Effect of Phytotoxicity of Pendimethalin Residues and its Bioremediation on Growth and Anatomical Characteristics of Cucumis sativus and Echinochloa crus-galli Plants
Mohamed F. El-Nady
Elsayed B. Belal
The aim of the present study was to investigate the influence of Pendimethalin (PM) on growth and anatomical characteristics of Cucumis sativus and Echinochloa crus-galli plants. Moreover, Psudomonas putida and compost were evaluated for detoxification of PM in soil. Seeds were sown in pots containing either PM treated soil or PM and P. putida or compost treated soil. Twenty eight days later, the phytotoxicity bioassay was performed on the growing plants. PM significantly decreased germination and increased seedling mortality percentages. Cotyledonary leaf and hypocotyls and true leaves of C. sativus seedling treated with PM seemed to be dark green colors, swelling and brittleness. In addition, reduction in fresh and dry weights of the treated plants was observed. In contrary, chlorophyll contents were significantly increased. Reducing in number of xylem vessels was found not only in hypocotyl but also in the first true leaf of C. sativus plants. Insignificant differences were observed in the most growth and anatomical parameters between P. putida or compost applying in PM contaminated soil comparing with PM treated plants. P. putida and compost were effective in PM degradation in soil with half-life of 4.67 and 5 days, respectively. PM half-life was 51.9 days in untreated clay soil. The results suggested that bioremediation by P. putida and compost was proved as an effective method for detoxification of pendimethalin in soil.
Received: November 12, 2012;
Accepted: February 20, 2013;
Published: May 18, 2013
Pendimethalin (N-(1-ethylpropyl)-2, 6-dinitro-3,-4-xylidine) has the empirical
formula C13H19N3O4, a selective
pre-emergent herbicide a dinitroaniline group, is used extensively for weed
control in cotton, rice, soybean and tobacco (Smith et
al., 1995). It has been reported that the use of pendimethalin (PM)
before crop emergence or planting resulted in the production of stunting plant
portions due to root and shoot growth inhibition. The reason of such inhibition
was due to the alteration of cell division steps needed for chromosome separation
and cell wall formation (Parka and Soper, 1977; Appleby
and Valverde, 1988). Studies in terrestrial ecosystems showed that 10-20%
of the herbicide vaporizes within the first week or two after application. The
observation of phytotoxicity to crops and weeds 200 days after application confirms
that the dissipation time of PM is high enough to harm plants far beyond the
period during which it is intended to be active (Strandberg
and Scott-Fordsmand, 2004). PM has been classified by the US Environmental
Protection Agency (EPA) as a Persistent Bioaccumulative Toxic (PBT) (Kamrin,
1997; Megadi et al., 2010).
In order to protect rotation crops from injury, the use of PM should be minimized.
As microorganisms can mineralize and detoxify pesticides and use them for their
growth, bioremediation should be considered for accelerating the rate of elimination
of pesticide from contaminated water and soil. Meanwhile, successful microorganisms
used for bioremediation should have high degradation ability and should be stable
under varied conditions, such as changes in pH and temperature. Therefore, it
is necessary to investigate the effects of various environmental factors on
the growth ability of the tested microorganisms (Pattanasupong
et al., 2004). On the other hand, it was found that various materials
were used as soil amendments, nutrients, to increase and enhance the degradation
potential of xenobiotics such as Yard manure compost (Guo
et al., 1991; Leoni et al., 1992;
Liu et al., 1995; Gan et
al., 1996; Zheng and Cooper, 1996; Grigg
et al., 1997; Vidali, 2001) biogas slurry
and compost (Belal et al., 2008). However, after
remediation toxicity assessments are needed. Firstly, is providing valuable
and complementary information to compound analysis. Secondly, the major advantage
of toxicity tests is the direct assessment of the potential hazard to the environmental
system by both original pollutants and its metabolites (Ahtiainen
et al., 2000). Therefore, this study attempted to evaluate Psudomonas
putida and compost in remediation of PM contaminated soil. In addition to
confirm the complete detoxification of pendimethalin by measuring the toxicity
of the treated soil in the presence of bacterial strain or compost against sensitive
target weed (Echinochloa crus-galli) and non-target plant (Cucumis
MATERIALS AND METHODS
Chemicals: Pendimethalin (N-(1-ethylpropyl)-2, 6-dinitro-3,4-xylidine)
standard was obtained from Ehrenstorfer (Germany). All other chemicals were
of analytical grade.
Microbial degradation of the pendimethalin
Media: M9-Minimal medium as Mineral Salt Liquid (MSL) and Luria Bertani
(LB) a complete medium were used through this study as described by Sambrook
et al. (1989).
Source and identification of microorganism: Pseudomonas putida
(E1) was isolated and identified in previous study (Belal
and El-Nady, 2012).
Bioremediation of PM contaminated soil and phytotoxicity test: Pot experiments
were conducted at the greenhouse of the Agriculture Botany Department, Faculty
of Agriculture, Kafrelsheikh University, Egypt. The phytotoxicity bioassay of
(PM) was performed on the contaminated soil after 28 days treatment with P.
putida (E1) and compost. Cucumber plants Cucumis sativus L., cultivar
Hisham and barnyardgrass Echinochloa crus-galli (Obtained from Rice Weeds
Research Department, Rice Research and Training Centre, Sakah, Kafrelsheikh)
were used as the test organisms. The phytotoxicity was determined as deformation
in morph-physiological and histological measurements comparing to the treatments
with P. putida (E1) and compost. All treatments were compared with control
treatment (untreated soil).
Clay soil had no previous history of PM concentration was collected from top
12-15 cm randomly following standard procedure and sieved through 2 mm size
sieve (Gupta, 2000). The experiments were conducted in
1000 g capacity pots (polyethylene pots, 20 cm inner diameter and 30 cm in depth),
each having 1000 g dried clay soil. Soil was contaminated with PM (100 μg
g-1 soil) at 2% moisture level in their respective treatment pot
before one week from cucumber sowing.
P. putida (E1) was cultured onto mannitol salt agar (MSA)+pendimethalin
for 7 days and then the growing colonies were washed with 3 mL sterilized Mineral
Salt Liquid (MSL) medium. One hundred mL from cell suspension (107
CFU mL-1 for bacterial strains) was then used to inoculate 1 kg clay
containing (100 μg g-1) from pendimethalin before one week from
cucumber sowing, mixed well and kept under incubation for 28 days at temperature
Compost was used as soil amendments. The calculated quantity i.e. 100 g of
compost was applied before sowing of trial in respective treatment pot, mixed
well and kept under incubation for 28 days at 30±2°C (Belal
et al., 2008). Physicochemical characteristics of used clay soil
and compost are presented in Table 1.
The soil used in this experiment was fertilized with nitrogen at rate a 360
kg ha-1 of urea fertilizer (contain 46% nitrogen). Super phosphate
fertilizer (phosphorus 15%) was added at a rate of 240 kg ha-1 before
planting. Potassium was not added because the Egyptian soil is rich in this
Five cucumber seeds of (Cucumis sativus L., cultivar Hisham) and barnyardgrass
(Echinochloa crus-galli) were sown on 1st of October 2010 in each pot
after one week from soil contamination with pendimethalin.
The residue half-live (RL50) for PM residues was calculated using
the equation of Moye et al. (1987). Control
pots of equal weight of soil and pesticide without any microbial population
or compost were run in parallel at all intervals to assess a biotic losses as
well as measuring of the botanical parameters on the tested plants.
Growth characters and chlorophyll pigment determination: Germination
percentage was determined at 15th day from sowing. Percentages of seedling mortality
were calculated as percentages of total number of germinated seeds. For seedlings
characters, samples were taken at 15 days from sowing to estimate seedling fresh
and dry weights (dried in an electric oven at 70°C for 72 h) g plant-1.
Chlorophyll a, b and total were determined in cotyledonary leaf and the first
true leaf of cucumber (C. sativus) plants and in the second leaf of barnyardgrass
(E. crus-galli) using spectrophotometer method as described by Moran
and Porath (1980).
Histological parameters calculation: C. sativus hypocotyl specimens
were taken from the middle region. The leaf specimens including the midrib were
taken from the first true leaf. For E. crus-galli, leaf specimens including
the midrib were taken from the second leaf from the plant tip. Specimens were
taken on day 15th of treating. Specimens were taken on 10th day of sowing. Specimens
were fixed in formalin alcohol acetic acid mixture (FAA, 1: 18: 1; v/v), washed
and dehydrated in alcohol series. The dehydrated specimens were infiltrated
and embedded in paraffin wax (52-54°C m.p.). The embedded specimens were
sectioned using a rotary microtome (Leica RM 2125) at a thickness of 8-10 μm.
Sections were mounted on slides and deparaffinized. Staining was accomplished
with safranine and azur II (Gutmann, 1995) cleared
in xylol and mounted in Canada balsam (Ruzin, 1999). Ten
reading from 3 slides were examined with electric microscope (Leica DM LS) with
digital camera (Lieca DC 300) and then photographed. The histological feature
of the hypocotyl was thickness of hypocotyl, vascular and cortex tissues as
well as number of vessels/bundle. Moreover, the histological features of the
first true leaf were thickness of lamina, midrib region, midrib vascular bundle,
mesophyll (palisade and spongy tissues) and vascular tissues (xylem and phloem)
in addition to the No. of vessels/midrib vascular bundle. Also, leaf lamina
thickness of E. crus-galli was calculated. The histological manifestation
was calculated using Lieca IM 1000 image manager software. Lieca software was
calibrated using 1 cm stage micrometer scaled at 100 μm increment (Leitz
Wetzler, Germany 604364) at 4 and 10 X magnifications.
Statistical analysis: Data were subjected to statistical analysis of
variance according to Gomez and Gomez (1984).
Analytical procedure: Extraction and determination of PM residues was
carried out by the described method by Jazwa et al.
(2009) at Central Agric. Pesticides Laboratory, Agricultural Research Center,
Ministry of Agriculture and Land Reclamation, Egypt. PM residue in soil was
monitored weekly after application date. At each sampling time four soil samples
were taken from randomly selected pots of cucumber plants. At the end of that
test, PM residues were determined. Soil samples were air-dried, ground and stored
at room temperature prior to analysis but no more than three days. Subsamples
(20 g) were extracted by shaking for one hour with 100 mL of dichloromethane-acetone
mixture (9:1 v:v) on a rotary shaker. The extract obtained, was decanted by
a layer of anhydrous sodium sulphate and the soil was rinsed two times with
10 mL of dichloromethane (Luke et al., 1975,
1981; Ambrus et al., 1981).
The extract was cleaned using florisil (Ahtiainen et
al., 2000). The analysis of the extract was performed using a Hewlett
Packard 5890A Gas Chromatograph, equipped with Nitrogen-phosphorus Detector
(GC-NPD). The column used in this study was an HP fused-silica capillary column
coated with cross-linked methyl silicone (length 25 m, ID 0.31, film thickness
0.52 μm). Nitrogen was used as both the carrier and make-up gas at a flow
rate of 30 mL min-1. Hydrogen was used at a flow rate of 3.5 mL min-1
and air at 120 mL min-1. The oven temperature was programmed as follows:
initial temperature 150°C (1 min), rate of 10°C min-1 and
final temperature 250°C. Recovery studies were carried out regularly by
spiking analytical samples with stock solution of pendimethalin standard.
RESULTS AND DISCUSSION
Effects of pendimethalin (PM) contaminated soil on growth and histological
parameters of C. sativus and E. crus-galli were studied. Investigated
plant growth parameters were seed germination, fresh and dry weight and chlorophyll
pigments contents. The detailed histological examinations included hypocotyl
and the first true leaf in C. sativus and leaf thickness in E. crus-galli.
In addition, P. putida and compost were evaluated for detoxification
of PM in soil.
Phytotoxicity assessment: The effect of the remaining toxicity of PM
in clay soil on germination, growth and anatomical characters of C. sativus
and E. crus-galli plants was estimated after it treated with compost
and P. putida (E1) as follow:
Germination characters: The results in Table 2 showed
the influence of the remaining toxicity of PM in clay soil on germination and
seedling mortality percentage of the two tested plants after it treated with
compost and P. putida (E1). PM caused the highest value in reduction
germination and increasing seedling mortality percentage comparing with control
treatment. These parameters were improved with compost and P. putida
(E1) treatment comparing with PM treatment. Compost treatment was more effective
in reduction of seedling mortality comparing with P. putida (E1) treatment.
The efficacy of compost and P. putida (E1) was similar in increasing
of germination percentage of the tested plants comparing with PM treatment.
All treatments were compared with unweedded treatment (control) after 15 days
from sowing. Germinating plants absorb PM through epidermis of root, coleoptile
or young shoots which come into close contact with the herbicide. Similarly,
to other dinitroanilines, PM inhibit the formation of mitotic apparatus microtubules
thus affecting chromosome movement and inducing formation of polyploid cells
(Tarkowska et al., 1994). They stated that PM
acts on fragmoplast causing formation of multinuclear and also on cortical microtubules
causing isodiametric growth of cells and disturbance in secondary cell wall.
These lead to the formation of swelling on root tips and at the base of the
stem (Smeda and Vaughn, 1997). This may lead the inhibition
of seed germination and increasing seedling mortality percentages.
Growth characters: Data presented in Table 3 and Fig.
1 illustrate the effect of the remaining toxicity of PM in clay soil on
fresh and dry weight of C. sativus and E. crus-galli seedlings
after it treated with compost and P. putida (E1).
||Effect of the remaining toxicity of pendimethalin in clay
soil on cucumber (C. sativus) and barnyardgrass (E. crus-galli)
seed germination and seedling mortality percentage after it was treated
with compost and P. putida (E1)
|| Seedling 15 days after sowing of (a): C. sativus and
(b): E. crus-galli, 1: Control (untreated), 2: PM+compost, 3: PM+P.
putida (E1), 4: PM, Hypocotyl (H), CL: Cotyledonary leaf, P: Plumule,
FTL: First true leaf, Bar = 1.5 and 3 cm
||Effect of the remaining toxicity of PM in clay soil on hypocotyl
length, fresh and dry weight of C. sativus and fresh and dry weight
of E. crus-galli seedlings after it was treated with compost and
P. putida (E1)
Reduction in C. sativus hypocotyl length values were found in PM treatment.
Fresh and dry weight/plant values were reduced in case of treatment with PM
comparing with the other treatments. These parameters were increased with compost
and followed by P. putida (E1). The control (without PM) treatment recorded
the highest value for the measured plant parameters comparing with the other
treatments. PM treatment reduced the measured botanical parameters more than
the other treatments and this due to PM residues in soil which were 95, 30 and
25% with PM, compost and P. putida (E1) treatments, respectively. These
plant parameters were improved gradually when PM residues were disappeared.
Chlorophyll pigments: Application of PM significantly increased chlorophyll
pigment (chlorophyll a, chlorophyll b and total contents of chlorophyll) in
cotyledonary and the first true leaf of C. sativus seedling compared
with the other treatments (Table 4). Chlorophyll pigment contents
in cotyledonary leaf were higher than in the first true leaf. Similar results
were recorded in E. crus-galli (Table 5). It was interesting
to note that, the increase in chlorophyll pigment contents was accompanied with
the increase in mesophyll tissue thickness.
||Effect of the remaining toxicity of pendimethalin in clay
soil on chlorophyll pigment (a, b and total chlorophyll) of cotyledonary
and the first true leaves of C. sativus seedlings after it was treated
with compost and P. putida (E1)
||Effect of the remaining toxicity of pendimethalin in clay
soil on chlorophyll pigment (a, b and total chlorophyll) in the second leaf
of E. crus-galli plants after it was treated with compost and P.
putida (E1) 15 days from sowing
Anatomical characters: The hypocotyls internal structure of cucumber
was similar to stems of dicotyledon plants. The hypocotyl structure of cucumber
plants as seen in transverse sections consists of the epidermis, ground tissue
and vascular system (Fig. 2). The regions between the bundles
were parenchymatous. The vascular bicollateral bundles arranged in complete
cylinder (Siphonostele: eustele). Two types of bicollateral vascular bundles
were present, i. e., large and small bundles. Data presented in Table
6 revealed that, effect of the remaining toxicity of PM in clay soil on
some anatomical parameters of cucumber seedling hypocotyl after it treated with
compost and P. putida (E1). Application of PM increased seedling hypocotyl
cross section, cortex and conductive vascular tissues (xylem and phloem) thickness
compared with the other treatments. On the other hand, the lowest number of
vessels per bundle was reduced by PM treated soil in comparison with the other
treatments. Application of compost and P. putida (E1) decreased these
anatomical parameters compared to control (Table 6).
The leaf lamina internal structure of C. sativus plants was similar
to other dicotyledons plants. It consists of upper and lower epidermis and mesophyll
tissue, which differentiate into palisade and spongy parenchyma. Epidermis,
one layer of completely arranged parenchymatous cells, which were flattened
parallel to the leaf surface. The palisade parenchyma cells elongated and completely
arranged. The spongy parenchymatous cells loosely arranged with numerous large
intercellular spaces. Data presented in Table 7 and Fig.
3 indicated that, anatomical parameters of the first true leaf of C.
sativus show similar trend as those of seedling hypocotyl. Lamina, palisade,
spongy, conductive vascular tissues as well as midrib thickness were induced
by PM soil treatment in comparing with other treatments. Number of vessels per
bundle was 3 for PM treatment and 13, 12, 14 for compost, P. putida (E1)
and control, respectively. Irregular xylem vessels and were noticed not only
in hypocotyl but also in the midrib vascular bundle of the first true leaf treated
with PM. Moreover, xylem vessel diameters seem to be smaller in comparing with
|| Cross sections through cucumber (C. sativus) hypocotyl,
a-b: PM, c-d: PM+P. putida (E1), e-f: PM+compost, g-h: Control (untreated),
HC: Hypocotyls cavity, Xy: Xylem, Eph: External phloem, Iph: Internal phloem,
C = Cortex (Co), V: Vessel, Bar = 500 μm
||Effect of the remaining toxicity of pendimethalin (PM) in
clay soil on some anatomical parameters of cucumber seedling hypocotyl after
it was treated with compost and P. putida (E1)
||Effect of the remaining toxicity of pendimethalin in clay
soil on some anatomical parameters of the first true leaf of cucumber plants
after it was treated with compost and P. putida (E1)
Concerning E. crus-galli leaf, internal structure of leaf lamina is
similar to other moncotyledonous plants.
|| Cross sections through the first true leaf of C. sativus
plants, a-b: Pendimethalin, c-d: Pendimethalin+P. putida (E1), e-f:
Pendimethalin+compost, g-h: Control (untreated), HC: Hypocotyls cavity,
Xy: Xylem, Eph: External phloem, IPh: Internal phloem, VC: Vascular cambium,
V: Vessel, UE: Upper epidermis, LE: Lower epidermis, T: Trichome, PT: Palisade
tissue, ST: Spongy tissue, Bar = 500 μm
||Effect of the remaining toxicity of PM in clay soil on E.
crus-galli leaf lamina cross section thickness after it was treated
with compost and P. putida (E1)
Data in Fig. 4 and Table 8 indicted that,
application of PM increased leaf lamina thickness and the cells of upper and
lower epidermis seemed to be wider compared with untreated plants. On the other
hand, application of PM in combination with each compost and P. putida
(E1) caused a reduction in lamina thickness relative to the control. The lowest
leaf lamina thickness was obtained by application of PM in combination with
P. putida (E1). Leaf cells seem to be wider in each PM and in the combination
with compost and P. putida (E1) than the control plants. It is interesting
to indicate that, the internal growth parameters were concomitant with the growth
parameters. No available literature was found concerning the anatomical differences,
which might be useful for understanding the effect mechanisms of PM on cucumber
Herbicides play an important role in the production of vegetables but their
residues may cause numerous environmental problems. First of all, they may contaminate
surface and groundwater through leaching and run-off.
|| Cross sections through leaf lamina of E. crus-galli
plants, a-c: PM, d-f: PM+compost, g-i: PM+P. putida (E1), j-l: Control
(untreated), UE: Upper epidermis, LE: Lower epidermis, MT: Mesophyll tissue,
MC: Motor cells, MVB: Midrib vascular bundle, Bar = 500 μm
They may also remain on the soil surface and potentially affect quality and
yield of the next crop cultivated on the same field. Finally, stable herbicides
might be taken up by a plant forming unwanted residues. With regard to plants,
PM shows differential toxicity to various species and there is a formulation-dependent
toxicity to non target plant species.
PM is similar to other broad-spectrum herbicides in that it is phytotoxic to
crop species to some extent. In the development of herbicides, screening experiments
are conducted to ascertain extent of phytotoxicity to crops. The phytotoxicity
of PM to crop species has been the focus in numerous experiments, for example,
rice grain and straw yield (Devi and Gowda, 1985),
root suppression of pampas grass (Green et al.,
1997), effect of repeated application on cotton yield and quality, cotton
fiber quality and yield (Keeling et al., 1996).
Tylicki et al. (2010) observed inhibition of
root elongation of Allium cepa after 48 h of incubation with PM. This
effect was caused by the inhibition of mitoses varying from 1/3 to 1/2 in the
case of 0.033, 0.066 and 0.099 g L-1 of pindimethalin and almost
complete restriction of mitoses under higher concentrations. PM caused mitotic
disturbances (c-metaphases, anaphasal and telophasal chromosome bridges, multipolar
anaphases) and interphase abnormalities (micronuclei, multinuclear cells). This
effect was irreversible during a 48 h postincubation in water. Mitotic disturbances
were caused by abnormalities in the organization of the tubulin cytoskeleton.
It suggests that even small amounts of PM can be a danger for dividing cells
There is indication that dinitroaniline herbicides (include PM) inhibit photosynthesis,
oxidative phosphorylation, protein, nucleic acid and lipid synthesis (Moreland
et al., 1972). Cotyledonary leaf and hypocotyls and first true leaf
of C. sativus seedling treated with PM seem to be dark green colors,
swelling and brittleness. PM treatment caused reduction in primary root length
and number of lateral roots. This may be due to the ridicule is the first organ
to come directly contact with PM in the soil. Compost and P. putida (E1)
disappeared the dark green colors and improved of the lateral roots. Smith
(2006) recorded, that PM markedly inhibited the growth of both seedling
weeds and crops. It was found that, dinitroaniline herbicides kill seedling
weeds by inhibiting the development of lateral roots in susceptible plants,
stunting the above-ground parts, with the development of a dark green color,
swelling and brittleness of the stem or seedling hypocotyl (Parka
and Soper, 1977). Severe crop phytotoxicity and damage symptoms reported
in literature range from reduced or inhibited germination, reduced root length,
protein and nucleic acid contents of root tips, injured flowers, to complete
crop failure and residual persistence of herbicides in crop and soil (Henderson
and Webber, 1993; Sinha et al., 1996). PM
caused seedling mortality (Aluka, 1997), but doesn't
prevent seedling emergence (Akobundu, 1984; Smith,
2004). In the present study, applications of PM reduced seedling emergence
lower than the other treatments. The higher seedling phytotoxicity could be
attributed to PM concentration in soil. Thus, a carryover of herbicide residues
from one crop season to following one may occur even through the development
of modern herbicides has been directed toward a short half-live in the environment
(Fayez and Kristen, 1996).
Bioremediation of pendimethalin contaminated soil test: Results in Fig.
5 show the degradation rate of PM by P. putida (E1) and compost in
clay soil. PM was degraded similar by P. putida (E1) and compost. PM
half-lives were 4.67 and 5 days for P. putida (E1) and compost in clay
soil, respectively. PM half-live was 51.9 days in untreated clay as control
treatment. The loss of PM treatment was 23% and this may be due to evaporation,
drift or leaching. The trend of degradation rate of PM by bacterial strain and
compost was similar in the tested soil. The obtained results showed that the
bacterial strain and compost play an outstanding role in degradation of PM in
clay soil. Exhibited increasing in loss of PM after initial phase (7 days) and
thereafter degradation of the PM was increased gradually till end of the incubation
time 28 days and this may be due to accumulation of biodegradation products.
Biodegradation of pesticides in soil was reported with microorganisms and compost
(Liu et al., 1995; Belal
et al., 2008). Previous studies by (Karpouzas
and Walker, 2000) have reported the isolation of two ethoprophos-degrading
P. putida strains, which were also able to degrade cadusafos but in a
less efficient way compared to the Flavobacterium and Sphingomonas
strains. Flavobacterium strains have been reported to be responsible
for the degradation of carbofuran (Chaudhry and Ali, 1988).
||Bioremediation of PM contaminated soil by P. putida
(E1) and compost and their effects on population of microorganisms in soil
More potent strains that degraded PM rapidly were obtained from a soil samples
which PM had been applied or exposed for a number of years or the time an enrichment
technique. This indicates that repeated applications or exposure of soil or
mature compost to xenobiotic compounds for a long period of time can result
in the evolution of microorganism's capability of degrading these compounds
rapidly and more extensively.
Although addition of these bioprocessed materials has been an integral part
of sustainable agriculture practices and offers a good nutrient source for microbes
(Laine and Jorgensen, 1996) and enhancers of microbial
activity include moisture, inorganic nutrients and oxygen. There are many well-established
bioremediation technologies applied commercially at contaminated sites. One
of such technology is the use of compost material and biogas slurry. Compost
is rich sources of microorganisms, which can degrade contaminants to innocuous
compounds such as carbon dioxide and water.
Earlier studies have also reported that bioprocessed materials such as compost
and biogas slurry were used to degrade of atrazine herbicide in contaminated
soil using various bioprocessed materials (Liu et al.,
1995). Due to their high organic matter content, all bioprocessed materials
accelerated cadusafos and carbofuran breakdown. Earlier studies have also reported
high microbial biomass in soil that received the organic carbon amendment (Devi
and Gowda, 1985), who found that addition of compost provided a rich source
of microorganisms. Kulshrestha and Singh (1992) observed
that 11-14% of PM degradation could be attributed to microbial transformation
in sandy soil after 91 day. Smith et al. (1979)
reported that, after application to soil, PM may dissipate through evaporation,
drift, leaching and runoff. A laboratory experiment simulating winter conditions
showed that as much as 10% of the applied pendimethalin (0.6 mg kg-1
applied) evaporated if it was applied on the soil surface. Nayak
et al. (1994) investigated the effect of PM on populations of bacteria,
fungi and actinomycetes in sesame soil (sandy loam, pH 5.8, available N, P and
K 21, 23.7 and 53.75 kg ha-1, respectively) at Bhubaneshwar, India.
The dilution plate method was used to enumerate populations of bacteria, fungi
and actinomycetes from soil samples. It was found that PM (0.5 kg ha-1)
significantly reduced bacteria (61%) after 25 days but not after 50 and 75 days,
at which time a slight stimulation was noted as compared with the unweeded control.
Fungi were significantly reduced by 19% after 25 days and stimulated after 50
and 75 days as compared with unweeded control. Actinomycetes were substantially
reduced by 21% after 25 days and stimulated after 50 and 75 days. Sidhu
et al. (1985) and Barua et al. (1991)
studied the effect of PM on populations of fungi, bacteria and actinomycetes.
A significant decrease was observed on the first few days after the application,
but after a period of 6 weeks, recovery to the level of the control was reached
or almost reached. Bacteria were almost unaffected after 42 days, while actinomycetes
were the most one.
In the present study, bioremediation of PM-contaminated soil was studied by
addition of pure culture from P. putida (E1) and compost in 28 days.
P. putida (E1) and compost showed high ability in PM degradation. There
was no toxicity of PM detected in clay soil after it treated with P. putida
or compost on C. sativus (non-target crop) and E. crus-galli (target
plants), therefore these residues did not affected the following economical
crops. It was observed that clay soil without any amendment (i.e. control) showed
least degradation of PM. PM significantly decreases germination rate and increases
in seedling mortality rate of the tested plants. The results suggest that bioremediation
by P. putida (E1) strain and compost were considered to be the effective
method for detoxification of PM in soil system.
This study was supported by Kafrelsheikh University (Researches Support Fund),
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