The Profile of Physico-Chemical Properties of Spilled Crude Oil in Marine Sediments in Niger Delta

This paper presents profile of the physico-chemical properties of study areas of the research. Most frequently, in the Niger Delta zone spilled oil in the marine sediments is prevalent. The research paper therefore focused at first instance to evolve the parametric control properties which have direct interactions with the spilled oil. Samples sediments A, B, C, and D were collected from the designated study areas of Southern Ijaw, Ekeremor, Ogbia, Brass and Nembe local government areas hosting the major oil producing companies along the coastal regions of Niger Delta-Nigeria. The samples were subjected to instrumental analysis for determination of pH 5.2 (acidic); electrical conductivity 169 µS/cm; redox potential -134 mv; temperature 25.7 centigrade; bulk density 3.3; particle density 2.75; porosity 41.6; organic matter 8.60; clay 28.70; silt 56.80;  sand 14.5; total hydrocarbon content 83.33; and the metallic components of the samples (mg/kg) stood as follows- Zinc (Zn) 1.47; Lead (Pb) 0.070; copper (Cu) 2.06; cadmium (0.51); Nickel (Ni) 0.82; manganese (Mn) 4.75; iron (Fe) 7.60; and chromium (Cr) 0.98. Table II showed sample Sediment A gave appreciable values on all the parameters for good judgment on the rest samples Sediment B, Sediment C and Sediment D results. The possible reasons being there are much physico-chemical interactions down the samples which bring concomitant effects on animals, fishes, humans’ health and regions degradation tendencies and perennial consequences of social agitations for remediation and compensations.

substances.An understanding of the processes involved and how they interact to alter the nature, composition and behaviour of oil with time is fundamental to all aspects of oil spill response.It may, for example, be possible to predict with confidence that oil will not reach vulnerable resources due to natural dissipation, rendering a clean-up response unnecessary.When an active response is required, the type of oil and its probable behaviour and fate will determine which response options are likely to be most effective and should therefore be selected.Insoluble solid particles resting at the bottom of water bodies (aquatic environment) constitute sediment.The sediment status of an area is thus an indicator of the toxicity or pollution status of the aquatic environment (marine ecosystem).Marine sediments can be sensitive indicators for monitoring contaminants in aquatic environments [1].The bottom sediments serve as a reservoir for heavy metals and therefore deserve special consideration in the planning and design of aquatic pollution research studies Heavy metals, such as cadmium, mercury, lead, copper and zinc, are regarded as serious pollutants of aquatic ecosystems because of their persistence, toxicity and ability to be incorporated into food chains.
Of all the processes that accompany the fate of oil spilled in a marine environment sedimentation accounts for up to 10-30%.During the sedimentation process oil is adsorbed on the suspended material and deposited to the bottom.This mainly happens in the narrow coastal zone and shallow waters where particulates are abundant and water is subjected to intense mixing.In deeper areas remote from the shore, sedimentation of oil (except for the heavy fractions) is an extremely slow process.The heavy oil fractions accumulated inside the sediments can be preserved for many months and even years.
A few heavier residual oils have specific gravities greater than sea water (more than 1.025), causing them to sink once In Nigeria, oil spillage occurs during exploration, production, transportation and storage either as a result of system failure or sabotage.In the event of crude oil spillage within a water body, most companies adopt the following clean up techniques: burning off or the use of chemical dispersants to redeem the system and consequently claimed to have restored the ecosystem.Frankly speaking, these two most practiced clean-up methods within a water body have not effectively cleaned up the spilled oil from the soil including sediments.Certain fractions of the spilled oil migrate and settle at the bed of the water body, which constitute mostly of sediments and its consequences on the ecosystem cannot be over emphasized.For example, after thirty years of oil spilled from the Berge Florida in Buzzards Bay near west Falmouth, residues of the oil was still found in salt marsh sediments, according to [2].Further evidence that oil persists in the marine environment for a long period of time even though the surface sediments recovers quickly and appear visually healthy was posited by [3].According to the report, samples collected from a spill site 30 years after the incident at a mat depth of 36-centimeter (14-inch) sediment were analyzed.No evidence of petroleum residues was detected in the top 6-centimeter (just over 2 inches) or the lower 8 centimeters (roughly 3 inches) of the core.However, the central section of the sediments to 28 centimeters (2-11 inches from the top of the core) contained petroleum hydrocarbon concentrations to those observed after the spill.The research concluded that the oil in the sediments may remain there indefinitely.
In Nigeria especially within the oil producing area such incidents of re-surfacing of spilled oil after clean-up activities have been observed over the years.However, This study serves to determine the physico-chemical characteristics of marine sediments that supports trapping of spilled crude oil.

A. The study Area
The study area is within the Niger Delta area of Nigeria.Sediment samples were collected from Southern Ijaw, Ekeremor, Ogbia, Brass and Nembe local government areass of Bayelsa State Fig. 1.These LGAs have communities hosting major oil producing companies and are located along the coastal region of Niger Delta in Nigeria.
The project area is within the humid tropical zone with defined dry (November -March) and rainy (April -October) seasons.The rainy season is brought about by the Southwest trade wind blowing across the Atlantic Ocean.
The dry, dusty and often cold Northeast trade wind blowing across the Sahara Desert dominates the dry season and brings a short spell of harmattan.The relative humidity of the area is high with values ranging from 70% in January to 80% in July.The area reveals the average atmospheric temperature to be 25.

B. Method
Four oil spill sites within the study area were selected for the study.All sampling points were geo-referenced.The choice of the sampling sites was based on palable history of oil spill and clean-up activities (Table I).
At each of the identified sampling sites, sediment samples were carried out using a stainless steel Eckman grab to a depth of about 10cm.The sediment samples were immediately transferred in plastic containers and frozen at -4 0 C for transport to Devine Concept Laboratory for samples preparation and analysis.At the laboratory, coarse materials (>2mm) like pebbles and plant debris were removed from the sediment samples and analysed for the following parameters; silt, sand, clay, pH, temperature, redox potential (Eh), electrical conductivity (EC), total hydrocarbon content (THC), Zinc (Zn), Lead (Pb), Copper (Cu), Cadmium (Cd), Nickel (Ni), Manganese (Mn), Iron (Fe), and Chromium (Cr).pH, temperature, redox potential (Eh), and electrical conductivity (EC) were measured in-situ using a multiparameter water quality monitor (Orion Model, 1260).At the determination of any of the parameter, the equipment was properly checked and calibrated before the after use.Samples for metal analysis were sieved at 200µm and stored in a dry atmosphere before analysis.The particle size distribution (PSD) was determined using the hydrometer method followed by sieving the sand fraction (>63µm) from silt (<63 and 2µm) and clay (<2µm).Levels of heavy metals in the sediment samples were measured using ATI Unicom Atomic Absorption Spectrophotometer, Model 939.On the 22 nd of November, 2010 to effect repair to the damaged pipeline and on 23 February 2011 clean -up of the impact area was carried out.On 20th of July, the area was visited for further investigation for eviedence of splled oil and the area was found to beclean.

III. RESULTS AND DISCUSSIONS
A summary of results of analysis of the sediment samples are given in Table II.From the table, the following observations and inferences can be made on the parameters of the samples.

A. Physico-chemical properties of sediment samples A, B, C, D 1) pH
Froth sediment samples are slightly acidic, with pH values ranging between 5. 2 to 6.8.At sampling sites A, B and C the pH values were more acidic than site D. The high acidic pH at these points may have resulted from humic acid formed from decaying organic matter.However, pH ranges compared well with reported values in similar water systems in the lower Niger Delta region [4].

2) Electrical conductivity
This is the ability to pass electric current.It is proportional to the concentration of dissolved solids (mostly inorganic salts).Thus electrical conductivity is an indicator of the total dissolved inorganic salts and other solids.The electrical conductivity of the sediment samples ranged between 17.7 -174 µs/cm.This could be related to the level of silt materials present.Levels of electrical conductivity values in any sediment can be attributed the levels of silts because decomposing vegetable matter can rapidly increase potassium ion.

3) Redox potential (Eh)
The redox potential (Eh) of all sediment samples ranged from -18mV and -178mV.A negative redox potential indicates a reducing environment.Spectrum of redox potential under which microbial life can be found ranges from -450mV to +850mV, where the negative side of the spectrum favors methanogenic bacteria, and the positive side corresponds to iron bacteria [5].

4) Temperature
The temperature of sediment samples is the most important parameter measured because excessive temperature (>35 o C) through the addition of heated liquid effluents to such environmental medium alters the state of the recipient body in a number of ways.For example, higher temperature causes suspended solid to settle at a faster rate (2.5 times faster at 35 o C than at 0 o C).Density and viscosity of sediment will also reduce at higher temperatures.
Temperature values recorded in the sediment samples ranged from 25.2 o C to 26.8 o C. Across all sampling points temperature values are below DPR limits of 30 o C for sediment samples and this may have resulted from the weather condition of the of the areas of study.

5) Bulk density (BD)
The ratio of the mass of an oven-dry soil per sediment samples volume of that sample at a specified moisture conditions.This volume includes both solids and pores.It provides a measure of soil porosity.

BD = Soil dry weight (g)/Total volume of dry soil (mL)
The bulk density of the sediment samples ranged from 3.3 -10.9g/cm 3 .

6) Particle density
Define as the mass of a unit volume of soil/sediment.It focuses on just the particles themselves and not the volume they occupy in the sediment.The particle density of the sediment samples ranged from 2.60 -13.30g/cm 3 .

7) Porosity
Porosity is the volume of pore space relative to the total volume (soil and/or sediment + pore space).Grain shape and cementation also affect porosity.Porosity = Volume of voids/Total volume of solids and voids.The relationship between porosity, particle density and bulk density can be expressed as: Porosity (%) = (1 -Bulk density/Particle density) x 100 The porosity of the sediment samples ranged from 37.5 -66.8%.The obtained values represent that for good soil and sediment that will promote permeability.

8) Organic Matter
Organic matter level in the sediment sample gives an indication of the number of carbon containing compounds in the sample and provides a means for determining the degree of organic contamination.High organic carbon content would result to an increase in the growth of microorganisms, which could contribute to the depletion of oxygen supplies.
The organic matter levels of the sediment samples ranged between 3.17 and 9.10%.

9) Particle Size Distribution (PSD)
Particle Size Distribution (PSD) is express in percentage of silt, clay and sand.The relative percentage of clay, silt and sand are in the range of (1.27 -37.20%) for clay, (10.00 -59.70%) for silt and (11.90 -88.73%) for sand.
The maximum amount of sand was obtained at site D and the minimum at site B. The maximum amount of silt was obtained at sites A, B and C. The sampled sediments are predominantly clay and silt mixture.

10) Total Hydrocarbon Content (THC)
Total hydrocarbon content (THC) the sediment samples ranged between 22.73mg/kg and 92.80mg/kg which is above regulatory limit of 10.0mg/kg indicating hydrocarbon/oil contamination of the sediment samples.
These interactions are affected by factors like pH, redox potential, temperature, CO2 level, the type and concentration of available ligands and chelating agents, as well as type and concentrations of the metal ions.Trace or heavy metals in environmental perspective have potential of bioaccumulation and bio-concentration in aquatic organisms.
Severe effects of heavy metal contamination include reduced growth and development, cancer, organ damage, nervous system damage, and in extreme cases, death.Exposure to some metals, such as mercury and lead, may also cause development of autoimmunity, in which a person's immune system attacks its own cells.

B. Results of metallic components of samples
The results of analysis of the concentrations of heavy metals in the sediment samples are: Fe (2.30 -8.30mg/kg); Cr (0.01-1.13mg/kg);Cu (0.06-3.54mg/kg);Zn(0.73-1.62mg/kg);Pb(0.01-0.081mg/kg);Mn(0.05-4.75mg/kg);Cd(0.01-0.64mg/kg)and Ni(0.03-0.91mg/kg).Studies showed that the distribution of heavy metals in marine sediments is influenced by composition in the forms of clay, silt, sand and organic carbon.Total metal contents are lower than results found in other sediments of the Niger Delta and similar ecosystems [6], [7].This can be attributed to the low levels of industrial activities in area.

C. Assessment of Sediment Trapping Potential of of Spilled Crude Oil
Sediment trapping potential of spilled oil have been severally investigated rivers and floodplains, shorelines and beaches along lakes and oceans, coastal and riparian wetlands, and deeper waters of oceans and lakes.Attention of the prvious studies have been particle size distribution (PSD).In view of the aforementioned a summary of the PSD and Total Hydrocarbon Content (THC) of the studied sites is presented in Table III.The relationship between the concentration of the levels of total petroleum hydrocarbon and the amount of silt was evaluated using correlation coefficient Fig. 2.This confirms that the trend of the concentration of the total petroleum hydrocarbon is positively linked to the percentage of silt in the sediments.The linear regression of the relationship between the levels of spilled oil in the percentage of silt in the sediment samples is shown in Fig. 2. A linear response was obtained between the datasets.The fitted equations on the entire data set can be explained with their corresponding correlation coefficients (r).Correlation coefficient is a measure of the strength and direction of the linear relationship between two variables that is defined as the (sample) covariance of the variables divided by the product of their (sample) standard deviations.Correlation values are bound between a value of -1 and +1.A correlation of +1 can be interpreted to suggest that both variables move perfectly positively with each other, and a -1 implies they are perfectly negatively correlated.Specifically, a correlation of 0.7 -1.0 is described as a strongly positive; 0.5 -0.69 is described as moderately positive and 0.0 -0.49 is described as weakly positive.The coefficient of determination (R 2 ) is a measure of how well the regression line represents the data.If the regression line passes exactly through every point on the scatter plot, it would be able to explain all of the variation.The further the line is away from the points, the less it is able to explain.
The coefficient of determination (R 2 ) of the fitted equation was 0.6973.This implies a positive correlation between levels of total hydrocarbon content and percentage of silt.This means that 69.73%, of occurence did not happen by chance rather it indicates that levels of total hydrocarbon content and percentage of silt are highly correlated.The simulations revealed that up to 65% of released oil might be removed from the water column as OSAs, and that the amount of oil partitioned into sediments was 4-5 orders of magnitude smaller than the amount of OSAs formed.

IV. CONCLUSION
The interactions between some physico-chemical properties of sediment in the marine environment has been a concern in developing effective oil spill clean-up activities.The research thrives to assess the potential of sediment to trap spilled oil in the Niger Delta area of Nigeria.The study confirms that the trend of the concentration of the total petroleum hydrocarbon in the sediment is positively linked to the percentage of silt particles.

Fig. 1 .
Fig. 1.Oil Spilled in Marine Environment Showing the Main Weathering Processes 5 o C in the rainy season and 30 o C in the dry season months (19.8 -50.1mm).

Fig. 2 .
Fig. 2. Image of the study area

Fig. 3 .
Fig. 3. Linear regression of the relationship between the levels of spilled oil in the percentage of silt in the sediment samples Fig. 3 exhibits a positive function plot of the relationship between concentration levels of total hydrocarbon and amount of silt.The simulations revealed that up to 65% of released oil might be removed from the water column as OSAs, and that the amount of oil partitioned into sediments was 4-5 orders of magnitude smaller than the amount of OSAs formed.
The Profile of Physico-Chemical Properties of Spilled Crude Oil in Marine Sediments in Niger Delta C. A. Mmecha, Y. T. Puyate, A. A. Wordu, and J. G. Akpa spilled.Most crude and fuel oils have sufficiently low specific gravities to remain afloat unless they interact with and attach to more dense sediment or organic particles.Dispersed oil droplets can interact with sediment particles suspended in the water column, thus becoming heavier and sinking.However, adhesion to heavier particles most often takes place when oils strand or become buried on beaches.Once exposed large amounts of sediment can be incorporated and the oil can form dense tar mats.Once oil has been mixed with beach sediment, it will sink if washed back out to sea by storms, tides or currents.

TABLE II :
PHYSICO-CHEMICAL PROPERTIES OF SEDIMENT SAMPLES A, B, C, D

TABLE III :
SUMMARY OF THE PSD AND TOTAL HYDROCARBON CONTENT (THC) OF THE STUDIED SITES