Based on concentrations of total Cr measured in RBCs and plasma,
RBC:plasma ratios were assessed in rats and mice for the different
dose groups. The ratio of Cr concentration in RBCs and
plasma has long been used in studies as a biomarker of systemically
absorbed Cr(VI) (Alexander and Aaseth, 1995; Buttner and
Beyersmann, 1985; Gray and Sterling, 1950). As shown in Fig. 4,
the RBC:plasma ratio increased in both species in a dose-dependent
manner, but the increase appears at lower doses in rats than
in mice. The RBC:plasma ratio was above unity (>1) in rats administered
drinking water concentrations of 20 mg/L Cr(VI) and higher
(dose of P2.90 mg/kg). In mice, the RBC:plasma ratio was >1 at
drinking water concentrations of 60 mg/L Cr(VI) and higher (dose
of P11.70 mg/kg).