Comparative bacteriological valorisation of pollution and some durable pollutants of seawater in eastern region of Adriatic coast for period 1970-1973
Abstract
We performed bacteriological valorisation of the polluted sea in the narrowest region of coast of the eastern Adriatic from Kopar to Ulcinj, in the period from 1970 to 1973. For that purpose, we determined number of heterotrophic bacteria and the most probable number of coliforms, at 99 stations, in postinvernal and postestival period. We also measured the quantity of mineral oils and phenols as more durable pollutants, at the same stations. Besides that, we measured the same parameters at 16 stations of some Adriatic islands.
The contamination with heterotrophic bacteria is not every where the same; it ranges from 500 to 10.000/ml. It is the greatest in the region of the strongest effluent sources of the organic waste, in ports and at big settlements; and it is the smallest in the coast region that is in direct contact with the open sea (Istria, South littoral), and in the closed canals with submarine springs of fresh water (the canals at the foot of Velebit and Biokovo). The number of these bacteria is remarcably increasing in postestival period, in the relation to postinvernal period.
The regions of Rijeka, Zadar, Split and Dubrovnik are separated as main sources of contamination. In each of these regions exists a contamination maximum, and the intensity of contamination is gradually decreasing from that maximum, in the direction of north and south. The regions of Rijeka and Split are occupying the broadest zone. Maximal and minimal values of heterotrophic bacteria are monotonously changing, only the differences are greater in the region of Istria and North littoral than in the middle and south Adriatic; that is connected with temperature amplitudes which are larger in north regions than towards the south.
The highest values of MPN were also established near the strongest effluent sources, and reached in that case more than 2.400.000/l of seawater. In other regions, these values were remarkably lower. The number of coliforms is increasing in postestival period at all stations without exception. At many of the stations we couldn’t establish any coliform bacteria in postinvernal period, and only in a few stations we could not establish any coliform bacteria in postinvernal as well as in postestival period.
There are not considerable differences in oscillations of minimal and maximal values of MPN between northern and southern regions. They run mainly monotonously, without greater amplitudes at individual stations. That can be connected with the constant influence of strong effluents during the whole year, in regions of the biggest settlements. Out of the influence of effluents, the number of coliforms is rapidly decreasing because of the weak adaptability of coliform bacteria to the conditions of seawater. For the same reasons, all the regions that are far from the influence of the sewage waters, are very weakly or even not at all contaminated with coliform bacteria. According to these data, we should consider also the mouths of great rivers, the strong sources of contamination with coliforms.
Preliminary data for the stations of some insular regions, show considerably reduced bacteriological contamination on island coasts, related to regions of continental coast. That is valid for heterotrophic as well as for coliform bacteria.
The quantity of mineral oils ranged usually from 1 to 2 mg/l at most stations, exceptionally from 3 to 6 mg/l. Just once it was measured 16 mg/l.
Phenols were found at most stations, at least in one of the two examined periods. They were not established at all on several stations that were in regions directly influenced by the open sea (west Istria, Montenegrin littoral) and by the river or some other kind of fresh water (submarine springs). We established, as a rule, a higher quantity in postinvernal, than in postestival period. Opposite mineral oils, the measured quantities of phenols differ a great deal at different places and range from 0 to 156 µg/l.
Comparing maximal and minimal quantities of mineral oils with maximal quantities of phenols, we could notice, in most cases, that the quantity of phenols increases together with that of mineral oils. That succeeds in regions of strongest contamination of seawater with these pollutants. There was also established that there exists, as a rule, a little difference between the maximal, and minimal value in quantity of mineral oils. Phenols, again, stay in large quantities in bays, where also bigger quantities of mineral oils were once measured.
We compared also mean values of number of heterotrophic bacteria, with, the mean values of measured quantities of mineral oils and phenols on single stations. According to that comparison, there was established on most stations that variations in quantity of measured pollutants follow, as a rule, also the changes in number of bacteria. On some stations, it was also noticed that, with the diminished quantity of measured pollutants, the number of heterotrophic bacteria strongly increases; on the other, there was established strongly diminished number of heterotrophic bacteria with the hightened quantity of pollutants, which indicates the possibility of some bactericidal activity of these pollutants.
Preliminary data about present quantity of mineral oils and phenols in seawater from some of our islands, refer to presumption, that the waters that wash our islands are, as a rule, contaminated. more or less, with these pollutants. Measured quantities of mineral oils in these regions ranged from 0,2 to 12,8 mg/, and phenols from 0 to 28 µg/.
