DISTRIBUTION, ACCUMULATION AND BIOINDICATION OF HEAVY METALS IN THE SOIL-PLANT SYSTEM OF THE DON RIVER ESTUARINE REGION, RUSSIA

ABSTRACT

The estuarine region of the Don River is a unique area occupied by a complex natural-technogenic system of interacting natural, urbanized, and agrarian ecosystems. The aim of this work was to study the level and degree of mobility of heavy metals (HMs) in the soil-plant system and to perform bioindication observations in the Don River estuarine region and the Russian sector of the Taganrog Bay coast. The soil cover is represented by following soils types: Fluvisols, Haplic Chernozem, Arenosol, Solonchak. The following higher plants were sampled: Phragmites australis Cav., Typha angustifolia L., Carex riparia Curtis, Cichorium intybus L., Bolboschoenus maritimus L. Palla, and Rumex confertus Willd. The gross content of HMs in soils was determined by X-ray-fluorescent technique. The concentration of HMs mobile forms was extracted using 1 N NH4Ac, pH 4.8. The mineralization of plant samples was performed by the dry ashing method. HMs were extracted from ash with 20% HCl. The total contents of HMs in the soil may be described with a successively decreasing series: Mn > Cr > Zn > Ni > Cu > Pb > As > Cd. Contamination of Fluvisols soils in the estuarine zone with mobile Сu, Zn, Pb, and Cd has been revealed, which is confirmed by the high bioavailability of Cu and Zn and, to a lesser degree, Cd and Pb accumulating in the tissues of macrophytic plants. Data on the translocation of elements to plant organs have showed their predominant accumulation in the roots. Bioindication by the morphofunctional parameters of macrophytic plants (with a Typha L. species as an example) can be used for revealing the existence of impact zones with elevated contents of metals in aquatic ecosystems. It was found that the contamination of topsoils with Zn, Pb, Cu, Ni, and As is due to the anthropogenic factor related to aerotechnogenic input, excessive discharge of industrial and municipal wastewater, and leaching of mineral fertilizers and pesticides from irrigation systems. The high content of Cr in the soils is mainly related to the lithogenic factor and, hence, has a natural source.

Keywords: Heavy metals, soil, plants, estuarine region, bioindication