Journal of Tropical Forest Sciences 5 (3): 342-352 342
DETERMINATION OF CYPERMETHRIN CONTENT IN
OSCILLATING PRESSURE TREATED RUBBERWOOD
Salamah Selamat, Wan Asma Ibrahim, Habibah Mohamad
Forest Research Institute Malaysia, Kepong, 52109 Kuala Lumpur, Malaysia
Universiti Pertanian Malaysia, 43400 UPM, Serdang, Selangor Darul Ehsan, Malaysia
Received August 1991
SALAMAH SELAMAT, WAN ASMA IBRAHIM, HABIBAH MOHAMAD & FAEZAH
ABOOD. 1993. Determination of cypermethrin content in oscillating pressure
treated rubberwood. Rubberwood samples at three different moisture contents were
treated with cypermethrin by oscillating pressure method. The amount of
cypermethrin in the wood was determined immediately after treatment and after
drying by calculation and by high performance liquid chromatography (HPLC).
Results showed that the amount of cypermethrin detected by HPLC was much lower
than that by calculation. Rubberwood samples of low moisture contents gave better
penetration of cypermethrin. Cypermethrin was detected only in the first layer
(1 cm) of the treated green samples at all drying conditions. For the samples treated
at lower moisture contents, cypermethrin was detected in all three layers taken.
However, the amount of cypermethrin detected decreased as the drying time
Key words : Rubberwood - oscillating pressure method - cypermethrin - HPLC
SALAMAH SELAMAT, WAN ASMA IBRAHIM, HABIBAH MOHAMAD & FAEZAH
ABOOD. 1993. Penentuan kandungan sipermethrin dalam kayu getah yang diawit
dengan kaedah tekanan berulang. Contoh kayu getah yang terdiri dari tiga kadar
kandungan kelembapan air yang berlainan diawet dengan bahan awet sipermethrin
menggunakan kaedah tekanan berulang. Kandungan sipermethrin di dalam kayu
berawet ditentukan sebaik sahaja selepas rawatan dan selepas dikeringkan dengan
cara kiraan dan kaedah kromatografi cecair berkuasa tinggi (High Performance
Liquid Chromatography, HPLC). Keputusan menunjukkan bahawa kandungan
sipermethrin yang dikesan dengan menggunakan kaedah HPLC lebih rendah dari
kaedah kiraan. Contoh kayu getah yang mempunyai kandungan kelembapan air
yang rendah menghasilkan penembusan sipermenthrin yang baik. Sipermethrin
juga dikesan hanya pada lapisan pertama (1 cm) pada semua contoh kayu yang
diawet dalam keadaan kelembapan tinggi pada semua keadaan kekeringan.
Sipermethrin dikesan pada kesemua lapisan (3 lapisan) dalam kayu yang diawet
dalam keadaan kelembapan air yang rendah. Walau bagaimanapun kandungan
sipermethrin yang dikesan berkurangan sekiranya masa kekeringan dipanjangkan.
Journal of Tropical Forest Science5 (3): 342-352 343
Boron treatment by the dip-diffusion and full-cell processes are two common
methods used for the protection of rubberwood against insects. Boron com-
pounds have been found to be suitable for the treatment of both green and
partially seasoned timber as they readily diffuse into the timber (Salamah et al.
1987, 1988). These compounds do not discolour wood but they readily leach
from the treated wood (Anonymous 1979, Zaitun & Salamah 1990). Due to this,
alternative insecticides such as synthetic pyrethroids have been tested for use in
Pyrethroids possess low mammalian toxicity and do not pose environmental
hazards. The compounds are strongly absorbed by soil and are non-leachable
and biodegradable (Briggs et al. 1983). Apart from being an agricultural insecti-
cide, pyrethroids have also been treated on logs and timbers (Berry 1979) and
have been found effective against marine borers (Rutherford et al. 1982), ter-
mites (Y oshimura et al. 1989) and wood boring insects (Baker & Berry 1980).
Oscillating pressure treatment is an effective method of treating timbers using
non-diffusible preservatives especially for refractory timbers (Wilkinson 1979).
This method has been practised in Malaysia for the treatment of rubberwood
with synthetic pyrethroids. However, the efficiency in terms of penetration and
retention of the compounds has not been assessed. The stability of the chemical
after penetration into the wood must be ensured for the treated wood to be
adequately protected during service. Its permanence inside the wood at various
stages of drying after treatment can be assessed by determining its retention
values. The results obtained can be used as a guideline to determine the required
concentration of the treatment solutions before treatment for various types of
The objective of this study was to assess the penetration and retention of
cypermethrin in rubberwood following treatment by the oscillating pressure
method (OPM) and to monitor the cypermethrin content at various stages of
drying after treatment.
Materials and methods
Preparation of rubberwood samples for treatment
In this study three sets of rubberwood samples dried at different conditions
were used as shown in Table 1. The sample size was 50 X 50 X 1200 mm. The
six replicates of the wood samples used for each drying of condition were
selected from a batch of 20 pieces. The samples selected were free from dirt, bark
and any natural or drying defects. The samples were end-coated with epoxy paint
and weighed before treatment.
Journal of Tropical Forest Sciences 5 (3): 342-352 344
Table 1. Conditions of rubberwood samples subjected to oscillating treatment
Freshly cut from newly
felled log (green)
The formulation of cypermethrin used in this study was in the form of an
emulsifiable concentrate at 0.2% w/v.
An oscillating pressure method was used for the treatment of rubberwood.
This process involves repeated applications of high and low pressures during
impregnation. The high pressure was 14.062 kg cm-2 (200 Ib in'-2), and the low
pressure was in the vacuum range of 0.98 mm Hg. The treatment time was two
hours with 40 cycles of oscillating high and low pressures. The treatment was
carried out in a wood preservation mill in Kedah. Gross retention was calculated
from the weight gain and solution concentration data.
Preparation of sample for chemical analysis
The wood samples of length 120 cm were sawn immediately after treatment
into various sections as shown in Figure la. Sections B and Bl of each sample
were used for the determination of the amount of cypermethrin in the sample.
Section Bl was cut into three layers and labelled as layer 1, 2 and 3 (see Figure
Ib). Section B and every layer of section Bl were then chipped and ground with
a hammermill separately. Special care was taken to avoid any contamination
between the three layers of ground samples.
Preparation of sample for further drying after treatment
The remainder of section X from each set of the treated sample was subjected
to air drying for four and eight weeks under shade (26°C. The remainder from
section Y of the same sets was subjected to oven drying (40°C) (maximum
temperature without shade at the Institute).
Journal of Tropical Forest Science5 (3): 342-352
• layer 1
• layer 2
Figure 1. Sampling for analysis. [A: discarded; B: Cypermethrin determination for the whole cross
section; B1: Cypermethrin determination for each layer; X: Dried in oven at 40°C;
Y: Dried in air (at room temperature) ]
After each sample had been exposed for four weeks drying time, a 5 cm length
was sawn from one end of the sample which was then cut into three layers
(similar to Figure Ib). The remaining portion was end-coated and left for eight
weeks drying time after which the same procedure of sample preparation was
followed for the chemical analysis.
Preparation of sample for HPLC analysis
Exactly 2.0 g of air dried samples were extracted in a soxhlet extractor with 125
ml hexane HPLC grade on a heated water bath for 3 h. After extraction, the extract
was filtered through a 0.5 micron PTFE membrane filter and concentrated by
evaporation. The concentrate was then transferred into a weighed
10 ml volumetric flask, made up to the volume with hexane, and the flask
reweighed. Each sample was analysed by a HPLC immediately after preparation.
The HPLC conditions were as follows;
Spherisorb 5 microns silica
1.5 ml min'-1
Journal of Tropical Forest Sciences 5(3): 342-352 346
Table 2. Factors and levels taken for statistical analysis
No. Factors Level (total no.)
green, partial dry, dry (3)
airdried, ovendried (2)
0,4,8 weeks (3)
Analysis of variance was carried out to determine if there was any significant
difference between the sample conditions and chemical retention, and between
all factors taken as shown in Table 2. The means of the main effect (factors) were
compared in order to detect any significant difference and to identify the best
among them using Duncan's Multiple range test at 5% level of significance.
Results and discussion
Table 3 shows the uptake of cypermethrin solution by the rubberwood samples
and the cypermethrin retention in samples of different moisture contents. The
mean weight gain retention values for the green, partially dry and dry samples
were 0.383, 0.775 and 0.927 kg m-3 respectively. The actual amounts of cypermethrin
determined by HPLC were 0.078, 0.173 and 0.759 kg m-3 for green, partially dry
and dry samples respectively. These results indicate significantly greater loading
values of treatment solution and cypermethrin retention as the wood moisture
content decreased (p<0.05). The actual amounts of cypermethrin in the wood
was also greatly influenced by the moisture content. However, the actual amounts
of cypermethrin detected by HPLC in the wood samples were 4.92, 4.48 and 1.22
times lower for green, partially dry and dry samples respectively, as compared to
weight gain retention. The amounts of cypermethrin in the wood samples based
on weight gain and HPLC analysis fulfill all the recommended toxic values
against Hylotrupes bajulus, Anobium punctatum (Berry 1983, 1984) and drywood
termites (Oliveira 1983) as shown in Table 4. These values are also much higher
than the recommended value given for local use which is 0.06 kg m-3 (Anonymous
1987). However, as the above toxic values are not based on local insect strains,
the recommended value should be increased since the weather for this country
is very conducive to the growth of insects and other biodeterioration agents
(Hong et al. 1982).
Cypermethrin content in the various depths of the wood after drying
The results obtained from chemical analysis carried out on the treated green
samples subjected to different drying times and conditioning show that
cypermethrin was present only in the first layers of the samples taken for all