Downward Movement of Five Synthetic Pyrethroids in Three Different Soils of Gujarat

Transcription

1 Pesticide Research Journal Vol. 24(1): 76-81, June 2012 Downward Movement of Five Synthetic Pyrethroids in Three Different Soils of Gujarat Susheel Singh*, KD Parmar, MN Joshi and PG Shah AINP on Pesticide Residues, ICAR Unit-9, Anand Agricultural University, Anand , Gujarat, India Synthetic pyrethroids have extensively been used against myriad of crop pests and sanitary purposes around the world. With such extensive use, the accumulation of synthetic pyrethroids in the environment is bound to be substantial. Pesticide residues in soil can diffuse, evaporate or leach, thus having the potential to cause water pollution and other ecological problems. Present investigation dealt with the downward movement of five synthetic pyrethroids viz., bifenthrin, λ-cyhalothrin, cypermethrin, fenvalerate and deltamethrin in three different soils of Gujarat through saturated column study. The results revealed that % residues of synthetic pyrethroids were accumulated in the top section i.e. 0-5 cm in sandy soil while that of 99% were retained in sandy loam and clayey soil. The low solubility in water and the high affinity towards organic carbon of synthetic pyrethroids are the main reason for their retention in top most section of the column. Key words: Synthetic pyrethroids, downward movement, column study, soil Pyrethroids are synthetic chemical analogues of pyrethrins, naturally occurring insecticidal compounds produces in the flower of chrysanthemum (Chrysanthemum cinerariea folium). Beginning in the late 1970s, synthetic pyrethroids pesticides were successfully introduced into the agricultural market as a new generation of insecticides, owing much to their unique ability to knock down insects at lower application rates, to their lower mammalian toxicity, and to their longer stability in outdoor environment. Because of higher mammalian safety, synthetic pyrethroids group of insecticides have been widely used to control insect pests in agriculture, public health, homes and garden 1,2. In agriculture, use of pyrethroids is recommended mainly in cotton 3, cereals and vegetables for the control of aphids, jassids and lepidopterous insect pests 4. In public health management, pyrethroids are most commonly used for the control of cockroaches, mosquitoes, ticks and flies, which may act as a potent vector of various diseases. Considering the widespread use of synthetic pyrethroids, their accumulation in the environment is most likely. Despite the fact that most synthetic pyrethroids (SPs) have lower mammalian toxicity compared to other classes of insecticides (organo-chlorines and organophosphates), they can still be harmful to certain vertebrate and mammalian species including bees 5, chicks 6 and aquatic organisms 7-9. Ground water contamination with pesticide *Corresponding author susheel112233@gmail.com residues is highly detrimental. The present study was therefore taken up to establish the leaching behavior of five synthetic pyrethroids viz., bifenthrin, cypermethrin, λ-cyhalothrin, fenvalerate and deltamethrin in three different soils of Gujarat under controlled conditions. The physicochemical properties of these compounds are mentioned in Table1. MATERIALS AND METHODS A laboratory experiment was conducted to study the downward movement of five synthetic pyrethroids at All India Network Project on Pesticide Residues, ICAR Unit-9, Anand Agricultural University, Anand (Gujarat) during March-April Three different soils viz., sandy loam, sandy, clayey soil representing the central, northern and southern regions of Gujarat were collected. Prior to sampling, history of the locations were thoroughly studied and only pesticides free sites were selected. Soils were collected by the standard soil sampling procedure. Soil sample were taken up to the depth of 15 cm. Sandy loam soil samples were collected from the farm of Bidi Tobacco Research Station, Anand Agricultural University, Anand while sandy soil were collected from the Agronomy farm, Sardar Krushinagar Dantiwada Agricultural University, Dantiwada. The clayey soils, representing black cotton soil of South Gujarat region were collected from Surat district of Gujarat. Soil sample were subjected to the physicochemical analysis for texture,

2 Pestic Res J 24(1): (2012) Downward movement synthetic pyrethroids in soils 77 Table 1. Physical and chemical properties of different synthetic pyrethroids Property Bifenthrin λ-cyhalothrin Cypermethrin Fenvalerate Deltamethrin IUPAC Name 2-Methyl-3-phenylphenyl) 3-(2-Chloro-3,3,3- (RS)α Cyano-3 (RS)-alpha-Cyano- [cyano-(3- methyl (1S,3S)-3-[(Z)-2- trifluoro-1-propenyl) phenoxybenzyl 3-phenoxybenzyl phenoxyphenyl)- chloro-3,3,3-trifluoroprop- -2,2-dimethylcyano (1RS, 3 RS ~1 RS, (RS)-2-(4- methyl] 3-(2,2-1-enyl]-2,2-dimethyl -(3-phenoxy phenyl) 3SR) 3(2,2 chlorophenyl)-3- dibromoethenyl)- cyclopropane-1- methyl cyclopropane- dichlorovinyl) 2,2- methylbutyrate 2,2-dimethyl- carboxylate 1-carboxylate dimethyl cyclopropane- cyclopropane-1-1-carboxylate carboxylate Chemical structure MW WS (mg L -1 ) <0.1 Soil Adsorption (Koc) Hydrolysis half-life d ph-5 Stable Stable 619 Stable Stable ph-7 Stable Stable 274 Stable Stable ph-9 Stable Soil degradation half-life, d Aerobic Anaerobic ph, ECe, organic content etc. which are mentioned in the Table 2. After collection, soil samples were air-dried, sieved through a 60-mesh sieve, and then stored in the dark at 4 C until analysis. Column preparation: PVC columns (40 cm length 10 cm i.d.) were carefully filled with 3.0 kg soils; the columns were thoroughly tapered to minimize the chances of cracking of the column. The bulk density of column was 0.95 g /cc. The lower end of the column was tightly covered with muslin cloth while upper end was covered with aluminum foil to minimize the evaporation losses. Prior to the fortification columns were irrigated until they attained field capacity with 0.1 M aqueous solution of CaCl 2 and leachates were collected in 500 ml capacity glass bottles. Fortification and extraction: The columns were fortified with available formulations of the pyrethroids. The fortification level was fixed to 10 µg g -1 on the basis of total soil filled in a column. A mixture was prepared by dissolving 3.0, 1.2, 16.7, 1.5 and 6.0 ml of the bifenthrin (10% EC), cypermethrin (25% EC), deltamethrin (1.8% EC), fenvalerate (20% EC) and λ-cyhalothrin (5% EC) respectively in 1.0 L of double distilled water. The columns were fortified with 100 ml of this mixture. The upper surfaces of the columns were wetted with 10 ml of aqueous solution of 0.1M CaCl 2 before fortification. The columns were wetted twice in day with 20 ml of aqueous solution of 0.1M CaCl 2 up to the termination of the experiment. The experiment was conducted in duplicate along with a control column for each soil type. After the termination of experiment (10 d Table 2. Physicochemical properties of different soils used in column study Soil sample Textural class Textural details WHC ECe ph Organic (%) (1:2.5) (1:2.5) carbon (%) Sand (%) Silt (%) Clay (%) Anand Sandy Loam Surat Clayey SKNagar Sandy

3 78 Susheel Singh et al. Pestic Res J 24(1): (2012) Table 3. Retention time (R t ) and linearity equation, co-efficient of determination (R 2 ) of synthetic pyrethroids S.No Compound Retention time (min) Equation of linearity and R 2 1. Bifenthrin y=175905x R² = λ-cyhalothrin y=318334x R² = Cypermethrin y=115219x R² = Fenvalerate y=83511x R² = Deltamethrin y=39458x R² = after fortification), each column was cut into six equal sections having dimension of 5 cm (length)x10 cm (i.d.). These sections were denoted as: D-1 (0-5 cm), D-2 (5-10 cm), D-3 (10-15 cm), D-4 (15-20 cm), D-5 (20-25 cm) and D-6 (25-30 cm). The soil of each blocks were air dried at room temperature and sieved from 4 mm sieve, a representative 100 g sample was filled in a paper thimble and subjected to soxhlet extraction with 250 ml of mixture n-hexane-acetone (1:1) at 15 o C for 6.0 h. Test materials and reference standards: Reference standards (98% purity) for bifenthrin, λ-cyhalothrin, cypermethrin, fenvalerate, and deltamethrin were obtained from Sigma-Aldrich, Ltd. (USA). All organic solvents used in the analysis were purchased from Ranbaxy India Ltd. and were subjected to distillation prior to use. Quantitative analysis: Quantitative estimation of residues of various synthetic pyrethroids was performed on Trace GC Ultra from Thermo Finnigen, equipped with electron capture detector (ECD) with Ni 63. Quantitation was carried out by external standard method. A liquid handling syringe of 10 µl was used for GLC injections. Prior to quantitation, the linearity of different compounds of SPs was carried out and by plotting the detector response against the concentration of the analytes. All synthetic pyrethroids were found to be linear in the range of 0.01 to 1.0 ng ml -1. The equation of linearity and co-efficient of determination (R 2 ) values, retention time of different SPs used in the experiments are mentioned in the Table 3. GC analysis: The samples were analyzed in Trace GC Ultra from Thermo Finnigen, equipped with electron capture detector (ECD) with Ni 63 with BPx- 50 capillary column (30 mx0.32 mm (i.d.)x0.25 µm film thickness). The operating conditions were as follow: The column was held initially at a temperature of 160 C for 0.0 min, and then ramped at 7 C min -1 to 290 C, held for 10 min. The temperature of injector and detector were maintained at 210 C and 300 C respectively while the current of the ECD detector was 1.0 na. Nitrogen was used as a carrier gas at a flow rate of 1.5 ml min -1 and the injections were made in the splitless mode. The injection was made manually and injection volume was 2.0 µl. The retention time co-relation equations for linearity study and co-relation coefficients of different SPs are mentioned in Table 3. Method validation study: Soil samples of different type viz., sandy, sandy loam and clay were fortified at the level of 0.05 µg g -1 with mixtures of 5 SPs to established the efficiency of method. The recovery of all synthetic pyrethroids from 3 soils along with % relative standard deviation (% RSD), limit of detection (LOD) and limit of quantification (LOQ) was determined. Recovery study was carried out with soxhlet extraction with 7 replicates along with a control and reagent blank. RESULTS AND DISCUSSION The result obtained in the recovery study reveals that recovery of different SPs from sandy, sandy loam and clayey soil was in the range of %. The % relative standard deviation was found in the range of %. Therefore the method applied for the extraction of SPs from different soils was found accurate and precise. LOD and LOQ of bifenthrin, λ-cyhalothrin, cypermethrin, fenvalerate, deltamethrin for individual soil are mentioned in Table 4. The value of limit of detection (LOD) determined for different SPs for sandy, sandy loam and clayey soil were in the range of µg g -1 while that for limit of quantification were µg g -1. While studying the downward movement of five different synthetic pyrethroids in three different soils, it was observed that all the synthetic pesticides remain confined on the top section of the column (D-1) i.e. 0-5 cm and ranging from to 99.71%. The tabular representation of the depth wise distribution of the SP residues in different soils is mentioned in Table 5. Nonetheless, slightly higher movement of these insecticides were observed in sandy soil. Residues of different SP compounds moved to D-2 depth (5-10 cm) in sandy soil

4 Pestic Res J 24(1): (2012) Downward movement synthetic pyrethroids in soils 79 Table 4. Recovery, LOD and LOQ of SPs from sandy, sandy loam and clayey soils Pesticides Parameters Soil type Sandy Sandy loam Clayey Bifenthrin % Recovery ±SD 87.42± ± ± 1.91 % RSD LOD (µg g -1 ) LOQ (µg g -1 ) λ-cyhalothrin % Recovery ±SD ± ± ± 2.55 % RSD LOD (µg g -1 ) LOQ (µg g -1 ) Cypermethrin % Recovery ±SD ± ± ± 2.98 % RSD LOD (µg g -1 ) LOQ (µg g -1 ) Fenvalerate % Recovery ±SD ± ± ±3.83 % RSD LOD (µg g -1 ) LOQ (µg g -1 ) Deltamethrin % Recovery ±SD ± ± ±4.04 % RSD LOD (µg g -1 ) LOQ (µg g -1 ) column while these were remained in top layer in other soil columns. The depth wise distribution of different SPs is presented in Table 5. The results revealed that residues of SPs viz. bifenthrin, λ-cyhalothrin, cypermethrin, fenvalerate and deltamethrin in sandy soil were in the range of µg g -1 in top layer (D-1). The maximum concentration of bifenthrin residue recorded in sandy soil i.e µg g - 1 which was 89.95% of total residues detected in sandy soil column while cypermethrin recorded minimum residues i.e µg g -1 which was 79.26% at top most section (D-1). The residues of SPs moved up to D-2 depth were in the range of % in sandy soil. Maximum movement was recorded for deltamethrin which were 12.97% of total loading while minimum movement was observed for cypermethrin (6.97%). A drastic reduction in concentration of movement of synthetic pesticides was observed from depth of D-3 to D-6. At lowest depth D-6 (25-30 cm), all synthetic pesticides were in the range of to µg g -1 of total loading of different SP pesticides. The similar pattern of downward movement of SPs was also observed in sandy loam soil. Maximum residues were detected from upper most section i.e. D-1 followed by D-2. The detected residues of various SPs were in the range of to µg g -1 at the upper most D-1 section. At depth D-1 in sandy loam soil, maximum residues were detected from bifenthrin (99.71% of total loading) while that for minimum was λ- cyhalothrin (99.30%) which indicates that only % of total concentration of SPs were moved beyond D-1 depth. Approximately 99.5% residues of all SPs remained in the top most section while remaining 0.5 per cent of the total amount moved beyond section D-1. In clayey soil, major chunk of SP residues were retained in the top most section which were in the range of µg g -1. Pattern of distribution of different SPs in clayey soil was quite similar to sandy loam soil residues confined to top most section and remaining 0.5% residues distributed in different sections of the column. The data obtained from the downward movement of synthetic pyrethroids from sandy soil indicates that > 99% amount retained in two upper most sections, while traces of synthetic pesticides moved further in lower depth. Sandy soils are comparatively more permeable and well drained but are less water retentive in nature as compare to loamy and clayey soils because macropores are more in numbers in sandy soil

5 80 Susheel Singh et al. Pestic Res J 24(1): (2012) Table 5. Depth wise recovery of SPs from different soils columns Depth Residues (µg g -1 ) (cm) Bifenthrin λ-cyhalothrin Cypermethrin Fenvalerate Deltamethrin Sandy Sandy Clayey Sandy Sandy Clayey Sandy Sandy Clayey Sandy Sandy Clayey Sandy Sandy Clayey loam loam loam loam loam (89.95)* (99.71) (99.65) (90.51) (99.30) (98.78) (79.26) (99.58) (99.58) (90.53) (99.47) (99.36) (86.70) (99.56) 99.24) (9.82) (0.18) (0.15) (9.23) (0.30) (0.11) (6.97) (0.31) (0.13) (9.21) (0.30) (0.17) (12.97) (0.27) (0.09) (0.14) (0.06) (0.07) (0.13) (0.05) (0.10) (0.05) (0.08) (0.07) (0.13) (0.14) (0.07) (0.05) (0.20) (0.08) (0.03) (0.03) (0.07) (0.04) (0.27) (0.10) (0.027) (0.02) (0.07) (0.04) (0.05) (0.06) (0.06) (0.03) (0.10) (0.03) (0.01) (0.06) (0.05) (0.07) (0.65) (0.027) (0.03) (0.07) (0.05) (0.10) (0.20) (0.08) (0.08) (0.22) (0.03) (0.01) (0.02) (0.03) (0.01) (0.28) (0.023) (0.01) (0.04) (0.03) (0.02) (0.15) (0.05) (0.01) (0.27) *Figures in parenthesis indicate % total loading of synthetic pesticides than micropores which are responsible for water retention and aeration. Sandy soil which was used in the experiment sand particles, low water holding capacity and organic carbon. (Table 2) Due to higher soil adsorption coefficients ( _ ) and comparatively low water solubility ( mg L -1 ) of most of synthetic pyrethroids were strongly adsorbed by the soil but lower water holding capacity of sandy soil enable them to moved down the column as compare to other soils (Table 5). In contrast to sandy soil, synthetic pyrethroids did not move beyond top most section of sandy loam and clay soils column. The reason might be the high organic content and mineralological composition. As these soils have high organic content and presence of 2:1 type clay mineral especially in clayey soil and in combination of high soil adsorption character of SPs did not allowed to move down in lower soil column sections as >99% SPs were retained in D-1 column in both sandyloam and clayey soils. Sakata et al. (1986) 10 observed no leaching of cypermethrin from three types of soil columns viz. clay loam, sandy and sandy loam soil of Japan after 30 d pre-incubation. Xiao-zhi et al. (2008) 11 found that the persistence and dissipation of cypermethrin, fenevalerate and deltamethrin were correlated with soil ph and soil organic matter contents of the red soils from Yangtze River Delta area. Gupta and Gajbhiye (2002) 12 studied the leaching of α-cyfluthrin in alluvial soil of India in a packed soil column under saturated flow conditions. α-cyfluthrin was found to be highly immobile in alluvial soil. No residues were detected in any leachate fraction under the experimental conditions. In column soil, residues were detected at 0-10 cm depth and the major amount (>99%) was recovered from 0-5 cm depth which was very much in agreement with the results obtained in this study. Bonding affinities of synthetic pyrethroids per unit surface area decreased in the order: corundum> quartz>montmorillonite>kaolinite. All minerals showed the same selectivity order with respect to sorption affinity of the four pyrethroids: lambda-cyhalothrin > deltamethrin > cypermethrin > fenvalerate (Oudou and Hansen 2002) 13. The adsorption of SPs was comparatively high in sandy loam and clayey soil as compare to sandy soils which are devoid of montmorillonite and other clay minerals. It might be a potential reason of downward movement of SPs to Depth D-2. The synthetic pyrethroids are strongly adsorbed to upper surface of soils, precluding the possibility of extensive leaching. It is highly unlikely that they will reach ground waters. The moderate to high persistence of the synthetic pyrethroids indicate that the chemicals are available for runoff for a relatively long period of time (weeks to months post application). The low solubility in water, the low mobility observed for all the pyrethroids, and the high soil/water adsorption coefficient observed for most of them indicates that the chemicals would remain adsorbed to the soils and would runoff during rain events causing erosion of the soil.

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