SynopsisUntil the late 1970s Edinburgh and the surrounding areas employed a series of relatively short sea outfalls to dispose of sewage to tidal waters. A centralised sewage treatment facility was provided in 1977, with disposal of liquid effluent by long sea outfall. The residual wet solids are dumped at two sites in the North Sea off the Firth of Forth. The sites, one near Bell Rock (56 25N 02 10W) and one ten miles north of St Abb's Head (56 04·5N 02 07·25W) are used on a rotational basis. The macrofauna at both sites shows a normal polychaete-dominated community exhibiting the normal low number/high diversity characteristics of many unimpacted communities in the North Sea. In general, seasonal differences in mean concentrations of lead, copper and zinc in sediments were small and within the limits of statistical variation. The concentrations of mercury and cadmium were mainly low and close to the detection limits of the analytical methods employed. The monitoring data from Bell Rock and St Abb's Head demonstrate that the dumping operation has had little effect on the benthic environment and that the macrobenthos showed no signs of stress due to the addition of sewage sludge.
