| Summary: | In 1989-1993, YugNIRO carried out investigations of the impact of undersea exploratory drilling on the ecosystem of Karkinit Bay, Crimea (Ukraine) and the adjacent shelf areas of the north-western Black Sea. Karkinit Bay and adjacent shelf zone of the Black Sea are home for wintering aggregations of sturgeons, feeding area for juvenile and adult mullets, a permanent residence for juvenile turbot, whiting, sprat. In the southern part of Karkinit Bay dense (up to 1100 g/m super(2)) mussel beds still exist, which has age composition characteristic for a virgin population. All stages of exploration on the gas bearing formation were controlled: before and during the building of the marine stationary platform, exploratory drilling and shut-in storage period, and upon completion of the assessment of the particular gas resource. During the exploratory drilling period, the levels of heavy metals (copper, lead, nickel, and cadmium) in the seabed sediments were below the maximum permissible concentrations (MPC), while the levels of mercury and chromium surpassed MPCs at individual stations by 2 and 27 times (0.17 and 27.8 mg/l, respectively). Following completion of the exploratory drilling, mercury concentrations varied from 0.14 to 0.23 mg/l and everywhere exceeded MPCs as a result of a secondary contamination of water; chromium levels dropped and varied within MPC, reaching 1.9 MPC or 1.9 mg/l at individual stations. In the seabed sediments within the region of the Marine Stationary platform, accumulation of copper, lead, and chromium was observed; during the final drilling stage, their average concentrations increased to 14.4 (copper), 6.9 (lead), 14.6 (chromium) mg/g dry weight. The highest concentrations of these metals surpassed geochemical background by factors of 4-5, 62, and 8, respectively. The spatial distribution of toxic metals with a radius of 0.1-mile distance from the exploratory well. Following completion of the exploratory drilling and related operations, a stabilisation of the ecosystem and substantial ...
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