Assessment of heavy metal status and identification of source in soils under intensive vegetable growing areas of Brahmaputra valley, North East India

This study investigated the content of Cd, Pb, Cr, and Ni in the soils of intensive vegetable growing areas of the Brahmaputra valley, North East India, to assess their status and detect any buildup of metals due to long-term and continuous application of agrochemicals and organic manures. The content of heavy metals was determined in eighty composite surface soil samples (0–20 cm) collected from eight different locations of the valley having a history of more than forty years of vegetable production. This finding is novel as no comprehensive investigation has been done till date in respect of the content of heavy metals in the intensive vegetable growing areas of Brahmaputra valley. The locations are considered free from any pollution caused by industrial effluent or urbanization processes. The investigational data showed that the content of Cd, Pb, Cr, and Ni in the soils ranged from 0.43 to 3.24, 6.00 to 22.90, 3.00 to 15.24, and 3.30 to 14.30 mg kg⁻¹, respectively. The overall mean values of the heavy metals showed a decreasing order of Pb (14.79 mg kg⁻¹) > Cr (8.87 mg kg⁻¹) > Ni (8.37 mg kg⁻¹) > Cd (1.43 mg kg⁻¹). The findings of the study indicated significant enrichment of the metals in the surface soils over the local background values of the elements measured in the C horizon. Though the concentrations of Pb, Cr, and Ni of the soils were well below the reference levels used in different countries, Cd showed distinctly higher value with maximum enrichment level. The soils were categorized as slightly to moderately polluted based on different pollution indices. Based on the ecological risk index, soils were in the low-risk category, but in respect of Cd, most of the soils fell under the moderately risky category. Multivariate analysis suggested the predominance of lithogenic influence on the content of Pb, Ni, and Cr while Cd content bears a distinct signature of the anthropogenic source. The buildup of Cd in the studied soils is a matter of critical concern and needs proper monitoring and management strategies to avoid any potential detrimental effect on soil, crop, and human health.