An international team of researchers is challenging the widespread accepted finding that hexavalent chromium is much more toxic than trivalent chromium. At least for freshwater algae they found the contrary.
The importance of speciation in controlling the environmental fate, toxicity and bioavailability of trace elements is now well recognized. With respect to chromium, a widely-used element in industry, specific attention has been devoted to distinguish hexavelent chromium that is classified to be carcinogenic from trivalent chromium that is believed to play a beneficial role in the glucose metabolism and therefore is included in some food supplements and health products. Therefore, during the last decade, a bunch of rules and legislation has been established, meant to restrict the exposure of humans to hexavalent chromium (see EVISA's Link database
With respect to toxicity test for aquatic organisms, most of the published literature and also the US EPA Ecotox database concludes that hexavalent chromium is more toxic than trivalent chromium (see EVISA's Link database
).The new study
An international team of researchers now found some biasing operational parameters that challenge such conclusion. They noticed that the concentration of trivalent chromium, to which the algae plants were exposed, declined by 60-90% during the toxicity test (72 h) while the concentration of hexavalent chromium stayed much more stable. While the necessity to control the concentration of the toxin during exposure tests has long been recognized and therefore is included in recommendations by authoritive, international bodies, such is not the case for many trivalent chromium salts. The speciality of these salts is that their concentration is not limited by pour solubility of the original salts but of hydrolysis products formed at the typical pH conditions of the toxicity test.
When accounting for the decreasing concentration of trivalent chromium by using the time weighted mean concentration for the evaluation of toxicity in algae, the researchers found that Cr(III) is more toxic than Cr(VI). Such finding indicate that protocols for dealing with sparingly soluble substances (e.g., OECD, 2000) must be used to study the toxicity of Cr(III) to algae (and to other organisms exposed to Cr(III) in solutions) to avoid gross underestimation of Cr(III) toxicity. Alternatively, other strategies to account for Cr(III) chemistry during algal tests might be useful which make use of flow-through exposures or critical body residue approaches.
The authors further warn, that given the big efforts to detoxify Cr(VI) by converting it to the “less toxic” Cr(III), the possibility that the toxicity of Cr(III) to algae and other organisms could currently be underestimated needs careful consideration and extensive verification. The original study
Davide A.L. Vignati, Janusz Dominik, Mamadou L. Beye, Maurizio Pettine, Benoît J.D. Ferrari, Chromium(VI) is more toxic than chromium(III) to freshwater algae: A paradigm to revise?
, Ecotoxicology and Environmental Safety, 73/5 (2010) 743-749. doi:10.1016/j.ecoenv.2010.01.011 Related studies
Arun Kumar Shanker, Maduraimuthu Djanaguiraman and Bandi Venkateswarlu, Chromium interactions in plants: current status and future strategies
, Metallomics, 1 (2009) 375 - 383, DOI: 10.1039/b904571f
J. López-Luna, M.C. González-Chávez, F.J. Esparza-García and R. Rodrìguez-Vásquez, Toxicity assessment of soil amended with tannery sludge, trivalent chromium and hexavalent chromium, using wheat, oat and sorghum plants
, J. Hazardous Mater., 163 (2009) 829–834. doi:10.1016/j.jhazmat.2008.07.034
L. Brito Paiva, J. Gonçalves de Oliveira, R.A. Azevedo, D.R. Ribeiro, M.G. Da Silva and A.P. Vitória, Ecophysiological responses of water hyacinth exposed to Cr3+ and Cr6+
, Environ. Exp. Botany, 65 (2009) 403–409. doi:10.1016/j.envexpbot.2008.11.012
D.A.L. Vignati, M.L. Beye, J. Dominik, A.O. Klingemann, M. Filella, A. Bobrowski, B.J.D. Ferrari, Temporal decrease of trivalent chromium concentration in a standardized algal culture medium: experimental results and implications for toxicity evaluation
, Bull. Environ. Contam. Toxicol., 80 (2008) 305–310. doi: 10.1007/s00128-008-9379-8
R. Bencheikh-Latmani, A. Obraztsova, M.R. Mackey, M.H. Ellisman, B.M. Tebo, Toxicity of Cr(III) to Shewanella sp. Strain MR-4 during Cr(VI) reduction
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Anna Speranza, Paola Ferri, Michela Battistelli, Elisabetta Falcieri, Rita Crinelli, Valeria Scoccianti, Both trivalent and hexavalent chromium strongly alter in vitro germination and ultrastructure of kiwifruit pollen
, Chemosphere, 66/7 (2007) 1165-1174. doi:10.1016/j.chemosphere.2006.08.019
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Fengxiang X. Han, B.B. Maruthi Sridhar, David L. Monts, Yi Su, Phytoavailability and toxicity of trivalent and hexavalent chromium to Brassica juncea
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S.L. Thompson, F.C.R. Manning, S.M. McColl, Comparison of the toxicity of chromium(III) and chromium(VI) to cyanobacteria
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Andrew M. Standeven, Karen E. Wetterhahn, Is there a role for reactive oxygen species in the mechanism of chromium(VI) carcinogenesis?
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, Mutat. Res., 90 (1981) 111–118. doi:10.1016/0165-1218(81)90073-2 Related EVISA Resources Link database: Toxicity of chromium valency species Link database: Legislation related to hexavalent chromium Brief Summary: Speciation and Toxicity Related EVISA News May 17, 2007: Hexavalent Chromium in Drinking Water Causes Cancer in Lab Animals
April 24, 2007: Nutrigenomics: The role of chromium for fat metabolism revisited
June 8, 2006: Scientific journal adds fuel to ongoing chromium debate March 20, 2005: United Kingdom's Food Standards Agency granted derogation to
Chromium (III) compounds as a food supplement
November 23, 2004: Chromium (III) - not only therapeutic?
last time modified: June 15, 2010