Marine suspensions ability to concentrate mercury depending on its contents in the shelf water area

A.P. Stetsiuk, V.N. Egorov

The A.O. Kovalevsky Institute of Marine Biological Research of RAS,

Russian Federation, Sevastopol, Nakhimov Av., 2

E-mail: Alex-ra-777@mail.ru; egorov.ibss@yandex.ru

DOI: 10.33075/2220-5861-2018-3-123-132

UDC 546.49(262.5)

Abstract:

   Based on the results of measurements of mercury concentrations in water samples taken in the Black Sea offshore of the Crimean shelf, the dependence of the concentration of mercury on the suspended matter was determined. The trend of saturation of suspensions with mercury is recorded with an increase in its concentration in water and the coefficients of accumulation of mercury by suspensions are determined. It was found that the dependence of the accumulation coefficients on the change in mercury concentration in the water of the Crimean shelf of the Black Sea is described by the Freundlich equation. The prevailing factor of sedimentation self-purification of waters in the range of low concentrations of mercury is determined.

   The purpose of our research is to study the regularities of concentrating mercury by a suspended substance of the Black Sea and to study its role in the sedimentation self-purification of mercury contamination of waters.

   Samples were analyzed from the surface water layer from 34 stations in the period 2012 – 2017. For this work, the results of observations for the spring season are chosen.

   The results of the study showed that in the observed period of time the specific mass of the suspended matter in the marine environment ranged from 0,5 to 15,0 g∙m3, the concentration of mercury in water varied from 1,0 to 168,0 ng∙L-1, and the concentration of mercury in the suspensions was 825–23167 ng∙g-1 dry weight. The results of calculation of the accumulation coefficients, indicated an extremely high concentrating ability of mercury suspensions (Kvs = (0,023 – 7,067) ∙106). As a result, the calculated mercury pool in the suspended areas of the investigated area ranged from 1 to 98% of the total mercury content in the aquatic environment.

   Using the Michaelis-Menten equation, it was possible, based on experimental observations, to estimate the maximum rate of mercury uptake by suspensions, and also to determine the value of the Michaelis-Menten constant, which is numerically equal to the concentration of mercury in water, at which its absorption rate by suspensions was half the maximum. Dependences of changes in the concentration of pollutants (including mercury) in living and stagnant matter can also be described by the Freundlich and Langmuir equations. Our task was to verify the adequacy of the observational results for each of the above equations.

   The conducted studies as a whole made it possible to conclude the following. With increasing concentration of mercury in water, its concentration in the suspended solids tends to the saturation limit. Dependence of the accumulation coefficients on the change in mercury concentration in the water of the Crimean shelf of the Black Sea is described by the Freundlich equation, and also with a lesser degree of reliability by the Langmuir equation. The prevailing factor of sedimentation self-purification of water in the low mercury concentration in water is the concentrating ability of suspensions, and with the increase of water pollution by mercury the relative influence of the concentrating ability of suspensions decreases.

Keywords: suspended substance, mercury, concentrating ability of suspensions, the Crimean shelf of the
Black Sea, the Freundlich and Langmuir equations.

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