Kean Goh - Academia.edu (original) (raw)
Papers by Kean Goh
Bulletin of Environmental Contamination and Toxicology, Dec 4, 2011
The objective of this analysis was to identify pesticide use scenarios that potentially contribut... more The objective of this analysis was to identify pesticide use scenarios that potentially contribute to the frequent surface water detections of diazinon in agricultural regions of California. Crop treated, pesticide product formulation, and pesticide application method were examined. The study targeted five regions with frequent detections and high concentrations in surface water: Salinas Valley, Sacramento Valley, San Joaquin Valley, Santa Maria Valley and Imperial Valley. Using surface water monitoring data from 2005 to 2010, sites with the most frequent exceedance of the 100 ng/L target concentration were identified in each of the five regions. For drainage basins where the identified monitoring sites were located, pesticide use was summarized by crop type, product formulation and application method. Salinas Valley had the highest use of diazinon between 2005 and 2010 accounting for about 35% of the statewide use. Sacramento Valley was the second-highest use region accounting for 14% of the statewide use. Uses in San Joaquin Valley, Imperial Valley and Santa Maria Valley were relatively lower, accounting for 9%, 6% and 2% of the statewide use, respectively. Top use crops in high detection areas varied among different regions with lettuce, broccoli and cauliflower being the top ones in the Lower Salinas Valley. Application method and product formulations did not vary significantly between areas with high and low detections. The majority of diazinon applications were made through ground application using EC formulated products. This analysis suggests that diazinon detections in surface water likely did not occur primarily due to the application method or formulation type. Besides use amount, other factors such as irrigation method, spray drift, timing of application, soil type, slope and field management practices are likely more relevant to the offsite movement of diazinon.
Water Research, Jun 1, 2013
Use of pesticides over impervious surfaces like concrete and subsequent washoff and offsite trans... more Use of pesticides over impervious surfaces like concrete and subsequent washoff and offsite transport significantly contribute to pesticide detection and aquatic toxicity in urban watersheds. This paper presents a comprehensive study on pesticide washoff from concrete surfaces, including reviews of reported experiments and existing models, development of a new model, and its application to controlled experimental conditions. The existing modeling approaches, mainly the exponential function and power-law function, have limitations in explaining pesticide washoff processes characterized from experimental data. Here we develop a mathematical and conceptual framework for pesticide washoff from concrete surfaces. The new modeling approach was designed to characterize pesticide buildup and washoff processes on concrete surfaces, including the timedependence of the washoff potential after application and the dynamics in pesticide washoff during a runoff event. One benefit is the ability to integrate and quantify multiple processes that influence pesticide washoff over concrete surfaces, including product formulation, aging effects, multiple applications, and rainfall duration and intensity. The model was applied to experimental configurations in two independent studies, and satisfactorily simulated the measured temporal variations of pesticide washoff loads from concrete surfaces for the five selected pyrethroids in 15 runoff events. Results suggested that, with appropriate parameterization and modeling scenarios, the model can be used to predict washoff potentials of pesticide products from concrete surfaces, and support pesticide risk assessments in urban environmental settings.
Bulletin of Environmental Contamination and Toxicology, Aug 1, 2003
During June, July, and August 2000, the Fresno County Department of Agriculture’s contract applic... more During June, July, and August 2000, the Fresno County Department of Agriculture’s contract applicators applied carbaryl to control the glassy-winged sharpshooter (GWSS) in Fresno County, California. During this time, the Department of Pesticide Regulation (DPR) collected air, tank, leaf, and produce samples at several sites within the cities of Fresno and Clovis. Air samples were taken at five locations before, during and after the applications. The highest concentrations occurred during applications and then declined over the next 48 hours. The highest concentration of 237 parts per trillion (ppt) detected was well below the preliminary health screening level of 6,3 13 ppt for 24-hour acute exposure to carbaryl. Tank samples showed concentrations ranging from 0.1% to 0.15% of carbaryl active ingredient within the nominal label-rate concentrations of 0.11% to 0.21%. Dislodgeable foliar residue from leaf punches had concentrations ranging from 2.97 to 7.12 pg/cm2. The ten fruit and vegetable samples collected at preharvest intervals, the required minimum number of days between last application and harvest as determined by the label for “7” Carbaryl Insecticide@, had residues ranging from 0.12 to 1.7 parts per million (ppm) which were below the established tolerance (U.S. EPA maximum allowable residues) of 10 ppm for all produce collected.
SUMMARY During May 2002, monthly surface water samples were collected from five sites in Orange C... more SUMMARY During May 2002, monthly surface water samples were collected from five sites in Orange County, California. Water samples showed no detects of fenoxycarb, hydramethylnon, pyriproxyfen, chlorpyrifos, dimethoate, malathion, and methidathion. Bifenthrin was detected in two samples at 0.277 and 0.502 parts per billion (ppb) at the two nursery sites. Diazinon was detected in three samples ranging from 0.056 to 0.382 ppb at two urban and an integrated site. Malathion was detected in two samples at 0.058 and 0.086 ppb at two nursery sites. Water samples collected from a mitigation filter strip planted with Canna showed 7% and 49% reductions of bifenthrin and malathion residues, respectively.
Journal of Economic Entomology, Apr 1, 1989
ABSTRACT
Journal of Environmental Quality, Nov 1, 2018
Journal of Environmental Quality, Nov 1, 2015
Environmental Entomology, Oct 1, 1980
ABSTRACT
Science of The Total Environment, Nov 1, 2016
Pesticides are routinely monitored in surface waters and resultant data are analyzed to assess wh... more Pesticides are routinely monitored in surface waters and resultant data are analyzed to assess whether their uses will damage aquatic eco-systems. However, the utility of the monitoring data is limited because of the insufficiency in the temporal and spatial sampling coverage and the inability to detect and quantify trace concentrations. This study developed a novel assessment procedure that addresses those limitations by combining 1) statistical methods capable of extracting information from concentrations below changing detection limits, 2) statistical resampling techniques that account for uncertainties rooted in the non-detects and insufficient/irregular sampling coverage, and 3) multiple lines of evidence that improve confidence in the final conclusion. This procedure was demonstrated by an assessment on chlorpyrifos monitoring data in surface waters of California's Central Valley (2005-2013). We detected a significant downward trend in the concentrations, which cannot be observed by commonly-used statistical approaches. We assessed that the aquatic risk was low using a probabilistic method that works with non-detects and has the ability to differentiate indicator groups with varying sensitivity. In addition, we showed that the frequency of exceedance over ambient aquatic life water quality criteria was affected by pesticide use, precipitation and irrigation demand in certain periods anteceding the water sampling events.
Environmental Science & Technology, Jun 15, 2004
Journal of Agricultural and Food Chemistry, Jul 29, 2000
The performance of a commercially available microtiter plate ELISA kit for the determination of d... more The performance of a commercially available microtiter plate ELISA kit for the determination of diazinon was evaluated for sensitivity, selectivity, intra-assay repeatability, accuracy, and matrix effects in fortified distilled water and filtered and unfiltered environmental surface water samples. Repeatability and reproducibility studies show that the kit satisfies current EPA criteria for the assessment of analytical methods. Mean recoveries from spiked samples averaged 80.3, 95.5, and 103.5% from distilled, unfiltered surface, and filtered surface waters, respectively. The experimentally determined method detection limit (MDL) for the commercial diazinon microtiter plate format (0.0159 µg L-1) was comparable to the least detectable dose (LDD) established by the manufacturer (0.022 µg L-1). Specificity studies indicate that the diazinon polyclonal antibody can readily distinguish the target compound from other structurally similar organophosphorus analogues, with the exception of diazoxon. Cross-reactivity with the oxon was approximately 29%, while reactivity with pirimiphosmethyl, pirimiphos-ethyl, and chlorpyrifos-ethyl was negligible. A slight matrix effect was discovered to be present in both filtered and unfiltered environmental water matrixes, but its effect on the immunoassays is insignificant within experimental error. For validation of the microtiter plate ELISA format, environmental surface and storm runoff water samples were collected, split, and analyzed directly by ELISA and by liquid-liquid extraction followed by GC (California State Department of Food and Agriculture method EM 46.0). Results of the two analytical methods were then compared statistically. A close correlation was found between methods for unspiked and untreated river water samples (r) 0.969) while a much less robust correlation was obtained for runoff waters (r) 0.728). Results from runoff waters exhibit a particularly high positive bias for the ELISA method relative to the GC method. Cross-reactivity of diazoxon and probably other unidentified cross-reacting components may be responsible for the exaggerated account of the target analyte in surface and runoff waters. While excellent for screening purposes, further study is required to elucidate and quantify the factors responsible for the consistent overestimation of ELISA results before the kit can be employed routinely for regulatory compliance monitoring.
AGU Fall Meeting Abstracts, Dec 1, 2004
Transport of pesticides by surface runoff during rainfall events is a major process contributing ... more Transport of pesticides by surface runoff during rainfall events is a major process contributing to pesticide contamination in rivers. This study presents an empirical regression model that relates pesticide loading over time in the Sacramento River with the precipitation and pesticide use in the Sacramento River watershed. The model closely simulated loading dynamics of diazinon, simazine, and diuron during 1991-1994 and 1997-2000 winter storm seasons. The coefficients of determination for regression ranged from 0.168 to 0.907, and were all significant at <0.001. The results of this study provide strong evidence that precipitation and pesticide use are the two major environmental variables dictating the dynamics of pesticide transport into surface water in a watershed. The capability of the statistical model to provide time-series estimates on pesticide loading in rivers is unique and may be useful for Total Maximum Daily Load (TMDL) assessment.
Journal of Economic Entomology, Feb 1, 1980
ABSTRACT
Reviews of Environmental Contamination and Toxicology, Oct 22, 2012
Environmental Monitoring and Assessment, Jun 19, 2010
The San Joaquin Valley is an important agricultural production area in California, where more tha... more The San Joaquin Valley is an important agricultural production area in California, where more than 1.5 million pounds of organophosphorous (OP) and pyrethroid insecticides are applied annually. The major river flowing through the valley, the San Joaquin River (SJR), is listed on the 2006 Clean Water Act §303(d) list for pesticide impairment. Several SJR tributaries are also listed, including Orestimba (ORC) and Del Puerto (DPC) Creeks. From December 2007 through June 2008, water and sediment samples were collected from ORC and DPC in Stanislaus County to determine concentrations of OP and pyrethroid insecticides, and to identify related toxicity to Ceriodaphnia dubia and Hyalella azteca. OPs were detected in almost half (10 of 21) of the water samples, at concentrations from 0.005 to 0.912 μg L-1. Diazinon was the most frequently detected OP, followed by chlorpyrifos and dimethoate. Two water samples were toxic to C. dubia; based on LC 50 s, chlorpyrifos was likely the cause of this toxicity. Pyrethroids were detected more frequently in sediment samples (18 detections) then in water samples (three detections). Pyrethroid concentrations in water samples ranged from 0.005 to 0.021 μg L-1. These concentrations were well below reported C. dubia LC 50 s and toxicity was not observed in laboratory bioassays. Cyfluthrin, bifenthrin, esfenvalerate, and λcyhalothrin were detected in sediment samples at concentrations ranging from 1.0 to 74.4 ng g-1 , dry weight. At DPC, all but one sample caused 100% toxicity to H. azteca. Based on estimated toxicity units (TUs) calculated from measured pyrethroid concentrations in sediment, bifenthrin was likely responsible for this toxicity; λ-cyhalothrin also probably contributed. At ORC, survival of H. azteca was significantly reduced in four of the 11 sediment samples. However, pyrethroids were detected in only two of these samples. Based on TUs, bifenthrin and λ-cyhalothrin likely contributed to toxicity in these two samples.
Environmental Pollution, Mar 1, 2018
Pesticides move to surface water via various pathways including surface runoff, spray drift and s... more Pesticides move to surface water via various pathways including surface runoff, spray drift and subsurface flow. Little is known about the relative contributions of surface runoff and spray drift in agricultural watersheds. This study develops a modeling framework to address the contribution of spray drift to the total loadings of pesticides in receiving water bodies. The modeling framework consists of a GIS module for identifying drift potential, the AgDRIFT model for simulating spray drift, and the Soil and Water Assessment Tool (SWAT) for simulating various hydrological and landscape processes including surface runoff and transport of pesticides. The modeling framework was applied on the Orestimba Creek Watershed, California. Monitoring data collected from daily samples were used for model evaluation. Pesticide mass deposition on the Orestimba Creek ranged from 0.08 to 6.09% of applied mass. Monitoring data suggests that surface runoff was the major pathway for pesticide entering water bodies, accounting for 76% of the annual loading; the rest 24% from spray drift. The results from the modeling framework showed 81 and 19%, respectively, for runoff and spray drift. Spray drift contributed over half of the mass loading during summer months. The slightly lower spray drift contribution as predicted by the modeling framework was mainly due to SWAT's under-prediction of pesticide mass loading during summer and over-prediction of the loading during winter. Although model simulations were associated with various sources of uncertainties, the overall performance of the modeling framework was satisfactory as evaluated by multiple statistics: for simulation of daily flow, the Nash-Sutcliffe Efficiency Coefficient (NSE) ranged from 0.61 to 0.74 and the percent bias (PBIAS) < 28%; for daily pesticide loading, NSE ¼ 0.18 and PBIAS ¼ À1.6%. This modeling framework will be useful for assessing the relative exposure from pesticides related to spray drift and runoff in receiving waters and the design of management practices for mitigating pesticide exposure within a watershed.
Journal of Pesticide Science, 2007
with an aqueous half life (t 1/2) of 125 hr and a soil t 1/2 of 438 hr. Fipronil is the active in... more with an aqueous half life (t 1/2) of 125 hr and a soil t 1/2 of 438 hr. Fipronil is the active ingredient in Icon ® , Frontline ® , Termidor ® , and Top Spot ®. It is classified as a chiral pesticide and released to the environment as a racemic mixture; approximately 66,824 lbs were used in California in 2005, primarily for structural pest control. 11) The insecticide is not registered for agriculture use in the state of California.
Bulletin of Environmental Contamination and Toxicology, Dec 4, 2011
The objective of this analysis was to identify pesticide use scenarios that potentially contribut... more The objective of this analysis was to identify pesticide use scenarios that potentially contribute to the frequent surface water detections of diazinon in agricultural regions of California. Crop treated, pesticide product formulation, and pesticide application method were examined. The study targeted five regions with frequent detections and high concentrations in surface water: Salinas Valley, Sacramento Valley, San Joaquin Valley, Santa Maria Valley and Imperial Valley. Using surface water monitoring data from 2005 to 2010, sites with the most frequent exceedance of the 100 ng/L target concentration were identified in each of the five regions. For drainage basins where the identified monitoring sites were located, pesticide use was summarized by crop type, product formulation and application method. Salinas Valley had the highest use of diazinon between 2005 and 2010 accounting for about 35% of the statewide use. Sacramento Valley was the second-highest use region accounting for 14% of the statewide use. Uses in San Joaquin Valley, Imperial Valley and Santa Maria Valley were relatively lower, accounting for 9%, 6% and 2% of the statewide use, respectively. Top use crops in high detection areas varied among different regions with lettuce, broccoli and cauliflower being the top ones in the Lower Salinas Valley. Application method and product formulations did not vary significantly between areas with high and low detections. The majority of diazinon applications were made through ground application using EC formulated products. This analysis suggests that diazinon detections in surface water likely did not occur primarily due to the application method or formulation type. Besides use amount, other factors such as irrigation method, spray drift, timing of application, soil type, slope and field management practices are likely more relevant to the offsite movement of diazinon.
Water Research, Jun 1, 2013
Use of pesticides over impervious surfaces like concrete and subsequent washoff and offsite trans... more Use of pesticides over impervious surfaces like concrete and subsequent washoff and offsite transport significantly contribute to pesticide detection and aquatic toxicity in urban watersheds. This paper presents a comprehensive study on pesticide washoff from concrete surfaces, including reviews of reported experiments and existing models, development of a new model, and its application to controlled experimental conditions. The existing modeling approaches, mainly the exponential function and power-law function, have limitations in explaining pesticide washoff processes characterized from experimental data. Here we develop a mathematical and conceptual framework for pesticide washoff from concrete surfaces. The new modeling approach was designed to characterize pesticide buildup and washoff processes on concrete surfaces, including the timedependence of the washoff potential after application and the dynamics in pesticide washoff during a runoff event. One benefit is the ability to integrate and quantify multiple processes that influence pesticide washoff over concrete surfaces, including product formulation, aging effects, multiple applications, and rainfall duration and intensity. The model was applied to experimental configurations in two independent studies, and satisfactorily simulated the measured temporal variations of pesticide washoff loads from concrete surfaces for the five selected pyrethroids in 15 runoff events. Results suggested that, with appropriate parameterization and modeling scenarios, the model can be used to predict washoff potentials of pesticide products from concrete surfaces, and support pesticide risk assessments in urban environmental settings.
Bulletin of Environmental Contamination and Toxicology, Aug 1, 2003
During June, July, and August 2000, the Fresno County Department of Agriculture’s contract applic... more During June, July, and August 2000, the Fresno County Department of Agriculture’s contract applicators applied carbaryl to control the glassy-winged sharpshooter (GWSS) in Fresno County, California. During this time, the Department of Pesticide Regulation (DPR) collected air, tank, leaf, and produce samples at several sites within the cities of Fresno and Clovis. Air samples were taken at five locations before, during and after the applications. The highest concentrations occurred during applications and then declined over the next 48 hours. The highest concentration of 237 parts per trillion (ppt) detected was well below the preliminary health screening level of 6,3 13 ppt for 24-hour acute exposure to carbaryl. Tank samples showed concentrations ranging from 0.1% to 0.15% of carbaryl active ingredient within the nominal label-rate concentrations of 0.11% to 0.21%. Dislodgeable foliar residue from leaf punches had concentrations ranging from 2.97 to 7.12 pg/cm2. The ten fruit and vegetable samples collected at preharvest intervals, the required minimum number of days between last application and harvest as determined by the label for “7” Carbaryl Insecticide@, had residues ranging from 0.12 to 1.7 parts per million (ppm) which were below the established tolerance (U.S. EPA maximum allowable residues) of 10 ppm for all produce collected.
SUMMARY During May 2002, monthly surface water samples were collected from five sites in Orange C... more SUMMARY During May 2002, monthly surface water samples were collected from five sites in Orange County, California. Water samples showed no detects of fenoxycarb, hydramethylnon, pyriproxyfen, chlorpyrifos, dimethoate, malathion, and methidathion. Bifenthrin was detected in two samples at 0.277 and 0.502 parts per billion (ppb) at the two nursery sites. Diazinon was detected in three samples ranging from 0.056 to 0.382 ppb at two urban and an integrated site. Malathion was detected in two samples at 0.058 and 0.086 ppb at two nursery sites. Water samples collected from a mitigation filter strip planted with Canna showed 7% and 49% reductions of bifenthrin and malathion residues, respectively.
Journal of Economic Entomology, Apr 1, 1989
ABSTRACT
Journal of Environmental Quality, Nov 1, 2018
Journal of Environmental Quality, Nov 1, 2015
Environmental Entomology, Oct 1, 1980
ABSTRACT
Science of The Total Environment, Nov 1, 2016
Pesticides are routinely monitored in surface waters and resultant data are analyzed to assess wh... more Pesticides are routinely monitored in surface waters and resultant data are analyzed to assess whether their uses will damage aquatic eco-systems. However, the utility of the monitoring data is limited because of the insufficiency in the temporal and spatial sampling coverage and the inability to detect and quantify trace concentrations. This study developed a novel assessment procedure that addresses those limitations by combining 1) statistical methods capable of extracting information from concentrations below changing detection limits, 2) statistical resampling techniques that account for uncertainties rooted in the non-detects and insufficient/irregular sampling coverage, and 3) multiple lines of evidence that improve confidence in the final conclusion. This procedure was demonstrated by an assessment on chlorpyrifos monitoring data in surface waters of California&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s Central Valley (2005-2013). We detected a significant downward trend in the concentrations, which cannot be observed by commonly-used statistical approaches. We assessed that the aquatic risk was low using a probabilistic method that works with non-detects and has the ability to differentiate indicator groups with varying sensitivity. In addition, we showed that the frequency of exceedance over ambient aquatic life water quality criteria was affected by pesticide use, precipitation and irrigation demand in certain periods anteceding the water sampling events.
Environmental Science & Technology, Jun 15, 2004
Journal of Agricultural and Food Chemistry, Jul 29, 2000
The performance of a commercially available microtiter plate ELISA kit for the determination of d... more The performance of a commercially available microtiter plate ELISA kit for the determination of diazinon was evaluated for sensitivity, selectivity, intra-assay repeatability, accuracy, and matrix effects in fortified distilled water and filtered and unfiltered environmental surface water samples. Repeatability and reproducibility studies show that the kit satisfies current EPA criteria for the assessment of analytical methods. Mean recoveries from spiked samples averaged 80.3, 95.5, and 103.5% from distilled, unfiltered surface, and filtered surface waters, respectively. The experimentally determined method detection limit (MDL) for the commercial diazinon microtiter plate format (0.0159 µg L-1) was comparable to the least detectable dose (LDD) established by the manufacturer (0.022 µg L-1). Specificity studies indicate that the diazinon polyclonal antibody can readily distinguish the target compound from other structurally similar organophosphorus analogues, with the exception of diazoxon. Cross-reactivity with the oxon was approximately 29%, while reactivity with pirimiphosmethyl, pirimiphos-ethyl, and chlorpyrifos-ethyl was negligible. A slight matrix effect was discovered to be present in both filtered and unfiltered environmental water matrixes, but its effect on the immunoassays is insignificant within experimental error. For validation of the microtiter plate ELISA format, environmental surface and storm runoff water samples were collected, split, and analyzed directly by ELISA and by liquid-liquid extraction followed by GC (California State Department of Food and Agriculture method EM 46.0). Results of the two analytical methods were then compared statistically. A close correlation was found between methods for unspiked and untreated river water samples (r) 0.969) while a much less robust correlation was obtained for runoff waters (r) 0.728). Results from runoff waters exhibit a particularly high positive bias for the ELISA method relative to the GC method. Cross-reactivity of diazoxon and probably other unidentified cross-reacting components may be responsible for the exaggerated account of the target analyte in surface and runoff waters. While excellent for screening purposes, further study is required to elucidate and quantify the factors responsible for the consistent overestimation of ELISA results before the kit can be employed routinely for regulatory compliance monitoring.
AGU Fall Meeting Abstracts, Dec 1, 2004
Transport of pesticides by surface runoff during rainfall events is a major process contributing ... more Transport of pesticides by surface runoff during rainfall events is a major process contributing to pesticide contamination in rivers. This study presents an empirical regression model that relates pesticide loading over time in the Sacramento River with the precipitation and pesticide use in the Sacramento River watershed. The model closely simulated loading dynamics of diazinon, simazine, and diuron during 1991-1994 and 1997-2000 winter storm seasons. The coefficients of determination for regression ranged from 0.168 to 0.907, and were all significant at <0.001. The results of this study provide strong evidence that precipitation and pesticide use are the two major environmental variables dictating the dynamics of pesticide transport into surface water in a watershed. The capability of the statistical model to provide time-series estimates on pesticide loading in rivers is unique and may be useful for Total Maximum Daily Load (TMDL) assessment.
Journal of Economic Entomology, Feb 1, 1980
ABSTRACT
Reviews of Environmental Contamination and Toxicology, Oct 22, 2012
Environmental Monitoring and Assessment, Jun 19, 2010
The San Joaquin Valley is an important agricultural production area in California, where more tha... more The San Joaquin Valley is an important agricultural production area in California, where more than 1.5 million pounds of organophosphorous (OP) and pyrethroid insecticides are applied annually. The major river flowing through the valley, the San Joaquin River (SJR), is listed on the 2006 Clean Water Act §303(d) list for pesticide impairment. Several SJR tributaries are also listed, including Orestimba (ORC) and Del Puerto (DPC) Creeks. From December 2007 through June 2008, water and sediment samples were collected from ORC and DPC in Stanislaus County to determine concentrations of OP and pyrethroid insecticides, and to identify related toxicity to Ceriodaphnia dubia and Hyalella azteca. OPs were detected in almost half (10 of 21) of the water samples, at concentrations from 0.005 to 0.912 μg L-1. Diazinon was the most frequently detected OP, followed by chlorpyrifos and dimethoate. Two water samples were toxic to C. dubia; based on LC 50 s, chlorpyrifos was likely the cause of this toxicity. Pyrethroids were detected more frequently in sediment samples (18 detections) then in water samples (three detections). Pyrethroid concentrations in water samples ranged from 0.005 to 0.021 μg L-1. These concentrations were well below reported C. dubia LC 50 s and toxicity was not observed in laboratory bioassays. Cyfluthrin, bifenthrin, esfenvalerate, and λcyhalothrin were detected in sediment samples at concentrations ranging from 1.0 to 74.4 ng g-1 , dry weight. At DPC, all but one sample caused 100% toxicity to H. azteca. Based on estimated toxicity units (TUs) calculated from measured pyrethroid concentrations in sediment, bifenthrin was likely responsible for this toxicity; λ-cyhalothrin also probably contributed. At ORC, survival of H. azteca was significantly reduced in four of the 11 sediment samples. However, pyrethroids were detected in only two of these samples. Based on TUs, bifenthrin and λ-cyhalothrin likely contributed to toxicity in these two samples.
Environmental Pollution, Mar 1, 2018
Pesticides move to surface water via various pathways including surface runoff, spray drift and s... more Pesticides move to surface water via various pathways including surface runoff, spray drift and subsurface flow. Little is known about the relative contributions of surface runoff and spray drift in agricultural watersheds. This study develops a modeling framework to address the contribution of spray drift to the total loadings of pesticides in receiving water bodies. The modeling framework consists of a GIS module for identifying drift potential, the AgDRIFT model for simulating spray drift, and the Soil and Water Assessment Tool (SWAT) for simulating various hydrological and landscape processes including surface runoff and transport of pesticides. The modeling framework was applied on the Orestimba Creek Watershed, California. Monitoring data collected from daily samples were used for model evaluation. Pesticide mass deposition on the Orestimba Creek ranged from 0.08 to 6.09% of applied mass. Monitoring data suggests that surface runoff was the major pathway for pesticide entering water bodies, accounting for 76% of the annual loading; the rest 24% from spray drift. The results from the modeling framework showed 81 and 19%, respectively, for runoff and spray drift. Spray drift contributed over half of the mass loading during summer months. The slightly lower spray drift contribution as predicted by the modeling framework was mainly due to SWAT's under-prediction of pesticide mass loading during summer and over-prediction of the loading during winter. Although model simulations were associated with various sources of uncertainties, the overall performance of the modeling framework was satisfactory as evaluated by multiple statistics: for simulation of daily flow, the Nash-Sutcliffe Efficiency Coefficient (NSE) ranged from 0.61 to 0.74 and the percent bias (PBIAS) < 28%; for daily pesticide loading, NSE ¼ 0.18 and PBIAS ¼ À1.6%. This modeling framework will be useful for assessing the relative exposure from pesticides related to spray drift and runoff in receiving waters and the design of management practices for mitigating pesticide exposure within a watershed.
Journal of Pesticide Science, 2007
with an aqueous half life (t 1/2) of 125 hr and a soil t 1/2 of 438 hr. Fipronil is the active in... more with an aqueous half life (t 1/2) of 125 hr and a soil t 1/2 of 438 hr. Fipronil is the active ingredient in Icon ® , Frontline ® , Termidor ® , and Top Spot ®. It is classified as a chiral pesticide and released to the environment as a racemic mixture; approximately 66,824 lbs were used in California in 2005, primarily for structural pest control. 11) The insecticide is not registered for agriculture use in the state of California.