Abstract
Increasing anthropogenic influences on the environment has caused negative changes in natural ecosystems and soil contamination with potentially toxic metals has become a worrying issue at global level, due to the negative impact on the environment and human health. For the purpose of assessing soil contamination in the riparian areas of the Lower Danube River, a number of 144 soil samples were collected twice a year, in the period of June 2013 � December 2016, from 9 monitoring locations, from 0.05 m and 0.3 m depths, and the following indicators: Cr, Cu, Mn, Ni, Pb, Zn, including Ca, Mg, Corg, SO42- and humus content have been monitored. The soil was sampled, conserved and analysed according to the European standards in force. Metal concentrations were determined using flame (FAAS) and graphite furnace (GFAAS) atomic absorption spectrometry after �aqua regia� digestion of dried, homogenised and 0.5 mm sieved soil sub-samples. Comparing the average concentration values of the analysed potentially toxic metals, a decreasing tendency following the order Cr]Pb]Ni]Cu]Zn]Mn was observed and by reporting the average values at the normal limits, the order Zn]Cu]Mn]Ni]Pb]Cr of magnitude was obtained. To investigate possible correlations and interdependencies of potentially toxic metals content in the riparian soil, multivariate statistical methods were used. After applying Principal Component Analysis (PCA), 3 main components were identified, with a combined share of about 74 % of the original data-set variance. It was observed that during the monitoring period the average values of the all monitored elements from the studied soils were slightly below the normal reference values, according to the national legislation.
Highlights
Increasing anthropogenic influences on the environment has caused negative changes in natural ecosystems and soil contamination with potentially toxic metals has become a worrying issue at global level, due to the negative impact on the environment and human health
The results showed that all 6 metals (Cr, Cu, Mn, Ni, Pb indicators and a descriptive analysis regarding behaviour and Zn) were situated below the normal values from the of potentially toxic metals in the riparian soil of the Lower national legislation
The order of performed using the Principal Component Analysis (PCA) absolute average values observed in this study is Cr> Pb>
Summary
The monitoring sites are located along the lower area of the Danube River (Fig. 1), between Calarasi (km 375) and Braila (km 175), where hydro-technical works were carried out to meet the recommendations of the Danube. The organic carbon content was extrapolated from the volumetric determination of unspent oxidant after the sample thermal treatment in the presence of a known quantity of potassium bichromate and sulphuric acid oxidant mixture. The pH, conductivity and soluble salts of calcium, magnesium and sulphates of the soil samples were determined from the 1:5 (soil weight: distilled water) aqueous extract. All reagents used in this study were of analytical grade and the all laboratory glassware used was pre-washed according to each method’s prescription and rinsed with double distilled or ultra-pure water before use.
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