Microbial assisted chromium mitigation: Impacts on germination, yield and quality of Amaranthus

The disposal of chromium (Cr) rich tannery sludge onto agricultural lands possesses a significant environmental threat. Oxidation of Cr often resulted in yields hexavalent chromium (Cr6+), a component that is extremely dangerous and cancer-causing. On the other hand, trivalent chromium (Cr3+) is considered to be a crucial trace element in human nutrition and is the most stable form of Cr that can be found naturally making it less toxic than hexavalent form. This study employed a pot experiment to evaluate the effects of hexavalent (Cr6+) and trivalent chromium (Cr3+) with and without the influence of microorganisms, on the germination, growth, uptake, biochemical properties and yield of Amaranthus gangeticus. Nine chromium concentrations were tested: 0, 50, 100, 150 and 200 mg/kg of Cr6+ as K₂Cr₂O₇ and 50, 100, 150 and 200 mg/kg of Cr3+ as [KCr(SO₄)₂]. These treatments were combined with four microbial treatments: a control (no microbes), Azospirillum, phosphate-solubilizing bacteria (PSB) and potassium-releasing bacteria (KRB). The results showed that irrespective forms the increasing chromium concentrations led to a consistent decline in germination, growth and yield parameters. Hexavalent chromium caused a more pronounced reduction in germination percentages compared to Cr3+, However, treatments supplemented with KRB exhibited a mitigating effect on Cr toxicity and significantly improved growth and yield parameters.