Sewage contamination assessment in an urbanized tropical estuary in Northeast Brazil using elemental, isotopic and molecular proxies

• Published in: Environmental pollution (1987) 2023-01, Vol.317, p.120726, Article 120726
• Main Authors: Arruda-Santos, Roxanny Helen de, Costa, Bruno Varella Motta da, Carvalho, Paulo Sérgio Martins de, Zanardi-Lamardo, Eliete
• Format: Article
• Language: English
• Subjects: Brazil; Carbon - analysis; Ecosystem; Environmental Monitoring - methods; Estuaries; Geologic Sediments - analysis; Linear alkylbenzenes; Mixing model; Sediment; Sewage - analysis; Stable carbon isotope; Urban effluents; Water Pollutants, Chemical - analysis
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2022.120726

The Capibaribe Estuarine System (CES) is a tropical estuary located within a densely populated metropolitan region in the Brazilian Northeast, providing multiple ecosystem services including artisanal fisheries, tourism, and navigation. A significant load of domestic and industrial effluents is causing visible environmental degradation that needs to be characterized. This study evaluated the degree of contamination by domestic sewage and the relative contribution of organic carbon (OC) sources in sediments, measuring carbon-to-nitrogen atomic (C/N)a ratios, δ13C of OC, and linear alkylbenzene concentrations (LAB). The SIAR mixing model indicated that estuarine phytoplankton and sewage contribute 73% and 22% to OC, respectively, based on sedimentary (C/N)a ratios that varied from 8.5 to 13, and δ13C ranging from −25.21 to −21.63‰. This suggests that eutrophication of CES is triggered by sewage inflow. The CES was moderately contaminated by LAB, and the highest concentrations observed in the inner portion, from 287 to 1349 ng g−1 dry weight, suggests the retention of sewage. The mixing isotopic model indicated a significant dilution process of sewage-derived OC by estuarine phytoplankton. The lowest LAB in the lower estuary (317–320 ng g−1 dw) probably resulted from marine dilution. Principal component analysis demonstrated that mud regulates sedimentary OC content, and that the sewage plume regulates sedimentary LAB. High degradation of LAB isomers probably reflects the net heterotrophic condition of this system, also suggesting these compounds are introduced into CES partially degraded. Our results pointed out that degraded OM is a result of chronic and long-term sewage input. Considering the implications of sewage pollution to environmental and public health, there is an urgent need of better policies to improve domestic effluent treatment capacity, reducing contamination of estuarine environments. [Display omitted] •Estuarine phytoplankton and sewage are the main organic carbon sources to sediments.•Capibaribe Estuarine System is moderately contaminated with domestic sewage.•LAB distribution is controlled by the influence of sewage plume and the ETM.•Degraded organic matter results from chronic and long-term sewage input.