Predicting bioavailable barium transfer in soil-bok choy systems: A study induced by shale gas extraction in Chongqing, China

Barium (Ba) is a significant contaminant from shale gas extraction and is also used in various other industries. However, there has been very limited attention paid to Ba. Elucidating the Ba in soil-crop system are of great significance for both human health risk assessment and pollution control. In this study, the bioavailability of Ba in soils was studied by using various characterization methods. Then the major factors dominating the transfer of Ba in soil-bok choy system and a suitable predicted model was derived. The results showed that Ba was mainly accumulated in the roots (transfer factor < 0.3). The relationships between Ba in shoots and the bioavailability of Ba characterizing with different methods increased in the order of CH₃COOH (R² = 0.81) < ethylenediamine tetraacetic acid (R² = 0.87) < pore water (R² = 0.89) < diffusive gradients in thin film (R² = 0.90) < CaCl₂ (R² = 0.91). The major soil properties affecting Ba in shoots were pH (r = -0.32, P > 0.05), cation exchange capacity (r = -0.43, P < 0.01) and labile Al (r = 0.38, P < 0.05). Bioavailability of Ba can preferably model the Ba transfer in soil-bok choy system. The best reliable model was LogBa[shoot] = 0.591LogBa[soil-Pore water] + 1.749 (R² = 0.963, P < 0.001). This model without measuring soil physicochemical properties, making it easier and more convenient to use in practice. Overall, these results highlight the role of metal bioavailability in predicting their transfer in soil-plant systems.