Geological appraisal of the influence area of the System for Oceanic Disposal of the Sewerage of Fortaleza, Ceará State, Brazil

Abstract

This research work was designed to make a geological appraisal of the marine substrate at the influence area of the System for Oceanic Disposal of the Sewerage of Fortaleza – SDOES, surveyed through twelve sampling stations located on the dispersion patch, from February to November, 2007, that is, at the rainy and dry seasons, respectively. Textural and compositional descriptions of the marine substrate were made and the contents of organic matter, calcium carbonate and trace metals (copper, cadmium, lead and zinc) were determined. The main objective of this research was to carry out a geological evaluation and to identify likely indicators of contamination at work on the surroundings of the SDOES zone. Its results point out to a predominant presence of a biodetritic substrate characterized by sediments whose texture varies from fine to coarse. The intensive biological activity going on at that area as a result of the sewerage-derived massive effluence of salt nutrients accounts for this type of substrate. The estimates of the organic matter contents ranged from 0.19 to 4.92%, with an overall mean of 1.44%. The calcium carbonate contents varied from 4.8 to 74.91%, having this latter value been observed on the second sampling campaign, at station number 7, nearer the coastline. The average of CaCO3 content was estimated as 29.54%. The content of copper varied from 0.05 to 2.35 µg.g-1, with an overall mean of 0.21 µg.g-1. The cadmium content was in the range of 0.05 – 6.63 µg.g-1, and its mean was 0.32 µg.g-1. As to lead, the content values ranged from 0.05 to 21.97 µg.g-1, with an overall mean of 3.26 µg.g-1. The range and mean values for zinc contents were 0.05 – 13.05 µg.g-1 and 2.85 µg.g-1, respectively.