Screening native plant species for hyperaccumulation and phytoremediation of chromium in Mardan industrial estate, Pakistan

Abstract

Industrial estates are key drivers of economic development but often contribute to environmental degradation through heavy metal contamination. This study evaluates industrial composition in the Mardan Industrial Estate and assesses chromium (Cr) accumulation in soils and associated plant species to understand contamination status and phytoremediation potential. Results showed that the estate comprises 181 registered industrial units, of which 121 are operational. The marble industry exhibited the highest production output (55-65 tons/day), followed by iron and steel, and chipboard/Formica industries, indicating their dominant contribution to industrial activity. Cr, particularly hexavalent Cr, was identified as a highly toxic contaminant exceeding permissible limits (0.5 mg/kg). Soil Cr concentrations ranged from 8.89 to 402.9 mg/kg, while plant roots and shoots accumulated 30.73-800.2 mg/kg and 0.784-765.8 mg/kg, respectively, indicating significant bioaccumulation and transfer into plant tissues. Based on bio-concentration, translocation, and accumulation indices, 29 species were classified as phytoextractors, 16 as phytostabilizers, and 5 as excluders. Strong accumulators included Sisymbrium officinale, Melilotus indicus, and Melia azedarach. Multivariate analyses (PCA and correlation heatmaps) explained up to 93.96% of variance, revealing distinct clustering patterns associated with Cr uptake, root-shoot translocation, and soil contamination gradients. The findings demonstrate severe chromium contamination in industrial soils of Mardan, with substantial uptake in diverse plant species. Several species show strong phytoremediation potential, highlighting their usefulness in environmental cleanup strategies, while also indicating potential risks of Cr entry into the food chain.