PHYTOREMEDIATION POTENTIAL OF SELECTED ORNAMENTAL PLANTS ON POLLUTED SOILS IN ONDO AND OSUN STATE, SOUTHWESTERN, NIGERIA

Abstract

Over the years, phytoremediation has been considered a promising technology for addressing soil contamination problems and ornamentals plants are used they are not edible therefore reducing the risk of contaminants getting into the food chain. Consequently, this study was conducted to examine the phytoremediation potential of four ornamental plants in polluted soils and spiked soil with lead. A two-stage experiment was conducted at the screen house of the Department of Crop, Soil and Pest Management, the Federal University of Technology, Akure. The experiments were laid out in a Factorial Experiment in Completely Randomized Design (CRD). The first experiment was a 5 by 4 factorial in CRD. The two factors were polluted soils and Ornamental plants. The polluted soils consisted of five levels; metal scrap soil (MSS), mechanic workshop soil (MWS), dumpsite soil (DSS), gold mine soil (GMS) and forest soil (standard) while the ornamental plants consisted of four levels; Aloe vera, Aglaonema commutatum, Dieffenbachia seguine and Chlorophytum comosum. The second experiment was a 4 by 4 factorial in CRD. The two factors were a Forest soil spiked with Lead (Pb) metal at different rates (5, 10, 35 and 50 g/kg) and ornamental plants (Aloe vera, Aglaonema commutatum, Dieffenbachia seguine and Chlorophytum comosum). Ornamental plants are transplanted on the polluted soils at the screen house of Crop, Soil and Pest Management. Growth parameter such as plant height, number of leaves and fresh and dry weight were collected while the physical and chemical analysis (Soil texture, pH, organic matter) and soil heavy metal concentration – Iron (Fe), Zinc (Zn), Copper (Cu), Chromium (Cr), Cadmium (Cd) and Pb) were analyzed at the soil laboratory of the aforementioned department. Data were subjected to analysis of variance (ANOVA), means separation were done using Tukey test at 5% probability level. Result obtained from the study showed that the concentration of heavy metals in MSS (Fe - 473.41 mg/kg, Zn – 323.67 mg/kg, Cu – 348.00 mg/kg, Cr – 16.00 mg/kg, Cd – 0.33 mg/kg and Pb – 106.00 mg/kg) was highest in pre-treated soil; the lead concentration (106.00mg/kg) was above WHO soil maximum permissible levels (100mg/kg). There were significant differences in the interaction effect of ornamental plants and polluted soils for heavy metal concentrations during the experiment. The accumulation of Fe in shoot was more in D. seguine (147 mg/kg) than in all other ornamental plants and also subceeded WHO permissible limit for Fe in plants (400-500 mg/kg). A. vera had the highest accumulation of Cr in shoot than other ornamental plants (2.30 mg/kg) and exceeded WHO permissible limit for Cr in plants (1.30 mg/kg). Also, A. vera had the highest accumulation of Pb in shoot (55.4 mg/kg) and exceeded WHO permissible limit for Pb in plants (2mg/kg). The result for the second experiment showed that lead concentrations in the spiked soil released almost all at 2 MAT and further released more at 4 MAT across the treatments. Aloe vera and Chlorophytum comosum phytoextracted lead rate at 5 and 10 g/kg at 2 MAT (0.04 mg/kg), 4 MAT (0.03 mg/kg) and 6 MAT (0.01 mg/kg) than at 35 and 50g/kg. There was higher accumulation of lead (Pb) in the root than shoot of all the ornamental plants. The result of bioaccumulation and translocation factor revealed that all the ornamental plants can be considered for phytoremediation each having specificity for heavy metals in the soil. However, Chlorophytum comosum on GMS soil indicated to be hyperaccumulator of Fe in soil and as accumulator of Cd on MSS and GMS soil. Aglaonema commutatum plant hyperaccumulated Cd in the shoot on MSS soil and accumulated Cd in the shoot on GMS soil. The result of the translocation factor for spiked soil revealed that the four ornamental plants were found to be excluder of lead metal on spiked soil.