Seasonal Dynamics Of Jarosite Crystallinity And Implications For Heavy Metal Bioavailability In Agricultural Soils: Insights Into Crop Uptake And Bioremediation Strategies

Abstract Jarosite, a secondary sulfate mineral prevalent in acid mine drainage (AMD) systems and hydrometallurgical zinc-processing wastes, serves as a transient repository for heavy metals such as lead (Pb), arsenic (As), cadmium (Cd), and zinc (Zn). However, its stability is profoundly influenced by seasonal environmental fluctuations. This study investigated the crystal-chemical transformations of jarosite-rich industrial waste across wet (monsoon) and dry seasons, elucidating their ramifications for heavy metal mobility, soil contamination, crop bioaccumulation, and human health risks. Soil and waste samples were collected from a jarosite dump (Site A), adjacent agricultural soil (Site B), and a reference site (Site C) during peak dry (March 2025) and wet (July 2025) periods. Analyses encompassed physicochemical properties (pH, EC, organic carbon, CEC), X-ray diffraction for mineralogy, ICP-MS for total and bioavailable metals, BCR sequential extraction for speciation, batch dissolution experiments simulating seasonal conditions, crop metal accumulation in wheat and maize, bioaccessibility assessments, and pilot remediation trials using lime, biochar, and bentonite. Results revealed heightened jarosite dissolution and reduced crystallinity (from 0.87 to 0.80) in the dry season, fostering transformation to goethite and anglesite, with Pb and As shifting from residual (65–75%) to labile fractions (45–55%). Bioavailable Pb and As at Site A surged from 5.59 and 2.08 mg/kg (wet) to 19.52 and 7.74 mg/kg (dry), respectively. Batch experiments confirmed amplified metal release (up to 70% Pb, 54% As) at elevated temperatures (45°C) and pH (7.5). Crop grains from Site B exhibited elevated accumulation (e.g., 2.5 mg/kg Pb in wheat), yielding hazard quotients exceeding 1 for children, indicating non-carcinogenic risks. Remediation amendments reduced bioavailable metals by 55–65%, enhancing pH and CEC. These findings underscore the vulnerability of semi-arid mining ecosystems to seasonal dynamics, advocating tailored waste management and bioremediation strategies to mitigate contamination and foster sustainable agricultural practices in affected regions.