Environmental relaxation in response to reduced contaminant input: The case of mercury pollution in Haifa Bay, Israel

Environmental relaxation, defined as the rate of return of a polluted environment to an acceptable state following a reduction in the input of contamination, was evaluated for the case of mercury pollution in northern Haifa Bay (Israel) on the basis of the longterm record of mercury levels in sediment cores and biota. Mercury was found to decrease with a half-time of 2, 5 and 6-33 years in filter-feeding bivalves, fish and sediments, respectively, after the influx of mercury into the area (from a chlor-alkali plant) was drastically reduced. The present levels of mercury in edible fish do not represent a risk to human health. The removal of mercury from the sediments is probably by particle resuspension and subsequent seaward transport. Although the mercury concentrations in the sediments will probably remain above background for a long time, the associated ecological risk does not appear to be high. It is concluded that evaluations of the environmental relaxation of different types of ecosystems, with respect to various contaminants, may provide important input to decision-making on marine waste disposal.