One of the biggest sources of heavy metal accumulation in the soil is phosphate fertilizers (Bolan et al. 2013; McPartland and McKernan 2017). Phosphate ions are considered to be the main carrier of heavy metal contaminants and specifically hydroponic fertilizers have been found to have the highest tendency for contamination (Karadjov 2014). Also different manures have been proven to be a source of heavy metal contamination (Singani and Ahmadi 2012).
Over one-third of the global arable lands are contaminated with heavy metals (Tripathi, Edrisi, and Abhilash 2016). More specifically in Austria, France, Hungary, Slovakia and Sweden there are some 200,000 heavy metal contaminated areas (Kumar Yadav et al. 2018).