Impact of Long Term Applications of Cotton Pesticides on Soil Biological
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XA0200259 Impact of long term applications of cotton pesticides on soil biological properties, dissipation of [14C]-methyl parathion and persistence of multi- pesticide residues* M.M. Andrea, T.B. Peres, L.C. Luchini, M.A. Marcondes, A. Pettinelli Jr., L.E. Nakagawa Institute» Biologico, Centra de Proteçâo Ambiental, Sâo Paulo, Brazil Abstract. Biological parameters were followed in soils from a cotton farm (Tatui) where the recommended pesticides have been used for years, and from an experimental field (Sâo Paulo) which was subdivided in two areas: one received the recommended pesticides and the other was maintained untreated. The soil bioactivities monitored from 1995 to 1998, after different pesticide applications, were: basal and glucose-induced respiration; anaerobic activity; nitrification rate; activity of the enzymes: dehydrogenase, aryl sulfatase and arginine deaminase; the soil capacity to mineralize an aromatic pesticide molecule ([14C]-2,4-D), fungal and bacterial contributions for soil respiration until the beginning of 1998, and fungal and bacterial numbers from the beginning of 1998. The dissipation of [14C]-methyl parathion - one of the recommended pesticides - was followed by radiometric techniques only in Sào Paulo, but persistence of multi-residues was determined in both soils by gas-liquid chromatography. All the biological parameters varied each sampling time and values also varied among soil samples, being inhibited or stimulated by the different pesticide applications, but they mostly recovered the initially detected activity. Dissipation of methyl parathion was fast and not affected by the other pesticide applications. Pesticide residues varied between the two soils but were mostly low after all applications, which indicates their dissipation. 1. Introduction The use of pesticides has proved to be the only means to protect crops on a large scale. However, the effects of pesticide usage must be seen also in the context of soil pollution and sustainability of the agroecosystem. Some crops, such as cotton, need heavy repeated applications of different pesticides, including organophosphates, carbamates, pyrethroids, and organochlorines [1] which reach the soil. Most of the studies of the behaviour of pesticides in the soil have focused mainly the behaviour of only one pesticide, but, although the results are very useful, the soil conditions from real situations are not being fully investigated. The soil is a heterogeneous environment in which the microbial population is involved in important cycles of the essential elements [2,3]. Pesticides reaching the soil may affect non-target organisms, disturbing the local metabolism [3,4,5] which is essential for soil fertility, and also for pesticide degradation processes [6]. Although there is a series of tests used to measure biodégradation of pesticides, the individual resultsof each test have limited value [7]. The combination of results from various tests provides information for a more realistic evaluation on the pesticide impact on the soil microbial population [6], and on the complexity of the soil population dynamics [8], This work evaluated some biological and chemical parameters in soils treated with different pesticides, as recommended for cotton crops. At the same time, the dissipation of one of the recommended * Part of a Research Contract (BRA-8078) with the IAEA - International Atomic Energy Agency, and partially financed by the Sâo Paulo State Research Support Foundation (FAPESP) and by the National Council of Scientific and Technological Research (CNPq). 15 pesticides — 14C-methyl parathion — under the influence of the other pesticide applications, was also studied using nuclear techniques. The remaining residues of the applied pesticides were also determined by solvent extraction and gas liquid-chromatography of the soil samples during the crop and between crop seasons. 2. Material and methods Soil from a cotton experimental station (Tatui, Sâo Paulo State) was collected after different pesticide applications (Fig. 1), and in the interval between crop seasons. The same application schedule used in Tatui was followed in half of an experimental field area in Sâo Paulo city. The other half did not receive pesticides. The rate and order of all pesticide applications (Fig. 1) were (per hectare) in the 1995-1996 season: monocrotophos (1.0 L); dimethoate (0.5 L); dimethoate again (0.5 L); endosulfan (1.2 L); deltamethrin (0.5 L); endosulfan (2.0 L); deltamethrin (300 mL); methyl parathion (1.0 L); endosulfan (2.0 L), and carbaryl (2.5 kg). Trifluralin (2.0 L/ha) was applied between the two crop seasons. In 1996-1997 the order was: monocrotophos (1.0 L); monocrotophos again (1.3 L); endosulfan (1.25 L); methylparathion (1.2 L); endosulfan (1.2 L); endosulfan (1.0 L) plus methyl parathion (1.0 L); endosulfan (1.5L) plus methyl parathion (1.5 L); endosulfan (2.0 L) plus methyl parathion (2.0 L); deltamethrin (1.0L); again deltamethrin (250 mL); endosulfan (1.2 L), and after the cropping, deltamethrin (250 mL) plus methyl parathion (1.25 L). Again trifluralin was applied between crop seasons In 1997 - 1998 the order was: diuron (4 kg); methyl parathion (1.2 L); endosulfan (IL); endosulfan again (1 L); methyl parathion (1 L) plus endosulfan (1 L); deltamethrin (350 mL); methyl parathion (1 L); deltamethrin (IL); and methyl parathion (2.5 L) plus deltamethrin (1.25 L). Soil samples were taken before the first pesticide application (Sampling 0), and after the first treatments with: monocrotophos (S. 1); methyl parathion (S. 2) and carbaryl (S. 3), and after the first harvest (S. 4). In the second year of the study the samples were taken after the two applications of monocrotophos (S. 5); the first application of methyl parathion (S. 6); the first application of deltamethrin (S. 7), and after the mixture of methyl parathion and deltamethrin (S. 8). Another sampling between the crop seasons (S. 9), and then, after the first application of endosulfan (S. 10); deltamethrin (S. II); the mixture of methyl parathion plus deltamethrin (S. 12), and after the crop season (S. 13) as shown in Fig. 1. The following parameters were studied in the soils: basal and glucose induced respiration [9]; Fe-III reduction [8]; total N and nitrification [10]; capacity to mineralize 14C-2,4-D as model aromatic molecule [11]; and the activity of the enzymes: dehydrogenase [12]; aryl sulfatase [13] and arginine deaminase [14]. The fungal and bacterial contributions for soil respiration were also evaluated until S. 8 using selective inhibitors [15, 16]. Nine (10 g) replicates of each area (i. e, Tatui, Sâo Paulo treated sub-area, and Sào Paulo untreated sub-area) from the 0-15 cm soil layer were placed in biometer flasks [18] and the water content was adjusted to 55% Of maximum water holding capacity. The behaviour and fate of 14C-methyl parathion was followed in soil columns in hard PVC tubes (5 cm i.d. x 50 cm long) which were driven in the Sao Paulo experimental field. Ring [14C]-methyl parathion, 95% pure, with specific activity of 1.073 GBq mmol'1 purchased by IAEA was applied on the soil surface of each tube in 5 mL of a hexane solution containing 148 kBq of the radiolabelled compound dissolved in 0.6 mg of methyl parathion, in a rate equivalent to 2 ug g"1 in the top 15 cm of the soil columns. This application was made at the same time as the first recommended application of methyl parathion. The area of the experimental field was subdivided in two sub-areas: one received all pesticide treatments and the other received only the 14C-methyl parathion into the tubes. At sampling times (0,3,6,9 and 12 months after the application) three tubes from each sub-area were collected, divided in two sections (0-15cm; 15-50 cm) from which the soil was taken and thoroughly mixed for analysis[17]. 16 carbaryl cropping of 95-96 methyl parathion deltamethrin endosulfan dimethoate monocrotophos .11 î î î î î SO planting S.I S.2 S.3 cropping of deltamethrin 96-97 I methyl parathion 1 1 1 endosulfan monocrotophos trifluralin ill- • î î î î 1 S.4 planting S.5 S.6 S.7 S.8 cropping of deltamethrin 97-98 endosulfan Iw methyl parathion diuron trifluralin ,1. r r r î r ' î î î î î î S.9 planting S.10 su S.12 S.13 FIG. I. Schedule of pesticide applications and samplings (S) during three crop seasons Three replicates were treated with 75 mg of streptomycin in 50 mg of talcum; three replicates were treated with 150 mg of cycloheximide in 50 mg of talcum, and the three control replicates were treated only with 50 mg of talcum [19]. All replicates received 4 mg of glucose g'1 soil and were kept at 28°C during the week of the test. The KOH of the side arm of the flasks was changed after 6h and 1, 2, 3 and 4 d. The CO2 produced was determined by titration with HCI, as for the basal and substrate induced respiration test. All these parameters were studied until S.8 in the 0-15 cm and 15-30 cm soil layers, and then, only in the surface layer. From S.8 to S.13 the total bacterial and fungal populations 17 were also examined by serial-dilution techniques and the pour-plate method, according to Johnson et al [20]. Multi-pesticide residues were monitored in the surface (0-15 cm) of treated soils. Triplicate soil samples (50 g) were Soxhlet extracted with 150 mL of methanol during 8 hours. Aliquots of 100 mL of the organic extracts were concentrated to dryness in rotary evaporator (Buchi 461) at 35°C. Residues were quantitatively suspended in 2 mL of methanol (pesticide grade) which was totally transferred to Bond Elut C18 cartridges (500 mg octadecyl) previously conditioned with 2x3 mL MilliQ water and 2x4 mL methanol.