Assessing the role of PGPR in spinach productivity and health risks in the context of wastewater irrigation

Sewage water, valued for its nutrient content, has become a common irrigation source for farming communities near urban areas. However, its utilization poses challenges due to diverse pollutants, especially toxic heavy metals like Pb, Cd, Cr, Cu, Mn, and Ni. This study investigates the physicochemical properties of canal, mixed, and sewage water used in irrigation, assessing their impact on soil, spinach productivity, nutrient and heavy metal accumulation, and potential health risks linked to harvested crops. Metal-resistant bacteria, including Bacillus megaterium (N8), Bacillus safensis (N11), Bacillus sp. (N18), and Bacillus megaterium (N29), were examined for their role in mitigating heavy metal effects on soil and crops. Water quality analysis shows safe pH levels, but elevated electrical conductivity (EC) and sodium adsorption ratio (SAR) in mixed and sewage water raise concerns about their suitability for irrigation. Micronutrient levels are notably high in sewage and mixed water, emphasizing their significance for irrigation. Heavy metal analysis reveals toxic level of Cd, Pb, Cr, and Ni concentrations in sewage water, highlighting contamination risks. Inoculation with metal-resistant bacteria (N11) proves promising in improving soil nutrients (Fe - 20.7 mg kg-1, Zn - 13.7 mg kg-1, N – 0.32%, P – 17.3 mg kg-1 and K – 173 mg kg-1), reducing heavy metal accumulation i.e., Pb (-11%), Cd (-12%), Cr (-8%), Ni (-5%), Cu (-6%) and Mn (-6%), and enhancing spinach growth such as plant height (26%), shoot fresh biomass (23%) and shoot dry biomass (25 %). The investigation described the elevated nutrient and heavy metal concentrations in spinach irrigated with sewage and mixed water. However, inoculation with metal-resistant bacteria emerges as a sustainable solution, maintaining bioaccumulation and health risk index (HRI) within permissible limits, positioning them as a reliable inoculum source for vegetable cultivation using sewage water.