American-Eurasian Journal of Sustainable Agriculture, 5(2): 209-215, 2011
ISSN 1995-0748
ORIGINAL ARTICLES
Leaching of Chlorpyrifos in Peat Soil of an Oil Palm Plantation in Malaysia
1
Halimah, M., 1Zulkifli, M., 1Tan, Y.A., 1Hasnol, O. and 2Ismail B.S.
1
Malaysian Palm Oil Board, P.O. Box 10620, 50720 Kuala Lumpur, Malaysia
2
School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti
Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
Halimah, M., Zulkifli, M., Tan, Y.A., Hasnol, O. and Ismail B.S.: Leaching of Chlorpyrifos in Peat
Soil of an Oil Palm Plantation in Malaysia
ABSTRACT
The aim of the paper is to determine the leaching and persistence of chlorpyrifos in a Malaysian peat soil.
Leaching of chlorpyrifos in this peat agroecosystem was conducted at an oil palm plantation in Sessang,
Sarawak, East Malaysia. The insecticide chlorpyrifos was applied as an aqueous solution into the trench which
was approximately 1 meter around the palm base at the rate of 3 L/palm. The insecticide was applied at the
manufacturer s recommended (2.11 gm ai/trunk) and double the recommended dosage (4.22 gm ai/trunk). The
control plot was not treated with insecticide. Soil samples were collected at different depths (viz. 0-15, 15-30
and 30-45 cm) at the following intervals; -1 (before treatment), 0,1, 3, 7, 14, 21, 30 and 60 days after
treatment. The recovery of chlorpyrifos as obtained from GC equipped with FPD was determined by analyzing
soil samples spiked with chlorpyrifos standard solutions at five different levels viz., 2, 20, 40, 60 and 80
g/kg. The recovery and relative standard deviation of chlorpyrifos in the spiked soil samples ranged from 93
to 97% and 1.1 to 9.6%; respectively. The results obtained were good and reproducible with high recovery
rates and therefore the extraction methods were used for determination of chlorpyrifos in soil samples collected
from the field. Chlorpyrifos was detected at all levels of the soil profile (0-45 cm), when applied at the
recommended and double the recommended dosages. Chlorpyrifos was detected in the soil up to day 5 after
treatment when applied at the recommended dosage. Chlorpyrifos was also detected in the soil at 0-45 cm
depth up to day 7 after treatment at double the recommended dosage. Therefore, chlorpyrifos has very low
persistence in the soiland therefore may have low impact on the environment.
Key words: Chlorpyrifos, Leaching, Peat soil, Oil palm plantation, Recommended dosage, Double
recommended dosage
Introduction
Pesticides are one of the major components of modern farming practices. Pesticides, a component of pest
management, are constantly used to safeguard the crop from deleterious effects caused by insects and disease
attack. Therefore, pesticides are of economic importance as they help prevent outbreaks that threaten the yield
and quality of crops. The fate of pesticides in the soil is greatly influenced by their interaction with the soil
components, the environment, and their transport from one environmental compartment to another (Ismail and
Kalithasan, 2003; Racke, 1993). The rate of degradation of pesticides in the soil is one of the most important
criteria that determine the behaviour of pesticides in the environment (Goring and Hamakers, 1975). Pesticides
applied to the field are potential environmental contaminants (Carton et al., 1997).
The environmental fate of pesticides has recently attracted much attention because of its potential to pollute
the environment. Lake and river water can undoubtedly be contaminated with the runoff water from adjacent
agricultural fields if the use of pesticides is not managed properly.
Heavy usage of pesticides in agricultural activities may cause adverse effects to the environment and
consequently human health. The leaching of pesticides into groundwater is a major environmental concern
Corresponding Author: Ismail, B.S., School of Environmental and Natural Resource Sciences, Faculty of Science
and Technology, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia.
E-mail: abqbzr@r.postjobfree.com
Am.-Eurasian J. Sustain. Agric., 5(2): 209-215, 2011 210
because it affects the quality of underground water (Lehmann et al., 1993). The number of different pesticides
in ground and surface water has been increasing steadily (Lehmann and Miller, 1989). Therefore, an
understanding of adsorption, desorption and mobility of pesticides in the soil warrants immediate attention.
The presence of insecticide residues in the runoff, sediment and leachate, as well as their mobility and
persistence in the soil, depends on factors such as the chemical and physical properties of the compound, soil
properties, amount of rainfall, soil bed construction and slope (Riley et al., 1994). Most pesticides, for example,
persist longer in soils with high organic matter content (Oppong and Sagar, 1992). Soil mobility and
degradation are the most important processes that determine the fate of pesticides in the soil.
Chlorpyrifos, a broad-spectrum chemical, is the most intensively used organophosphate insecticide in
agriculture (Larson et al., 1997). It is registered for the control of soil insects and some foliar insect on a wide
range of crops, including citrus fruits, bananas, strawberries, vegetables, as well as for household use (Kidd
and James, 1991). The heavy use of chlorpyrifos poses the risk of environmental pollution.
In Malaysia it was registered in 1997 for use on crops such as oil palm, rubber, coconut, chilly, cocoa,
leguminous crops, pepper and rice. Formulations of chlorpyrifos for use in Malaysian agriculture are available
under the trade name Dursban. In Malaysia, chlorpyrifos is extensively used for effective control of the leaf
folder and leafhopper that threaten the production of food crops such as rice (Racke, 1993; Arthur, 1995;
Chung et al., 1991; Hamish and David, 1991; Wood and Ng, 1969) as well as in oil palm plantations for the
control of the rhinoceros beetle, bagworm, termites, nettle caterpillar and bunch moth (Mohd. Basri and
Norman, 2000).
There has been a steady increase in the use of pesticides in developing countries although integrated pest
management (IPM) programmes are being promoted and implemented. The increasing use of pesticides poses
a growing concern regarding their presence in food and the danger of their residues in the environment.
Pesticides used in tropical countries could affect environmental quality (Tanabe et al., 1990). It has been
reported that pesticide pollution of ground and surface water is an issue in tropical countries, with heavy
rainfall, high humidity and high temperature (Halimah et al., 2010; Ismail et al., 2009; Cheah et al., 2000;
Ismail et al., 2002; Khakural et al., 1995). However, there is limited information on the impact of chlorpyrifos
in tropical environments such as Malaysia. Although extensive research has been carried out in other countries,
the results are not applicable in Malaysia because of differences in climatic and soil conditions. Therefore, the
objective of this study is to determine the downward movement of chlorpyrifos through the soil profile and
its persistence in the peat soil of an oil palm plantation, near Sessang, Sarawak.
Meterials and methods
Experimental Site
The study was conducted at the oil palm plantation of the Malaysian Palm Oil Board (MPOB) located at
Sessang, Sarawak. The experimental site was level and nine plots, each measuring approximately 0.75 hectare
were used for the study. Analysis showed that the soil contained clay (0%), coarse sand (35.5%), fine sand
(4.91%), silt (41.81%) with a total Carbon content of 49.50%, pH 3.48, soil moisture 14.85% and CEC of 59.3
Cmol /kg soil. The soil was classified as peat soil according to its soil characteristics. The palms in the
plots were treated with chlorpyrifos at either the recommended or double the recommended dosage. No
pesticide was applied to the control plots which were sprayed with water. Each treatment was replicated thrice,
the randomized complete block design was used and spraying was carried out simultaneously for all plots. The
trial was conducted from 26th July 2006 to 25th October 2006. The monthly rainfall was obtained from the
Sessang Meteorological Station during the study period (January till December 2006).
Chlorpyrifos (LORSBAN 40EC; Dow Elanco Ltd)) used in the treatments contained 21.2% a.i. (active
ingredient). It was applied as an aqueous solution to the palms by spraying using a conventional knapsack
sprayer (nozzle 5/64, fine droplets). To prepare the recommended and double the recommended dosages, 18
and 36 mL of the commercial product were diluted respectively in 9 L of water which is equivalent to 2.11
ai/trunk and 4.22 ai/trunk, respectively. Five L of the diluted product were sprayed on the trunk surface up
to the spear and the area around the palm base was drenched.
Sampling of Peat Soil from the Field Trial
The application of the insecticide chlorpyrifos was carried out in all experimental plots (in triplicate). Soil
samples were randomly collected from each replicate (plot) using an auger at different depths; 0-15 cm, 15-30
cm and 30-45 cm. Samples were collected at the following intervals: -1 (before treatment), 0 (6 h after
treatment), 1, 5, 7, 14, 21, 30, 60 and 90 days after treatment. Soil samples were dried in an air conditioned
Am.-Eurasian J. Sustain. Agric., 5(2): 209-215, 2011 211
room at 16 C and sieved through a 2 mm sieve to remove debris and large particles. The soil samples were
then stored at -4 C to inhibit microbial activity before analysis.
For the mobility study, soil samples were collected at a distance of 200 m from the base of each palm
and at different depths (0-15 cm, 15-30 cm, 30-45 cm). For each plot, five samples were taken from each
depth and combined. The soil sampling was done using an auger at the following intervals: -1, 0, 1, 3, 7, 14,
30, 60 and 90 days after treatment. The soil samples collected were air-dried in an air-conditioned room at
16 C for one week, and then ground using a mortar and pestle. Prior to the analyses, the air-dried soil samples
were sieved through a 4 mm sieve and stored at -4 C.
Reagents and Insecticide
All reagents and solvents used in the study were of analytical grade. Acetone, hexane, petroleum ether,
acetonitrile and dichloromethane were obtained from Merck. Standard chlorpyrifos (98.7% purity) was
purchased from the Laboratories of Dr. Ehrenstorfer, Germany. Commercial silica cartridges, supelclean LC-SI
(1 gm) were purchased from Supelco. Sodium chloride was obtained from Merk.
Apparatus
A Gas Chromatograph (GC: HP 6890 series) fitted with an auto sampler was used. The rotary evaporator,
N-Evap Model 1111 for evaporating the solvent, was purchased from Organomation Associates Inc., US. The
vortex mixer Type 37600 (used to shake the oil added with the acetonitrile saturated with petroleum ether for
extracting chlorpyrifos from the oil) was purchased from Thermolyne Co., USA. A solid phase extraction
manifold was purchased from Supelco. Centrifuge tubes (15 mL), vials (20 mL), volumetric flasks (10 mL)
and round bottomed flasks 10 and 50 mL were used. The WARING commercial blender was used to cut the
leaf.
Conditions for GC-FPD
A Hewlett-Packard Model 6890 GC with a Flame photometric detector (FPD) fitted with a non-polar
column coated with 5% phenyl methyl siloxane (HP-5MS), 30 m length, 0.25 mm i.d. and 0.25 mm film
thickness was used. Operating conditions for the GC-FPD were as follows: in column flow (Nitrogen) 1.2
mL/min, and inlet pressure 12.20 psi. The injector temperature was 250 C, on splitless mode. The oven
temperature was programmed from 40oC for 1 min followed by a gradual increase of 30oC/min to 220oC. After
holding for 6 min, the temperature was then increased at 20oC/min from 220 to 280EC and held for 2 min.
Determination of Chlorpyrifos in Peat Soil
The method used for determination of chlorpyrifos in the peat soil samples was according to the method
of Halimah et al. (2010) and Halimah (2007). Ten gram soil samples were placed in 250 mL conical flasks.
The soil was spiked with standard chlorpyrifos solution in acetone to obtain 2 to 80 mg/kg chlorpyrifos in the
soil, and the contents were mixed using a vortex mixer. Fifty mL of hexane were then added to each conical
flask and contents were mixed again for 30 sec on the vortex mixer. The conical flask was placed on a shaker
for 20 min. Twenty five mL of the extract were then transferred into a 100 mL round bottomed flask using
a 20 mL pipette. The solution was evaporated down to about 5 mL using a rotavapour and then transferred
into a graduated micro-vial. The extract was further evaporated to 2 mL using a N- evaporator. The contents
were then mixed in a vortex mixer for 3 sec prior to injection into the GC-FPD. The same procedure was
adopted for both the untreated and treated from the field trial samples before injection into the GC-FPD, with
the exception of the spiked standard solutions.
Results and discussion
Standard Calibration Curve for GC-FPD
To determine the reproducibility of the injection technique and linearity of the FPD response, repeated
injections of 0.02 - 0.10 mg/mL standard chlorpyrifos solution were made into the capillary GC column. The
calibration curve of the various concentrations of standard chlorpyrifos against the gas chromatographic peak
area is as shown in Figure 1. The equation derived from the above data is Y = 2462.6x + 3.7375, where y
is the peak area of standard chlorpyrifos solution and x is the concentration in mg/mL. The r2 for the curve
is 0.9955 at 99% confidence.
Am.-Eurasian J. Sustain. Agric., 5(2): 209-215, 2011 212
Fig. 1: Calibration curve of standard chlorpyrifos solution against the peak area (GC-FPD)
Recovery of Chlorpyrifos from Peat Soil Samples
Table 1 shows the recovery of chlorpyrifos from spiked soil ranging from 93- 97% with relative standard
deviation of 1.1 to 9.6%. The retention time of chlorpyrifos was around 10.40 min. Figure 2A shows the GC
chromatogram of standard chlorpyrifos solution at 0.02 g/mL. Figures 2B and 2C show the chromatograms
of untreated soil samples and spiked soil samples containing 0.02 mg/g chlorpyrifos, respectively. Figure 2D
shows the chromatogram of chlorpyrifos in soil from the field at 0 DAT. The limit of quantification for
chlorpyrifos in soil was 2 g/kg.
Fig. 2: GC-FPD Chromatograms of A) Chlorpyrifos standard solution @ 0.02 g/mL, B) Blank sample of
soil and C) Spiked soil samples containing 0.02 g/g of chlorpyrifos D) Soil samples from the field
trial at 0 DAT
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Table 1: Recovery of chlorpyrifos from spiked soil samples
Amount added g/kg Mean recovery Relative standard deviation
N=5 2 97 6.1
20 93 1.1
40 93 9.6
60 94 3.3
80 95 1.6
The Level of Chlorpyrifos Residue in the Soil
Figure 3 shows the chlorpyrifos residue in soil samples with treatment at the recommended dosage.
Residues of chlorpyrifos were detected in the soil samples collected at intervals of 0, 1, 3 and 5 days after
treatment at the recommended dosage. Amounts of chlorpyrifos residue detected in the soil, ranged from 0.005
- 0.306 mg/g for sampling intervals of 0 and 5 days after treatment. Chlorpyrifos residue was detected at the
depth of 0-45 cm on day 0 (the sample was taken 6 hours after application) and up to day 5 after treatment.
The highest concentration (0.0306 mg/g) was found at the depth of 15-30 cm on day 0. The rapid downward
movement of chlorpyrifos may be due to the high rainfall during the study period. It should be noted that the
monthly rainfall recorded for July, August, September and October 2006 were 96.40, 132.0, 336.80 and 212.0
mm, respectively. The total amount of chlorpyrifos at the depth of 0-45 cm was reduced by 52% from 0 Day
after treatment (DAT) to 1 DAT and by 17.41% from 1 DAT to 3 DAT for the recommended dosage.
Meanwhile, at 3 DAT to 5 DAT, the total amount of chlorpyrifos was further reduced by 42.8%. It was also
observed that chlorpyrifos was not detected at all depths tested on 7 DAT onwards (0-45 cm).
ND: Not detected =
a
DAT: Days after treatment
Fig. 3: The concentration of chlorpyrifos residue in the soil profile when applied at the recommended and
double the manufacturer s recommended dosage
Figure 3 also shows chlorpyrifos residue in the soil when applied at double the recommended dosage. A
similar pattern was observed in the downward movement of chlorpyrifos for both the recommended and double
the recommended dosages, where it was observed that the applied insecticide moved downwards through the
soil profile from 0-45 cm depth.
On 1 DAT, the amount of chlorpyrifos ranged from 0.0936 to 0.1540 mg/g at all soil depths when the
plot was sprayed at double the recommended dosage. It was also found that on the first day after treatment,
chlorpyrifos was deposited mostly at the depths of 30-45 cm. However, this compound did not persist long
in the environment and it was not detected on 14 DAT.
Am.-Eurasian J. Sustain. Agric., 5(2): 209-215, 2011 214
Conclusion
In conclusion, chlorpyrifos was observed to have easily leached into the lower layers of the soil profile
(0-45 cm depth), probably due to heavy rainfall during the study period. The persistence of chlorpyrifos in the
soil occurred for a shorter period when applied at the recommended dosage compared to persistence at double
recommended dosage. However, the chlorpyrifos residue in the soil was not detected at 14 DAT when applied
at double the recommended dosage. The results clearly showed that the half-life is shorter in tropical areas and
may not cause detrimental effects on the environment. However, this primary conclusion needs to be proved
with further research and experiments.
Acknowledgement
The authors would like to thank the Director-General of the MPOB for permission to publish this article.
Thanks are also extended to Puan Rosilawati and Rosliza Razak for their technical assistance.
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