ISSN: 2394-0638
www.rjaes.com Volume-2, Issue-6, Nov-Dec-2015, Res.J.Agr.Env.Sci
Research Article
Received: 10/09/2015
Revised: 19/11/2015
Copyrights@2015
Open Access
Accepted: 20/11/2015
SHORT TERM EFFECT OF OIL SPILL ON SOIL FERTILITY AND CROPS GROWTH:
BENIN, WEST AFRICA
Bachir Bounou Issoufa1,2* and Addam Kiari Saidou2
1
Committee for Supporting Local Development (CADEL-NGO), BP 2006 Niamey, Niger
2
National Institute of Agronomic Research of Niger (INRAN), BP 429, Niamey, Niger
ABSTRACT: The study was conducted at Guémé/Republic of Benin, West Africa on contaminated and
uncontaminated soil. The objective of the study was to assess the short term effect of oil spilling on soil
fertility parameters, ground water and crops growth (maize and cassava), allowing a post-impact evaluation of
approximately 8 months. Contaminated and uncontaminated soil (0-15 cm depth) and ground water (0-50 cm
depth); uncontaminated maize grain and cassava cutting were collected. The soil and ground water were
labeled and submitted to laboratory analysis. Maize grain and cassava cutting were planted on the 2 types of
soils for determining the percentage of seedlings germination. The results indicated that soil organic carbon
was significantly (Fpr < 0.001) higher (1.17%) in contaminated soil whereas available phosphorus and pH
were significantly (Fpr < 0.002) higher (9.44 mg kg-1 and 5.95, respectively) in uncontaminated soil. The pH
(8.05) and electrical conductivity (139.6 us cm-1) recorded were significantly (Fpr ≤ 0.002) higher in the
contaminated ground water. Maize showed excellent seedling germination under contaminated soil. Based on
these results, oil spilling improves soil total carbon, total exchangeable base, nitrogen contents and maize
germination and on the other hand reduced soil available phosphorus and pH contents.
Key words: Crop, nutrients availability, soil pollution
*Corresponding author: Bachir Bounou Issoufa, 1Committee for Supporting Local Development
(CADEL-NGO), BP 2006 Niamey, Niger E-mail: bachirou_issoufa@yahoo.fr
Tel: (+227) 96639539/90108784
Copyright: ©2015 Bachir Bounou Issoufa. This is an open-access article distributed under the terms of the
Creative Commons Attribution License
, which permits unrestricted use, distribution, and reproduction
in any medium, provided the original author and source are credited.
INTRODUCTION
Soil pollution is a major environmental hazard. In recent years, it has been considerably attracting the global
attention. Generally, it is recommended that land as a component of the environment deserves appropriate
attention and protection as water and air [1,2] Man’s environment is under threat from his own activities [3].
For instance, the industrial activities of man are known to have negative impact on terrestrial and aquatic biota.
Allard and Neilson [4] reported that the spilled crude oil from the source, through a plausible transport
mechanism and exposure pathway, gets to the receptors such as soil and ground water and pollute the
environmental media. The intensity of oil damage depends on a number of abiotic and biotic factors including
the season of spill, type and amount of oil, prevailing weather condition and soil compositions [5]. Soil
fertility, measured by physical, chemical and biological parameters, is adversely affected by oil spilling [6].
Soil fertility is defined as the capacity of the soil to support the growth of plants on sustained basis under given
conditions of climate and other relevant properties of land [7].
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Bachir Bounou Issoufa and Addam Kiari Saidou
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The impacts of oil include loss in the productive capacity of soil, with implications on living organisms in the
polluted area. Crude oil is known to reduce the availability of plant nutrient in soil [8,9]. Petroleum
hydrocarbon contamination may affect plants by retarding seed germination and reducing plant height, stem
density, photosynthesis rate and biomass or resulting in complete mortality [5,10,11]. Agbogidi [12] also did a
similar work on effect of crude oil pollution on soil fertility and the growth of plants and uptake of nutrients
and observed that germination and yields were drastically reduced as the level of pollution increased. The
amount of organic carbon, total nitrogen increased in the soil with level of crude oil addition while extractable
phosphate and exchangeable calcium were reduced. Moreover, Wokocha [13] examined the impact of crude
oil spillage on soil properties and food production in Ogba/Egbema/Ndoni Area in Rivers State, Nigeria. Thus,
their findings indicated that the pH status of soil in heavily and moderately contaminated zones varied from
acidic (pH 4.0) to neutral (pH 6.0). The chemical properties of soil indicated that, percentage organic matter
increased from 1.34 to 2.62, available phosphorus decreased from 15 kg mg-1 in control to 7.34 - 5.42 kg mg-1
in soil polluted with high level of crude oil. The experiment on the effect of poultry manure on maize planted
on crude oil polluted soils showed that percentage growth rate in plant height and yield decreased with increase
in crude oil contamination [14]. This study examined the natural attenuation process in the remediation of oil
polluted soil in Guémé, Republic of Benin, West Africa. Its aim was to investigate the effect of oil pollution on
soil fertility and ground water under contaminated and uncontaminated soils after 8 months of spilling. The
study assessed also the growing of maize and cassava under soil from contaminated and uncontaminated sites.
MATERIALS AND METHODS
Description of experimental site
The experiment was conducted at Guémé which is 81 km away from Cotonou/Benin. The area lies between
06°45’22’’ N and 002°12’46’’ E. The study site size was around 11 hectares and the main crops growth was:
maize, cassava and pineapple. The arable land was then contaminated by oil spill of tanker accident which had
affected over more than 4 hectares of land. The incident took place on the 23rd September 2010 and sampling
was carried out on the 1st of June 2011, allowing a post-impact evaluation of approximately 8 months. Samples
of soil and ground water from contaminated and uncontaminated sites were conserved in the refrigerator prior
to laboratory analyses on 15th of June 2011. An estimated 65 000 liters of oil was spilled.
Climate and type of soil
The study area lies in the subequatorial climatic region, characterized by two dry seasons (from December to
middle of March and middle of July to August) and two rainfall seasons [from middle March to July (season 1)
and September to November (season 2)]. The study area recorded a mean monthly temperature which varied
from 27 to 31oC. The relative humidity varied between 65% (January to March) and 97% (June to July). The
mean rainfall of season 1 and season 2 was 1100 mm and 800 mm, respectively [15]. The soil of the study area
is classified as sols ferrugineux tropicaux lessivés et hydromorphes [16].
Sampling and soil collection
Soil (0-15 cm depth) and ground water (0-50 cm depth) were sampled from both contaminated and
uncontaminated plots (control), replicated four times. However, maize grain and cassava cutting were collected
only from the uncontaminated site. Subsequent soil and ground water samples were labeled and taken to
laboratory for analysis.
Laboratory analyses
The soil pH was determined using soil water ratio (1:2.5). A 10 g dry soil sample was ground to pass through 2
- mm mesh size and weighed into a 50 ml beaker, mixed with 25 ml distilled water then the suspension was
stirred continuously for 15 minutes and allowed to stand for 30 minutes. After calibrating the pH meter with
buffer solutions of pH 4.0 and 7.0, the pH was read by immersing the electrode into the upper part of the
suspension as described by McLean [17]. Organic carbon was determined by the modified Walkley – Black
wet oxidation method [18]. Total nitrogen was determined by the semi micro Kjeldahl digestion and
distillation procedure as described by Motsara and Roy [19]. The available phosphorus was extracted with
Bray’s No.1 extracting solution (0.03 M NH4F and 0.025 M HCl) as described by Bray and Kurtz [20]. The
total exchangeable bases (calcium, magnesium, potassium and sodium) in the soil were determined in 1.0 M
ammonium acetate (NH4OAc) extract, at pH = 7.0 as described by Black [21]. The pH and conductivity of
water were measured by meter methods from slurry of 50/50 w/v sample in water. The pH and conductivity of
water were recorded from pH meter (model: Jennway 3015) and conductivity metre (HACH Ecttesr
microprocessor series), respectively.
Assessing maize germination and cassava cutting development under soil from contaminated
and uncontaminated sites
Soil samples were collected from study area (contaminated and uncontaminated). Indeed, maize grain and
cassava cutting were planted under the two types of soil at National Institute of Agronomic Research of Niger
(INRAN). The maize and cassava plant vigour was evaluated 25 days after planting.
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Statistical analysis
The data generated after laboratory analyses were subjected to ANOVA, where significant treatment means
was separated using Lsd at 5% level. GENSTAT v.9 software programme was used to perform the data
analysis [22].
RESULTS AND DISCUSSION
Effect of oil on soil fertility and ground water
The results of the study indicated differences between both contaminated and uncontaminated soil as presented
in Table 1. Soil pH for both contaminated and uncontaminated sites were significant (Fpr = 0.015) with 5.80
and 5.95, respectively. Furthermore, the pH values were within the acidic pH scale range and oil spill affected
soil pH. Similar results were reported by Abu and Nwosu [23] working on soil polluted by crude oil in the
Niger Delta/Nigeria and strengthened by the observation made by Gighi and Albert [24]. The acidity of soil
can be also caused by high precipitation (observed in the study area) which leached cations down in the soil
profile.
Table 1: Effect of oil spilling on selected soil fertility parameters
OC (%)
TEB (cmol kg-1)
TN (mg kg -1 )
Avail-P (mg kg-1)
pH-H2O
1.17
7.64
828
3.98
5.8
C.S
0.9
7.17
793
9.44
5.95
U.C.S
F pr.
< 0.001
0.27
0.245
0.010
0.015
Mean
1.04
7.4
810
6.71
5.87
Lsd
0.08
0.9
64.8
3.81
0.11
CV (%)
7.8
12.1
7.9
56.2
1.9
C.S : Contaminated soil ; U.C.S : Uncontaminated soil ; F pr : Probability ; Lsd : least significant difference ;
CV : coefficient of variability; OC: Organic carbon; TEB : Total exchangeable bases ; TN : Total nitrogen ;
Avail-P: Available phosphorus; pH-H2O : pH-water
Total organic carbon (TOC) was significantly (Fpr < 0.001) high on contaminated soil compared with the
uncontaminated soil (Table 1). The result disagrees with the observation made by Wegwu [25]. This can be
explained by the fact that diverse species of bacteria and fungi can be developed under soil contaminated by
oil. Thus, Chaineau [26] reported that microorganisms degraded oil in the soil and release dioxide of carbon
and water. This is also made possible as a result of the range of pH observed in the study. The range of pH 5 9 provides better condition for microbial growth in a hydrocarbon polluted soil [27, 28].
There was no significant difference in total nitrogen content between contaminated and uncontaminated soil.
However, total nitrogen content was higher in contaminated soil compared with the uncontaminated soil (Table
1). This result was contrary to the finding of Atlas [29] who demonstrated that total nitrogen content decrease
in soil contaminated by oil. However, available phosphorus was higher in uncontaminated (9.44 mg kg-1) soil
than contaminated (3.98 mg kg-1) soil. This result corroborated with the observation made by Agbogidi et al.
(12). However, Atlas [29] reported that if soil environment is limited by organic matter and therefore if a large
amount of nitrogen-free substrates like crude oil is added, phosphorus become limiting. There was no
significant difference in total exchangeable bases between contaminated and uncontaminated soils. However,
total exchangeable bases were higher in contaminated soil compared with the uncontaminated soil (Table 1).
Ground water pH for both contaminated and uncontaminated soils were significantly different (Fpr <.001) with
8.05 and 7.32, respectively (Table 2).
Table 2: Effect of oil spilling on pH and electrical conductivity of ground water
pH
Electrical conductivity (us/cm)
8.05
139.6
C.S
7.32
98.2
U.C.S
F pr.
< 0.001
0.002
Mean
7.68
118.9
Lsd
0.07
15.25
CV (%)
0.5
7.3
C.S : Contaminated soil ; U.C.S : Uncontaminated soil ; F pr : Probability ; Lsd : least significant difference ;
CV : coefficient of variability; pH-H2O : pH-water
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The electrical conductivity of ground water collected from 0-50 cm depth was found to be higher under
contaminated soil than the uncontaminated soil (Table 2). The difference was statistically significant (Fpr. =
0.002). This result agreed with observation made by Gighi and Albert [24] working on post-impact soil
assessments of crude oil spill.
Contaminated soil
Uncontaminated soil
Vigour of cassava under contaminated soil
Figure 1: Cassava vigour under soil from contaminated and uncontaminated site
Vigour of maize under
contaminated soil
Vigour of maize under
uncontaminated soil
Figure 2: Vigour of maize under soil from contaminated and uncontaminated site
Effect of oil spilling on maize and cassava growth
Ten (10) days after planting, the result showed that germination rate of maize seed was 100% from
contaminated soil while uncontaminated soil had 80%. On the other hand, the result from cassava cutting
showed a development rate of 70% under soil from contaminated and uncontaminated sites. The cassava
cutting did not adapted to the climate of experimental trial while only one cutting of cassava was grown in the
soil from contaminated site (Figure 1).
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The result disagreed with the observation made by Pezeshki et al. (5) and Anyanwu and Tanee [11] who
reported that petroleum hydrocarbon contamination may affect plants by retarding seed germination or
resulting in complete mortality. Figure 2 showed the vigour of maize under soil from contaminated and
uncontaminated sites. The high vigour of maize plant under soil from contaminated site can be explained by
the fact that maize, through microorganisms around its root rhizosphere, has the capacity to uptake the
degraded nutrients from oil. The result of this study agreed with observation made by Migeon [30] working in
phytoremediation. However, the result contrary the finding of Agbogidi et al. [12] who reported that the
germination of maize reduced when the level of oil pollution increased.
CONCLUSION
Soil total carbon, exchangeable base and nitrogen were higher in the soil from contaminated site compared to
uncontaminated site. However, soil available phosphorus and pH was lower in the soil from contaminated site
compared to uncontaminated site. Based on these results, oil spilling improves soil total carbon, exchangeable
base and nitrogen contents and on the other hand reduced soil available phosphorus and pH contents. The
results of the study also revealed that, pH and electrical conductivity of ground water were higher in water
from contaminated site compared to which from uncontaminated site. From this study, maize showed excellent
seed germination under contaminated soil.
ACKNOWLEDGEMENT
The authors are grateful to CAREN-Assurance Niger for funding the study.
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