Measurement of Stable and Radioactive Cesium in Natural Waters by the Diffusive Gradients in Thin Films Technique with New Selective Binding Phases Weijia Li,* ,† Feiyue Wang, ‡ Weihua Zhang, § and Douglas Evans † Worsfold Water Quality Centre, Trent University, 1600 West Bank Drive, Peterborough, Ontario, K9J 7B8, Canada, Department of Environment and Geography, and Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada, and Radiation Protection Bureau, Health Canada, A.L.:6302D1, 775 Brookfield Road, Ottawa, Ontario, K1A 1C1, Canada A cesium-specific diffusive gradients in thin films (DGT) technique was developed using copper ferrocyanide (CFCN) as the binding agent. Two types of DGT binding phases were evaluated, one by immobilizing CFCN on Chelex 100 resin gels (Chelex-CFCN) and the other on poly(acrylic acid) gels (PAA-CFCN). Both DGT devices were successfully applied to the measurement of low levels of stable 133 Cs and radioactive 137 Cs in synthetic solutions and in natural river waters. In all cases, the DGT labile concentrations measured with the PAA- CFCN DGT agreed very well with total dissolved Cs concentrations, whereas those measured by the Chelex- CFCN DGT were much lower than total Cs concentra- tions. The difference was attributed to the different binding kinetics of Cs + on the two gels suggesting that this might be a promising means of measuring biologi- cally relevant Cs concentrations in natural waters. Radiocesium is one of the most important artificial radionu- clides in the environment and has been of great concern over the past few decades. It may be released from anthropogenic activities such as nuclear weapons testing, 1 nuclear facility accidents, 2 and nuclear waste management. 3 Once entering the aquatic environ- ment, Cs can be assimilated by aquatic organisms and thus enter the food chain because of its biochemical similarity to the essential element potassium. 4 Both external and internal exposure to cesium can occur, with higher concentrations occurring usually in muscle and lower in bones. 5 Among the radiocesium isotopes, 137 Cs, a γ ray emitter, is of particular concern because of its moderately long (several decades) radiation impact as a medium-lived fission product (τ 1/2 ) 30.17 years). 137 Cs has received much attention as a result of the 1986 accident at the Chernobyl Nuclear Power Plant in the former Soviet Union, which released a large plume of radioactive fallout to the adjacent and other areas including the western part of the former Soviet Union, most of Europe, and parts of eastern North America, resulting in elevated concentrations of 137 Cs in water and fish. 6 As of 2005, 137 Cs was still the principal source of radiation in and around the zone of alienation. 7 Other radioactive isotopes of cesium, 134 Cs (T 1/2 ) 2 years) and 135 Cs (T 1/2 ) 2.3 million years), are also important in the environment. Although they are less hazardous than 137 Cs due to their quick decay or weak radiation, 8 their unique decay half-lives can be indicators of their transport and remaining radiation activity 9 in the environment. Traditional methods to measure the extremely low concentra- tions of cesium in waters in the presence of high concentrations of coexisting matrix cations, such as Na + ,K + , Ca 2+ , and Mg 2+ , usually involve the collection 10 and preconcentration 11 of large amounts of water. This approach is therefore labor intensive, time-consuming, cost ineffective, and prone to cross contamina- tion. Potentially these constraints could be improved by the application of the diffusive gradients in thin films (DGT) technique. 12,13 DGT is an in situ preconcentrating device consist- ing mainly of a well-defined diffusive layer and a binding phase. The concentrating process in DGT also resembles biological mechanisms, and thus provides a means of estimating “bioavail- able” metal concentrations in natural waters. 14,15 Chang et al. 16 were the first to apply the DGT technique, with a cation exchange resin (AG50W-X8) as the binding agent, for cesium measurements in natural waters. However, the practice has been problematic * Corresponding author. Phone: 1-705-748-1011-7886. Fax: 1-705-748-1625. E-mail: woodyllaa@gmail.com. † Trent University. ‡ University of Manitoba. § Health Canada. (1) Almgren, S.; Isaksson, M. J. Environ. Radioact. 2006, 91, 90–102. (2)Ra¨a ¨f, C. L.; Hubbard, L.; Falk, R.; Ågren, G.; Vesanen, R. Sci. Total Environ. 2006, 367, 324–340. (3) Harjula, R.; Lehto, J.; Paajanen, A.; Brodkin, L.; Tusa, E. Nucl. Sci. Eng. 2001, 137, 206–214. (4) Anjos, R. M.; Mosquera, B.; Sanches, N.; Cambui, C. A.; Mercier, H. Environ. Exp. Bot. 2009, 65, 111–118. (5) Yamada, M.; Nagaya, Y. J. Radioanal. Nucl. Chem. 1998, 230, 111–114. (6) Saxe ´n, R. L. Boreal Environ. Res. 2007, 12, 17–22. (7) Gaziev, I. Y.; Kryshev, I. I.; Gaziev, Y. I.; Uvarov, A. D. Izvestiya Vysshikh Uchebnykh Zavedenii, Yadernaya Energetika 2005, 40–47. (8) Lieser, K. H. Nuclear and Radiochemistry, Fundamentals and Applications; Wiley-VCH: Berlin, Germany, 2001. (9) Taylor, V. F.; Evans, R. D.; Cornett, R. J. J. Environ. Radioact. 2008, 99, 109–118. (10) Kautsky, H. Ocean Dynamics 1976, 29, 217–221. (11) Folsom, T. R.; Mohanrao, G. J. J. Radiat. Res. 1960, 1, 150–154. (12) Davison, W.; Fones, G.; Harper, M.; Teasdale, P.; Zhang, H. In Situ Monitoring of Aquatic Systems, Chemical Analysis and Speciation; John Wiley & Sons Ltd.: Chichester, England, 2000. Anal. Chem. 2009, 81, 5889–5895 10.1021/ac9005974 CCC: $40.75  2009 American Chemical Society 5889 Analytical Chemistry, Vol. 81, No. 14, July 15, 2009 Published on Web 06/17/2009