Predicting Heavy Metal Accumulation in Turnip (Brassica rapa var. rapa L.) Using Soil Properties: A Study of Plants Grown in Agricultural Soils Amended with Varying Levels of Biosolid

Biosolids, a byproduct of wastewater treatment, are often used as organic amendments in agricultural soils. However, the potential for heavy metal contamination of crops grown in biosolid-supplemented soils is a concern for food safety and environmental protection. The present study aimed to develop predictive models to evaluate the uptake of eight heavy metals (Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) by the shoots and roots of turnip (Brassica rapa var. rapa L.) grown in soil mixed with varying concentrations of biosolid (0, 10, 20, 30, and 40 g/kg). The concentrations of heavy metals were significantly different (p < 0.05/0.01/0.001) between the root and shoot tissues of the turnips, except for Cd (p > 0.05), indicating varying degrees of uptake by the different plant parts. Pearson correlation analysis (r-values) showed that soil properties had a strong influence on the bioconcentration and translocation factors of heavy metals in the turnips. The generated predictive equations can be used to estimate the concentrations of heavy metals in the shoots and roots of turnips grown in biosolid-amended soils, considering soil pH, organic matter, electrical conductivity, and heavy metal concentrations as independent factors. The feasibility of the model equations was confirmed by high R2 values (0.536 to 0.938 for shoots, and 0.504 to 0.787 for roots) and model efficiency (ME) values (0.512 to 0.949 for shoots, and 0.468 to 0.787 for roots). Furthermore, the results of Student’s t-tests (unpaired two-tailed) showed no statistically significant differences between the experimentally observed and predicted heavy metal concentrations in the shoot and root systems of the turnip plants. This study provides a predictive framework for assessing heavy metal uptake by turnips in biosolid-amended soils, facilitating biomonitoring efforts, and informing regulatory guidelines to ensure safe biosolid application rates that minimize risks to food safety and soil health.