Determinação de esteróis em sedimentos de igarapés de Manaus utilizando cromatografia líquida acoplada a espectrometria de massas sequencial (LC–MS/MS)

Abstract

With the implementation of the Zona Franca de Manaus (AM), the city underwent a great population growth that was not accompanied by investments in infrastructure and control over land use and occupation. Problems such as lack of sanitation, urbanization and housing have grown over the years, influencing the environment. Contamination of aquatic environments can be evaluated from the sedimentary organic matter (OM) that accumulates hydrophobic compounds. In this sense, the sterols are very useful as geochemical biomarkers in the evaluation of the sources of biogenic OM (terrestrial and aquatic) and anthropogenic (domestic sewage). This work quantitatively determined a series of sterols in sediments from three streams of Manaus (Mindu, Quarenta and Tarumã-Açu) by liquid chromatography coupled to sequential mass spectrometry. Cholesterol, epicoprostanol, coprostanol, cholestanol, campesterol, β-sitosterol, stigmasterol, brassicasterol, ergosterol and stigmastanol were selected in order to evaluate the various sources of OM in the streams. Most samples from urban streams, Mindu and Quarenta, presented coprostanol (fecal sterol) as the most abundant sterol with concentrations ranging from 523 to 6113 ng.g-1 and from 509 to 12 830 ng.g-1, respectively. Coprostanol concentrations in the Tarumã-Açu streams samples were much lower, ranging from <LQ to 142 ng.g-1. Similarly, the percentages of coprostanol ranged from 0 to 7% (m / m) for the Tarumã-Açu stream samples, from 21 to 54% (m / m) for the Mindu streams and from 31 to 50% m) for the Quarenta stream. Furthermore, diagnostic indices were calculated in order to obtain a more robust evaluation of the levels of contamination in the study streams. Coprostanol / (coprostanol + cholestanol), coprostanol / cholesterol and coprostanol / epicoprostanol ratios corroborates the results reported above and indicate an intense inflow of untreated domestic sewage in the Mindu and Quarenta streams.