Article pubs.acs.org/JAFC
Environmental Behavior of Chlorpyrifos and Endosulfan in a Tropical Soil in Central Brazil Eliana F. G. C. Dores,*,† Claudio A. Spadotto,§ Oscarlina L. S. Weber,‡ Ricardo Dalla Villa,† Antonio B. Vecchiato,# and Alicio A. Pinto† †
Department of Chemistry, Universidade Federal de Mato Grosso, ICET, Av. Fernando Correa da Costa, n. 2367, CEP−78060-900 Cuiabá, Mato Grosso, Brazil § Embrapa Gestão Territorial, Av. Soldado Passarinho, n. 303, Fazenda Chapadão, CEP−13070-115 Campinas, São Paulo, Brazil ‡ Department of Soil and Rural Engineering. Universidade Federal de Mato Grosso, FAMEV, Av. Fernando Correa da Costa, n. 2367, CEP−78060-900 Cuiabá, Mato Grosso, Brazil # Department of Geology, Universidade Federal de Mato Grosso, ICET, Av. Fernando Correa da Costa, n. 2367, CEP−78060-900 Cuiabá, Mato Grosso, Brazil ABSTRACT: The environmental behavior of chlorpyrifos and endosulfan in soil was studied in the central−western region of Brazil by means of a field experiment. Sorption was evaluated in laboratory batch experiments. Chlorpyrifos and endosulfan were applied to experimental plots on uncultivated soil and the following processes were studied: leaching, runoff, and dissipation in top soil. Field dissipation of chlorpyrifos and endosulfan was more rapid than reported in temperate climates. Despite the high Koc of the studied pesticides, the two endosulfan isomers and endosulfan sulfate as well as chlorpyrifos were detected in percolated water. In runoff water and sediment, both endosulfan isomers and endosulfan sulfate were detected throughout the period of study. Observed losses of endosulfan by leaching (below a depth of 50 cm) and runoff were 0.0013 and 1.04% of the applied amount, whereas chlorpyrifos losses were 0.003 and 0.032%, respectively. Leaching of these highly adsorbed pesticides was attributed to preferential flow. KEYWORDS: sorption, leaching, runoff, dissipation, pesticides, water contamination
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INTRODUCTION
frequency due to its high interaction with soil particles and low water solubility.12 In agricultural regions, water resource contamination by pesticides is mainly due to leaching and runoff, which are complex processes and depend upon factors beyond soil and pesticides’ physical−chemical properties. Soil mechanization and crop management techniques, for example, may alter the soil structure and organic matter content, which in turn affects water infiltration and percolation, as well as pesticide sorption to soil. Clay and organic matter contents in soil control the retention of pesticides and consequently their leaching;13,14 however, they have little effect on runoff associated with erosive processes. Climatic factors such as precipitation and temperature can directly affect pesticide mobility in soil.15 Laabs et al.16 suggested that in tropical regions, the high temperatures can increase volatilization and biological degradation of pesticides. In the case of technical endosulfan, it is also important to consider that it is a mixture of two isomers (αand β-endosulfan) and has a main degradation product, endosulfan sulfate, the toxicity of which is similar to that of the parent compound.17 Chlorpyrifos and endosulfan have low water solubility (1.05 and 0.32 mg L−1, respectively), are
The large Brazilian agriculture production is sustained largely by the use of chemical inputs, among which pesticides are included. As one of the world’s greatest consumers of pesticides, in 2013, Brazil used >495,000 tons of pesticides.1 Inevitably, great environmental concern arises from this large consumption, mainly related to water resource contamination. This intense pesticide utilization is particularly worrying in Mato Grosso state, central western Brazil, which is one of the main agricultural regions in the country and the greatest pesticide user.2 Moreover, the northern Pantanal, known worldwide due to its biodiversity,3 is situated in this state. Chlorpyrifos and endosulfan are among the most used pesticides in the past decade (2000−2010), when the greatest expansion of agriculture occurred. In 2011, endosulfan was included as a persistent organic pollutant (POPs) in Annex A of the Stockholm Convention,4 and in 2013 the use of this insecticide was forbidden in Brazil. However, there is unofficial information that its illegal use continues. The inclusion of this insecticide as a POP reinforces the need for environmental monitoring. Several studies have reported the occurrence of pesticides in water bodies in agricultural areas in Mato Grosso, including these two above-mentioned insecticides.5−7 Water contamination by endosulfan and its adverse effects on aquatic organisms are well documented in several parts of the world.8−11 Chlorpyrifos has been detected in water in low © XXXX American Chemical Society
Special Issue: Pesticide Fate and Effects in the Tropics Received: September 14, 2015 Revised: November 23, 2015 Accepted: December 3, 2015
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DOI: 10.1021/acs.jafc.5b04508 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry nonionizable, and are considered slightly volatile (vapor pressures: chlorpyrifos, 2.7 mPa; α-endosulfan, 0.4 mPa; and β-endosulfan, 0.08 mPa).18,19 Although endosulfan and chlorpyrifos have been used for decades,20 studies on the dynamics of these compounds in tropical soils are still relatively scarce. In this context, the present study aimed to investigate the dynamics of chlorpyrifos and endosulfan in the main class of soil in a tropical environment. The study investigated dissipation rate, sorption, leaching, and runoff.
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Table 2. Daily Precipitation (mm) during the Study Period month day 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
MATERIALS AND METHODS
Experimental Area. Soil in the experimental area was classified as a Yellow Latosol according to the Brazilian Soil Classification System,21 which corresponds to Oxisol according to the classification of Soil Taxonomy.22 The granulometric and chemical characteristics of the soil horizons in the study area are presented in Table 1. This soil is slightly acidic, sandy-clayey, with increasing clay content with depth. This variation leads to a greater water retention capacity in deeper soil horizons.
Table 1. Granulometric and Chemical Characteristics of the Soil Horizons of an Oxisol in Mato Grosso State, Brazil g kg−1 soil horizon
depth (cm)
clay
silt
Ap BA Bw1
0−30 30−42 42−83
316 450 484
60 26 26
organic C sand
pH, H2O
%
g kg−1
624 524 490
5.1 5.0 5.1
1.55 0.79 0.47
15.54 7.87 4.72
Slopes of experimental plots varied from 3.6 to 4.7%, which characterizes an undulating, very gently sloping soil. The average basic infiltration rate is 58.6 mm h−1. Despite the high infiltration rate and relatively low slope, runoff is a common occurrence due to intense rainfall events. During the sampling period there was a total precipitation of 1746.5 mm, with monthly precipitation rates of 244, 212.5, 472.5, 484, 173.5, and 160 mm from November 2003 to April 2004. The first rain event occurred 20 days after application of herbicides. Detailed daily precipitation is shown in Table 2. Average (n = 6) total water and soil losses during the experimental period per plot area were 3.8 m3 and 27.6 kg, respectively, which extrapolating to 1 ha correspond to 1510 m3 ha−1 (151 mm of water lamina) and 11 ton ha−1, respectively. Field Sampling System. In a cotton farm, a 180 m × 80 m area was isolated and six 5 m × 10 m experimental plots were set up with a boundary wall (about 30 cm high) at the top of each plot to prevent runoff from the outside to enter the plots. In each plot, one lysimeter, one runoff collector system, and one monitoring well were installed as shown in Figure 1. The six plots were located in two lines parallel to the river. Two trenches were dug along the direction of these two lines, and samples from the different soil horizons were collected. Trench dimensions were as follows: depth, 2 m; length, 2 m; and width, 1 m. Granulometric and chemical properties of the soils in these horizons are presented in Table 1. Endosulfan [1,4,5,6,7,7-hexachloro8,9,10-trinorborn-5-en-2,3-ylenebismethylene sulfite] and chlorpyrifos [O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate] were applied by backpack sprayer, on October 15, 2003. Endosulfan and chlorpyrifos were applied at a dose of 2.5 L ha−1 (DISSULFAN CE as a concentrated suspension at 350 g L−1) and 1.5 L ha−1 (NUFOS 480CE as a concentrated suspension at 480 g L−1), respectively. The applied dosage corresponded to that recommended for use in cotton crops. Lysimeter installation and gravity sampling were performed as described by Laabs et al.16 Six lysimeters (50 cm deep) were installed by means of six small trenches opened bordering the upper part of
total
Oct
Nov
Dec
Jan
Feb
17.5 5
5 7.5 10 7.5 30
15
18.5
22 50 50
15 10
12
7.5 50 10 15 22.5
12
21 100
April 45
22
19 8
15
4 44 4
15
30 20 5
10 28 18
10 5
March
5
15 8 20 22.5
30 12.5 16
22.5 12.5 50
10 22 20
200 80 10 10
82.5 18.5 30 18 5 42.5 15
75
4
30 25
25 25
244
212.5
472.5
484
2 2
16
173.5
160
Figure 1. Scheme of experimental plots.
each plot. Monitoring wells were installed at the lower end of the experimental plots for monthly water table sample collection. Depth of monitoring wells varied from 3.8 to 4.2 m. To evaluate the amount of insecticides lost from the field by runoff, a collection system composed of a triangular container (2.5 m × 2.5 m × 2.5 m) was installed at the lower end of the plot. Water was drained from the collector via a tap, and the remaining deposited sediment was withdrawn using a scoop. Water volume and runoff sediment mass were measured at each sampling date. B
DOI: 10.1021/acs.jafc.5b04508 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry Field sampling started at the application date and lasted until March 2004. Topsoil (0−10 cm) samples for field dissipation study were collected on pre-established dates: 0, 1, 2, 4, 8, 16, 32, 64, and 128 days after application. The day 0 samples were collected around 2 h after pesticide spraying. Composite sampling soil positions were chosen randomly in a grid system, avoiding subsequent collection from the same points. Percolated water from lysimeters, runoff water, and sediment were collected per event. Water samples from monitoring wells were collected monthly. Samples from each experimental plot were analyzed individually. Each sample was analyzed in duplicate. Water table levels ranged from 3.1 m (October 2003) to 0.5 m (March 2004) below soil surface. Water samples were collected in amber glass 1 L bottles, placed in thermal boxes, and taken to the laboratory, where they were kept under refrigeration at
