Comparison of different types of diffusive gradient in thin film samplers for measurement of dissolved methylmercury in freshwaters Cristal Fernández-Gómez, Josep M. Bayona, Sergi Díez n Environmental Chemistry Department, Institute of Environmental Assessment and Water Research, IDÆA-CSIC, E-08034 Barcelona, Spain article info Article history: Received 10 March 2014 Received in revised form 6 June 2014 Accepted 11 June 2014 Available online 19 June 2014 Keywords: Methylmercury DGT Bioavailable Agarose Polyacrylamide abstract Determination of bioavailable concentrations of methylmercury (MeHg þ ) in freshwater is key to further understanding its potential risk and toxicity. In this work, two in-house-manufactured mercury-specific diffusive gradients in thin films (DGT) were used in laboratory to assess the lability of MeHg þ , and to develop a relationship between chemical lability and bioavailability. After diffusing through the diffusive gel, the MeHg þ accumulated in a thiol functionalised resin gel was extracted using acidic thiourea that was analysed using aqueous-phase propylation followed by headspace solid-phase microextraction (HS-SPME) and gas chromatography (GC) coupled to pyrolysis-atomic fluorescence spectrometry (Py- AFS) detection. The diffusion coefficient (D) at 25 1C in agarose (A-DGT) in the absence and presence of dissolved organic matter (DOM) was obtained. Moreover, these values were experimentally compared against polyacrylamide (P-DGT), which is the most frequently used DGT for mercury to date. Statistically significant differences were observed between D values for A-DGT in the absence (3.15 Â 10 À6 cm 2 s À1 ) and presence of DOM (2.68 Â 10 À6 cm 2 s À1 ) and also for P-DGT (2.49 Â 10 À6 and 1.69 Â 10 À6 cm 2 s À1 ). Interestingly, our results show that diffusion of MeHg þ was higher on agarose diffusive gel with and without DOM in comparison with those observed in polyacrylamide. Even with higher diffusion coefficients of MeHg þ in the agarose diffusion layer, however, DGT based on polyacrylamide seems to be a better choice for eutrophic waters, when monitoring very low concentrations of MeHg þ , considering its slightly higher uptake capacity. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Among mercury (Hg) species occurring in the environment, methylmercury (MeHg þ ) is identified as one of the most critical regarding its biotic effects. The reason for this is that it is a potent neurotoxin that has the ability to pass through biological mem- branes, low metabolism and excretion rates and, consequently, can bioaccumulate and biomagnify throughout aquatic trophic chains [1,2]. Since contamination by mercury in aquatic ecosystems is of great concern, monitoring of its species has attracted special attention. In freshwater environments, both inorganic and organic (e.g. MeHg þ ) mercury can be partitioned between suspended particulate matter (SPM), dissolved and to colloidal water phases. The latter is associated with the DOM occurring in freshwater ecosystems [3,4]. This influences the speciation and potentially the bioavailability (i.e. its availability to be taken up by biota) of mercury [5]. Determining the bioavailability of MeHg þ is also essential in order to assess its risk and potential effects on exposed biota. For this purpose, the diffusive gradients in thin films (DGT) technique can be used. This technique was developed in 1994 [6] for in situ determination of kinetically labile metal species in aquatic systems. The principle of the DGT technique is based on the diffusion of the dissolved species through a membrane- diffusive layer and their accumulation in an ion-exchange resin. A hydrogel and a membrane filter are commonly used as the diffusive layer and the resin is incorporated into a polyacrylamide gel. These three layers are enclosed and sealed in a small plastic device, so that only the membrane is exposed to the deployed solution. The time-average concentration of metal in the solution, C, can be calculated with the help of Fick's first law of diffusion as follows: C ¼ MΔg DAt ð1Þ where D is the diffusion coefficient of the metal in the diffusive layer, t is the deployment time, A is the exposure surface area, and Δg is the thickness of the gel layer. The mass of the analyte accumulated by the resin is experimentally measured and the absolute mass M then provides the average labile metal concen- tration during the exposure time. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta http://dx.doi.org/10.1016/j.talanta.2014.06.025 0039-9140/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ34 93 4006100; fax: þ34 93 2045904. E-mail address: sdsqam@cid.csic.es (S. Díez). Talanta 129 (2014) 486–490