Determination of the environmental capacity of Haifa Bay with respect to the input of mercury

Abstract

The Environmental Capacity of Haifa Bay, on the Mediterranean shoreline of Israel, has been estimated with respect to inputs of mercury. From 1956–1975, a chlor-alkali plant discharged effluent to the Bay without pollution abatement measures with a maximum discharge of 1900 kg yr −1 in 1975. From 1976 the input flux was drastically reduced until in 1981 the present level of 35 kg yr −1 was reached. It was not possible to relate any specific changes in the marine ecosystem of Haifa Bay to this particular input. Diplodus sargus is a commercially important fish, and it was decided to use it as a critical path to man. As in other fish species, mercury accumulates as a function of weight (age). A series of linear regressions of mercury content vs weight for the size-range 40–175 g were calculated. Both the slopes of the regression lines of mercury content which are measures of the rate of bioaccumulation, and the calculated concentrations in a ‘standard 150 g fish’ decreased with time in the polluted area, although the present level of 0.6 ppm is still significantly greater than the levels of 0.15 ppm in adjacent uncontaminated areas. This was attributed to elevated levels of mercury in the sediment and benthic food chain. A simple linear regression was made between the mercury content in the muscle of Diplodus sargus and the mercury input to Haifa Bay over the preceding 3 yr (the estimated age of a 150 g fish). If the unacceptable level of mercury in the fish is taken as 1 ppm (US EPA), then the level of mercury in the Bay is now acceptable. If, however, the action level is 0.3 ppm (Preston & Portmann, 1981), then despite the installation of pollution abatement measures, the mercury levels in the Bay are still considered to be unacceptably high. It is premature, even in Haifa Bay, to use the concept of Environmental Capacity as a basis for management decisions. However this concept is very useful as a framework for designing scientific studies for examining the problems of waste disposal in the sea.