gh THE AZOV SEA: RADIATION RECEDES

The Murmansk biologists left for the radio-ecological expedition to the Azov Sea to execute a regular examination of changes in its radio-active contamination. The results are promising: the current contamination level is not increased. But this good news is only applicable to the water: the concentration of radioactive substances in uliginous sediments on the bottom on the sea is still higher than it used to be before the Chernobyl catastrophe. The scientists warn that intense exchange processes between the bottom and the water may once cause the secondary radionuclid contamination of the Azov Sea.

To obtain new data, the researchers collected water samples (one sample - 100 liters) and bottom sediment samples from six stations. The bottom sediments were dried at the temperature of 110 degrees and crumbled up. Then the samples were checked for the caesium, strontium and plutonium content. The water was also checked up for salinity to find out whether the level of contamination depended on salinity. As a result, the researchers discovered the pattern of strontium and caesium distribution in the Azov Sea.

The highest caesium content turned out to be in the area of Kerch Strait where the Azov Sea joins the Black Sea. Closer to the central part of the sea the concentration of this element becomes lower, the least concentration of caesium in in the North - in Taganrog Bay. The researchers account for such uneven radionuclid distribution by its restlessness. In the river water, caesium travels within suspended substance and precipitates in the bottom sediment - that is why the caesium content is low in Taganrog Bay where the Don and other rivers flow into. Further to the South, more and more salt water comes from the Black Sea bringing a lot of caesium. In other words, the higher the salinity of water is, the larger the content of this radioactive element is in the water.

The concentration of other radioactive element - strontium - has decreased and does not exceed now the level which existed before the Chernobyl catastrophe. However, this does not mean a completely favorable situation with this element. As a matter of fact, in the mid-1960s nuclear weapon tests took place in the air above the Azov Sea. Apparently, by early 1980s the situation improved but it is still far from ideal.

As for the strontium content in the bottom sediment, this element evidently prefers certain places. The highest content of this radionuclid was found in the location of the sea shell accumulations, as well as in silts and sands rich in calcium carbonate. Plutonium is not characterized by such selectivity - it can be found everywhere on the bottom of the Azov Sea, but its concentration is insignificant.

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