Spatial and Vertical Variations and Heavy Metal Enrichments in Irrigated Soils of the Syr Darya River Watershed, Aral Sea Basin, Kazakhstan

Geochemical behavior of rare earth elements in agricultural soils along the Syr Darya River within the Aral Sea Basin

The widespread use of rare earth elements (REEs) across various industries makes them a new type of pollutant. Additionally, REEs are powerful indicators of geochemical processes. As one of the two main rivers in the Aral Sea, identifying the geochemical behavior of REEs in agricultural soils of the Syr Darya River is of great significance for subsequent indicative studies. In this study, the geochemical characteristics, influencing factors, and potential application significance of REEs in agricultural soils from three sampling areas along the Syr Darya River were analyzed using soil geography and elemental geochemical analyses. The results showed that the highest total concentration of REEs in the agricultural soil was in Area I, with a mean value of 142.49 μg/g, followed by Area III with a mean value of 124.56 μg/g, and the lowest concentration was in Area II with a mean value of 122.48 μg/g. The agricultural soils in the three regions were enriched in light rare earth elements (LREEs), with mean L/H values of 10.54, 10.13, and 10.24, respectively. The differentiation between light and heavy rare earth elements (HREEs) was also high. The concentration of REEs in agricultural soil along the Syr Darya River was primarily influenced by minerals such as monazite and zircon, rather than human activities (the pollution index of all REEs was less than 1.5). The relationship between Sm and Gd can differentiate soils impacted by agricultural activities from natural background soils. The results of this study can serve as a basis for indicative studies of REEs in Central Asia.

Heavy Metals and Related Human Health Risk Assessment for River Waters in the Issyk-Kul Basin, Kyrgyzstan, Central Asia

The water resources of Central Asia play an important role in maintaining the fragile balance of ecosystems and the sustainable development of human society. However, the lack of research on the heavy metals in river waters has a far−reaching influence on public health and the sustainable development in Central Asia. In order to reveal the possible sources of the heavy metals and to assess the associated human health risks, thirty−eight water samples were collected from the rivers of the Issyk−Kul Basin during the period with low river flow (May) and the period with high river flow (July and August), and the hydrochemical compositions and major ions of heavy metals were analyzed. No changes in hydrochemical facies were observed between the two periods and the river water type was calcium bicarbonate. Carbonate dissolution and silicate weathering controlled the variation of cations and anions in river waters from the Issyk−Kul Basin. There were some differences in the sources of heavy metals in water bodies between the two periods. During the period with low river flow, heavy metals (Cr) were closely clustered with major ions, indicating that they were mainly affected by water–rock interactions. During the period with high river flow, all heavy metals studied in this paper had different sources of major ions, and the heavy metals maybe influenced by human activities. From the human health risk assessment, the hazard quotients for all samples were less than 1, reflecting that there was no noncarcinogenic risk in the river waters of the Issyk−Kul Basin during the two sampling periods. However, the water samples with carcinogenic risk of arsenic exceeding the threshold (10⁻⁴) accounted for 21.1% of the total, indicating that there were some certain carcinogenic hazards for human health via water drinking with direct oral ingestion. The results are of certain significance for the utilization and protection of water resources in the basin as well as the protection of public health.