS þ system. Details of the instrumentation can be found elsewhere (Gao et al., 2008). A retention times with CH3CH2Hg under the same experimental  m þ C18 column (Shimadzu Shimpack CLC-ODS, 6 mm 150 mm, 5 m particle size) and conditions would have been wrongly recognized as CH3CH2Hg .