Distribution of potentially toxic soil elements along a transect across Kazakhstan

Abstract

The present study aims to investigate the distribution of selected potentially toxic elements (PTEs) in Kazakhstan's topsoils. Soil samples collected across a north-south gradient (n=40) near main highways connecting major residential/industrial areas were characterized for their As, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn content as well as for soil physio-chemical properties. The majority of the soils had neutral pH (no significant relationship between pH and PTE concentrations). The soil organic carbon was higher at the northern and farther southern parts of the transect (along with higher concentrations of PTEs in soils). As, Mn, and Ni concentrations in soils were elevated in comparison to relevant background concentrations. Critical concentrations of As, Cd, Co, Mn, and Ni (with respect to regulatory limits) were found at multiple locations, with As being particularly of potential concern (range: 8.7-42 mg × kg −1 ). The distance from the nearest settlement seems to influence the soil PTE concentrations, however the relationship is not statistically significant. In total, eight locations had statistically outlier PTE concentrations for Cd, Mn, Ni, and Zn. The overall results were comparable to similar studies across the world except that the Pb content of the study soils was less elevated. Studies on site characterization and human health risk assessment covering identified hotspots and PTEs are recommended.

Spatial and In-Depth Distribution of Soil Salinity and Heavy Metals (Pb, Zn, Cd, Ni, Cu) in Arable Irrigated Soils in Southern Kazakhstan

“…In the case of Nitot content, the EU limits were exceeded in 0.3% of the studied samples, yet the Kazakhstani limits are once again stricter and if compared to them, Nitot content in all the studied samples exceeds this threshold. Interestingly, the Kazakhstani thresholds for Cdtot, Zntot, and Nitot are noticeably higher, and in the case of Pbtot and Cutot, are equal to the natural backgrounds provided for Central Asia by Guney [29]. This observation will be further discussed in the following parts of the article.…”

“…Considering the EU thresholds for the total content of heavy metals in soils [28], 90.3% of the studied samples exceeded the threshold of 1.5 mg/kg given for Cdtot (Table 1). If we use the threshold of 0.5 mg/kg provided by the Ministry of Environment in Kazakhstan [27,29], 98.4% of the samples will exceed it. In the case of Cutot, Pbtot, and Zntot, all our results were below the EU thresholds.…”

“…The high content of Cdtot in the soils of the Shauldara massif results mainly from anthropogenic input, including inflow with irrigation water, mineral fertilizers, pesticides, eolian deposits, and other industrial sources. These inputs add to the natural background values that are already relatively high in Central Asian soils [29]. In the case of agricultural soils in the Shauldara massif, the main source of heavy metal contamination is irrigation water provided by the contaminated Syr Darya River [34].…”

Assessment of the Ecotoxicity of Pollution by Potentially Toxic Elements by Biological Indicators of Haplic Chernozem of Southern Russia (Rostov region)

“…Moreover, the study was conducted on Haplic Chernozem that is characterized by high buffer capacity with respect to chemical pollution. In soils with a lighter granulometric composition, less organic matter, and more acidic, the ecotoxicity of most pollutants will be even higher (Kolesnikov et al, 2020 , 2021 ; Guney et al, 2020 ; Minnikova et al, 2017 ). According to the degree of inhibition of biological activity in Haplic Chernozem, the studied metals formed the following series: Cd > Pb > Zn > Cu (Gromakova et al, 2017 ).…”

Potential Human Exposure to Mercury (Hg) in a Chlor-Alkali Plant Impacted Zone: Risk Characterization Using Updated Site Assessment Data

“…Hg and its common compounds (i.e., HgS (cinnabar), HgCl 2 ) can enter the environment through a variety of natural mechanisms in the Earth's crust. Anthropogenic activities such as agriculture and overland traffic, in addition to geogenic sources of PTEs, including Hg, can increase the severity of site contamination [9][10][11]. Anthropogenic sources of Hg include combustion of fossil fuels, mining activities, electricity-generating power stations, incineration, and production of chlorine along with caustic soda by chlor-alkali plants (CAPs) based on the Hg-cell technology.…”