Comparative toxicity of copper and zinc contaminated wastewater irrigation on growth, physiology, and mineral absorption of wheat.

Abstract

A comparative pot study was performed to assess the toxic effects of copper (Cu) and/or zinc (Zn) contaminated wastewater (WW) irrigation on the growth, physiology, and element concentration of wheat grown for two months. The treatments included irrigation with uncontaminated wastewater (WW) as control, Cu-contaminated WW (CuWW), Zn-contaminated WW (ZnWW), and Cu + Zn contaminated WW (CuZnWW) in a completely randomized design. Compared to ZnWW, irrigation with CuWW or CuZnWW had severe effects on growth, physiology, and mineral absorption by wheat. Irrigation with CuWW or CuZnWW reduced shoot length, root length, root and shoot dry weights by 44-45%, 54-56%, 5-6%, and 33-34%, respectively, against WW control. Similarly, these treatments diminished chlorophyll a, b, carotenoids, and SPAD by 33-34%, 59-60%, 49-51%, and 26-27%, respectively. Conversely, contaminated irrigation improved the total polyphenols, polyphenolic acids, total flavonoids, and antiradical activity, however, a maximum increase in these parameters up to 65% was observed when irrigated with ZnWW. Pearson correlation showed that the decline in growth and physiology of wheat was negatively correlated with shoot metal concentration and uptake. Dehydrogenase activity is severely hampered by CuWW or CuZnWW and to a lesser extent by ZnWW as well. These results suggest that irrigation with contaminated WW adversely affects wheat growth and physiology, however, ZnWW is found to be less toxic to wheat crops than Cu. Thereby, this data highlights the need for a tailored approach to prioritize the metal (Zn) with lower toxicity during the use of WW in irrigation practice. PRACTITIONER POINTS: Cu-contaminated wastewater (20 ppm Cu) substantially reduced the growth and physiology of wheat. Zn (80 ppm) contaminated wastewater was found lesser toxic compared to Cu. Wheat irrigation with contaminated wastewater increased biologically active compounds in wheat shoot. Contaminated wastewater affected minerals concentration in the root and shoot part of wheat. Dehydrogenase activity in soil is less affected by Zn-contaminated wastewater. Irrigation with wastewater and leftover crop residues resulted in the accumulation of organic matter in soil.