Assessing the transfer factors of potentially toxic elements in primary agricultural products based on their bioavailable fractions in soil

Introducing potentially toxic elements (PTEs) into the food chain through ingesting agricultural products can be considered one of the main factors favouring human exposure to these elements, with potential health risks. The study’s main aim was to improve the understanding of the transfer dynamics of PTEs from soil to Primary Agricultural Products (PAPs). Unlike what has been done in several former studies, bioavailable fractions, instead of total concentrations, were used to assess transfer factors (TFs) of PTEs from soil toward PAPs. Further, the variability of some soil physicochemical characteristics such as organic matter (OM), grain size (GS), cation exchange capacity (CEC), pH, salinity and electrical conductivity (EC) was considered, and their potential influence on the elements’ transfer process was evaluated. Statistical analyses, including boxplots, Schoeller diagrams, Robust Principal Component Analysis (RPCA), and Multiple Regression Analysis (MRA), were employed to explore the data. On average, results showed that TF Zn > > TF Cu > TF Cd > TF Co > TF Hg > TF Pb > TF Ni > TF V > TF Se > > TF Tl, with a shared trend for all species despite differences in TF magnitudes observed. In our case, the RPCA allowed the identification of three principal components accounting for 91% of the total variance, and the MRA revealed significant influences of clay content, CEC, and OM on TFs variability, particularly for Zn and Co. The use of the bioavailable fraction of PTEs in the soil to calculate transfer factors provided new insight into the mobility along the food chain of elements, unveiling the general “propensity” of some elements to migrate to the biological compartment (e.g., Zn) and the marked resistance of others to be transfered (e.g., Tl). Our study also demonstrated that identifying physicochemical factors potentially favouring or limiting the transfer of PTEs from soil to plant is a very complex task, and even when it is successful, only a limited portion of the overall process can be explained.