Soil quality, risk assessment and source identification of heavy metals in native and improved paddy soil and rice grains from Tamil Nadu, India.

The present study aims to assess the soil quality, source analysis, and risk assessment of heavy metals in native and improved rice paddies in Tamil Nadu, India. The mean values of DTPA-extractable heavy metal levels in native paddy soil were 0.06, 0.52, 2.61, 3.15, 0.48, 39.48, 97.61 mg kg, while improved paddy soil had values of 0.11, 1.98, 0.91, 3.21, 1.54, 20.30, 7.78 mg kg for Cd, Pb, Ni, Cu, Zn, Fe and Mn. These levels were below the acceptable limits set by Indian and European Union soil quality guidelines. All native rice varieties had grain Pb concentration ranging from 0.71 to 1.34 mg kg, but all improved rice varieties had higher levels of Cd, Pb, and Fe then prescribed limits. Nemerow pollution index (NPI) level of Ni indicated high pollution in native soil. Potential ecological risk index (RI) values of Cd indicated moderate risk in improved soil. Based on the EF and TF values, the paddy fields and rice plants are classified as 'severe enrichment' and 'accumulator' of heavy metals (Cd and Pb), respectively. The HI and THQ levels (Ni, Cd and Pb) were > 1 for both adults and children. Principal component analysis (PCA) found that PC1 eigenvalue of 5.63 (40.21%) and 6.91 (49.37%) and PC2 with 4.84 eigenvalue of 5.63 (34.56%) and 3.97 (28.37%) for native and improved soil, respectively, while cluster analysis (CA) revealed three distinct groups between the metals studied.