Article pubs.acs.org/JAFC
Cite This: J. Agric. Food Chem. 2018, 66, 1765−1772
Impact of Simulated California Rice-Growing Conditions on Chlorantraniliprole Partitioning Zachary C. Redman* and Ronald S. Tjeerdema Department of Environmental Toxicology, College of Agricultural and Environmental Sciences, University of California, One Shields Avenue, Davis, California 95616-8588, United States S Supporting Information *
ABSTRACT: Chlorantraniliprole (3-bromo-N-[4-chloro-2-methyl-6-(methylcarbamoyl)phenyl]-1-(3-chloro-2-pyridine-2-yl)1H-pyrazole-5-carboxamide, CAP; water solubility 1.023 mg·L−1) was recently registered for application on California rice fields. Air− and soil−water partitioning of CAP were investigated under simulated California rice field conditions through calculation of KH and ΔawH and a batch equilibrium method following OECD 106 guidelines, respectively. KH and ΔawH were determined to be 1.69 × 10−16 − 2.81 × 10−15 atm·m3·mol−1 (15−35 °C) and 103.68 kJ·mol−1, respectively. Log(Koc) ranged from 2.59 to 2.96 across all soil and temperature treatments. Log(KF) ranged from 0.61 to 1.14 across all soil, temperature, and salinity treatments. Temperature and salinity increased sorption significantly at 35 °C (P < 0.05) and 0.2 M (P < 0.0001), respectively, while soil properties impacted sorption across all treatments. Overall results, corroborated using the Pesticides in Flooded Applications Model, indicate that volatilization of CAP is not a major route of dissipation and sorption of CAP to California rice field soils is moderately weak and reversible. KEYWORDS: chlorantraniliprole, rice, fate, partitioning, soil, sorption, desorption, volatilization
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INTRODUCTION Chlorantraniliprole (CAP, trade name Coragen, Figure 1), an anthranilic diamide insecticide, is a potent insect ryanodine
cyhalothrin (trade name Warrior) and clothianidin (trade name Belay).3−5 However, CAP is highly toxic to aquatic invertebrate species; although it is reportedly nonmobile in soil (product label reports CAP to remain 1−3 in. from the point of application), it was recently detected in 72% of water samples collected along the central California coast.6−8 The environmental fate of CAP under California rice field conditions should be investigated to ensure water quality for both endemic species and human consumers upon tailwater release into the Sacramento River. California rice fields are nearly impermeable, due to high clay content, and seasonally experience water temperature oscillations between 5−35 °C at a depth of 5 cm.9,10 As a result, evapotranspiration, rather than percolation, is a greater contributor to water loss in California than other rice growing regions.11 Current water management practices include recirculating water systems, extended water holding periods, and overwinter flooding in order to conserve water, prevent surface water contamination, aid rice straw decomposition (as an alternative to burning), and provide wildlife habitats. However, aqueous salt concentrations in California rice fields above 4.0 dS·m−1, exceeding the 1.9 dS·m−1 threshold for crop yield reduction, have been measured as a result of evapoconcentration caused by lengthy flooding periods and elevated evapotranspiration.12 Increased ionic strength is known to reduce the aqueous solubility of neutral organic compounds as well as increase their sorption to sediments;
Figure 1. CAP, an anthranilic diamide insecticide.
receptor agonist.1 It was registered for agricultural use with the U.S. Environmental Protection Agency (USEPA) in 2008 and was granted supplemental labeling in 2016 for use on California rice fields until December of 2018. The most damaging insect pest in California rice production is the rice water weevil (Lissorhoptrus oryzophilus), whose larvae account for 10−25% yield loss annually through extensive root pruning.2 While current chemical controls used in California target the adult weevil, CAP targets weevil larvae, reducing the need for carefully timed applications. Furthermore, CAP is comparatively less toxic to nontarget organisms, including crayfish and pollinators, than currently used insecticides such as λ© 2018 American Chemical Society
Received: Revised: Accepted: Published: 1765
December 11, 2017 January 30, 2018 February 1, 2018 February 13, 2018 DOI: 10.1021/acs.jafc.7b05775 J. Agric. Food Chem. 2018, 66, 1765−1772
Article
Journal of Agricultural and Food Chemistry Table 1. Soil Propertiesa
a
soil
pH
foc
fom
CEC (meq/100 g)
texture
% sand
% silt
% clay
Davis Richvale (unburned) Richvale (burned)
6.81 4.46 4.44
0.0160 0.0120 0.0184
0.0394 0.0282 0.0393
37.9 6.54 6.25
silty clay loam loam
11 42 39
42 34 35
47 24 26
Texture defined according to Natural Resources Conservation Service soil texture classifications.
however, the impact of salinity on partitioning in a rice field environment has yet to be investigated.13−16 Air−water partitioning (characterized by the Henry’s Law constant KH) and soil−water partitioning (characterized by the partitioning coefficient Kd) are the primary chemodynamic processes in a flooded rice field. The USEPA calculated a Henry’s Law constant for CAP of 3.1 × 10−15 atm·m3·mol−1 from the registrant’s experimentally derived solubility and vapor pressure at 20 °C, and Freundlich sorption coefficients ranged between 0.94 and 2.30 L·kg−1 on Chinese soils (fraction of organic matter (fom) and percent clay were 0.012−0.046 and 12−56%, respectively) at room temperature.6,17 However, these values were derived at a single temperature under conditions that do not reflect those of rice fields in the Sacramento Valley. This investigation aims to characterize the primary processes driving CAP air−water and soil−water partitioning under simulated California rice field conditions and to identify the factors impacting those processes to provide regulators with data important for the development of safe and economical farming practices. To accomplish this, KH was calculated as a function of temperature and soil sorption and desorption were measured at 15, 25, and 35 °C on three rice field soils from the Sacramento Valley. The effects of increased salinity and preflood application of CAP on soil sorption were also investigated to derive sorption parameters relevant to its use in California.
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interest. Water solubility was calculated by the AQUAFAC group contribution method and eq 3:20 log X w = − 0.01(Tm − T ) −
MATERIALS AND METHODS
VP Cwsat
(1) Csat w
are the Henry’s law constant, vapor pressure, where KH, VP, and and water solubility of CAP at a given temperature, respectively. Vapor pressure was calculated using eq 2:19
log VP = − {[(50 − 19.2log(σ ) + 7.4τ )(Tm − T ) − (88 + 0.4τ + 1421HBN)(Tb − T )]/19.1T } ⎛ T ⎞⎤ (− 91 − 1.2τ ) ⎡ (Tb − T ) + − ln⎜ b ⎟⎥ ⎢ ⎝ T ⎠⎦ ⎣ T 19.1
(3)
where Xw is the mole fraction of CAP in water, q is the AQUAFAC group parameter, and n is the number of times the respective group occurs within the molecule. Soil−Water Partitioning. Soil was collected from the top 10 cm of three rice fields in the Sacramento Valley near Davis, CA (38° 33′ 22″ N, 121° 43′ 57″ W) (Sacramento silty clay loam classified as a fine, smectic, thermic, cumulic Vertic Endoaquoll), and Richvale, CA (39° 29′ 22″ N, 121° 44′ 12″ W) (Esquon Neerdobe clay series classified as fine, smectic, thermic Xeric Epiaquerts), and sieved to
