TECHNICAL REPORTS 111 Little is known about the presence of the element Cr in its toxic hexavalent form Cr(VI) in stormwater runof from urban areas. Most studies report only total Cr concentration, i.e., including also the nontoxic Cr(III) molecular form. Te objective of this study was to evaluate a feld method based on cation-exchange for characterization of Cr species in urban stormwater runof and soil leachate. We used a 0.05 mol L −1 Na and Ca solution and a soil leachate as matrices and spiked these with Cr(III), Cr(VI), or both in the concentration range of 1 to 100 mg L −1 . We then fltered the test samples through cation-exchange cartridges. In the Na–Ca salt matrix, the Cr(III) was retained 100% and recovery values of Cr(VI) were 86 to 100%. Furthermore, in such a matrix, each cartridge could be reused at least nine times without a drop in retention of Cr(III) or recovery of Cr(VI). In a soil leachate matrix, the method appeared less applicable. Apparently Cr(III) forms complexes with dissolved organic matter, allowing it to bypass the cartridge, resulting in incomplete Cr(III) retention and thus incomplete speciation. Te complexes are formed rapidly afer spiking, thus changes in the Cr-species distribution are likely to occur within a few hours when fresh samples are stored. Furthermore, we concluded that Cr(III) at neutral pH in pure solution or complexed with dissolved organic C can sorb irreversibly to polyethylene and polypropylene containers. Our fndings show that there is still a need for a method that can be applied to urban runof in the feld. Furthermore, cartridge speciation methods should ideally be tested before being applied on solutions containing organic matter. Characterization of Chromium Species in Urban Runof K. Cederkvist,* M. B. Jensen, and P. E. Holm I n the environment, the element Cr exists in two stable forms, Cr(III) and Cr(VI). While Cr(III) is an essential element for all living organisms, Cr(VI) is acutely toxic, carcinogenic, and mutagenic to both humans and ani- mals (Fendorf, 1995). Chromium(III) is the predominant molecular species under reducing conditions, while Cr(VI) is the predominant molecular species under oxidative conditions. In aqueous solution, dissolved Cr(III) exists as the cation Cr 3+ . At pH 4 to 6, it hydrolyzes into Cr(OH) 2+ and from pH 6 to 8 to Cr(OH) 2 + . Above pH 8, it is found as the neutral molecular form Cr(OH) 3 0 . In soils, Cr(III) is strongly bound to soil solid phases, particularly to organic matter, or it is present as the mineral Cr(OH) 3 , which has an extremely low solubility at pH values >5.5 ( James and Bartlett, 1983; Kimbrough et al., 1999). In aqueous media, Cr(VI) hydrolyzes into anionic species, predominantly the oxyanions CrO 4 2− (chromate), HCrO 4 − , and Cr 2 O 7 2− (dichromate) (Mohan and Pittman, 2006), with HCrO 4 − dominating at pH <6.5 and CrO 4 2− dominating at pH >6.5. Several other factors, especially the presence of organic matter, are known to infuence the speciation of Cr (Wittbrodt and Palmer, 1997) because organic matter can reduce Cr(VI) to Cr(III), as can Fe 2+ and sulfdes. Furthermore, Cr(III) can be oxidized to Cr(VI) by MnO 2 . Te reaction system is complex, and Cr(III) precipitated as Cr(OH) 3 (s) might not be oxidized (Rai et al., 1989). Because of the toxicity of Cr(VI) and the mobility of oxyanions, the molecular Cr(VI) forms are of major environmental concern (Khaodhiar et al., 1998). Te WHO guideline for total Cr in drinking water is 50 mg L −1 (World Health Organization, 2003), whereas the Danish threshold in drinking water is 25 mg L −1 for total Cr but only 1 mg L −1 for Cr(VI) (Danish Environmental Protection Agency, 2010). Elevated Cr concentrations are seen in stormwater runof due to leaching from concrete, corrosion of welded metal plating present on cars, and wear and tear of engines, brakes, and other Cr-containing devices (Göbel et al., 2007; Kayhanian et al., 2009). Kayhanian et al. (2003) reported values of dissolved Cr in stormwater ranging from 0.6 to 22 mg L −1 , and values from 2 to 50 mg L −1 of total Cr was reported by Göbel et al. Abbreviations: DOC, dissolved organic carbon; DPC, diphenylcarbazide; IC-H cartridge, cation-exchange cartridge; PE, polyethylene; PP, polypropylene; sl, soil leachate; TOC, total organic carbon. K. Cederkvist and P.E. Holm, Dep. of Basic Sciences and Environment, Faculty of Life Sciences, Univ. of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark; K. Cederkvist and M.B. Jensen, Forest and Landscape, Faculty of Life Sciences, Univ. of Copenhagen, Rolighedsvej 23, 1958 Frederiksberg C, Denmark. Assigned to Associate Editor James Ippolito. Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. J. Environ. Qual. 42:111–117 (2013) doi:10.2134/jeq2012.0182 Received 1 May 2012. *Corresponding author (karince@life.ku.dk). Journal of Environmental Quality HEAVY METALS IN THE ENVIRONMENT TECHNICAL REPORTS Published December 14, 2012