Identifying avian sources of faecal contamination using sterol analysis

Abstract

Discrimination of the source of faecal pollution in water bodies is an important step in the assessment and mitigation of public health risk. One tool for faecal source tracking is the analysis of faecal sterols which are present in faeces of animals in a range of distinctive ratios. Published ratios are able to discriminate between human and herbivore mammal faecal inputs but are of less value for identifying pollution from wildfowl, which can be a common cause of elevated bacterial indicators in rivers and streams. In this study, the sterol profiles of 50 avian-derived faecal specimens (seagulls, ducks and chickens) were examined alongside those of 57 ruminant faeces and previously published sterol profiles of human wastewater, chicken effluent and animal meatwork effluent. Two novel sterol ratios were identified as specific to avian faecal scats, which, when incorporated into a decision tree with human and herbivore mammal indicative ratios, were able to identify sterols from avian-polluted waterways. For samples where the sterol profile was not consistent with herbivore mammal or human pollution, avian pollution is indicated when the ratio of 24-ethylcholestanol/(24-ethylcholestanol + 24-ethylcoprostanol + 24-ethylepicoprostanol) is ≥0.4 (avian ratio 1) and the ratio of cholestanol/(cholestanol + coprostanol + epicoprostanol) is ≥0.5 (avian ratio 2). When avian pollution is indicated, further confirmation by targeted PCR specific markers can be employed if greater confidence in the pollution source is required. A 66% concordance between sterol ratios and current avian PCR markers was achieved when 56 water samples from polluted waterways were analysed.

Sterols and stanols as novel tracers of waterbird population dynamics in freshwater ponds

“…Of the total plant sterols (combining sitosterol and stigmastanol), ring-billed gulls had the greatest proportion and concentration within their faeces. Similar to previous work [29,52,54], these results suggest that cholesterol is the dominant sterol in bird faeces; however, the diet of a single bird living in a dynamic landscape and close to a city centre may vary widely. For example, herring gulls are generalist predators on fishes, insects, small mammals and birds, and the eggs and young of co-occurring species, as well as opportunistic scavengers of dead animals or garbage from landfills [36,55].…”

Expression of caveolin‐1 in the interfollicular but not the follicle‐associated epithelial cells in the bursa of fabricius of chickens

“…Cholesterol efflux is maintained by a concentration gradient between the cell membrane and the extracellular space. In mammals, the enterocytes and hepatocytes (through bile) release cholesterol into the intestine, where anaerobic bacteria convert it to coprostanol (Devane et al, ). Therefore, mammalian feces even those of ruminants contain very small amount of cholesterol, unlike the feces of birds, which has high cholesterol contents (Devane et al, ).…”

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

“…Mainly because of their respective diets, cholesterol-derived 5β-stanols are found in high proportions in the faeces of omnivores and carnivores (coprostanol and epicoprostanol), while 5β-stanols derived from β-sitosterol, a phytosterol (plant sterol), are found in high proportions in herbivore faeces (24-ethylcoprostanol and 24-ethylepicoprostanol) [1]. In order to improve the distinction between the faecal signature of different mammal species in modern [16, 17, 20, 21, 24, 28, 29] and ancient [2, 3, 5, 7, 9, 11–15, 18, 32–34] environments, efforts have been made to develop the technique of faecal steroid biomarker analysis, mainly focused on the ratios of the four above-mentioned important 5β-stanols, sometimes in combination with the analysis of another group of faecal steroids, bile acids. However, the use of ratios calculated from four compounds has significant limitations.…”