Comparative Efficacies of Organic and Inorganic Fertilizers as Amendment to Enhance Pesticides Biodegradation in Contaminated Soil
1.0 INTRODUCTION
1.1 Background of the Study
Pesticides are the chemical substances that kill
pests and herbicides are the chemicals that kill pests. In the context of soil,
pests are fungi, bacteria insects, worms, and nematodes etc. that cause damage
to field crops (Kearney and Roberts, 1998). Thus, in broad sense pesticides are
insecticides, fungicides, bactericides, herbicides and nematicides that are
used to control or inhibit plant diseases and insect pests. Although wide-scale
application of pesticides and herbicides is an essential part of augmenting
crop yields; excessive use of these chemicals leads to the microbial imbalance,
environmental pollution and health hazards. An ideal pesticide should have the
ability to destroy target pest quickly and should be able to degrade non-toxic
substances as quickly as possible (Peng, Zhang, Li, Li, Xu and Yan, 2008).
Biodegradation of organic compounds is often slow
because one or more inorganic nutrients needed for microbial growth are in low
concentrations in the natural environment (Convey and Wetzel, 1992). The
addition of nitrogen and phosphorous may therefore enhance biodegradation of
organic compounds but it can also have no effect or decrease the rate of biodegradation
(Pritchard and Coasta, 1991).
Concern
for pesticide contamination in the environment in the current context of
pesticide use has assumed great importance (Zhu et al., 2004). The fate of the pesticides in the soil environment
in respect of pest control efficacy, non-target organism exposure and offsite
mobility has become a matter of environmental concern (Hafez and Thiemann,
2003) potentially because of the adverse effects of pesticidal chemicals on
soil microorganisms (Araújo et al.,
2003), which in turn may affect soil fertility (Schuster and Schröder, 1990).
An ideal pesticide should be toxic only to the target organism, biodegradable
and should not leach into ground water. Unfortunately, this is rarely the case
and the widespread use of pesticides in modern agriculture is of concern
(Johnsen et al., 2001).
Pesticides reaching to the soil are acted upon by
several physical, chemical, and biological forces. However, physical and
chemical forces are acting upon/degrading the pesticides to some extent,
microorganisms plays major role in the degradation of pesticides (Kearney and
Roberts, 1998). Many soil microorganisms have the ability to act upon
pesticides and convert them into simpler non-toxic compounds. This process of
degradation of pesticides and conversion into non-toxic compounds by
microorganisms is known as biodegradation. Globally, an estimated 1 to 2.5 million tons of active
pesticide ingredients are used each year, mainly in agriculture. Forty percent
are herbicides, followed by insecticides and fungicides. Since their initial
development in the 1940s, multiple chemical pesticides with different uses and
modes of action have been employed. Pesticides are applied over large areas in
agriculture and urban settings. Pesticide use therefore represents an important
source of diffuse chemical environmental inputs (Anderson
and Domsch, 1993).
Heterotrophic microbial activity appears to be
severely limited in most soils by a lack of easily available carbon substrate.
The addition of sugars leads to a marked increase in soil microbial activity,
which under aerobic conditions can be most readily observed as an increase in
soil respiratory activity (Falih and Wainwright, 1996).
The activity of the microbial biomass is commonly
used to characterize the microbiological status of a soil (Nannipieri, Grego
and Ceccanti, 1990) and to determine the effects of cultivation (Anderson and
Domsch, 1993) or contamination (Chander and Brookes, 1993) on soil
microorganisms. Total organic carbon and pH have important effects on the
microbial biomass level. Also, the structure and distribution of carbon in soil
affect biological activity. Soil organic residues from plants, dead organisms
and fertilizers are decomposed by microorganisms and transformed to humic compounds.
The easily available organic compounds (proteins, polysaccharides etc) are
preferred as energy sources by microorganisms (Burns and Martin, 1986). In
contrast, the positive effects of farmyard manures or cow dung in increasing
nutrient supply, pH, organic carbon and cation exchange capacity of savanna
soils has been reported (Heathcote, 1970).
Manure-based fertilization or organic farming
systems necessarily involves the addition of large quantities of carbon in
addition to the nutrient elements with which the crops are being fertilized.
Carbon additions of virtually any form to arable soils often stimulate
microbial biomass size and activity (Joergensen, Schmaedeke, Windhorst and
Meyer, 1995).
The application of organic and inorganic manure
usually increases the soil microbial biomass (Sakamoto and Oba, 1991).
Introduction of organic amendments to soils have been reported to significantly
enhance global farming systems. Farmyard manure is commonly used as organic
manure in the tropics. It is a composted mixture of cattle dung, the bedding
used in the stable, and the remnants of straw and plant stalks fed to cattle
(Smaling and Dixon, 2006).
1.2 Statement of
Research Problem
It has been estimated that over 500,000
tonnes of active ingredients of pesticides are applied in the third world and
developing countries annually (Brader, 1987). In such places pesticide use is
still growing rapidly and compounds that have long been banned or restricted on
health grounds in the developed countries are still used in many third world
countries (Repetto and Boliga, 1996). Moreover, pesticide regulations are weak
and local farmers lack the training and equipment to handle pesticides safely.
The cycling of nutrients in soils is largely governed by the soil microbial
biomass and it is the supply of energy principally in the form of fixed carbon
that drives this function (Wardle, 1992; Witter and Martenssion, 1993).
Introduction of organic amendments to soils have been reported to significantly
enhance global farming systems (Smaling and Dixon, 2006).
These amendments using organic or inorganic
fertilizers makes the soil more suitable for more microbial growth and thereby
enhancing the biodegradation of these pollutants in the soil. This study will
show the impact of organic and inorganic amendments on the microbial biomass of
a soil treated with pesticides and to determine the effect of applied
pesticides on bacterial species in treated soil.
1.3 Aims and Objectives
of Study
In the quest of mankind seeking information on the area biodegradation
of pesticides on contaminated soil, the research is designed to investigate
comparative efficacies of organic and inorganic fertilizers as amendment to
enhance pesticides biodegradation in contaminated soil. To achieve the
objective of the research, studies shall be specifically conducted to:
(i)
Estimate the densities of heterotrophic
bacteria, coliform bacteria, faecal coliform bacteria and fungi in non-contaminated
soil
(ii)
Estimate the effects of pesticides on the
microbial flora of the soil
(iii)
Estimate the densities of heterotrophic
bacteria, coliform bacteria, faecal coliform bacteria and fungi in pesticide
contaminated soil enriched with organic and inorganic fertilizer
(iv)
Statistically evaluates the difference in
densities of microorganisms from pesticide contaminated soil and that of the
contaminated soil enriched with organic and inorganic fertilizer.
(v)
Characterize and identify the diverse species
of microorganisms found in both soil type
1.4 Justification
Due
to the continuous use of pesticides in agriculture, appreciable quantities of
pesticides and their degraded products may accumulate in the ecosystem leading
to serious problem to man and the environment. Therefore, it is essential to
study the residue and degradation pattern of pesticides in our soils in order to generate meaningful data from the point of view of
plant protection, public health and environmental safety. The study on the degradation of
pesticides in soil and their effect on microorganisms was recommended by Lynch ( 1995). To our
knowledge, little is known about the biodegradation of pesticides in
contaminated soil around our region. Enriching the pesticide contaminated soil
with organic manure and/or inorganic fertilizer improves the soil fertility
levels and this in turn improves microbial growth and proliferation. This
increase in microbial biomass enhances the biodegradation of pollutants in the
contaminated soil.
2.0 MATERIALS
AND METHODS
2.1 Source and Collection of
Samples
Top soil sample (0-20 cm deep) shall
be collected from a maize farm in Nya Odiong village in Mkpat Enin Local
Government Area of Akwa Ibom State. Mkpat Enin is one of the thirty one Local
Government Areas of Akwa Ibom State in which farming is the major source of
livelihood of the people. The soil samples shall be collected
into new polyethylene bags and labeled properly. Organic manure
(cow dung) shall be collected in nylon bags from the popular “Nasarawa”
livestock market cattle ban, along Uyo L.G.A. road, by Ibom Science Park, Uyo,
Akwa Ibom State. Inorganic fertilizer and pesticides shall be purchased from
Akpan Andem Market in Uyo metropolis, Akwa Ibom State. Akwa Ibom State is located within the belt of the
Niger Delta region of Nigeria. The State
lies between Lat 7030’N and 7045’N and Long 7030’E
and7040’E. All the samples shall be transported to the Postgraduate Laboratory of the Department of
Microbiology, University of Uyo for analyses.
2.2 Soil Sample Treatment with Test Pesticides
The
soil sample shall be sieved through a 2.00 mm width mesh to remove stones and plant
debris. One kilogramme of soil sample shall be treated with one and half times
of recommended doses of each pesticide to be studied. Generally, the use of
x1.5 recommended pesticides rates shall be taken to correspond approximately
with the local peasant farmer’s practice (Mathews, 1992). Four pesticides shall
be used for this study. One kilogramme of the soil samples shall be first separately
treated with x1.5 doses of each of the pesticides, while another set treated with
distilled water to served as control.
2.3 Application of
soil amendments to pesticide-treated soil samples
Each of the pesticide treated soil
samples shall be exposed to organic manure and inorganic fertilizer amendments (50g/1kg
of soil sample for organic manure and 5g/1k of soil sample for inorganic
fertilizer). The treatments shall be replicated and kept in plastic bowls in
the laboratory. The experimental design and sampling method shall be completely
randomized. Soil samples shall be taken for analysis on a weekly basis for eight weeks to test for biodegradation
of the pesticides.
2.4 Microbiological Analysis of the Sample
The analysis will be conducted in line with the submissions and
approved quality assurance and quality control plan for microbial studies. The
quality control and quality assurance policy adopted will cover all aspects of
the activities from sample collection, to accurate preservation techniques
through laboratory analysis to data validation. Every sample will be
aseptically collected and preserved appropriately. Analysis will be conducted
using scientifically accepted techniques and high quality standard non-expired
reagents and culture media.
2.4.1 Enumeration of Bacteria and Fungi Loads
Serial dilutions of each
of the soil samples in 0.1% peptone will be
used for microbial isolation. Isolation method will be similar to those
recommended by van den Berg et al. (1993) in which a ten-fold serial dilution of the samples using
one ml unpasteurized
milk samples in 9 ml of sterile water
will be carried out. One
ml of the desired dilution levels shall be plated in triplicates using the pour
plate method on nutrient agar (NA) for total heterotrophic
bacteria counts (THBC), McConkey agar for total coliform counts, Eosine
Methylene Blue (EMB) for faecal coliform (E.
coli) counts and Saboraud dextrose agar (SDA) for fungi counts (APHA,
1992).
The bacterial plates shall be incubated for 24
hours at 37oC in a Gallenkamp incubator and fungal plates at room
temperature (28oC + 2oC) for four days. Microbial
colonies that emerged on the incubated plates after 24 hours shall be
enumerated with the aid of a Quebec Colony counter and recorded as colony
forming units (cfu) per millilitre of soil samples.
2.4.2 Isolation and Maintenance of Stock Cultures of Pure
Bacterial Isolates
Discrete
colonies of bacterial and fungal isolates shall respectively and repeatedly be
sub-cultured onto Petri dishes containing freshly prepared nutrient agar and
SDA respectively to obtain pure (cultures) isolates. Thereafter, the pure
microbial isolates shall be preserved in McCartney bottles containing 10% of
sterilized Glycerol solution (autoclaved at the temperature of 121oC
for 15 minutes) and shall be
kept refrigerated at 4oC for subsequent
characterization, a method recommended by Wellington, Griffiths and Bailey (2003).
2.4.3 Characterization
of Bacterial Isolates
The
pure bacterial isolates shall be grouped into recognizable taxonomic units and
characterized to their generic level using standard procedures. The pure
isolates shall be examined for colonial morphology, cultural and biochemical
characteristics according to the methods of Gerhardt, Murray, Kostilow, Nester,
Wood, Krieg and Philips, (1981); and Ogbulie, Uwaezuoke, and Ogiehor, (2001).
The biochemical tests to be used for characterization of the isolates shall include
Citrate, Oxidase, indole, Urease, Catalase, Methyl red and VogesProskauer,
Motility, Starch hydrolysis, Carbohydrate fermentation tests (Glucose, Sucrose,
Lactose, Maltose, Fructose, Galactose and Dextrose).
2.4.4 Characterisation
of Fungal Isolates
Similarly
the pure fungal isolates shall be grouped into recognizable taxonomic units and
characterized to their generic level according to the taxonomic schemes of
Cowan (1985) and Barnett and Hunter
(1987). Identification was based on morphological characteristics of the colony
including colony diametre, colour, exudate and colony texture, which is
primarily used to establish the genera.A direct mount to determine the genus
using lactophenol, microscopic characteristics for the verification were
asexual structures such as pseudo-hyphae, septate or non-septate hyphae,
endoconidia and sexual structures such as arrangement of cell wall, number,
shape and size of ascospores or basidiospores (Barnett and Pankhurst, 1987; and
Abbey, 1995).
2.5 Data
Analysis
Data generated shall be subjected to analysis of
variance (ANOVA), while Duncan’s Multiple Range Test and Least Significance
Difference (LSD) at P<0 .05="" be="" for="" o:p="" of="" shall="" significance.="" statistical="" test="" used="">
3.0 COST
ESTIMATION
S/N
|
TASK
|
AMOUNT (
|
1
|
Acquisition of Materials
|
50,000.00
|
2
|
Samples Collection
|
100,000.00
|
3
|
Laboratory Analysis
|
200,000.00
|
4
|
Statistical Analysis
|
50,000.00
|
5
|
Typing/Printing/Binding of Work
|
30,000.00
|
6
|
Transportation
|
20,000.00
|
7
|
Miscellaneous
|
100,000.00
|
Total
|
550,000.00
|
4.0 TIME FRAME
FOR COMPLETION OF WORK
S/N
|
TASK
|
DURATION
|
1
|
Acquisition of Materials
|
May, 2017
|
2
|
Writing/Correction of Chapters 1 –
3.
|
June – Aug., 2017
|
3
|
Sample Collection
|
September, 2017
|
4
|
Laboratory Analysis
|
Sept. – Nov., 2017
|
5
|
Research Documentation/Discussion/Correction
|
Dec., 2017. – Feb., 2018
|
6
|
Submission of Final Work
|
April, 2018
|
5.0 CONCLUSION
At the end of the research, microbial
species capable of degrading pesticides in soil shall be investigated. A baseline information on the effects
pesticides on soil micro flora in Mkpat Enin Local Government Area shall
be established.Bestupdate
No comments