Aim: To assess the phytoremediation potential of Cyperus esculentus and Phyllanthus amarus in crude oil polluted soil and ascertain the enhancement of augmented microbes (fungi).
Study Design: The study employs experimental design, statistical analysis of the data and interpretation.
Place and Duration of Study: Rivers State University demonstration farmland in Nkpolu- Oroworukwo, Mile 3 Diobu area of Port Harcourt, was used for this study. The piece of land is situated at Longitude 4°48’18.50” N and Latitude 6ᵒ58’39.12” E measuring 5.4864 m x 5.1816 m with a total area of 28.4283 square meter. Phytoremediation process monitoring lasted for 240 days, analyses were carried out weekly at 30 days’ interval.
Methodology: Seven (7) experimental plots (two Control (Unpolluted and polluted soil) and five polluted amended/treated plots) employing Randomized Block Design (each having dimensions: 100 x 50 x 30 cm LxBxH) were formed and mapped out on agricultural soil and left fallow for 6 days before contamination on the seventh day; after which it was allowed for 21 days for proper contamination and exposure to natural environmental factors (to mimic soil crude oil spill site); thereafter bioaugmenting organisms were applied. Baseline studies were carried out on the top soil before and after contamination, major parameters monitored and assessed were Total Petroleum Hydrocarbon (TPH) uptake by plant roots and stem, Polycyclic Aromatic Hydrocarbon (PAHs) and TPH reduction in soil. Other physicochemical analyzed in the soil of different plots were pH, Electrical Conductivity, Moisture Content, Total Nitrogen, Available Phosphorus, Potassium, Total Organic Carbon, Plant Height, Iron, Lead at regular intervals; days 1, 60, 90, 120, 150, 180, 210 & 240. Application of augmenting organisms was to enhance phytoremediation by test plant Cyperus esculentus (Cyp) and Phyllanthus amarus (Phy). The rate of phytoremediation was estimated from percentage (%) uptake of Total petroleum hydrocarbon (TPH) in plant roots and stem from day 1 -240; while percentage (%) reduction of TPH and PAHs in soil was estimated from day 1 to the residual at day 240.
Results: The test plants decreased significant amount of crude oil as revealed in TPH uptake in their roots and Stem. Mean amount and percentage Total Petroleum Hydrocarbon (TPH) uptake by Cyperus esculentus roots and stem were; 152.33±50.34mg/kg, 12.57±4.16% and 201.13±8.80mg/kg, 13.27±0.58% respectively; while that of Phyllanthus amarus roots and stem were 141.50±35.62mg/kg, 11.68±2.94% and 174.44±19.98mg/kg, 11.51±1.32% respectively. Similar trend was observed in the control plots were TPH uptake by Cyperus esculentus roots and stem were; 24.2mg/kg, 2.00% and 20.01mg/kg, 1.32% respectively while in control plot of Phyllanthus amarus TPH uptake by roots and stem were 23.19mg/kg, 1.91% and 19.80mg/kg, 1.31% respectively. Comparatively, uptake of TPH was higher in plant stem than roots. From the initial TPH contamination value of 5503.00mg/kg , Total Petroleum Hydrocarbon Reduction and % Hydrocarbon Reduction in soil at 240 days in the different treatment plots in a decreasing order were as follows: PS+AN+MR+SMS+Phy (5470.9mg/kg; 99.43%) >PS+MR+SMS+Phy (5460.60mg/kg; 99.23%) >PS+AN+MR+Phy (5451.30mg/kg; 99.06%) >PS+MR+Cyp (5448.30mg/kg; 99.01%) >PS+AN+MR+Cyp (5440.00mg/kg; 98.86%) >PS+AN+Phy (5422.905mg/kg; 98.54%) >PS+Cyp (no amendment) (5380.90mg/kg; 97.78%). Comparative evaluation revealed higher reduction of PAHs in soil (plot) planted with Phyllanthus amarus. Highest PAHs reduction in soil was seen in PS+AN+MR+SMS+Phy (31.3mg/kg; 65.89%) while least was recorded in PS+ Cyp (no amendment) (23.4mg/kg, 49.26%).
Conclusion: it was observed that plots planted with Cyperus esculentus (TPH 5492.75±76.36mg/kg) showed higher reduction of TPH from soil than those planted with Phyllanthus amarus (TPH 5449.72±18.27mg/kg); while PAHs degradation/reduction in plots planted with Phyllantus amarus (PAHs 28.72±2.74mg/kg; 60.46±5.77%) was higher than plots planted with Cyperus esculentus (PAHs 25.77±2.12mg/kg, 54.24±4.47%). More so, plots amended with augmentating microbes showed significant higher percentage reduction in hydrocarbon in the polluted soil than unamended polluted soil. It is therefore recommended that Cyperus esculentus is a suitable plant species for phytoremediation of crude oil contaminated soil with high TPH value while Phyllanthus amarus is the best option for phytoremediation of polluted soil with high PAHs value, in combination with augmenting microbes.