Characteristic Levels of Total Petroleum Hydrocarbon in Soil Profiles
of Automobile Mechanic Waste Dumps
Chukwujindu M.A. Iwegbue,
This communication present the results of the determination of total
petroleum hydrocarbon content of soil profiles of automobile mechanic
waste dumps. The levels of petroleum hydrocarbon in all sites ranged from
486-4438.7, 116.3-433.4 and 54.5-244.2 mg kg-1 for 0-15, 15-30
and 30-60 cm depths, respectively. The concentrations of petroleum hydrocarbon
in automobile waste dump sites are relatively high and represent elevated
concentrations above background levels found in unpolluted soils. The
hydrocarbon concentrations show no relationship with the soil physicochemical
characteristics and ages of the dumpsites. Automobile mechanic waste dumps
represent a potential sources of petroleum hydrocarbon contamination in
soils, sediments, surface water and groundwater in areas remote from oil
exploration and production sites.
Petroleum hydrocarbon oils are of environmental interest because they
are toxic to the human system, plants and animal resources. Yet, they
pervade the environment beyond the vicinities of petroleum exploration
and production activities due to storage, disposal and other handling
activities during which contamination of the environment sometimes occur.
Hence urban centre remote from production activities are sometimes as
much polluted as the surrounding production areas (Onianwa and Essien,
1999). Previously, in Port Harcourt, automobile workshops were scattered
all over the city and occupied almost every vacant lot along major roads.
Waste were indiscriminately dumped on every available space and all categories
of urban waste ranging from lubricating oil films, junked cans to tyres
were found to litter along street and major roads. In 1990, two mechanic
villages were established in Port Harcourt municipality by River State
Government to curb the menace of wastes deposited by automobile works
and to improve the general aesthetics of the city (Iwegbue et al.,
Wastes from automobile workshop activities include solvent, paints, spent
heat transfer fluids, hydraulic fluids, spent lubricants and stripped
oily sludge. Most of these wastes are dumped on land. In such urban centre,
there is contamination of surface water, sediment and groundwater with
petroleum hydrocarbon from poor handling and disposal practices. Limited
data are currently available on petroleum contamination from a non-petroleum
production sites in the Nigeria. The aim of present study is to determine
the characteristic levels of total petroleum hydrocarbon in soil profiles
of automobile mechanic waste dumps.
MATERIALS AND METHODS
Soil samples were collected from 5 designated automobile waste dumps
in January - March 2005 within Port-Harcourt metropolis, namely East West
Road (1) Elekohia (2), Miles 3 Diobu (3), Trans Amadi (4) Borokiri (5)
and control site (6), which was collected from the Rivers State University
of Science and Technology, Port Harcourt teaching farm. The status of
the automobile mechanic waste dump studied has been reported elsewhere
(Iwegbue et al., 2006a). The soil samples were collected within
100x100 m quadrant around the dumpsites. The quadrant was divided into
10 cells (10x10 m) with each cell denoting a sample station. A composite
sample consisting of at least 5 random samples were collected in each
cell at 0-15, 15-30 and 30-60 cm depths (Iwegbue et al., 2006a).
Soil particle size distribution, electrical conductivity (EC), soil pH,
Cation Exchange Capacity (CEC) and total organic matter determination
have been previously described by Iwegbue et al. (2006a).
Total petroleum hydrocarbon of the soil sample was determined by the
method of Intergovernmental Oceanographic Commission (IOC) as described
by Onianwa and Essein (1999), Iwegbue et al. (2007). Hundred gram
of the soil samples were refluxed with 100 mL of methanol containing about
3.0 g of KOH for 2.5 h. The refluxed mixture was filtered and the filtrate
was extracted with two 2.5 mL portion of redistilled hexane. The combined
extracts were evaporated to about 1.0 mL and then subjected to clean up
in a silica column, eluted with n-hexane. The eluate was subsequently
evaporated to isolate the hydrocarbon oil which was then weighed. A recovery
study of the procedure was carried out with varying amount of fresh automobile
engine oil and then repeating the analysis. An average recovery of 90.7±2.3%
RESULTS AND DISCUSSION
The results of physico-chemical characteristics and total petroleum hydrocarbon
content of soil profile of automobile mechanic dumps are presented in
Table 1 and 2, respectively. Sand
forms the predominant particle size and ranged from 66.8-88.4% in all
sites and depth. The sand fractions showed a regular decrease with depth
while the silt and clay fractions increase with depth of the soil profile.
The silt and clay fraction never exceeded 10-22.2%, respectively in all
sites and depths. pH, total organic matter (OM) and cation exchange capacity
(CEC) decreases with increasing depth of the profile. The pH values reported
in this study are similar to pH value recorded for some other Nigeria
soils (Odu et al., 1985; Isirimah, 1987; Banjoko and Sobulo, 1990;
Iwegbue et al., 2006b). All sites and depth showed significant
higher values of cation exchange capacity, total organic matter and conductivity
than the control site. The reason for the high organic matter content
of the waste dumps was due to co-deposition of domestic wastes and carbon
compounds present in automobile mechanic wastes.
||Some physicochemical properties of soils profiles of the automobile
mechanic waste dumps
|CEC: Cation Exchange Capacity, EC: Electrical Conductivity
||Levels of total petroleum hydrocarbon in soil profiles automobile
mechanic waste dumps (mg kg-1)
Analysis of variance show no significant variability when samples collected
from a given site and horizon are compared. However, significantly variability
is found in sites 4 (at 15-30 and 30-60 cm) and 5 (at 30-60 cm depth).
Significant and apparent variability exists when concentration of petroleum
hydrocarbons on the various dumps sites and profiles are compared. The
concentrations of total petroleum decreases with depth in all sites. This
implies that most of the petroleum hydrocarbon oil accumulates at the
topsoil compared to the other depths. The accumulation pattern of petroleum
hydrocarbon depends on the textural and physical soil, contaminant supplies,
amount that are water soluble and the hydrology the area. Surface runoff
forms the major dispersing mechanism of petroleum hydrocarbon oil in these
The processes of alteration of composition of hydrocarbon occur as it
gets into soil. Clearly, those hydrocarbons that are most strongly sorbed
onto soil organic matter will be resistant to loss or alteration by the
other process. Conversely, the more volatile/soluble hydrocarbons will
be the most susceptible to change by volatilization/reaction/leaching
and biodegradation. The ultimate result will be weathering of hydrocarbon
mixture discharged to soil, within accompanied changes in its composition
and a preferential transport of certain fractions to other environmental
compartment (Sadler and Connell, 2003).
As oil infiltrate the soil, it has a considerable effect on the structure
and welting ability of soil. A complete breakdown in structure and dispersion
of soil particulate has been noted. The rate of soil movement into and
through the soil will large depend on the type oil, organic matter content,
moisture content of the soil and depth to water table. As soil infiltrates
the soils, it physically displaces soil air and water. This has been considered
significant effect in promoting anaerobic conditions in soil (Iwegbue
et al., 2007).
The highest concentration of petroleum hydrocarbon was recorded in site
4 (4438.7 mg kg-1). The order of concentration of total petroleum
in the surface horizon follows 4>5>2>3>1. In sites the subsurface
horizon contained less than 450 mg kg-1 petroleum hydrocarbon
oil. There was no significant relationship was found between total hydrocarbon
concentration, age of the dump and soil physicochemical characteristics.
This is a suggestive evidence that the petroleum hydrocarbon content of
the soil profiles of these waste dumps is purely of anthropogenic origin.
The concentration of total hydrocarbon oil found in the surface horizons
are higher than concentration range reported by Onianwa and Essien (1999),
Adekambi (1989) and Iwegbue et al. (2007) for crude oil impacted
soil in the Niger Delta.
Toxicity of petroleum hydrocarbon oil in soils has been studied using
a number of species including bacteria, algae, earthworms and plants and
a range of lethal to sub lethal effects, such as seed germination, root
elongation and reproduction. The toxicity effects have appeared over a
large range of test concentrations. However, most effects are found in
concentrations range greater 1000 mg kg-1. The lowest EC50
for germination studies (typically lettuce) are in the range of 2000-3000
mg kg-1 (Chaineous et al., 1997; Saterbak et al.,
1999). The concentrations of total hydrocarbon recorded in the present
study are within or greater than this range and therefore will produce
toxicity effect on crops. Site 1 and subsurface of horizons of the other
sites have concentrations low than this range.
The data obtained from this study revealed that concentration of petroleum
hydrocarbon in soil profiled automobile mechanic waste dumps are relatively
high and represent elevated concentrations above background levels found
in unpolluted soil. The levels of petroleum hydrocarbon decreases with
depth of profiles and showed no relationship with ages of dump sites and
the soil physicochemical properties. The mechanic waste dumps represents
a potential possible source of hydrocarbon contamination of soils, sediment,
surface and groundwater in area far from oil production sites.
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