Insights about sources, distribution, and degradation of sewage and biogenic molecular markers in surficial sediments and suspended particulate matter from a human-impacted subtropical estuary☆
Graphical abstract
Introduction
Geochemical organic markers have been extensively used to characterize the input of organic matter (OM) in different environments and timescales and can be assigned to a specific source (Takada and Eganhouse, 1998; Derrien et al., 2017). Sterols are one of the most useful molecular markers for allochthonous (sewage and continental material) and autochthonous (zooplankton and phytoplankton) contributions (Volkman, 1986; Derrien et al., 2017). Linear alkylbenzenes (LABs) are aromatic hydrocarbons always related to anthropogenic (sewage and oil) sources (Takada and Eganhouse, 1998).
Sewage is one of the main stressor agent in coastal ecosystems, especially in estuaries where the water circulation is restricted, which hinders its dilution in the environment. The precariousness (or absence) of sanitary services in coastal regions allows the chronic input of sewage with a bulk of nutrients, pesticides, drugs, and pathogens which interferes with the natural ecosystem and public health (UNEP, 2008; Lim et al., 2017).
Because the development of sanitary systems does not keep up with accelerated increases in population density (UNEP, 2008; IBGE, 2011), the detection of environmental sewage is still the most used alternative to monitor areas susceptible to eutrophication and prevent human contact with contaminated water (e.g. WHO, 2003; CONAMA, 2000).
Because sewage is the main source of coprostanol and LABs in coastal environments, these molecular markers have been widely used in the detection of sewage input or contamination (Takada and Eganhouse, 1998; Bull et al., 2002). Coprostanol is the main product of cholesterol degradation inside the intestinal tract of homeothermic vertebrates and corresponds to about 60% of total sterols in human feces (Murtaugh and Bunch, 1967; Hatcher and McGillivary, 1979). LABs are used as raw matter in the manufacture of commercial detergents; the 3–5% that do not react remain as a tracing product in the final composition and can be detected in environmental samples (Eganhouse et al., 1983). Both groups of molecular markers are hydrophobic and are mainly adsorbed in the suspended particulate matter (SPM) and sediments in aquatic environments (Bull et al., 2002; Dauner and Martins, 2015).
The analysis of SPM provides information about recent input as well as origin and input pathways, while the analysis of sediments provides historical and chronic OM input information (LeBlanc et al., 1992) which is potentially useful in identifying sink areas of sediment deposition (with adsorbed OM) as probably contaminated hot spot areas (Roussiez et al., 2006; Cardoso et al., 2016). Moreover, the intense diagenetic transformation that occurs in the water column can alter the concentration and composition of organic markers, therefore providing different results about OM sources and contamination in each compartment (Cardoso et al., 2016). Therefore, it is important to determine if hydrophobic markers such as sterols and LABs, also show different distributions in SPM and sediments.
This study investigated the spatial distribution of sterols and LABs in SPM and surficial sediments from a human-impacted subtropical estuary in order to determine sewage and biogenic OM inputs and provide comparative insights about their behavior, compositions, and sources in both compartments. The integrated approach has special relevance to estuarine environments, which have a restricted hydrodynamic circulation and are susceptible to contamination and eutrophication processes.
Section snippets
Study area
This study was performed in the E–W axis of the Paranaguá Estuarine System (PES), which includes Antonina (W side) and Paranaguá (E side) bays (25º30′S, 48º25′W) (Fig. 1). This area comprises approximately 46 km length, 10 km of maximum width and 330 km2 of surface water area (Marone et al., 2005). The clime is (rainy and moderately warm), with higher precipitation between austral spring and summer (three times more intense than in austral autumn and winter) (Lana et al., 2001). The
Sampling
Surface sediment and suspended particulate matter (SPM) were sampled in fifteen sites along the E-W axis of PES (Fig. 1) during one ebb spring tide in February of 2012. These sites were selected to obtain a wide spatial coverage according to a known salinity gradient in the area (Lana et al., 2001), and including sites where sewage markers have already been recorded (Martins et al., 2010a, 2011).
SPM samples (4 L of surface water) were collected in amber glass bottles at each site.
Sedimentary bulk parameters
Sedimentary %TOC, %TS, and %TN ranged from 0.03 to 4.29% (average of 1.44 ± 1.46%), from 0.01 to 1.09% (average of 0.42 ± 0.37%), and up to 0.44% (average of 0.17 ± 0.13%), respectively (Table S2). The highest values of TOC, TS, and TN were recorded at fluvial and mixture zones (at site 3) following a decreasing gradient towards the east (Table S2). This pattern was expected due to grain size variation which tends to be larger towards the east (Lamour and Soares, 2007; Cattani and Lamour, 2016).
Conclusions
The local hydrodynamic factors seem to provide relevant water column homogenization in this estuarine ecosystem. Consequently, the terrestrial and marine OM dispersion occurs and explains the uniform distribution and composition predominance of total sterols in SPM. These factors can also explain the relatively more homogeneous spatial distribution of LABs and coprostanol in SPM than sediments because they tend to promote the dispersion and dilution of sewage particles through the water column
Acknowledgments
A.C. Cabral would like to thank CAPES (Coordenação de Aperfeiçoamento de Pessoal de Ensino Superior) for the Ph. D. Scholarship. C.C. Martins would like to thank CNPq (Brazilian National Council for Scientific and Technological Development) (477047/2011-4; 305734/2014-8) and Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Estado do Paraná (408/2014; 42.799) for research grants received. The authors are grateful to J. Silva, F. Ishii, M. M. Cintra, and S.C.T. Barbosa
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