Accumulation of heavy metals by lettuce (Lactuca sativa L.) irrigated with different levels of wastewater of Quetta city.

Abstract

Heavy metal contamination of soils resulting from irrigation by wastewater is causing major concern due to the potential health risk involved. This study was therefore designed to investigate the heavy metal ions viz., Cu 2+ , Fe 2+ concentrations by lettuce (Lactuca sativa L.) grown in pots. This leafy vegetable was irrigated with 5 different concentrations of wastewater collected from 3 different localities viz., Chiltan town, Chiltan Ghee Mill (oil industry) and Zarghoon town of Quetta city. Tap water was used as background water. Plant samples were analyzed for their heavy metal contents using Atomic Absorption Spectroscopy (AAS). Results showed that localities, treatments and their interactions (except Cu 2+ & Pb 2+ ) generally exhibited highly significant (P≤0.01) influence on the accumulation of heavy metals. The maximum values of 9.71; 509.06; 32.47; 94.38; 8.58; 5.05 and 7.45 mg kg -1 for Cu 2+ , total Fe 2+ , Mn 2+ , Zn 2+ , Ni 2+ ,Pb 2+ , and Cd 2+ respectively, were generally obtained in highest concentration of effluents. While maximum values of 9.02; 4.47 and 7.90 mg kg -1 of Cu 2+ , Ni 2+ and Cd 2+ were obtained for Chiltan ghee mill effluents. However, maximum values i.e., 435.96 and 80.47 mg kg -1 of total Fe and Zn 2+ were recorded for Chiltan town. The highest values of 30.09 and 6.32 mg kg -1 for Mn 2+ and Pb 2+ were noted in Zarghoon town, respectively. On the basis of grand mean values,the magnitude of heavy metals detected for various metals is in order: Fe > Zn >Mn> Cu >Pb> Cd > Ni. Results further demonstrated that the total concentrations of Cu 2+ , Fe 2+ , Mn 2+ , Zn 2+ and Ni 2+ are within the recommended international standards set by WHO/FAO, but could be reached to toxic level either by the consecutive use of effluents or by increased dietary pattern of the consumers. Whereas, the amount of Pb 2+ and Cd 2+ are at par than the international maximum permissible limits. This study highlights the potential health risks associated with the cultivation and consumption of leafy vegetables on wastewater- contaminated soils. Wastewater used for irrigation around the peri-urban area of Quetta is highly polluted especially in term 2+ & Cd 2+ metals. Therefore, domestic and industrial waste of the city should be properly disposed and or recycled so as to avoid the present/ future health risks.