Comparative Toxicity and Speciation of Two Hexavalent Chromium Salts in Acute Toxicity Tests

Abstract

The comparative acute toxicity of potassium chromate and dichromate salts to six aquatic species including both freshwater and marine forms was investigated. A thermodynamic equilibrium model was developed to aid in interpreting toxicity data with respect to hexavalent chromium speciation. Although parallel acute toxicity tests conducted with both salts yielded similar LCSO values, toxicity differences tended to become more pronounced as the sensitivity of the test species to the chemical decreased. Observed changes in pH and predicted changes in chromium speciation that occurred between the two salts in tests with less sensitive species were postulated to explain these findings. The implication of the aqueous chromium species to the relative toxicity of the hexavalent chromium are discussed. If hexavalent chromium is widely adopted as a standard reference toxicant for aquatic toxicity testing then the chromate salt should be used since it does not appreciably alter the initial pH of the dilution water and subsequent speciation to the extent that would be expected if the dichromate salt was employed. Standardization of the source of hexavalent chromium used in reference tests will facilitate intralaboratory comparison of toxicity data.

Toxicity identification of metals: Development of toxicity identification fingerprints

“…The increased toxicity at lower pHs is frequently associated with an increasing activity of hydrochromate ( ) ions. Jop et al [27] and Van der Putte Ϫ HCrO 4 [28] stated that the greater uptake, and thus bioavailability, and the stronger oxidizing activity of hydrochromate ions compared with the chromate ions (Cr 2 O 4 2Ϫ ) were responsible for the increased toxicity. From the species distribution, it seems that mainly hydrochromate ions are present at lower pHs while the chromate ions predominate (93%) at pH 7.5 and higher.…”

Sensibilidade da microalga marinha Dunaliella tertiolecta BUTCHER a diferentes substâncias químicas utilizadas como referência em ensaios ecotoxicológicos

“…Contudo, a toxicidade de cromato de potássio, CI50-96h = 150,6 mg/L para D. tertiolecta foi menor, comparada ao dicromato de potássio, CI50-96h = 113,0 mg/L. Jop et al (1987) estudaram duas espécies de crustáceos e quatro de peixes encontraram diferença significativa entre os resultados obtidos para dicromato de potássio e cromato de potássio apenas para os peixes. O cromato de potássio apresentou ainda a vantagem de não influenciar o pH da solução.…”