Evaluation of heavy metal-induced stress in Brassica rapa treated with tannery-borne wastewater from Kasur, Pakistan

Abstract

This study investigated the effects on mustard plants of wastewater from leather tanneries in Kasur over 15, 30, and 45 days. The sample population was grouped as T0, T1, T2, T3, and T4, given zero (controls), low, moderate, high, and maximum doses of wastewater, respectively. Effluent analysis revealed excess levels of chromium, lead, manganese, and nickel. Metals accumulated chiefly within the plant roots, indicating functional primary defenses. Growth was inhibited at all stages of harvest: average shoot growth was minimally affected in T2 plants (19-57%), and maximally effected in T4 plants (42-74.5%). Root elongation diminished after 30 days (38-61%). Maximal loss of dry weight was recorded in T4 shoots (75.5% and 63% after 15 and 45 days, respectively), and in T1 and T3 after 30 days (61%). Dry root weights declined by at least 33%, 25%, and 19% after 15, 30, and 45 days of treatment, respectively. Leaf area declined in test plants by >300%, 34%, and 30% on average at 15, 30, and 45 days, respectively. Protein levels fell in the majority of test samples, with T4 plants exhibiting decreases averaging 70%, 56%, and 60% after 15, 30, and 45 days, respectively. Significant (p<0.05) test H2O2 and MDA levels indicated overproduction of reactive oxygen species (ROS). The activities of superoxide dismutase (SOD EC 1.15.1.1), ascorbate peroxidase (APX EC 1.11.1.11), ascorbic acid, and catalase (CAT EC 1.11.1.7) were significantly (p<0.05) heightened. These results demonstrated the substantial effects of metals on growth and biochemical function in plants irrigated with tannery effluent.