Development of the Analysis of Fecal Stanols in the Oyster Crassostrea gigas and Identification of Fecal Contamination in Shellfish Harvesting Areas

Alterations in the sterol signature of detritivorous fish along pollution gradients in the Río de la Plata basin (Argentina): From plant to sewage-based diet

In order to assess the impact of sewage pollution on the diet of the strict detritivorous and migratory South American fish, Prochilodus lineatus, 16 sterol biomarkers were analyzed by gas chromatography-mass spectrometry from fish muscle (n: 144) collected along 1200 km in the Rio de la Plata basin. Sterol concentrations were fairly homogeneous (2.4 ± 1.3 mg g^-1 dry weight), but their proportion in lipids was highly variable and inversely related to both body mass and lipid contents, reflecting the more conservative character of sterols compared to the rapid accumulation of fat as fish grows. As expected, the muscle sterol signature was widely dominated by cholesterol (92 ± 4.5% of total sterols), but it exhibited a remarkable diversity with variable proportions of fecal coprostanol (4.0 ± 4.4%) and plant sterols (3.1 ± 1.9%, e.g. sitosterol and campesterol). Muscle sterols exhibited contrasting geographical differences associated with dietary shifts from plant-derived detritus in the northern reaches of the basin (N: Paraná and Uruguay Rivers), to sewage dominated inputs at Buenos Aires (BA). Fish from BA are fattier (lipids: 35 ± 18 vs. 15 ± 9.0% at N), with higher total sterol contents (2.6 ± 1.3 vs. 1.9 ± 1.0 mg g^-1), abundant coprostanol (5.3 ± 4.4 vs. 0.46 ± 1.1%) and lower plant sterols (2.6 ± 1.6 vs 4.6 ± 2.0%), reflecting a diet shifted to anthropogenic organic matter as opposed to vegetal detritus in the north. Accordingly, BA fish presented lower phyto/fecal sterol ratios (0.37 ± 0.21 vs. 0.91 ± 0.12 at N) and higher copro/epicoprostanol ratios (0.95 ± 0.082 vs 0.51 ± 0.25 at N), indicating fresh fecal inputs which provide a valuable supply of easily absorbed organic matter at this site. In addition, the sterol signature allowed to distinguish migratory fish from BA collected 900 km north (previously identified by their pollutant fingerprint and biochemical composition). In fact, coprostanol concentrations show a direct relationship with human populations along the basin, highlighting the usefulness of fecal sterol biomarkers as tracers of polluted fish stocks.

Faecal biomarkers can distinguish specific mammalian species in modern and past environments

Identifying the presence of animals based on faecal deposits in modern and ancient environments is of primary importance to archaeologists, ecologists, forensic scientists, and watershed managers, but it has proven difficult to distinguish faecal material to the species level. Until now, four 5β-stanols have been deployed as faecal biomarkers to distinguish between omnivores and herbivores, but they cannot distinguish between species. Here we present a database of faecal signatures from ten omnivore and herbivore species based on eleven 5β-stanol compounds, which enables us to distinguish for the first time the faecal signatures of a wide range of animals. We validated this fingerprinting method by testing it on modern and ancient soil samples containing known faecal inputs and successfully distinguished the signatures of different omnivores and herbivores.

Are fecal stanols suitable to record and identify a pulse of human fecal contamination in short-term exposed shellfish? A microcosm study

In this study, the capacity of oysters to bioaccumulate fecal stanols and to record a source-specific fingerprint was investigated by the short-term contamination of seawater microcosms containing oysters with a human effluent. Contaminated oysters bioaccumulated the typical fecal stanols coprostanol and 24-ethylcoprostanol and their bioaccumulation kinetics were similar to that of the Fecal Indicator Bacteria Escherichia coli used in European legislation. Although stanol fingerprints of contaminated water allowed the identification of the human specific fingerprint, this was not the case for oysters. This discrepancy is attributed to (i) high concentrations of endogenous cholestanol and sitostanol, responsible for "unbalanced" stanol fingerprints, (ii) different accumulation/depuration kinetics of fecal coprostanol and 24-ethylcoprostanol and (iii) the limits of the analytical pathway used. These results show that fecal stanols bioaccumulated by oysters are useful to record fecal contamination but the usefulness of stanol fingerprints to identify specific sources of contamination in shellfish currently seems limited.