Assessment of phytoremedial potential of some commercial tree species as irrigated by wastewater

Abstract

Over population, urbanization and industrialization are profoundly polluting our environment with various types of organic and/or inorganic pollutants, especially, the heavy metals. This is the outcome of blind use of fertilizers, pesticides, petroleum products and raw wastewater for irrigation in agriculture. Urban wastewater is one of the sources of heavy metal, causing serious threat to urban and agro-ecosystems. A newly emerging phytoremedial (eco-friendly) approach is being used globally to minimize the heavy metal pollution from air, soil and wastewater. This research work was designed to examine the potential of woody plants to reduce heavy metal pollution. The present study was conducted during 2012-2014 in the Department of Forestry and Range Management, University of Agriculture, Faisalabad. The study was carried out to assess phytoremedial potential of four tree species viz: Acacia ampliceps, Acacia nilotica, Azadirachta indica and Morus alba. The randomly selected four species were linearly planted in 2008 in field experimental area, Directorate of Farms University of Agriculture, Faisalabad (Pakistan) under three different sources of irrigation (treatments) viz: canal water (IS1), domestic wastewater (IS2) and municipal wastewater (IS3). As preliminary study, plant data were collected and analyzed for growth behavior and heavy metal uptake by the tree species under each source of irrigation. Secondly, a pot experiment was conducted to study the response of the same tree species as irrigated by wastewater. Tree seedlings were grown in plastic pots by applying prescribed types of irrigations (treatments). In the third experiment, tree seedlings of four species were grown in polythene bags and subjected to irrigation water of four qualities (treatments) viz: Tap water (control), distilled water with three different levels of Cd and Pb (a- 0.02 mg Cd and 10 mg Pb L-1, b- 0.04 mg Cd and 20 mg Pb L-1, c- 0.06 mg Cd and 30 mg Pb L-1). The focus of the third study was to reasses heavy metal uptake potential of the same species under controlled conditions. Data (from three experiments) revealed that A. ampliceps got top ranking with regard to heavy metal (Cd & Pb) uptake showing no or limited growth stress. Whereas, M. alba was found least active in this regard. For instance, A. ampliceps absorbed average concentration 12.79 mg kg-1, 3.38 mg kg-1 and 1.91 mg kg-1 of Cd contents in first, second and third experiments, respectively. Similarly, it absorbed average concentration 85.93 mg kg-1, 70.93 mg kg-1 and 31.70 mg kg-1 of Pb in the same experiments, respectively. However, M. alba absorbed average concentration 4.22 mg kg-1, 1.42 mg kg- 1 and 0.49 mg kg-1 of Cd in first, second and third experiments respectively. Whereas, Pb uptake by M. alba in the same experiments was an average concentration: 27.34 mg kg-1, 12.34 mg kg-1 and 6.36 mg kg-1 respectively. Based on our findings, it was concluded that Acacia ampliceps is the best phytoremedial tree species for polluted soil and water contaminated with Cd and Pb metal. Raising A. nilotica and M. alba as browse species in not risky for our food chain system. On the other hand, A. ampliceps should not be used for forage purpose when planted with wastewater irrigation.