Disposal of sewage sludge at the continental shelf of Israel

The results of four years of monitoring at a sewage sludge disposal site did not reveal any influence on the marine environment. Implementation of an improved sampling scheme helped to delimitate the area affected by sewage sludge disposal both concerning water quality and heavy metal contents in the sediments. The new sampling scheme showed that water quality parameters depicted a momentary picture of the sewage sludge dispersion pattern. Increased turbidity and elevated concentrations of o-phosphate and chlorophyll-a were detected at the sewage plume emanating from the outfall. The new sampling scheme also detected mercury and cadmium enrichment in the sediments in the area. The spatial distribution of cadmium delimited the area affected by the sludge, covering about 1.3 km(2) of the sea floor, and described the long-term influence of the sludge in the area.