Interactive Effects of Copper-Silver Mixtures at the Intestinal Epithelium of Rainbow Trout: An In Vitro Approach.

While metals are present in mixture in the environment, metal toxicity studies are usually conducted on an individual metal basis. There is a paucity of data in the existing literature regarding specific metal-metal interactions and their effect on metal toxicity and bioavailability. We studied interactions of a silver (Ag)-copper (Cu) mixture at the intestinal epithelium using an intestinal cell line derived from rainbow trout (Oncorhynchus mykiss), the RTgutGC. Exposures were conducted in media containing different chloride concentrations (low chloride, 1 mM; high chloride, 146 mM), thus resulting in different metal speciation. Cytotoxicity was evaluated based on two endpoints, cell metabolic activity and cell membrane integrity. The Ag-Cu mixture toxicity was assessed using two designs: independent action and concentration addition. Metal mixture bioavailability was studied by exposing cells to 500 nM of Ag or Cu as a single metal or a mixture (i.e., 500 nM of Cu plus 500 nM of Ag). We found an antagonistic effect in the low-chloride medium and an additive/synergistic effect in the high-chloride medium. We found that Cu dominates over Ag toxicity and bioavailability, indicating a competitive inhibition when both metals are present as free metal ions in the exposure media, which supports our hypothesis. Our study also suggests different mechanisms of uptake of free metal ions and metal complexes. The study adds valuable information to our understanding of the role of metal speciation on metal mixture toxicity and bioavailability. Environ Toxicol Chem 2024;43:105-114. © 2023 SETAC.

The acute toxicity of pesticide mixtures to honeybees.

Honeybees (Apis mellifera) frequently live in complex environments where exposure to mixtures of pesticides is possible. Although several studies have expressed concern regarding the combined effects of pesticide mixtures, other studies did not find increased toxicity. Thus, the primary objective of this study was to identify peer-reviewed literature measuring the toxicity of pesticide mixtures to honeybees and determine how frequently synergistic interactions occur. Many experiments (258) were identified that met the criteria for inclusion. When considering all experiments, 34% of experiments had model deviation ratios (MDR; expected toxicity/observed toxicity) greater than 2, suggesting greater-than-additive toxicity. Twelve percent of experiments had MDR values greater than 5, with several studies exceeding 100. However, most experiments that had higher MDRs included azole fungicides or acaricides as a component of the mixture. After removal of these groups, only 8% of experiments exceeded an MDR of 2, and no experiments exceeded 5. Moreover, the influence of the azole fungicides was dose dependent. If only experiments that used azole exposure at environmentally relevant concentrations were considered, azole fungicides had limited impact on neonicotinoid insecticides. However, pyrethroid insecticides still had greater than expected toxicity with 80% of experiments having MDR values greater than 2. Acaricides also had greater than expected incidence of synergy with approximately 30% of studies reporting MDR values greater than 2. It should be noted that even the azole studies considered environmentally relevant frequently used maximum exposure rates and worst-case exposure scenarios. The primary finding is that synergy is uncommon except for a few cases where known synergists (azole fungicides) and pesticides with variable metabolism potential, such as some pyrethroids, are in combination. Future work is still needed to refine the relevance of azole fungicides at commonly occurring environmental concentrations. Integr Environ Assess Manag 2022;18:1694-1704. © 2022 SETAC.

Parenting, Pesticides and Adolescent Psychological Adjustment: A Brief Report.

Pesticides used to control insects, such as pyrethroids, are neurotoxicants, yet adolescent researchers often overlook their potential role in adolescent psychological adjustment. This brief report is guided by bioecological theory and considers the possible independent and interactive effects of environmental pyrethroid pesticide exposure for adolescent depressive symptoms. Self-reported adolescent appraisals of the parent-child relationship and depressive symptoms were obtained from a convenience sample of impoverished, predominantly Latino urban youth (n = 44). Exposure to environmental pyrethroids was obtained from wipe samples using a standardized protocol. Parent-adolescent conflict was higher in households with bifenthrin than those without, and adolescent depressive symptoms were elevated in homes where cypermethrin was detected. In addition, the presence of bifenthrin in the home attenuated the protective effects of parental involvement on adolescent depressive symptoms. The current results suggest that adolescent mental health researchers must consider the synergistic combinations of adolescents' environments' physical and social features. Given the endemic presence of pesticides and their neurotoxic function, pesticide exposure may demand specific attention.

Environmental Characterization of Underwater Munitions Constituents at a Former Military Training Range.

As a result of military activities, unexploded ordnance and discarded military munitions are present in underwater environments, which has resulted in the release of munitions constituents including the high explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), along with their primary degradation products, to the water column and adjacent sediments. The present study focused on the characterization of underwater exposure and concentrations of energetics such as TNT and RDX at the former Vieques Naval Training Range at Bahia Salina del Sur (Vieques, Puerto Rico, USA), a bay with documented high incidence of munitions. In situ passive sampling using polar organic chemical integrative samplers (POCIS) was used for the detection and quantification of constituents in water at target locations approximately 15 to 30 cm from 15 individual potentially leaking munitions, and also at 15 unbiased locations approximately evenly spaced across the Bay. For comparison with POCIS-derived concentrations, grab samples were taken at the POCIS target locations. The POCIS-derived and averaged grab samples agreed within a factor of 3. When detected, munitions constituent concentrations (primarily TNT and RDX) were observed at ultratrace concentrations (as low as 4 ng/L for RDX), except 30 cm from one General Purpose bomb where the TNT concentration was 5.3 µg/L, indicating that low-level contamination exists at Bahia Salina del Sur on a very localized scale despite the relatively high density of munitions, similar to previously reported results for other munitions sites around the world. Sediment and porewater sampled at 4 stations where munitions constituents were detected in the water column had concentrations below detection (approximately 5 µg/kg and 5 ng/L, respectively), suggesting that the sediment was not a sink for these constituents at those locations. Environ Toxicol Chem 2022;41:275-286. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Applications of the RTgill-W1 Cell Line for Acute Whole-Effluent Toxicity Testing: In Vitro-In Vivo Correlation and Optimization of Exposure Conditions.

The cell line RTgill-W1 was evaluated as an in vitro alternative model for acute fish whole-effluent toxicity (WET) testing. We determined the 50% effective concentration (EC50) that reduces the viability of RTgill-W1 cells for selected toxicants commonly found in effluent samples and correlated those values with the respective 50% lethal concentration (LC50) of freshwater (fathead minnow, Pimephales promelas) and marine (sheepshead minnow, Cyprinodon variegatus) fish species obtained from the literature. Excluding low water-soluble organics and the volatile sodium hypochlorite, significant correlations were measured for metal, metalloids, ammonia, and higher water-soluble organics between in vitro EC50 values and in vivo LC50 values for both species. Typically, toxicity studies with RTgill-W1 cells are conducted by adding salts to the exposure medium, which may affect the bioavailability of toxicants. Osmotic tolerance of RTgill-W1 cells was found between 150 and 450 mOsm/kg, which were set as the hypoosmotic and hyperosmotic limits. A subset of the toxicants were then reexamined in hypoosmotic and hyperosmotic media. Copper toxicity decreased in hyperosmotic medium, and nickel toxicity increased in hypoosmotic and hyperosmotic media. Linear alkylbenzene sulfonate toxicity was not affected by the medium osmolality. Overall, RTgill-W1 cells have shown potential for applications in measuring metal, metalloids, ammonia, and water-soluble organic chemicals in acute WET tests, as well as complementing current toxicity identification and reduction evaluation strategies. In the present study, RTgill-W1 cells have been established as a valid animal alternative for WET testing, and we show that through manipulation of medium osmotic ranges, sensitivity to nickel was enhanced. Environ Toxicol Chem 2021;40:1050-1061. © 2020 SETAC.

Effects of Copper on the Neuromasts of Xenopus Laevis.

Fish and aquatic amphibians possess neuromasts on the surface of their body that constitute the lateral line, a sensory system used to detect water displacement. Copper is known to inactivate the neuromast organs of this system. Copper-induced neuromast loss in African clawed frogs, Xenopus laevis, was examined by exposing Nieuwkoop-Faber stage 54-55 larvae to copper concentrations of 0, 100, 200, 300, and 400 µg/L for 96 h, followed by an examination of neuromast counts, staining intensity, and behavioral responses. Neuromasts were counted using a novel imaging method across four different body regions: the whole body, partial body, head, and tail. Neuromast counts showed a decreasing, but nonsignificant, trend across increasing levels of copper exposure. Intensity of neuromast staining showed a stronger concentration-dependent decrease in all four body regions. The decrease in staining intensity, but not neuromast number, may indicate that although neuromasts are still functioning, they have a decreased number of viable hair cells. Potential loss of responsiveness related to neuromast damage was examined via sensitivity to puffs of air at varying distances. We detected little to no difference in response to the air puff stimulus between control tadpoles and tadpoles exposed to 400 µg/L of copper. Neuromasts of X. laevis may be more resistant to copper than those of North American tadpole species, possibly suggesting greater tolerance of the lateral line to environmental stressors in species that maintain this sensory system throughout their lifespan as compared with species that only have the lateral line during the larval period.

Field studies of pollutant removal from nursery and greenhouse runoff by constructed wetlands.

Plant nursery runoff commonly contains pesticides and nutrients that often threaten aquatic ecosystems. Constructed wetlands could be a tool to remove pesticides and nutrients from nursery runoff but have not been extensively studied in this setting. Two field-scale constructed wetlands (one subsurface-flow constructed wetland [SFCW] and one free-surface constructed wetland [FSCW]) were implemented and monitored for water quality improvement. The SFCW demonstrated significant mass reduction of 78% or greater for nitrate, orthophosphate, total nitrogen, total phosphorus, and total suspended solids. The SFCW also demonstrated significant mass reduction of 79% or greater for 10 of the 12 pesticide compounds detected in over half of the collected samples. The FSCW demonstrated significant mass reduction of 46% or greater for all nonpesticide analytes except total nitrogen. Loading rate and actual storage volume compared with inflow volume likely affected performance. Reduced size and increased loading rate of the FSCW likely reduced its ability to effectively reduce pesticides. Results from this study indicate that constructed wetlands are likely an effective tool for nursery runoff management. When designing and implementing constructed wetlands, it is important for practitioners to consider the tradeoff between system size (additional cost and land otherwise dedicated to production) and performance.

Effects of sublethal application of Deepwater Horizon oil to bird eggs on embryonic heart and metabolic rate.

Following large crude oil spills, oil from feathers of brooding birds and oiled nesting material can transfer to eggs, resulting in reduced embryonic viability for heavily oiled eggs. Eggs may also be subjected to trace or light oiling, but functional teratogenic effects from sublethal crude oil exposure have not been examined. We assessed whether sublethal application of weathered Deepwater Horizon crude oil to the eggshell surface alters heart rate and metabolic rate in Zebra Finch (Taeniopygia guttata) embryos. We first determined sublethal applications with a dosing experiment. Embryo viability for eggs exposed to 5 µL or more of crude oil decreased significantly. We conducted a second experiment to measure heart rate and metabolic rate (CO2 production) 5 and 9 d after 1 sublethal application of crude oil to eggshells on day 3 of incubation. One application of 1.0 or 2.5 µL of crude oil reduced embryonic heart rate and metabolic rate on day 12 of incubation. Using unfertilized eggs, we measured the transfer of polycyclic aromatic hydrocarbons (PAHs) from the eggshell surface to egg contents 9 d after a single application of sublethal crude oil. Our results suggest avian eggs externally exposed to small amounts of crude oil may exhibit protracted embryonic development and impaired postnatal cardiac performance.

Aplicaciones Subletales de Petróleo de la Plataforma Deepwater Horizon en los Huevos de Aves y sus Efectos sobre la Frecuencia Cardíaca y la Tasa Metabólica de Embriones Resumen Después de grandes derrames de crudo, el petróleo que se encuentra en las plumas de las aves incubadoras y el petróleo adherido al material para nidos puede transferirse a los huevos, lo que resulta en la reducción de la viabilidad embrionaria en el caso de los huevos con un contacto alto con el petróleo. Los huevos también pueden estar sujetos a manchas de petróleo ligeras o por contacto, pero no se han examinado los efectos teratogénicos funcionales de la exposición subletal al crudo. Evaluamos si la aplicación subletal de petróleo crudo desgastado del derrame de la plataforma Deepwater Horizon a la superficie de los cascarones altera la frecuencia cardíaca y la tasa metabólica de los embriones de gorrión cebra (Taeniopygia guttata). Primero determinamos las aplicaciones subletales con un experimento de dosificación. La viabilidad de los embriones en huevos expuestos a 5 µL o más de crudo disminuyó significativamente. Realizamos un segundo experimento para medir la frecuencia cardíaca y la tasa metabólica (producción de CO2 ) cinco y nueve días después de una aplicación subletal de crudo a los cascarones durante el tercer día de incubación. La aplicación de 1.0 o de 2.5 µL de crudo redujo la frecuencia cardíaca y la tasa metabólica al décimo segundo día de incubación. También medimos la transferencia de hidrocarburos aromáticos policíclicos (PAHs) en huevos sin fertilizar desde la superficie del cascarón hasta el contenido del huevo nueve días después de una aplicación subletal única de crudo. Nuestros resultados sugieren que los huevos de aves expuestos externamente a pequeñas cantidades de crudo pueden tener un desarrollo embrionario prolongado y un desempeño cardíaco postnatal deteriorado.

Release of Munitions Constituents in Aquatic Environments Under Realistic Scenarios and Validation of Polar Organic Chemical Integrative Samplers for Monitoring.

Munitions constituents (MC) may be released into aquatic environments as a result of underwater military munitions (UWMM) corrosion and breach. The present study investigated the release of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from Composition B fragments under 2 realistic exposure scenarios in a large flume with flow set at 15 cm/s: the first represented the release of MC from fully exposed Composition B, and the second represented release through a small hole, simulating a breached munition. Release of MC through a small hole was approximately 10 times lower than from exposed Composition B, demonstrating the strong influence of exposure to flow on release. The rate of release of MC into the flume was similar to that previously reported in a related field experiment, but a similar mass loss resulted in MC concentration in the field >300 times lower, likely by the dilution effect of hydrodynamic transport. The present study corroborates previous findings of release of MC at UWMM sites resulting in concentrations below the toxicity threshold to most species. In the flume water, MC was quantified using frequent grab sampling and polar organic chemical integrative samplers (POCIS). For TNT, POCIS-estimated time-weighted average concentrations were up to 40% higher than those derived from grab samples, whereas for RDX differences were 6% or less, demonstrating that POCIS provide reliable temporal integration of changing environmental concentrations for common MC. Environ Toxicol Chem 2019;38:2383-2391. Published 2019 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Relative Abundance Trends of Bird Populations in High Intensity Croplands in the Central United States.

Declining bird populations across the United States have been noted in a number of studies. Although multiple explanations have been proposed as causes of these declines, agricultural intensification has often been suggested as a significant driver of bird population dynamics. Using spatially explicit USDA-NASS Cropland Data Layer, we examined this relationship by comparing bird count data from the Breeding Bird Survey collected between 1995 and 2016 across 13 states in the central United States to corresponding categorical changes in land cover within a 2-km radius of each survey transect. This approach allowed us to compare the slopes of counts for 31 species of birds between grassland- and cropland-dominated landscapes and against increasing levels of cropland (all types combined) and pooled corn and soybean land cover types. Nearly all birds demonstrated significant responses to land cover changes. In all cases, the number of species exhibiting positive or negative responses was comparable, and median differences in percent change per year ranged from -0.5 to 0.7%. Species that responded either positively or negatively did not appear to fall into any particular foraging guild. If changes in agricultural practices are a major cause of declines, we would expect to see it across the spatial scale studied and across the majority of species. While these results do not rule out potential agricultural effects, such as toxicity resulting from pesticide exposure, which may have species-specific or localized effects, a variety of factors related to habitat are likely the most significant contributor overall. Given these results over a large spatial scale basis (multistate) and across numerous bird species, there is not a broad general trend of greater decline in crop-intensive areas. Integr Environ Assess Manag 2018;14:692-702. © 2018 SETAC.

Field validation of POCIS for monitoring at underwater munitions sites.

The present study evaluated polar organic chemical integrative samplers (POCIS) for quantification of conventional munitions constituents, including trinitrotoluene (TNT), aminodinitrotoluenes, diaminonitrotoluenes, dinitrotoluene, and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in a field setting. The POCIS were deployed at varying distances from the commonly used explosive formulation composition B (39.5% TNT, 59.5% RDX, 1% wax) in an embayment of Santa Rosa Sound (Pensacola, FL, USA). Time-weighted averaged water concentrations from a 13-d deployment ranged from 9 to 103 ng/L for TNT and RDX, respectively, approximately 0.3 to 2 m from the source. Concentrations decreased with increasing distance from the source to below quantitation limits (5-7 ng/L) at stations greater than 2 m away. Moderate biofouling of POCIS membranes after 13 d led to a subsequent effort to quantify potential effects of biofouling on the sampling rate for munitions constituents. After biofouling was allowed to occur for periods of 0, 7, 14, or 28 d at the field site, POCIS were transferred to aquaria spiked with munitions constituents. No significant differences in uptake of TNT or RDX were observed across a gradient of biofouling presence, although the mass of fouling organisms on the membranes was statistically greater for the 28-d field exposure. The present study verified the high sensitivity and integrative nature of POCIS for relevant munitions constituents potentially present in aquatic environments, indicating that application at underwater military munitions sites may be useful for ecological risk assessment. Environ Toxicol Chem 2018;37:2257-2267. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Investigation of polar organic chemical integrative sampler (POCIS) flow rate dependence for munition constituents in underwater environments.

Munition constituents (MC) are present in aquatic environments throughout the world. Potential for fluctuating release with low residence times may cause concentrations of MC to vary widely over time at contaminated sites. Recently, polar organic chemical integrative samplers (POCIS) have been demonstrated to be valuable tools for the environmental exposure assessment of MC in water. Flow rate is known to influence sampling by POCIS. Because POCIS sampling rates (Rs) for MC have only been determined under quasi-static conditions, the present study evaluated the uptake of 2,4,6-trinitrotoluene (TNT), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and 2,4- and 2,6-dinitrotoluenes (DNT), by POCIS in a controlled water flume at 7, 15, and 30 cm/s in 10-day experiments using samplers both within and without a protective cage. Sampling rate increased with flow rate for all MC investigated, but flow rate had the strongest impact on TNT and the weakest impact on RDX. For uncaged POCIS, mean Rs for 30 cm/s was significantly higher than that for 7 cm by 2.7, 1.9, 1.9, and 1.3 folds for TNT, 2,4-DNT, 2,6-DNT, and RDX, respectively. For all MC except RDX, mean Rs for caged POCIS at 7 cm/s were significantly lower than for uncaged samplers and similar to those measured at quasi-static condition, but except for 2,6-DNT, no caging effect was measured at the highest flow rate, indicating that the impact of caging on Rs is flow rate-dependent. When flow rates are known, flow rate-specific Rs should be used for generating POCIS-derived time-averaged concentrations of MC at contaminated sites.

Incorporating the joint toxicity of co-applied pesticides into the ecological risk assessment process.

Pesticides are frequently formulated as mixtures of active ingredients. Although traditionally ecological risk assessments (ERAs) have focused on individual active ingredients, there is an ongoing effort in many jurisdictions to more formally include assessment of mixtures. The overall goal of this project was to describe an approach for conducting ERA of jointly applied pesticides. We suggest that standard testing of formulation mixtures is not warranted due to the low probability of synergy occurring at a high-enough magnitude to be measurable above experimental variability. Thus, empirical testing should focus on formulations for which there is a greater likelihood of synergy due to known toxicological interactions of the pesticide class or a priori knowledge of synergy, such as intellectual property claims. Additionally, empirical testing should focus on species that are above levels of concern and limit testing on species for which it is unlikely that synergy would significantly change the outcome of the ERA. If empirical testing is warranted, we suggest that results be compared to the concentration addition model (CA). If the empirical data deviates from the model by a factor of greater than 5, then synergy is considered likely and the ERA is based on the empirical data. Otherwise, the ERA may use CA to calculate risk quotients or be based on the most toxic active ingredient. To evaluate the approach, we reviewed formulation mixtures for which data were available. Only 3 of 24 mixture studies were found to deviate from CA by more than 5. The majority of the studies had a single component that dominated toxicity, suggesting that the ERA for these formulations will not be meaningfully different if based on the most toxic active ingredient. Overall, this approach balances risk assessment conservatism and reduces testing that would likely not result in improvement of the ERA. Integr Environ Assess Manag 2018;14:79-91. © 2017 SETAC.

Assessment of biochemical mechanisms of tolerance to chlorpyrifos in ancient and contemporary Daphnia pulicaria genotypes.

The evolution of tolerance to environmental contaminants in non-target taxa has been largely studied by comparing extant populations experiencing contrasting exposure. Previous research has demonstrated that "resurrected" genotypes from a population of Daphnia pulicaria express temporal variation in sensitivity to the insecticide chlorpyrifos. Ancient genotypes (1301-1646AD.) were on average more sensitive to this chemical compared to the contemporary genotypes (1967-1977AD.). To determine the physiological mechanisms of tolerance, a series of biochemical assays was performed on three ancient and three contemporary genotypes; these six genotypes exhibited the most sensitive and most tolerant phenotypes within the population, respectively. Metabolic tolerance mechanisms were evaluated using acute toxicity testing, while target-site tolerance was assessed via in vitro acetylcholinesterase (AChE) assays. Acute toxicity tests were conducted using i) the toxic metabolite chlorpyrifos-oxon (CPF-oxon) and ii) CPF-oxon co-applied with piperonyl butoxide (PBO), a known Phase-I metabolic inhibitor. Both series of toxicity tests reduced the mean variation in sensitivity between tolerant and sensitive genotypes. Exposure to CPF-O reduced the disparity from a 4.7-fold to 1.6-fold difference in sensitivity. The addition of PBO further reduced the variation to a 1.2-fold difference in sensitivity. In vitro acetylcholinesterase assays yielded no significant differences in constitutive activity or target-site sensitivity. These findings suggest that pathways involving Phase-I detoxification and/or bioactivation of chlorpyrifos play a significant role in dictating the microevolutionary trajectories of tolerance in this population.

Factors influencing the toxicity of Headline® fungicides to terrestrial stage toads.

Amphibians are susceptible to exposure from contaminants via multiple pathways. Pyraclostrobin fungicides have been shown to be toxic to terrestrial amphibians at environmentally relevant concentrations; however, these studies did not account for factors that may influence exposure and effects, such as fungicide formulation, age of the individual, exposure route, and physiological state of the individual. We examined Headline® and Headline AMP® fungicide toxicity to adult Anaxyrus cognatus and Anaxyrus woodhousii by direct overspray, as well as acute toxicity of Headline AMP to juvenile A. cognatus through direct overspray, previously exposed soils, and diet. We also assessed effects of hydration state on fungicide toxicity in juvenile A. cognatus and sublethal effects of fungicide exposure on prey-orientation ability of juvenile A. cognatus. Neither formulation of Headline caused mortality of adult A. cognatus and A. woodhousii at up to 5 times the maximum label rate in North American corn (1052 and 879 mL formulation/ha for Headline AMP and Headline fungicides, respectively, corresponding to 1.52 and 2.2 µg pyraclostrobin/cm2 , respectively). Exposures of juvenile A. cognatus to Headline AMP via direct overspray and previously exposed soils (2 types) resulted in median lethal rate (LR50) values of 2.4, 3.34, and 3.61 µg pyraclostrobin/cm2 , respectively. Dietary Headline AMP exposure was not toxic, prey-orientations were not influenced by exposure, and effects were similar between dehydrated and hydrated treatments (LR50 = 2.4 and 2.3 µg pyraclostrobin/cm2 , respectively). These results, combined with exposure concentrations reported in previous studies, suggest that risk of acute mortality for amphibians in terrestrial environments is low and is dictated by body size and site-specific factors influencing exposure. Environ Toxicol Chem 2017;36:2679-2688. © 2017 SETAC.

Characterization of performance reference compound kinetics and analyte sampling rate corrections under three flow regimes using nylon organic chemical integrative samplers.

Performance reference compounds (PRCs) can be spiked into passive samplers prior to deployment. If the dissipation kinetics of PRCs from the sampler corresponds to analyte accumulation kinetics, then PRCs can be used to estimate in-situ sampling rates, which may vary depending on environmental conditions. Under controlled laboratory conditions, the effectiveness of PRC corrections on prediction accuracy of water concentrations were evaluated using nylon organic chemical integrative samplers (NOCIS). Results from PRC calibrations suggest that PRC elimination occurs faster under higher flow conditions; however, minimal differences were observed for PRC elimination between fast flow (9.3cm/s) and slow flow (5.0cm/s) conditions. Moreover, minimal differences were observed for PRC elimination from Dowex Optipore L-493; therefore, PRC corrections did not improve results for NOCIS configurations containing Dowex Optipore L-493. Regardless, results suggest that PRC corrections were beneficial for NOCIS configurations containing Oasis HLB; however, due to differences in flow dependencies of analyte sampling rates and PRC elimination rates across the investigated flow regimes, the use of multiple PRC corrections was necessary. As such, a "Best-Fit PRC" approach was utilized for Oasis HLB corrections using caffeine-(13)C3, DIA-d5, or no correction based on the relative flow dependencies of analytes and these PRCs. Although PRC corrections reduced the variability when in-situ conditions differed from laboratory calibrations (e.g. static versus moderate flow), applying PRC corrections under similar flow conditions increases variability in estimated values.

Comparisons of discrete and integrative sampling accuracy in estimating pulsed aquatic exposures.

Most current-use pesticides have short half-lives in the water column and thus the most relevant exposure scenarios for many aquatic organisms are pulsed exposures. Quantifying exposure using discrete water samples may not be accurate as few studies are able to sample frequently enough to accurately determine time-weighted average (TWA) concentrations of short aquatic exposures. Integrative sampling methods that continuously sample freely dissolved contaminants over time intervals (such as integrative passive samplers) have been demonstrated to be a promising measurement technique. We conducted several modeling scenarios to test the assumption that integrative methods may require many less samples for accurate estimation of peak 96-h TWA concentrations. We compared the accuracies of discrete point samples and integrative samples while varying sampling frequencies and a range of contaminant water half-lives (t50 = 0.5, 2, and 8 d). Differences the predictive accuracy of discrete point samples and integrative samples were greatest at low sampling frequencies. For example, when the half-life was 0.5 d, discrete point samples required 7 sampling events to ensure median values > 50% and no sampling events reporting highly inaccurate results (defined as < 10% of the true 96-h TWA). Across all water half-lives investigated, integrative sampling only required two samples to prevent highly inaccurate results and measurements resulting in median values > 50% of the true concentration. Regardless, the need for integrative sampling diminished as water half-life increased. For an 8-d water half-life, two discrete samples produced accurate estimates and median values greater than those obtained for two integrative samples. Overall, integrative methods are the more accurate method for monitoring contaminants with short water half-lives due to reduced frequency of extreme values, especially with uncertainties around the timing of pulsed events. However, the acceptability of discrete sampling methods for providing accurate concentration measurements increases with increasing aquatic half-lives.

Occurrence of current-use fungicides and bifenthrin in Rainwater Basin wetlands.

Wetlands in the Rainwater Basin (RWB) of Nebraska are commonly in close proximity to or embedded within row-crop agriculture. Several fungicides and bifenthrin are applied aerially to corn throughout the RWB during tassel stage. Thus, aerial spray drift and runoff may result in pesticide contamination of wetlands. The primary objective of this study was to determine water concentrations of five fungicides and bifenthrin in wetlands located in and near fields during a heavy application period (July 16th-26th 2014) to evaluate the influence of distance from crop field on wetland contamination. In addition, the sampling sites were grouped based upon the type of water body sampled and environmental concentrations were compared to relevant "levels of concern" (LOCs) from invertebrates, fish, and amphibians selected from the literature based upon relevant toxicity data. Bifenthrin was the most frequently detected analyte, appearing in 83% of the samples. The 95th percentile concentrations across all wetlands were found to be 0.07 µg/L for bifenthrin, 0.28 µg/L for pyraclostrobin, 0.28 µg/L for azoxystrobin, and <0.14 µg/L for all other analytes. Analyte concentrations did not differ by wetland type and were not correlated with distance from closest crop. Environmental concentrations of fungicides were lower than LOCs, indicating limited acute toxicity risk. However, bifenthrin concentrations were frequently higher than LOCs for aquatic arthropods. Because the water samples included particulate bound pesticides, further work is needed to determine if this bifenthrin is bioavailable and contamination levels within the sediment.