DOI 10.1007/s10661-009-0788-x
Persistence and behavior of pesticides in cotton
production in Turkish soils
C. Turgut· O. Erdogan · D. Ates · C. Gokbulut· T. J. Cutright
Received: 18 September 2008 / Accepted: 27 January 2009 / Published online: 26 February 2009 © Springer Science + Business Media B.V. 2009
Abstract Turkey is the sixth largest producer of cotton in the world. Two of the most commonly applied pesticides used in cotton production are trifluralin and endosulfan. Although both are very effective at controlling pests, their persistence in the environment poses risks to human health and the environment. Four loam soils and one silty-loam soil were studied to evaluate the persis-tence of trifluralin and endosulfan in relation to soil characteristics. Degradation with trifluralin reached as high as 70% of the applied doses. Soils with the highest organic matter content had the lowest degradation rate, indicating a tighter sorp-tion of trifluralin. Endosulfan degradasorp-tion was a
C. Turgut (
B
)· D. AtesFaculty of Agriculture, Adnan Menderes University, 09100 Aydin, Turkey
e-mail: [email protected]
O. Erdogan
Nazilli Cotton Research Institute, Nazilli, Aydin, Turkey
C. Gokbulut
Department Pharmacology and Toxicology, Faculty of Veterinary Medicine,
Adnan Menderes University, 09100 Aydin, Turkey
T. J. Cutright
Department of Civil Engineering, The University of Akron, Akron OH 44325–3905, USA
function of soil type and the specific isomer, with β-endosulfan depicting the highest degradation. Keywords Pesticides· Cotton · Soil · Turkey
Introduction
Cotton is second largest agricultural crop in Turkey (Unlu and Bilgic 2004). Production reached to 3.2 million tons in 2004, making Turkey the sixth largest worldwide producer (Yilmaz et al.
2005). Many pesticides are applied to control pests, diseases, and weeds that would adversely affect cotton crops. Trifluralin has been used on almost all of the cotton crops since 1970 (Uludag et al. 2006). Since then, Turkey’s pesticide con-sumption has reached up to 960 g/ha for the 700,000 ha used to grow cotton in the Aegean and Mediterranean regions (Uludag et al. 2006,
2007). In spite of many restrictions on pesticide usage, pesticide consumption in the country is still very high. Due to their wide application, concern exists over the environmental fate of pesticides due to their potential impact on both human and environmental health.
The environmental fate of pesticides, particu-larly those in soils, is closely related to their avail-ability. A large proportion of the spray-applied pesticide dose reaches the soil surface, either di-rectly and/or through foliage wash off (Schweizer
et al. 2000; Turgut and Fomin 2002; Mamy and Barriuso 2007). Further migration to groundwa-ter, plants, subsurface soil, etc. depends strongly on the compound’s physicochemical characteris-tics. The most critical parameter that controls pesticide fate in the subsurface is sorption, which is influenced by the compound’s hydrophobicity (often expressed in terms of the octanol–water partitioning coefficient, Kow; Hiller et al.2008).
Environmental contamination by pesticides can occur as a result of direct application of as a result of spillage. It is estimated that 10–100% of field applied pesticide will be deposited on the soil surface. Runoff from these surfaces represents a potential link to contamination of waters (Turgut and Fomin 2002; Jensen and Spliid2003; Turgut
2003).
Trifluralin is a dinitroaniline selective herbi-cide, which acts by entering the seedling in the hypocotyls region (Konen and Cavas 2008). At higher dosages, trifluralin also inhibits root de-velopment and is often used as a pre-emergence control of many annual grasses and broad leaved weeds in cotton. Trifluralin has a log Kow4.91 and
4 × 10−5 mPa (20◦C; Cooke et al. 2004). Since Trifluralin is hydrophobic, it is strongly sorbed by soil organic matter (Tiryaki et al. 2004; Oldal et al. 2006). Once bound, it persists in the soil and can injure sensitive crops grown in the years following herbicide application. For instance in Jokioinen, southern Finland, trifluralin was found to persist in the peas soil 1.5 years after treatment was ceased (Braunschweiler1992).
The degradation of low concentrations of tri-fluralin occurs mostly by UV-visible light or pho-tooxidaton (Uludag et al. 2006). Degradation is also facilitated by indigenous fungi (Critter et al.
2004) and other microorganisms. Microbial degra-dation rates are faster in flooded, anaerobic envi-ronments (Uludag et al.2006); therefore, it tends to persist in arid regions.
Although Trifluralin has been very effective at controlling agricultural pests, its persistence and toxicity poses a serious environmental concern. Recent research has found that it is toxic to fish and aquatic invertebrates (Turgut2007; Winkaler et al.2007; Zaidenberg et al.2007). Trifluralin has been implicated increasingly in mammalian toxic-ity (Fennell et al.2006) and genotoxicity (Gebel
et al. 1997; Fernandes et al. 2007). Studies by Saghir et al. (2008) have shown that it increases the thryroid follicular cell tumors in rats. It is also a suspected human carcinogen with an USEPA lifetime advisory in drinking water of 5 μg/L (Konen and Cavas2008).
Endosulfan has become the most commonly used pesticide in recent years. It is a non-systemic insecticide with contact and stomach action used to control the chewing and boring of insects and mites (Tomlin 2006). Endosulfan formulations are a mixture of alpha and beta isomers at 7:3 ratio (Kumar and Philip 2006). It can be biodegraded by fungi and other microorganisms.
Aspergillus niger has been the most effective fungi
at degrading endosulfa (Bhalerao and Puranik
2007). Researches by Hussain et al. (2007) and Arshad et al. (2008) found Pseudomonas spinosa,
Pseudomonas aeruoginosa, and Burkholderia cepacia to be the most effective bacteria for
degrading endosuflan, degrading 90% of the ap-plied amount within 2 weeks. Endosulfan sulfate was the most persistent metabolite of endosulfan (Hussain et al. 2007). As with triflurain, endo-sulfan is very toxic to many organisms, e.g., fish and invertebrates (Ghardiri and Rose2001).
A clear understanding of the persistence and distribution of trifluralin in soil is necessary for both agricultural practice and environmen-tal safety. Hence, the present study concentrates on the persistence and distribution of trifluralin residues in soil. The time required to convert to the organic farming from conventional farming may be expected with the results of this study.
Materials and methods
A total of five fields were selected for the ex-periments. The different chemical and physical properties of each field is shown in Table1. Four blocks from each field were selected randomly for sample collection.
Trifluralin was sprayed once at a concentration of 960 g a.i./ha before sowing the cotton. Cotton was sown at the end of April 2007 in Nazilli Cotton Research Institute. First sampling was started 1 day after application of trifluralin.
Endo-Table 1 Chemical and
physical properties of soils and field samples
Coded ha Soil Salinity pH CaCO3 P2O5 K2O Organic type (%) (%) (kg/ha) (kg/ha) matter (%) SS-1 8.3 Silty/loam 0.054 7.78 13.2 43 602 1.2 Tuzlu (TZ) 7.8 Loam 0.160 7.80 12.8 163 572 1.1 ˙I¸syeri (IY) Loam 0.077 7.78 10.4 40 572 1.1 Amasyalı (AT) 9.5 Loam 0.073 7.79 12.4 59 557 1.1 Büyük korgalı (BK) 6.3 Loam 0.083 7.88 19.6 39 753 1.4
sulfan was applied after germination of seeds and pests appeared.
Trifluralin, α-endosulfan, β-endosulfan, and endosulfan sulfate standards were purchased from Dr. Ehrensdorfer GmbH. A standard was pre-pared by dilution of the stock solutions (100 μg/l) and stored at 4◦C. The stock solution was stored at −20◦C, and all chemicals used in this study were analytical grade commercially available. Soils were selected for this study based upon their chemical and physiochemical nature (Table1).
Four different regular blocks were chosen to detect variability in trifluralin residues on each field, and the soil was taken from a depth of 5 to 25 cm over a 1-m2 area. The collected soil samples were thoroughly mixed, and for-eign materials, such as roots, stones, and gravel, were removed. The mixture was reduced to 1 kg and transported to the laboratory. The soil mix-tures were remixed, and 100 g of each sample were stored at −20◦C until analysis. Soils were extracted with MeOH/acetone by means a 1/2-h sonification (5 g soil was added to 10 ml MeOH/acetone). Extraction was followed by cen-trifugation at 3,500 rpm for 10 min, and super-natants were filtered and evaporated by vacuum concentrator 1 mbar, 40 C (Thermo). Finally, 1 ml acetone was used for analysis by gas chromatog-raphy tandem mass spectrometry (GC/MS/MS). GC-MS was performed using a Varian 3800 GC and 2200 MS instrument. Injection was performed by an autosampler. The GC separation was con-ducted with an Agilent 5 MS column (30 m ×
0.25-mm id× 0.25-μm film thickness). Helium was used as the carrier gas with a constant flow of 1 ml/min. The oven program was as follows: 80◦C held for 3.5 min, ramped to 230◦C at 10◦C/min, and finally ramped to 300◦C at 45◦C/min and held for 10 min. The MS transfer temperature was held at 280◦C. Electron ionization was used at 70 eV in SIM and full-scan (50–600 m/z) modes in different experiments. Varian ChemStation was used for data acquisition/processing. The pesti-cide analytes in GC-MS consisted of trifluralin,
α-endosulfan, β-endosulfan, and endosulfan
sul-fate. Table2provides the SIM program used for analysis.
To evaluate the procedure, the percent recov-ery of trifluralin,α-endosulfan, β-endosulfan, and endosulfan sulfate was performed by spiking with known concentrations of the endosulfan mixtures and trifluralin to the soil. Four replicates were used for reproducibility and reliability purposes.
Results and discussion
The basic physical and chemical characteristics of the soil samples are given in Table 1. The soil texture of sampling sites was loamy with or-ganic matter between 1.1% and 1.4%. Salinity var-ied from 0.054% to 0.160%, and pH values ranged from 7.78 to 7.88. CaCO3 in the samples ranged from 10.4 to 19.6, P2O5 from 3.9 to 16.3 kg/da, and K2O from 55.7 to 75.3 kg/da. The Ca, P, and
Table 2 GC-MS SIM
conditions for the monitored pesticides
Pesticide tR(min) Quantitation ion(s)
Trifluralin 8.158 265 + 306
α−Endosulfan 10.914 241 + 239 + 195 + 237 + 339
β−Endosulfan 11.886 195 + 241 + 237 + 207 + 339
K values are all within acceptable levels for an agricultural soil.
The analysis of the spiked samples was per-formed according to the abovementioned proce-dure. Average recovery of trifluralin was found to be 86%. Recovery ofα-endosulfan, β-endosulfan, and endosulfan sulfate was 92%, 82% and 91%, respectively. All recoveries were within the ac-cepted values for compounds that can be abioti-cally degraded by UV-visible light.
All samples from the five different fields showed low degradation rates of trifluralin the first day after it was applied. The trifluralin res-idues dissipated rapidly to 55% on the 23rd day. Afterwards, the degradation rate was only 14% for samples collected form field AT (Fig.1). The BK field exhibited lower degradation of trifluralin in comparison to other selected soil types. For the BK soil, only 27.2% of the trifluralin was degraded by day 60, with a very low degradation rate until the experiment was finished (Fig.2). It is hypothesized that the lower rate was due to trifluralin having a stronger sorption to the BK soil. As shown in Table 2, BK has an organic matter content of 1.4% versus the 1.1% contained in the other four soils. Other researchers have shown that the extent of trifluralin sorption is di-rectly proportional to the organic matter content (Boivin et al. 2005; Kyriakopoulos et al. 2005). The higher the organic matter content, the higher the sorption. Cooke et al. (2004) found the parti-tioning coefficient (Kd) for five soils to be from
0 50 100 150 0 20 40 60 80 100 Time (days) Degradation (%)
Fig. 1 Degradation of trifluralin in soil from field Amasyali
(AT) 0 50 100 150 0 20 40 60 80 100 Time (days) Degradation (%)
Fig. 2 Degradation of trifluralin in soil from field Buyuk
Kargali (BK)
106 to 204. For soils with high organic content, sorption was almost irreversible.
The soil of field Isyeri (IY) had a higher degra-dation in the experiment (Fig.3). The maximum degradation was reached up to 70% in 70 days and then degradation maintained until the end of experiment. Similarly, the degradation rate of field Tuzlu (TZ) increased sharply up to 70 days and achieved the highest degradation rate of 75% by the end of the experiment. Fifty-five percent of the degradation occurred within 35 days of initiating the experiment (Fig. 4). Both of these soils had an organic matter content and pH of 1.1% and 7.8%, respectively. Boivin et al. (2005) also compared pesticide sorption in different soils
0 20 40 60 80 100 120 140 0 20 40 60 80 100 Time (days) Degradation (%)
Fig. 3 Degradation of trifluralin in soil from field
0 20 40 60 80 100 120 140 0 50 100 150 Time (days) Degradation (%)
Fig. 4 Degradation of trifluralin in soil from field Tuzlu
(TZ)
and reported lower sorption parameters for soils with lower organic matter and pH. Therefore, it is hypothesized that trifuralin did not bind as tightly to IY and TZ soils enabling a faster abiotic degradation.
Similar results were found for the SS1 samples. The degradation was very fast in SS1 soils, with 90% of applied trifluralin degraded by 120 days. As with the TZ soils, the majority of the degrada-tion had occurred within the first 35 days (63%). This was followed by a slow but cumulative degra-dation that achieved 80% in 60 days and 84% in 75 days (Fig. 5). The faster degradation in SS1 soil was attributed to the soil texture. SS1 was classified as silty-loam soil. The silt content enabled more of the trifluralin to be desorbed in
0 20 40 60 80 100 120 140 0 50 100 150 Time (days) Degradation (%)
Fig. 5 Degradation of trifluralin in soil from field SS1
(SS1)
comparison to the other soils (Ying and Williams
2000).
The degradation of trifluralin in field IY was found 55% within 23 days after application. An-other 14% was degraded over the next 100 days, resulting in a cumulative degradation of 69%. As shown in Fig.3, the degradation rate was relatively flat for the last 100 days.
Aydin’s climate is characterized by hot and dry summer and warm winters. The field studies reported herein were undertaken during summer, so the dissipation rates were expected to be af-fected by climate conditions. Jolley and Johnstone (1994) found that half lives for trifluralin in three Victorian soils varied from 100 to 214 days un-der field conditions. The half lives of triflural-in after 9 and 10 years of conttriflural-inued use were 8.7–10.1 months in Dundee silt loam and 11– 15 months in Sharkey soil (Jolley and Johnstone
1994).
At the end of 350 days, 39% and 29.9% were extracted and bound in Gurgelen soil. This means that 61% and 69.8% of trifluralin was degraded under laboratory conditions in Gurgelen soil and Harran plain, respectively. The degradation of trifluralin in Harran soils were between 53.8% and 71.6% and in Ikizce soils from 59.4% to 78.5% (Tiryaki et al.2004).
The persistence or dissipation of chemicals is mainly controlled by its physico-chemical properties, management practices, and environ-mental conditions including climate, soil physics– chemistry, and microbial activity in soil (Trapp
2004; Turgut2005; Pu and Cutright2007). Studies on trifluralin suggested that cool and/or dry envi-ronmental conditions led to increased persistence in soil (Jolley and Johnstone1994; Johnstone et al.
1998). Uludag et al. (2006) reported half-lives in cool dry areas that were three times that of warm, wet environments (120 versus 45 days).
Soil characteristics will also impact how much of endosulfan will be degraded. Overall, endosul-fan was reported to have stronger binding to clays than organic matter (Singh and Kumar 2004), with montmorillonite binding more than kaolinte (Hengpraprom et al. 2006). For instance, a clay soil depicted an adsorption coefficient of 18.75 versus 6.7 with a sandy-loam (Ismai et al. 2002). In addition to the soil type, the specific isomer will
Amasyali 0 20 40 60 80 100 120 140 0 20 40 60 80 100 Endosulfan alpha Endosulfan beta Endosulfan sulfate Time (Days) Cumulative Degradation (%)
Fig. 6 Degradation of endosulfan in soil from field
Amasyali (AT)
also impact the binding and subsequent degrada-tion of endosulfan.
The degradation products α-endosulfan and endosulfan sulfate gave the same degradation ten-dency as shown in Fig. 6. The highest degra-dation was 20% of applied dose, which was achieved within 50 days, with no further degrada-tion evident by the end of the experiments. Con-versely, β-endosulfan degradation rate increased very sharply and reached up to 50% at the end of the experiments in field AT. Other researchers have also found that the sorption and subsequent degradation of endosulfan was dependent on the isomer and soil organic matter content. Kumar and Philip (2006) reported higher Freudlich sorp-tion parameters forα-endosulfan (0.7–0.52 mg/g) than β-endosulfan (0.03–0.37 mg/g).
Endosulfan sulfate degradation was lower than
α- and beta-endosulfan in field BK. The
degra-dation rate was 4% for α-endosulfan, 6% for β-endosulfan, and 3% for endosulfan sulfate. This was not surprising since endosulfan sulfate is the most persistent metabolite (Bhalerao and Puranik
2007; Deger et al. 2003). Endosulfan half-lives have been reported ranging from 60 to 800 days, depending on the isomer (Kumar et al.2008). The half-life of endosulfan sulfate in soil has been esti-mated to be 120 days to several months (Awasthi et al.2000).
Jayashree and Vasudevan (2007) studied the soil of Nazarath and found that the degradation
was 70% in 225 days for endosulfan sulfate, whereas 80% of β-endosulfan was degraded in only 135 days. This is different than what they found for soils from Ekkadu. In Ekkadu soils, 50% of endosulfan sulfate was degraded in 45 days, while β-endosulfan was degraded much lower (only 20% in 225 days; Jayashree and Vasudevan2007). Turkish soils appeared to depict the same trend as Nazarath soils. As shown in Fig. 5, the cumulative degradation for endosul-fan sulfate and α-endosulfan was approximately 20%. β-Endosulfan degradation was significantly higher, reaching 43% by the end of the experi-ment. Therefore, sorption, desorption, and subse-quent degradation of endosulfan is a function of both its isomers and the soil characteristics.
Conclusion
Five Turkish soils were studied to investigate the fate of trifluralin and endosulfan after applica-tion in cotton fields. Degradaapplica-tion with trifluralin reached as high as 70% of the applied dosage. Soils with the highest organic matter content had the lowest degradation rate, indicating a tighter sorption of trifluralin. This was not surprising since other researchers have found triflurlin to exhibit an almost irreversible sorption to organic matter. The silty-loam soil had the highest degra-dation of triflurlin, indicating an easier desorption. Endosulfan degradation was a function of soil type and the specific isomer, with β-endosulfan depicting the highest degradation. Forty-three percent β-endosulfan was degraded by the end of the experiment, whereas the rate was only 20% for α-endosulfan and endanosulfan sulfate. This was different from literature results. Therefore, degradation of endosulfate cannot be based solely on the soil characteristics or isomer. Future stud-ies to determine the sorption parameters in these soils would be beneficial to ascertain the full fate of the pesticides.
Acknowledgements Authors would like to thank Adnan Menderes University for funding and Ali Turunc, Didem Kazar, Sevdiye Demir for the assistance during the extrac-tion and collecting samples.
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