The sterol compositions in sediments from an oxic pond of Bungaku-no-ike (Hachioji, Tokyo, Japan) using tetramethylammonium hydroxide (TMAH) thermochemolysis and gas chromatography-mass spectrometry (GC-MS) analysis were determined. In the sediments, four 5α(H)-stanols (cholestanol, campestanol, sitostanol, and brassicastanol) and their corresponding Δ5-sterols were identified. We detected high concentrations of cholestanol (1.08 – 1.07 µg / g), campestanol (0.97 – 1.37 µg / g), and sitostanol (2.78 – 3.88 µg / g) and high values of those 5α(H)-stanol / Δ5-sterol ratios (0.76 – 0.85, 0.80 – 0.60, and 0.29, respectively) in the sediments. In contrast, the concentrations of brassicastanol is low (0.16 – 0.28 µg / g) with low brassicastanol / brassicasterol ratios (0.11 – 0.16). The 5α(H)-stanols are known to be typically formed by bacterial reduction of Δ5-sterols under anoxic condition. However, the pond was confirmed to be in an oxidative condition (dissolved oxygen in bottom water, 5.5 ± 0.5 mg / L). From these results, the high 5α(H)-stanol / Δ5-sterol ratios, except the brassicastanol / brassicasterol, in the pond suggest that the source(s) of the 5α(H)-stanols may be terrigenous matter containing high 5α(H)-stanols resulting from preferential degradation of the Δ5-sterols. In any cases, our study indicates that there is some possibility of 5α(H)-stanol inputs even though the sampling location is not anoxic conditions, and thus, the redox indicator using the 5α(H)-stanol / Δ5-sterol ratio should pay attention to source effects.
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