The profile of steroid congeners was evaluated in Caspian seals Pusa caspica by age, sex, and tissue-specific bioaccumulation, and compared with that of abiotic matrices (seawater, surface sediment, and suspended particulate materials, SPMs) from Miankaleh Wildlife/Gorgan Bay, (Caspian Sea, Iran). To identify the level of human fecal contamination, ∑25 sterol congeners were measured in all abiotic/biotic samples, revealing coprostanol, a proxy for human feces, as the most abundant sterol (seawater: 45.1–20.3 ng L–1; surface sediment: 90.2–70.3 ng g–1 dw; SPMs: 187.7–157.6 ng g–1 dw). The quantification of ∑25 sterols in seals followed the order of brain > liver > kidney > heart > blood > spleen > muscle > intestine > blubber > fur, and in both sexes coprostanol level (8.95–21.01% of ∑25s) was higher in blubber and fur, followed by cholesterol in brain, liver, kidney, heart, and blood, cholestanone in intestine and muscle, and β-sitosterol in spleen. Though no age/sex differentiation was observed, the mean concentration of ∑25s was higher in male than females and pup. Different diagnostic ratios revealed sterols originating from human and nonhuman sewage sources. Findings pinpoint the urgent necessity to investigate the ecotoxicity of fecal sterols in mammals, and consequent implications for human health.

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