Geochemical composition of agricultural soils and its link to plant Pb contents

The compositional peculiarities of the soil’s chemical environment must be taken into account to study the possibility of toxic elements (TE) to be accumulated in plants. This research covered 7 provinces (marzes) of Armenia providing around 80.1% of the national total gross agricultural production. From June to October 2019, the sampling procedure was carried out as part of the national residue monitoring program. Pb geochemical associations in agricultural soils were investigated, revealing the link between these associations and Pb contents in plants, as well as determining the source-specific transfer of Pb from soil to plants, using both compositional data analysis (CoDa) and geospatial mapping. CoDa included the combination of the results of k-means clustering and CoDa-biplot and was applied to study the relationship between the TEs and identify their geochemical associations (CoDaPack v.2.02.21 and R statistics). In addition, a hierarchical cluster analysis (HCA) was used to study the links between food Pb contents and soil TE contents in each group of sub-samples identified by k-means clustering.

The obtained results showed that the research area’s unique geology and probable chemical element release sources influenced the soil’s chemical composition. Using HCA, it was discovered that in every sub-sample, the Pb soil and plant contents were in the same cluster. Particularly, CoDa-biplot and k-means clustering enable the distinction of three distinct sub-samples. However, the geochemical associations of the elements in subsamples I and III showed that Pb plant contents were shown in a geochemical association (K, Rb, Pb, and Zn) typical of both fertilizers and potassium feldspar. In contrast, sub-sample II showed that Pb plant contents were in a geochemical association (K, Rb, Pb, and Zn) typical of carbonates. The transfer factor (TF) for the similarly higher values is observed for the sub-sample associated with the geochemical relationship of K, Rb, Pb, and Zn. Moreover, it has been demonstrated that carbonates had a negative impact on the availability of Pb in plants. This can be explained by the capacity of carbonates in sub-samples I and III to fix Pb and reduce its availability in plants. Based on the study’s findings, it is important to emphasize that further research on compositional characteristics of chemical elements via the identification of geochemical associations can enable to reveal of possible connections between the elements in various media.