Differential effects on the toxicity and bioconcentration of hexavalent and trivalent chromium on the rotifer Lecane papuana (Rotifera: Monogononta)

Abstract Heavy metals are still a matter of concern as they might reach aquatic environments due to anthropogenic activities like metal-mechanic or mining, which are part of the main economic activities in different regions around the world. The exposure to chromium may be linked to discharges from automotive and tannery industries, representing a threat to aquatic biota. In the environment, chromium presents two stable forms, the trivalent (CrIII) and the hexavalent (CrVI), which differ on their chemical properties, and thus, on their bioavailability and effects on organisms exposed to this metal. Therefore, this work was aimed to assess the effects of both chromium III and VI on the demographic responses of the rotifer Lecane papuana and describe how the bioconcentration of chromium affects survival and fecundity. For this purpose, acute toxicity (48 h) and chronic toxicity test (alterations on the intrinsic growth rate) were carried out. Moreover, the bioconcentration factor (BCF) and metal body burden (MBB) were estimated after 24-h exposure to either CrIII or CrVI. Our results indicate that CrIII was less toxic according to their respective LC50 values (CrIII = 2.613 mg/L; CrVI = 0.177 mg/L). The intrinsic growth rate was significantly affected by CrIII while CrVI caused no significant changes but only at 0.0885 mg/L, which represents 0.5 of their respective LC50 value. Bioconcentration experiments demonstrated that L. papuana accumulated more CrIII before causing deleterious effects, although it was not as toxic as CrVI, which elicited toxic effects on L. papuana at concentrations of environmental concern.