Chromium(VI) much more toxic than chromium(III): At least for freshwater algae a paradigm to revise?

Background:
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 (newest first)

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, Environ. Sci. Technol., 41 (2007) 214–220. DOI: 10.1021/es0622655

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

A.K. Shanker, C. Cervantes, H. Loza-Tavera, S. Avudainayagam, Chromium toxicity in plants, Environ. Int., 31 (2005) 739–753.  DOI: 10.1016/j.envint.2005.02.003

Fengxiang X. Han, B.B. Maruthi Sridhar, David L.  Monts, Yi Su, Phytoavailability and toxicity of trivalent and hexavalent chromium to Brassica juncea, New Phytol., 162 (2004) 489–499. DOI: 10.1111/j.1469-8137.2004.01027.x

S.L. Thompson, F.C.R. Manning, S.M. McColl, Comparison of the toxicity of chromium(III) and chromium(VI) to cyanobacteria, Bull. Environ. Contam. Toxicol., 69 (2002) 286–293. DOI: 10.1007/s00128-002-0059-9

K. D. Sugden, R. D. Geer, S. J. Rogers, Oxygen radical-mediated DNA damage by redox-active chromium(III) complexes, Biochemistry, 31/46 (1992) 11626–11631. DOI: 10.1021/bi00161a049

Andrew M. Standeven, Karen E. Wetterhahn, Is there a role for reactive oxygen species in the mechanism of chromium(VI) carcinogenesis?, Chem. Res. Toxicol., 4/6 (1991) 616–625. DOI: 10.1021/tx00024a003

G. Warren, P. Schultz, D. Bancroft, K. Bennet, E.H. Abbott and S. Rogers, Mutagenicity of a series of hexacoordinate chromium(III) compounds, 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 (newest first) 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?