PHYTOREMEDIATION OF HYDROCARBON POLLUTED SOIL USING KENAF (HIBISCUS CANNABINUS L.) PLANT

ABSTRACT

Contamination of existing and potential agricultural lands is a major problem associated with the processing and distribution of crude and refined petroleum products in many oil producing countries like Nigeria. Hydrocarbon contaminants in soil are potentially phytotoxic to plants and can  interfere  with  plant  establishment  and  growth  as  well  as  other  potential  land  uses. Pollution control strategies involving physico-chemical methods are usually expensive and have often aggravated the problem rather than eliminate it. Phytoremediation is recently being favoured as a good option for the remediation of polluted sites and has proven to be a better alternative; hence there is  the need to  identify various plants especially native ones with potential for the phytoremediation of petroleum-polluted soils. The objectives of this study were to plant Kenaf (Hibiscus cannabinus L.) in a three media of simulated diesel polluted soil samples – soil amended with compost (Sample A), soil amended with fertilizer (Sample B) and unamended soil (Sample C); monitor the rate of reduction of TPH in the soil samples; determine pollutant concentrations in the plant parts and; and to identify the medium most suitable for the effective breakdown of hydrocarbons in the contaminated soils. From an initial TPH concentration of 32387.68 ± 15.70 mg/kg, a Total Petroleum Hydrocarbon (TPH) reduction of 68.14 % was recorded in sample A while a reduction in TPH of 65.13 and 12.12 % were recorded in soil samples B and C respectively after 15 weeks of planting. Analysis of variance (ANOVA) carried out showed a significant different (P<0.05) in the TPH in the soil samples A (10319.53 ± 284.25 mg/kg), B (11293.85 ± 446.75 mg/kg) and C (28462.77 ± 90.95mg/kg) after 15 weeks of planting. Predictive models were developed using regression analysis to predict the TPH reduction in the three soil samples with time. A strong negative correlation (P<0.05) were observed (R2  for sample A = 0.9687, R2  for sample B = 0.9614 and R2  for sample C = 0.8600). Analysis of contaminant accumulation in the plant parts revealed that 405.45 ± 4.59, 126.85 ± 3.15 and 273.39 ± 4.32 mg/kg were recorded in the root, stem and leaf parts respectively. The results showed that a total of 57.44, 17.97 and 38.76 % of the contaminant were stored in the root, stem and leaf of Kenaf (Hibiscus cannabinus L.) plant. Generally, the plant showed no adverse growth effect, hence presents itself as a good candidate for phytoremediation of diesel contaminated soil samples amended with compost and fertilizer.

CHAPTER 1

1.0 INTRODUCTION

Soil is a fundamental and irreplaceable natural resource which provides a variety of ecosystem services and is the essential link between the components air, bedrock, water and biota that make up our environment. Contaminated land is defined as sites having levels of contaminants present in the soil that pose a significant possibility of harm to the ecosystem (DEFRA, 2009). There are a significant number of petroleum hydrocarbon impacted sites across the world resulting from a wide range of past industrial, military, and petroleum production, and distribution practices (Total Petroleum Hydrocarbon Criteria Working Group Series, 1998). The chemical composition of petroleum products is complex and varied and changes over time and distance when released to the environment (Bellmann & Otto, 2003). Oil pollution in soils can cause interference with the ecosystem and in most cases causes the non-productive use of land. The European Commission (2002; 2006a; 2006b) has identified soil contamination as one of eight major threats to European soils. Contaminants can enter the soil from points (local) and diffuse sources (DEFRA, 2009). It is not easy to estimate the costs of the soil contamination in terms of rehabilitating and restoring due to the lack of sufficient quantitative and qualitative data, but studies have pointed out that soil contamination results in great costs to society (European Commission, 2006c).

Global industrialization over the past centuries has resulted in widespread contamination of the environment with organic and inorganic wastes. Contaminated land has generally resulted from industrial activities connected with the production, use, and disposal of substances potentially hazardous  to  the  environment.  The  problem  is  worldwide, and  the  estimated  number  of contaminated sites is significant and increasing (Mougin, 2002; Kaimi et al., 2006). Soil contaminants include heavy metals, mineral pollutants, monocyclic aromatic hydrocarbons, phenolic compounds, polycyclic aromatic hydrocarbons (PAHs), chlorinated hydrocarbons, pesticides and other pollutants such as mineral oils and gasoline (Beyer 1990). Accurate detail

regarding the extent of hydrocarbon contamination in the terrestrial environment has been difficult to quantify because of the unintentional nature of the contamination (largely through accidental spillage or distribution line vandals).

In more recent years, as recognition grew of the damage around the world from decades of an industrial economy and extensive use of chemicals, so did interest in finding technologies that could address the residual contamination (McCutcheon & Schnoor, 2003). Many methods can be used for the  remediation of  oil pollution.  Methods of  oil  pollution remediation in the environment can be done in three ways i.e. physical, chemical and biological (Okoh & Trejo- Hernandez, 2010). Soil microbes as well as plants and biota are effective indicators to reflect the levels of soil contamination. They are capable of degrading or retaining more than 99% of all the types of soil pollutants (EA, 2006) and preventing them from entering the wider environment. However, when the amount of contaminants exceeds the buffering capacity of a soil, it leads to a long-term negative impact on soil quality and biodiversity, and also damages to its functions as a producer of fiber, fuel and food. Once the contaminants enter the food chain, they can become a threat to human health.

There have been increasing international efforts to remediate contaminated sites using “green” technologies, either as a response to the risk of adverse health or environmental effects or to enable site redevelopment (Vidali, 2001). Phytoremediation is a broad term that has been in use since 1991 to describe the use of plants to reduce the volume, mobility, or toxicity of contaminants in soil, groundwater, or other contaminated media (McCutcheon & Schnoor,

2003).  Phytoremediation is  an  emerging  technology  that  uses  various  plants  to  degrade, extract, contain, or immobilize contaminants from soil and water. This technology has been receiving attention lately as an innovative, cost-effective and widely accepted alternative to the more established treatment methods used at hazardous waste sites (U.S. EPA, 2000). It is suitable  for  low  to  moderate soil  contamination over  large  areas, and  to sites  with  large volumes of groundwater with low  levels of contamination. It takes advantage of a plant’s

natural ability to absorb, accumulate, or metabolize contaminants from the soil or other media in which it grows.

1.1 Problem Statement

Contamination of existing and potential agricultural lands is a major problem associated with the processing and distribution of crude and refined petroleum products in many oil producing countries like Nigeria (Ayotamuno et al., 2006). Since the exploration of crude oil in Nigeria, with the influx of many oil firms, there has been high tendency of and spillage of oil onto the ground and also into water bodies. The country has over the years experienced environmental pollution of different forms especially in the Niger-Delta region of the country, which has resulted in the formation of many militant groups fighting for compensation and better management of their polluted lands and water bodies. Efforts are being made by both governmental  and  non-governmental  organizations  in  the  drive  towards  finding  a  lasting solution to this oil pollution menace in the south-south region of the country as evidenced by programs initiated by the Niger Delta Development Commission.

Hydrocarbon contaminants in soil are potentially phytotoxic to plants and can interfere with plant establishment and growth (Adam and Duncan, 1999). The problems of pollution have led to the exploration of many remedial approaches to effect the clean-up of the polluted soils. Pollution control strategies involving physico-chemical methods have often aggravated the problem rather than eliminate it. Numerous sites are contaminated worldwide with crude or refined oil in different countries. Hence, there is a vast need of various plants especially native ones for the phytoremediation of petroleum-polluted soils.

1.2 Objectives of the Study

The general objective of this study is to assess the potential of the use of a Nigerian native plant (Kenaf (Hibiscus cannabinus L.)) in the phytoremediation of a simulated petroleum hydrocarbon (PHC) contaminated soil.

The specific objectives of the study are:

i.           To plant Kenaf (Hibiscus cannabinus L.) in a three media of simulated diesel polluted soil samples – soil treated with fertilizer (urea and sulphate of ammonia), treated with compost and untreated.

ii.          To monitor the rate of reduction of TPH in the soil samples with time;

iii.         To determine pollutant concentration in the plants parts and to identify parts where the pollutant is stored;

iv.         To identify which media combinations is most suitable for the effective breakdown of diesel in the contaminated soil samples.

1.3 Project Justification

Phytoremediation  technologies  are  in  the  early  stages  of  development,  with  laboratory research and limited field trials being conducted to determine processes and refine methods. Additional research, including genetic engineering, is being conducted to improve the natural capabilities of plants to perform remediation functions and to investigate other plants with potential phytoremediation applications (Ralinda & Miller, 1996). Although phytoremediation may not be the perfect remedial solution that some envisioned when its use at hazardous waste  sites  was  first  pioneered, its  implementation continues  to  be  appropriate  or  even preferable at a variety of sites. As the technology matures and its use expands beyond research laboratories and government-funded remediation, site owners and consultants will want comparative data on phytoremediation to determine its appropriateness for a particular site (Amanda, 2006).

Growing awareness of the harm that pollutants do to the soil as well as to the whole ecological chain has led to more research into how to clean up contaminated sites. Due to the great diversity of pollutants, however, there is no common solution to solve all types of soil contamination. Therefore studies related to petroleum hydrocarbon contamination of soil and its biological cleanup is of great importance. The provision of a viable phytoremediation technology would offer an economically feasible and environmentally sustainable option for the remediation of hydrocarbon contaminated sites in Nigeria especially in the south–south

region of the country. This research work, therefore, seeks to assess the efficiency of phytoremediation technology of the hydrocarbon contaminated soil as an effective method of remediating oil polluted soil. The findings will be useful in the remediation of oil contaminated soils  in Niger-Delta region  of the  country and  any other  oil polluted part of the country. Biodegradation is recently being favoured as a good option for the remediation of polluted sites mainly because it uses inexpensive equipment, environmentally friendly and simple. Phytoremediation is one of the forms of biodegradation which involves the in situ use of plants and associated microbes for the remediation of polluted sites. It has been evaluated by several research studies to remediate petroleum polluted soils (Merkl et al., 2005; Issoufi et al., 2006; Diab, 2008).

1.4 Scope of the Study

The  study  was  limited  to  the  study  of  the  phytoremediation potential  of  Kenaf  (Hibiscus cannabinus L.) using a simulated environment comprising of soil samples contaminated with diesel fuel only and amended with fertilizer and compost.

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