ABSTRACT
Twenty three soil samples
were characterized for the incidence of fungal strains from Herbicides treated
agricultural soils. A total of 59 fungal strains were isolated and 33 fungi
were characterized using various isolation and identification methods. Soil
samples were also characterized for physiochemical properties. The isolated
fungal strains were successfully identified belonging to the phylum ascomycota
(7 genera), deuteromycota (2) and zygomycota (1). Alternaria, Aspergillus,
Drechslera and Fusarium were predominant genera. Curvularia, Exserohilum,
Humicola, Rhizopus and Torula were the most frequently isolated genera. Rests
of the strains were not identified owing to the lack of sporulating structures
under presently used incubation conditions. Such strains were designated as
Mycelia sterilia. Further, these species will be used in biodegradation of
commonly used Herbicides.
CHAPTER
ONE
1.0
INTRODUCTION
The agrochemical
spreading is a common and essential agricoltural practice to obtain high
quality, large harvests.
Agrochemicals are
classified according to the target organisms designed to be controlled
(insects, weeds, fungi). Of all the target organisms, weeds cause by far the
greatest economic loss due to their interference in crop production. It is not
surprising therefore, that herbicides are the most common class of
agrochemicals in the world (48% of the total expenditure) and in Europe (43%)
outstripping fungicides (35%) and insecticides (14%). Europe, Asia, and the
United States are the largest consumers of agrochemicals; in Europe, France has
the biggest agricoltural areas, and is the highest-ranking country for
pesticide consumption followed by Germany and Italy (see http://www.croplife.org/ and
http://www.ecpa.be).
Bad agricoltural practice
and accidental spreading of high doses of agrochemicals can determine toxic
effects in humans and the environment; pesticides can accumulate in organisms
and achieve critical concentrations for the human and ecosystem health.
Agrochemicals were used
for the treatment of human diseases like malaria and typhus. However, high
doses of some pesticides can be highly toxic to humans. Laboratory experiments
have shown that the administration of high doses of pesticides to animals can
cause cancer, mutagenesis, and even death; moreover, exposure to low doses can
cause skin irritation and breathing problems. In the “infamous” case of DDT,
for instance, which was introduced onto the market in 1940 for the malaria and
typhus control, the central nervous system was attacked causing loss of memory,
tremblings, and personality changes. Paraquat, a dipyridylic herbicide, is an
extremely toxic systemic pesticide; it can enter in the body by inhalation,
ingestion or direct contact. It is expecially toxic to the lungs, but can cause
gastrointestinal apparatus, kidney, liver, and heart disorders and the
weakening of other organs with vital functions.
Plants that are sensitive
to pesticide molecules may show signs of growth inhibition and loss in biomass
even as far as necrosis, but may be able to develop resistance to certain
pesticides (see http://www.weedscience.org; Yuan et al, 2007). Agrochemicals
may also have a toxic effect on nontarget plants (Madhun & Freed, 1990)
when transported away from the treated site (soluble herbicides or surface
erosion).
Soil and aquatic
ecosystems contain a multitude of microorganisms. After pesticide spreading,
microbic activity may be reduced. However, in some situations an enhancement in
microbial activity may occur (Lewis et al., 1978; Pozo et al., 1994).
The leaching of soluble
and highly mobile molecules, wilful discharge in underground wells and
accidental dumping in water bodies contribute to water contamination. Carabias
Martinez et al. (2000) monitored the concentration of fifteen herbicides
selected owing to their frequency of use, the amounts used, their toxicity and
their persistence in river basins in the provinces of Zamora and Salamanca
(Spain). After six months, the presence of six out of the fifteen herbicides
monitored, was detected at levels ranging from the detection limit to 1.2 μg/L. The presence of these herbicides
was related to agricultural activities as well as the kind of crop and its
treatment period.
The prediction of
herbicide movement and fate in soils represents an important strategy in
limiting their environmental impact (Figure 1). Physical, chemical, and
biological processes regulate herbicide mobility and degradation in soil:
rainfall and irrigation water can move herbicides along the soil profile; sites
negatively charged of clay mineral surfaces and/or organic matter can adsorb
herbicides in their cationic form at soil pH; microbial activity can promote
herbicide transformation. Different transfer and degradation processes which
control the movement and the pesticides
in the environment are reported in the Table
Justification
of the study
Various
studies have identified some micro-organisms to be able to degrade soil.
The degrading ability of these micro organisms have been determined using
different methods. However it have been agreed on by researchers that more
damage to the soil is carried out by
bacteria and fungi. This study scientifically justifies the use of fungi to
degrade soil. This project was therefore carried out to determine the degrading
ability of fungi isolated from soil-contaminated soil samples.
1.2
Objective of the study
The specific objectives of the study are to :
I.
Isolate
and identify fungi from soil-contaminated soil sample.
II.
Screen
the isolates from herbicide treated soils.
III.
Assessment
of the degrading abilities of the fungi
isolates
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