Regulatory Modeling of Pesticide Aquatic Exposures in California's Agricultural Receiving Waters.

For the aquatic exposure assessment of pesticides, the USEPA uses the Variable Volume Water Model (VVWM) to predict the estimated environmental concentrations (EECs) of a pesticide in a water body that receives runoff inputs from the Pesticide Root Zone Model (PRZM). The standard farm pond and additional generalized static and flowing water bodies used in endangered species assessment (aquatic bins) are used by USEPA to model the worst-case aquatic exposure for the nationwide exposure assessment. However, whether or not model results are relevant to state-specific conditions has not been validated. In this study, the USEPA water body scenarios are examined for their capability of providing a conservatively realistic estimate of pesticide aquatic exposures in California's agricultural settings. The sensitivity of modeled EECs to key water body parameters (dimensions, flow, and mass transfer) was explored with a one-at-a-time approach by using the standard farm pond as a baseline. The EECs generated from different USEPA water bodies for the worst-case loading were compared with the monitoring data observed in California's agriculturally influencing water bodies. Results showed that the farm pond EECs well captured the worst-case monitoring data, whereas the aquatic bins EECs, especially the flowing bins, tended to overestimate data. The conceptual model of the standard farm pond was also found to be relevant to the highly vulnerable water bodies in California's agricultural areas. The study confirms that VVWM with the standard farm pond scenario is appropriate for the screening-level regulatory exposure assessment in California's agricultural settings.

A review of diazinon use, contamination in surface waters, and regulatory actions in California across water years 1992-2014.

Diazinon is an organophosphorus insecticide that has been widely used in the USA and in California resulting in contamination of surface waters. Several federal and state regulations have been implemented with the aim of reducing its impact to human health and the environment, e.g., the cancellation of residential use products by the USEPA and dormant spray regulations by the California Department of Pesticide Regulation. This study reviewed the change in diazinon use and surface water contamination in accordance with the regulatory actions implemented in California over water years 1992-2014. We observed that use amounts began declining when agencies announced the intention to regulate certain use patterns and continued to decline after the implementation of those programs and regulations. The reduction in use amounts led to a downward trend in concentration data and exceedance frequencies in surface waters. Moreover, we concluded that diazinon concentrations in California's surface waters in recent years (i.e., water years 2012-2014) posed a de minimis risk to aquatic organisms.

Evaluation of Three Models for Simulating Pesticide Runoff from Irrigated Agricultural Fields.

Three models were evaluated for their accuracy in simulating pesticide runoff at the edge of agricultural fields: Pesticide Root Zone Model (PRZM), Root Zone Water Quality Model (RZWQM), and OpusCZ. Modeling results on runoff volume, sediment erosion, and pesticide loss were compared with measurements taken from field studies. Models were also compared on their theoretical foundations and ease of use. For runoff events generated by sprinkler irrigation and rainfall, all models performed equally well with small errors in simulating water, sediment, and pesticide runoff. The mean absolute percentage errors (MAPEs) were between 3 and 161%. For flood irrigation, OpusCZ simulated runoff and pesticide mass with the highest accuracy, followed by RZWQM and PRZM, likely owning to its unique hydrological algorithm for runoff simulations during flood irrigation. Simulation results from cold model runs by OpusCZ and RZWQM using measured values for model inputs matched closely to the observed values. The MAPE ranged from 28 to 384 and 42 to 168% for OpusCZ and RZWQM, respectively. These satisfactory model outputs showed the models' abilities in mimicking reality. Theoretical evaluations indicated that OpusCZ and RZWQM use mechanistic approaches for hydrology simulation, output data on a subdaily time-step, and were able to simulate management practices and subsurface flow via tile drainage. In contrast, PRZM operates at daily time-step and simulates surface runoff using the USDA Soil Conservation Service's curve number method. Among the three models, OpusCZ and RZWQM were suitable for simulating pesticide runoff in semiarid areas where agriculture is heavily dependent on irrigation.

Monitoring Fipronil and Degradates in California Surface Waters, 2008-2013.

The phenylpyrazole insecticide fipronil has become a popular replacement pest management tool as organophosphorus insecticides have been phased out for residential use and pyrethroids have come under scrutiny as a surface water contaminant. There has been an increasing concern of offsite transport of fipronil to surrounding surface waters and a corresponding increase in potential toxicity to aquatic organisms. The California Department of Pesticide Regulation Environmental Monitoring Program has collected over 500 urban surface water samples throughout California since 2008 to determine the presence and concentrations of fipronil and five degradate products. Statewide, fipronil was detected at high frequency (49%), as were the sulfone (43%) and desulfinyl (33%) degradates. Data collected at long-term monitoring stations indicate higher concentrations in southern California, corresponding to a higher use pattern in the region. There is a clear pattern of increased transport of fipronil with higher flow associated with rain events. However, the lack of seasonality effects on degradates' concentrations suggest a constant source of fipronil with a corresponding lag time of transport to surface waters during the dry season. Receiving waters had a diluting effect on concentrations; however, a significant proportion (46%) of receiving water samples had associated fipronil concentrations above USEPA aquatic life chronic benchmark values. Total mass loading estimates from a long-term monitoring site suggest that the annual fipronil loading is greater in the dry season than during storm events. This could have implications for future mitigation efforts because most runoff during this period was generated from irrigation and outdoor residential use.

Insecticide washoff from concrete surfaces: characterization and prediction.

Pesticide runoff from impervious surfaces is a significant cause of aquatic contamination and ecologic toxicity in urban waterways. Effective mitigation requires better understanding and prediction of off-site transport processes. Presented here is a comprehensive study on pesticide washoff from concrete surfaces, including washoff tests, experimental data analysis, model development, and application. Controlled rainfall experiments were conducted to characterize washoff loads of commercially formulated insecticides with eight different active ingredients. On the basis of the analysis of experimental results, a semimechanistic model was developed to predict pesticide buildup and washoff processes on concrete surfaces. Three pesticide product specific parameters and their time dependences were introduced with empirical functions to simulate the persistence, transferability, and exponential characteristics of the pesticide washoff mechanism. The parameters were incorporated using first-order kinetics and Fick's second law to describe pesticide buildup and washoff processes, respectively. The model was applied to data from 21 data sets collected during 38 rainfall events, with parameters calibrated to pesticide products and environmental conditions. The model satisfactorily captured pesticide mass loads and their temporal variations for pesticides with a wide range of chemical properties (log KOW = 0.6-6.9) under both single and repeated (1-7 times) rainfall events after varying set times (1.5 h∼238 days after application). Results of this study suggested that, in addition to commonly reported physicochemical properties for the active ingredient of a pesticide product, additional parameters determined from washoff experiments are required for risk assessments of pesticide applications on urban impervious surfaces.

Diazinon-chemistry and environmental fate: a California perspective.

Diazinon, first introduced in USA in 1956, is a broad-spectrum contact organophosphate pesticide that has been used as an insecticide, and nematicide. It has been ond of the most widely used insecticides in the USA for household and agricultural pest control. In 2004, residential use of diazinon was discontinued; as a result, the total amount applied has drastically decreased. [corrected]. Consequently, the amounts of diazinon applied have been drastically decreased. For example, in California, the amount of diazinon applied decreased from 501,784 kg in 2000 to 64,122 kg in 2010. Diazinon has a K(oc) value of 40-432 and is considered to be moderately mobile in soils. Diazinon residues have been detected in groundwater, drinking water wells, monitoring wells, and agricultural well. The highest detection frequencies and highest percentages of exceedance of the water quality criterion value of 0.1 µg/L have been reported from the top five agricultural counties n California that had the highest diazinon use. Diazinon is transported in air via atmospheric processes such as direct air movement and wet deposition in snow and rain, although concentrations decrease with distance and evaluation from the source. In the environment, diazinon undergoes degradation by several processes, the most important of which is microbial degradation in soils. The rate of diazinon degradation is affected by pH, soil type, organic amendments, soil moisture, and the concentration of diazinon in the soil, with soil pH being a major influencing factor in diazinon degradation rate. Studies indicate tha soil organic matter is the most important factor that influences diazinon sorption by soils, although clay content and soil ph also play an important role in diazinon sorption. Diazinon is very highly to moderately toxic aquatic arganisms, Diazinon inhibits the enzyme acetylcholinesterase, which hydrolyzes the neurotransmitter acetylcholine and leads to a suite of intermediate syndromes including anorexia, diarrhea, generalized weakness, muscle tremors, abnormal posturing and behavior, depression, and health. Differences in metabolism among species and exposure concentrations play a vital role in diazinon's bioaccumulation among different aquatic organisms in a wide range of accumulating rates and efficiencies.

Pesticide occurrence and aquatic benchmark exceedances in urban surface waters and sediments in three urban areas of California, USA, 2008-2011.

Urban pesticide use has a direct impact on surface water quality. To determine the extent of pesticide contamination, the California Department of Pesticide Regulation initiated a multi-area urban monitoring program in 2008. Water and sediment samples were collected at sites unaffected by agricultural inputs in three areas: Sacramento (SAC), San Francisco Bay (SFB), and Orange County (OC). Samples were analyzed for up to 64 pesticides or degradates. Multiple detections were common; 50 % of the water samples contained five or more pesticides. Statewide, the most frequently detected insecticides in water were bifenthrin, imidacloprid, fipronil, fipronil sulfone, fipronil desulfinyl, carbaryl, and malathion. Bifenthrin was the most common contaminant in sediment samples. Key differences by area: OC had more pesticides detected than SAC or SFB with higher concentrations of fipronil, whereas SAC had higher concentrations of bifenthrin. The most frequently detected herbicides were 2,4-D, triclopyr, dicamba, diuron, and pendimethalin. Key differences by area: OC and SFB had higher concentrations of triclopyr, whereas SAC had higher concentrations of 2,4-D and dicamba. Detection frequency, number of pesticides per sample, and pesticide concentration increased during rainstorm events. In water samples, all of the bifenthrin, malathion, fipronil, permethrin, and λ-cyhalothrin detections, and most of the fipronil sulfone and cyfluthrin detections were above their lowest US EPA aquatic benchmark. Diuron was the only herbicide that was detected above its lowest benchmark. Based on the number of pesticides and exceedances of aquatic benchmarks or the high number of sediment toxicity units, pesticides are abundant in California surface waters.

Chlorpyrifos-treated crops in the vicinity of surface water contamination in the San Joaquin Valley, California, USA.

Due to frequent contamination of streams in the San Joaquin Valley, California, USA, with the insecticide chlorpyrifos, researchers are working to identify crop-specific management practices that will reduce the offsite movement of this compound into surface waters. To guide this effort, crops treated with chlorpyrifos in the vicinity of contaminated streams were identified; walnut, alfalfa, and almond were the primary crops identified. Use was higher on walnut and almond, but due to irrigation practices offsite movement in surface runoff may be more likely from alfalfa. Based on these findings, development of management practices to reduce off-site movement of chlorpyrifos in irrigation runoff from treated alfalfa fields is recommended.

Detections of the neonicotinoid insecticide imidacloprid in surface waters of three agricultural regions of California, USA, 2010-2011.

Seventy-five surface water samples were collected from three agricultural regions of California and analyzed for the neonicotinoid insecticide imidacloprid. Samples were collected during California's relatively dry-weather irrigation seasons in 2010 and 2011. Imidacloprid was detected in 67 samples (89%); concentrations exceeded the United States Environmental Protection Agency's chronic invertebrate Aquatic Life Benchmark of 1.05 µg/L in 14 samples (19%). Concentrations were also frequently greater than similar toxicity guidelines developed for use in Europe and Canada. The results indicate that imidacloprid commonly moves offsite and contaminates surface waters at concentrations that could harm aquatic organisms following use under irrigated agriculture conditions in California.

Analysis of diazinon agricultural use in regions of frequent surface water detections in California, USA.

For five agricultural regions in California, USA, detection frequency of diazinon in surface water and several aspects of its use were determined from recent data (2005-2010): application method, product formulation and primary crops. Diazinon detection frequencies ranged from 10% to 91%. Application method and product formulations used were similar in all regions. The primary crops treated varied from lettuce (77%) in the regions with highest detections frequencies to tree crops (53%) in those with the lowest. The results suggest that the variation in diazinon detection frequencies likely was not due to the application method or formulation type.

Pesticide concentrations in water and sediment and associated invertebrate toxicity in Del Puerto and Orestimba Creeks, California, 2007-2008.

The California's San Joaquin River and its tributaries including Orestimba (ORC) and Del Puerto (DPC) Creeks are listed on the 2006 US EPA Clean Water Act §303(d) list for pesticide impairment. From December 2007 through June 2008, water and sediment samples were collected from both creeks in Stanislaus County to determine concentrations of organophosphorus (OP) and pyrethroid insecticides and to identify 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 median lethal concentrations (LC50), chlorpyrifos was likely the cause of this toxicity. Pyrethroids were detected more frequently in sediment samples (18 detections) than 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 LC50s, and toxicity was not observed in laboratory bioassays. Cyfluthrin, bifenthrin, esfenvalerate, and λ-cyhalothrin were detected in sediment samples at concentrations ranging from 1.0 to 74.4 ng g(-1), dry weight. At DPC, all but one sediment sample caused 100% toxicity to H. azteca. Based on estimated toxicity units (TUs), bifenthrin was likely responsible for this toxicity and λ-cyhalothrin also 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 the toxicity.

Detections of eleven organophosphorus insecticides and one herbicide threatening Pacific salmonids, Oncorhynchus spp., in California, 1991-2010.

California's surface water monitoring results from 1991 through 2010 were analyzed to determine whether 12 organophosphorus insecticides and herbicides (i.e., azinphos methyl, bensulide, dimethoate, disulfoton, ethoprop, fenamiphos, methamidophos, methidathion, methyl parathion, naled, phorate, and phosmet) and their degradates have been detected above maximum concentration limits (MCLs) in Pacific salmonid habitats. Methidathion, methyl parathion, phorate, phosmet, and the oxygen analogue of naled (DDVP) detections exceeded MCLs. Methyl parathion detections may be accounted for by monthly use trends, while methidathion detections may be explained by yearly use trends. There were inadequate phorate, phosmet, or DDVP data to evaluate for correlations with use.

Environmental chemistry, ecotoxicity, and fate of lambda-cyhalothrin.

Lambda-cyhalothrin is a pyrethroid insecticide used for controlling pest insects in agriculture, public health, and in construction and households. Lambda-cyhalothrin is characterized by low vapor pressure and a low Henry's law constant but by a high octanol-water partition coefficient (K(ow)) and high water-solid-organic carbon partition coefficient (K(oc)) values. Lambda-cyhalothrin is quite stable in water at pH < 8, whereas it hydrolyzes to form HCN and aldehyde under alkaline conditions. Although lambda-cyhalothrin is relatively photostable under natural irradiation, with a half-life > 3 wk, its photolysis process is fast under UV irradiation, with a half-life < 10 min. The fate of lambda-cyhalothrin in aquatic ecosystems depends on the nature of system components such as suspended solids (mineral and organic particulates) and aquatic organisms (algae, macrophytes, or aquatic animals). Lambda-cyhalothrin residues dissolved in water decrease rapidly if suspended solids and/or aquatic organisms are present because lambda-cyhalothrin molecules are strongly adsorbed by particulates and plants. Adsorbed lambda-cyhalothrin molecules show decreased degradation rates because they are less accessible to breakdown than free molecules in the water column. On the other hand, lambda-cyhalothrin adsorbed to suspended solids or bottom sediments may provide a mechanism to mitigate its acute toxicity to aquatic organisms by reducing their short-term bioavailability in the water column. The widespread use of lambda-cyhalothrin has resulted in residues in sediment, which have been found to be toxic to aquatic organisms including fish and amphipods. Mitigation measures have been used to reduce the adverse impact of lambda-cyhalothrin contributed from agricultural or urban runoff. Mitigation may be achieved by reducing the quantity of runoff and suspended solid content in runoff through wetlands, detention ponds, or vegetated ditches.

Environmental fate and toxicology of carbaryl.

Carbaryl is an agricultural and garden insecticide that controls a broad spectrum of insects. Although moderately water soluble, it neither vaporizes nor volatilizes readily. However, upon spray application the insecticide is susceptible to drift. It is unstable under alkaline conditions, thus easily hydrolyzed. Carbaryl has been detected in water at ppb concentrations but degradation is relatively rapid, with 1-naphthol identified as the major degradation product. Indirect and direct photolysis of carbaryl produces different naphthoquinones as well as some hydroxyl substituted naphthoquinones. Sorption of the insecticide to soil is kinetically rapid. However, although both the mineral and organic fractions contribute, because of its moderate water solubility it is only minimally sorbed. Also, sorption to soil minerals strongly depends on the presence of specific exchangeable cations and increases with organic matter aromaticity and age. Soil microbes (bacteria and fungi) are capable of degrading carbaryl; the process is more rapid in anoxic than aerobic systems and with increased temperature and moisture. Carbaryl presents a significant problem to pregnant dogs and their offspring, but some have questioned the applicability of these data to humans. In addition, for toxicokinetic and/or physiological reasons, it has been argued that dogs are more sensitive than humans to carbaryl-induced reproductive or developmental toxicity. However, these arguments are based on either older pharmacokinetic studies or on speculation about possible reproductive differences between dogs on the one hand and rats and humans on the other. In view of the wider evidence from both human epidemiological and laboratory animal studies, the question of the possible developmental and reproductive toxicity of carbaryl should be considered open and requiring further study.

Modeling spray drift and runoff-related inputs of pesticides to receiving water.

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 = 0.18 and PBIAS = -1.6%. 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.

Chemistry and fate of simazine.

Simazine, first introduced in 1956, is a popular agricultural herbicide used to inhibit photosynthesis in broadleaf weeds and grasses. It is a member of the triazine family, and according to its physicochemical properties, it is slightly soluble in water, relatively nonvolatile, capable of partitioning into organic phases, and susceptible to photolysis. Sorption and desorption studies on its behavior in soils indicate that simazine does not appreciably sorb to minerals and has the potential to leach in clay and sandy soils. The presence of organic matter in soils contributes to simazine retention but delays its degradation. The primary sorptive mechanism of simazine to OM has been proposed to be via partitioning and/or by the interaction with functional groups of the sorbent. Farming practices directly influence the movement of simazine in soils as well. Tilled fields lower the runoff of simazine when compared to untilled fields, but tilling can also contribute to its movement into groundwater. Planting cover crops on untilled land can significantly reduce simazine runoff. Such practices are important because simazine and its byproducts have been detected in groundwater in The Netherlands, Denmark, and parts of the U.S. (California, North Carolina, Illinois, and Wisconsin) at significant concentrations. Concentrations have also been detected in surface waters around the U.S. and United Kingdom. Although the physicochemical properties of simazine do not support volatilization, residues have been found in the atmosphere and correlate with its application. Although at low concentrations, simazine has also been detected in precipitation in Pennsylvania (U.S.), Greece, and Paris (France). Abiotically, simazine can be oxidized to several degradation products. Although hydrolysis does not contribute to the dissipation of simazine, photolysis does. Microbial degradation is the primary means of simazine dissipation, but the process is relatively slow and kinetically controlled. Some bacteria and fungal species capable of utilizing simazine as a sole carbon and nitrogen source at a fast rate under laboratory conditions have been identified. Metabolism of simazine in higher organisms is via cytochrome P-450-mediated oxidation and glutathione conjugation.

Performance assessment and validation of a paramagnetic particle-based enzyme-linked immunosorbent assay for chlorpyrifos in agricultural runoff waters.

A commercial magnetic particle-based enzyme-linked immunosorbent assay (ELISA) kit for the insecticide chlorpyrifos [O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] was evaluated for its specificity, precision, and accuracy, its susceptibility to matrix interferences in agricultural and environmental surface waters, and its comparability to a gas chromatographic/flame photometric (GC/FPD) method for the determination of organophosphorus pesticides in natural waters. Repeatability, reproducibility, and accuracy studies show that the kit satisfies current U.S. Environmental Protection Agency criteria for the assessment of analytical methods. Observable matrix effects were found to be present in all of the environmental test waters, with the slopes of calibration curves generated in each of the test matrices deviating from that of the control matrix by as much as 16%. Specificity studies indicate that the chlorpyrifos polyclonal antibody adequately differentiates the target compound from other structurally similar organophosphorus pesticides, with the exception of its methyl analogue. Cross-reactivity with chlorpyrifos-methyl was approximately 37%, while reactivity with diazinon, pyridaphenthion, diclofenthion, bromiphos-ethyl, bromiphos-methyl, pirimiphos-ethyl, and chlorpyrifos oxon ranged from 1.6 to 10.7%. Cross-reactivity with pirimiphos-methyl, 3,5,6-trichloro-2-pyridinol, diethyl phosphate, and diethyl thiophosphate was negligible (<1%). Validation of the paramagnetic particle ELISA format was accomplished using water samples from two monitoring studies that were collected, split, and analyzed directly by ELISA and by GC/FPD. Results of the two analytical methods were then compared using standard t tests, regression analysis, and differences against mean measurement (bias) plots. While the agreement between the two methods was determined to be satisfactory, ELISA exhibits consistent positive bias in environmental matrices. Several preanalysis mitigation steps were suggested that may help moderate bias, but additional study is recommended to explicate the exact factors responsible for its consistent overestimation of results.

Evaluation of sources and loading of pesticides to the Sacramento River, California, USA, during a storm event of winter 2005.

A monitoring study was conducted in the tributaries and main stem of the Sacramento River, California, USA, during the storm event of January 26 to February 1, 2005. The purpose of the study was to evaluate the sources and loading of pesticides in the Sacramento River watershed during the winter storm season. A total of 26 pesticides or pesticide degradates were analyzed, among which five pesticides and one triazine degradate were detected. Diuron, diazinon, and simazine were found in all streams with a total load of 110.4, 15.4, and 15.7 kg, respectively, in the Sacramento River over the single storm event. Bromacil, hexazinone, and the triazine degradate diaminochlorotriazine were only detected in two smaller drainage canals with a load ranged from 0.25 to 7 kg. The major source of pesticides detected in the main stem Sacramento River was from the most upstream subbasin, the Sacramento River above Colusa, where detected pesticides either exceeded or were close to those at the main outlet of the Sacramento River at Alamar Marina. The higher precipitation in this subbasin was partly responsible for the greater contribution of pesticides observed. Diazinon was the only pesticide with concentrations above water quality criteria, indicating that additional mitigation measures may be needed to reduce its movement to surface water.

Continuous low-level aquatic monitoring (CLAM) samplers for pesticide contaminant screening in urban runoff: Analytical approach and a field test case.

Monitoring of surface waters for organic contaminants is costly. Grab water sampling often results in non-detects for organic contaminants due to missing a pulse event or analytical instrumentation limitations with a small sample size. Continuous Low-Level Aquatic Monitoring (CLAM) samplers (C.I.Agent® Solutions) continually extract and concentrate organic contaminants in surface water onto a solid phase extraction disk. Utilizing CLAM samplers, we developed a broad spectrum analytical screen for monitoring organic contaminants in urban runoff. An intermediate polarity solid phase, hydrophobic/lipophilic balance (HLB), was chosen as the sorbent for the CLAM to target a broad range of compounds. Eighteen urban-use pesticides and pesticide degradates were targeted for analysis by LC/MS/MS, with recoveries between 59 and 135% in laboratory studies. In field studies, CLAM samplers were deployed at discrete time points from February 2015 to March 2016. Half of the targeted chemicals were detected with reporting limits up to 90 times lower than routine 1-L grab samples with good precision between field replicates. In a final deployment, CLAM samplers were compared to 1-L water samples. In this side-by-side comparison, imidacloprid, fipronil, and three fipronil degradates were detected by the CLAM sampler but only imidacloprid and fipronil sulfone were detected in the water samples. However, concentrations of fipronil sulfone and imidacloprid were significantly lower with the CLAM and a transient spike of diuron was not detected. Although the CLAM sampler has limitations, it can be a powerful tool for development of more focused and informed monitoring efforts based on pre-identified targets in the field.

An integrated vegetated ditch system reduces chlorpyrifos loading in agricultural runoff.

Agricultural runoff containing toxic concentrations of the organophosphate pesticide chlorpyrifos has led to impaired water body listings and total maximum daily load restrictions in California's central coast watersheds. Chlorpyrifos use is now tightly regulated by the Central Coast Regional Water Quality Control Board. This study evaluated treatments designed to reduce chlorpyrifos in agricultural runoff. Initial trials evaluated the efficacy of 3 different drainage ditch installations individually: compost filters, granulated activated carbon (GAC) filters, and native grasses in a vegetated ditch. Treatments were compared to bare ditch controls, and experiments were conducted with simulated runoff spiked with chlorpyrifos at a 1.9 L/s flow rate. Chlorpyrifos concentrations and toxicity to Ceriodaphnia dubia were measured at the input and output of the system. Input concentrations of chlorpyrifos ranged from 858 ng/L to 2840 ng/L. Carbon filters and vegetation provided the greatest load reduction of chlorpyrifos (99% and 90%, respectively). Toxicity was completely removed in only one of the carbon filter trials. A second set of trials evaluated an integrated approach combining all 3 treatments. Three trials were conducted each at 3.2 L/s and 6.3 L/s flow rates at input concentrations ranging from 282 ng/L to 973 ng/L. Chlorpyrifos loadings were reduced by an average of 98% at the low flow rate and 94% at the high flow rate. Final chlorpyrifos concentrations ranged from nondetect (<50 ng/L) to 82 ng/L. Toxicity to C. dubia was eliminated in 3 of 6 integrated trials. Modeling of the ditch and its components informed design alterations that are intended to eventually remove up to 100% of pesticides and sediment. Future work includes investigating the adsorption capacity of GAC, costs associated with GAC disposal, and real-world field trials to further reduce model uncertainties and confirm design optimization. Trials with more water-soluble pesticides such as neonicotinoids are also recommended. Integr Environ Assess Manag 2017;13:423-430. © 2016 SETAC.