Abstract
The Dutos e Terminais do Centro Sul (DTCS) is one of the largest petroleum terminals of the South America located in the São Sebastião Channel (SSC) on the southeastern Brazilian coast. The aims of this study were to compare the sediment quality near the DTCS with that of several sites in the SSC region including the Araçá (AR) domestic sewage outfall and to assess the efficiency of the DTCS wastewater treatment plant. To achieve these goals, textural, geochemical, and living benthic foraminifera results were analyzed for the DTCS, AR, and SSC regions. Sediments in the DTCS area were silty with high concentrations of total organic carbon (1.7–2.4%), total nitrogen (0.2–0.3%), total sulfur (0.4–0.6%), and total (0.12–0.18%) and inorganic phosphorous (0.07–0.11%). These values were higher than those in sediments collected in the SSC and Araçá regions. The sediments’ concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the SSC and AR regions were lower than their corresponding probable effect levels (PELs). However, sediments near the DTCS were enriched with As, Cu, and Ni, whose concentrations exceeded their corresponding threshold effect levels (TELs). Around the DTCS outfall diffusers, living foraminiferal densities and diversities were lower than those for the other areas studied. In the DTCS area, it was necessary to search 50 to 190 cm3 of sediment to find 100 live specimens. In the SSC and Araçá areas, a maximum of 40 cm3 of sediment was enough to locate 100 live specimens. The lower density and diversity of living foraminifera around the DTCS than around the other areas illustrates the impact of the environmental stress caused by the presence of pollutants. These results indicate that the wastewater treatment plant efficiency is low and its discharge of pollutants from petrochemical waste liquids affects the benthic fauna around the DTCS in a potentially harmful manner.
Highlights
Aquatic environments, including coastal areas, have been affected by the exponential increase in human activities during the last century
Weak thermohaline stratification was observed at all stations excluding the reference station (SSC3; Fig 1), where the water column was homogeneous
total sulfur (TS) percentages observed for TB7, TB9 and TB10 were 4 to 6 times higher than those observed in Araca [25], 10 times higher than those of the insular side of the Sebastião Channel (SSC) [37], and 9 times higher than those of the reference station. These results suggest a local pollution source from the Dutos e Terminais Centro Sul (DTCS) effluent discharges because sulfur is an important compound of petroleum and an important potential contaminant [83]
Summary
Aquatic environments, including coastal areas, have been affected by the exponential increase in human activities during the last century. Anthropogenic contaminants are introduced into the water column in different forms. Heavy metals, which are a major source of contamination, may be introduced in particulate, colloidal, or dissolved forms [1]. They are adsorbed onto particles, after being deposited and accumulating in sediments. Owing to desorption and remobilization processes, heavy metals may be released from sediments into interstitial waters and into the water column [2], [3], [4]. Sediments may act either as sinks for or as sources of heavy metals. The evaluation of metal distribution in surface sediments is important when assessing the degree of pollution in a marine environment [5]
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