Nitrate/nitrite [Nox; A, 10 mg/m3 frack sand dust (FSD) 8, or C, 30 mg/m3 FSD 8] and hydrogen peroxide (H2O2;B, 10 mg/m3 FSD 8, or D, 30 mg/m3 FSD 8) levels in the kidneys of rats at 1, 7 or 27 d after exposure (n = 8 animals/group and at each time point). Exposure to 10 mg/m3 FSD 8 did not significantly affect Nox (A) or H2O2 (B) concentrations in the kidneys. However, Nox concentrations were decreased in FSD 8-exposed compared to air-exposed rats 27 d after exposure to the 30 mg/m3 FSD 8 (C). Nox concentrations also were lower on day 7 and 27 than on day 1 in air-exposed rats (C and D; #P < 0.05). FSD 8 exposure at 30 mg/m3 did not alter H2O2 concentrations in the kidney.