Effects of Natural and HDTMA-Br-Modified Zeolite on Cr Accumulation in Apium graveolens Grown in Cr(VI)-Spiked Soils

Hexavalent chromium (Cr(VI)) contamination in agricultural soils poses a significant risk to environmental and food safety owing to its high mobility and acute toxicity. To investigate possible mitigation strategies, a greenhouse pot experiment was conducted using sandy loam and silty loam soils spiked with Cr(VI) at 30 mg kg−1 and amended with natural clinoptilolite and modified HDTMA-Br (hexadecyl-trimethyl-ammonium-bromide) zeolite, while celery (Apium graveolens) was cultivated to assess chromium bioavailability and plant accumulation. Hexavalent chromium concentrations declined in all treatments (up to 88.2% in sandy loam and 73.5% in silty loam), indicating progressive reduction to Cr(III), although amendment effectiveness varied by soil type. In addition, celery accumulated extremely high chromium concentrations, particularly in sandy loam soil, where root Cr(VI) reached 1776 mg kg−1, indicating substantial safety concerns. Translocation factor values were below 1 across treatments, indicating limited relocation of Cr from roots to shoots. In the zeolite treatments, Cr(VI) concentrations in aboveground biomass decreased; however, plant uptake was not completely inhibited. Nonetheless, the high bioaccumulation factor (Cr in plant over available Cr in soil) of as high as 34 in the Cr(VI)-amended treatment indicated an uptake potential under Cr load. We conclude that modified zeolite was successful in mitigating Cr(VI) uptake in plants. Further investigation on the effectiveness of the materials in open-field conditions is required to establish a remediation framework for Cr species