“…These substances are insoluble in acidic conditions, but their solubility increases with increasing pH, and as a result, they can increase the solubility, mobility, translocation, and bioavailability of HMs (Fox and Comerford 1990, Evangelou and Marsi 2001, Halim, Conte et al 2003, Marschner and Kalbitz 2003, Chen and Zhu 2006, Park, Kim et al 2013, Mani, Kumar et al 2015, Noroozisharaf and Kaviani 2018, Kleber and Lehmann 2019, Abourayya, Kaseem et al 2020, Li, Wang et al 2022. Probably, the acidic nature of humic substances plays an essential role in their reactivity and performance in alkaline soils.…”