Pesticide Monitoring Program Research Articles

Use of the Pesticide Toxicity Index to Determine Potential Ecological Risk in the Santiago-Guadalajara River Basin, Mexico

The Santiago-Guadalajara River Basin (SGRB), located in western Mexico, is one of the most polluted rivers in the country. A pesticide monitoring program was carried out from January 2022 to September 2022, during which time water samples collected at 25 sites in the main stem and tributaries revealed the presence of 13 of the 24 pesticides analyzed, including α-BHC, β-BHC, γ-BHC (Lindane), γ-Chlordane, Hexachlorobenzene, Heptachlor, Aldrin, α-Endosulfan, DDT, -4,4, Methoxychlor, Chlorpyrifos-methyl, Endosulfan sulfate, and Dicofol. A high level of correlation was found between the identified pesticides, which could mean that several of these pesticides reached a stable level within the monitored water bodies. Most of the identified pesticides are classified as high environmental risk according to the Stockholm Convention because of their persistence and high degree of toxicity to the environment and human health. A Pesticide Toxicity Index (PTI) was applied to identify the streams considered to be of concern due to the presence of pesticides exceeding the threshold limits established by national and international guidelines. Performing a calculation for the entire Santiago-Guadalajara River Basin, the PTI reached a value of 0.833, which, according to the criteria of this method, classifies it as a “Moderate” level of risk for aquatic life. Increased regulatory and surveillance measures by state and federal authorities are required to prevent the use of these pesticides, which have been restricted globally.

HRMS analysis of pesticides in vegetables from Shanghai and risk assessment

ABSTRACT A rapid analytical method for the simultaneous determination of 550 pesticide residues in vegetable samples was developed based on ultra-high performance liquid chromatography-tandem Q/Orbitrap high-resolution mass spectrometry (UPLC-Q/Orbitrap-HRMS). To investigate the risk of exposure to pesticide residues through vegetable consumption, 704 leafy vegetable samples from Shanghai were analysed for multiple residues using this method. A total of 54 pesticide residues were identified in these vegetable samples and 302 samples contained one or more pesticide residue. The levels of the detected pesticides did not pose a health risk in the long term and were acceptable according to the results of the chronic dietary risk assessment. Risk rankings displayed that most of the pesticides were low to medium risk. The findings of this study provide a reference for future pesticide monitoring programmes.

Pesticide dynamics in three small agricultural creeks in Hesse, Germany.

Due to their high biodiversity, small water bodies play an important role for freshwater ecosystems. Nonetheless, systematic pesticide monitoring in small creeks with a catchment <30 km2 is rarely conducted. In this study, event-driven water samples were taken from May until November 2017 and March until July 2018 after 20 rain events at three sampling sites with catchment areas of <27 km2 in the Wetterau, a region with intensive agriculture in Southern Hesse, Germany. Additionally, enriched extracts of the native water samples from the campaign in 2018 were used for the Microtox assay to determine baseline toxicity to invertebrates over time and sum of toxic units (STU) were calculated to compare the potential toxicity of the samples. Overall, 37 pesticides and 17 transformation products were found, whereby the herbicide metamitron (79 µg/L) showed the highest concentration. Regularly, pesticide concentrations peaked at the time of the highest water level within each sampling event. Within each sampling event maximum pesticide concentration was mostly reached in water samples taken during the first two hours. The sum of the time-weighted mean concentration values of all pesticides was between 2.0 µg/L and 7.2 µg/L, whereby the measured concentrations exceeded their regulatory acceptable concentration (RAC) at 55% of all sampling events for at least one pesticide. The mean EC50 values varied between 28.6 ± 13.1 to 41.3 ± 12.1 REF (relative enrichment factor). The results indicated that several samples caused baseline toxicity, whereby the highest activity was measured at the time of highest water levels and pesticides concentrations, and then steadily decreased in parallel with the water level. Median STUs of invertebrates ranged from -2.10 to -3.91, of algae/aquatic plants from -0.79 to -1.84 and of fish from -2.47 to -4.24. For one of the three sampling sites, a significant linear correlation between baseline toxicity and STUinvertebratewas found (r2=0.48). The results of the present study suggest that (1) current pesticide monitoring programs underestimate risks posed by the exposure to pesticides for aquatic organisms and (2) pre-authorization regulatory risk assessment schemes are insufficient to protect aquatic environments.

Monitoring and Exposure Assessment of Fosetyl Aluminium and Other Highly Polar Pesticide Residues in Sweet Cherry.

Cherries are popular fruits due to their health benefits, organoleptic quality, and attractive appearance. Since highly polar pesticides are of low mass and amphoteric character, and are not amenable to traditional multi-residue extraction methods, they are more commonly not included in the pesticide monitoring program. This study aims to determine twelve highly polar pesticide residues in cherry samples intended for export from Turkey. A total of 16,022 cherry samples from 2018-2020 harvests in four production areas of Turkey were analyzed using a modification of the Quick Polar Pesticides method and liquid chromatography-tandem mass spectrometry. The method was validated at two fortification levels (0.01 and 0.05 mg kg-1), and good recoveries (87.4-111.4%) and relative standard deviations (&lt;6%) were achieved for all analytes. The limits of quantification were in the range of 1.08-2.55 μg kg-1. Overall, 28.4% of the analyzed cherry samples were detected with phosphonic acid, calculated as fosetyl aluminium (fosetyl-Al) in amounts up to 77.7 mg kg-1. For 2304 samples (14.4%), the residues exceeded the European Union maximum residue level of 2 mg kg-1. There is no reason to be concerned about long-term exposure to phosphonic acid/fosetyl-Al, and the other highly polar pesticides through the consumption of sweet cherry.

A novel approach for tailoring pesticide screens for monitoring regional aquatic ecosystems

• An approach for tailoring regional specific pesticide screens. • Untested Pesticides locally used and toxic to aquatic ecosystems were selected. • 144 pesticides from a broad range of 3977 registered products were identified. Pesticide monitoring programs are required to understand pesticide contamination in the environment. They can be used to compare existing water quality guidelines and associated their presence with activities related to catchments. Thus, provide crucial information for management actions. A major challenge with such programs is to determine which pesticides should be screened and this determination is made more difficult as many new pesticides are continuously emerging on markets. We have developed a robust method to identify those pesticides which should be included in screens based on whether they are likely to be used within the region surveyed and if they pose a threat to aquatic ecosystems. This approach is illustrated by comparing the Warrnambool South West (WSW) and Mornington Peninsula (MP) regions within Victoria, Australia that have contrasting land-use practices. Pest control products registered and approved for land-use activities within the two regions during the past decade were identified using a government database. Those pesticides in these products which were not screened by commercial laboratories were then identified. Region-specific identification of prevalent pesticide usage was estimated by matching the highest-grossing agricultural commodities within the two regions with pesticide-specific land-uses. A total of 56 (WSW) and 54 (MP) unique pesticides and another 34 being common in both regions were identified that can be augmented to standard screens of analytical laboratories. Different pesticides of concern are likely to be identified for aquatic ecosystems in other regions of the world; as they will have different regional land-uses, laboratory screens and different pesticide use to those identified in this study. The approach presented here can assist authorities in identifying which pesticides should be incorporated into local pesticide monitoring programs.

Pesticides groundwater modelling relies on input data characterised by a high intrinsic variability: Is the resulting risk for groundwater credible?

In the framework of Regulation (EC) 1107/2009, concerning the placing of plant protection products (PPP) on the market, FOCUS models are used to predict active substances concentration in groundwater. The predicted environmental concentration in groundwater (PECGW) are influenced by active substance specific parameters, namely DT50, KOM and Freundlich coefficient (1/n), whose minimal variation in certain combinations of intervals significantly affects PECGW output. Considering that minimal variation are intrinsic in all laboratory studies, this approach may lead to not acceptable variations in the results for regulatory purposes. In the present article, PECGW were calculated for all maize crop scenarios, using 808 dummy active substances with different combinations of DT50, KOM and 1/n values, in order to quantify the influence of each single parameter on the final result of PEARL and PELMO models. The results obtained were used to create a classification system for the input parameters KOM and DT50 in order to minimise the input uncertainty effects. Even if this approach is scientifically viable yet, due to its conservative nature, it cannot be considered suitable in the regulatory framework, where acceptability of an active substance is strictly related to the limit value of 0.1 μg/L. Nevertheless, this classification system could represent an important screening or preliminary assessment to plan pesticide monitoring programmes. Based on the results of this analysis, it is believed that the assessment of pesticide leaching into groundwater should be revised to take into account this variability. Considering that both PEARL and PELMO FOCUS models deal with interaction between a chemical and a complex system like soil and weather, the selection of input data cannot pretend to rely on single specific number. Considering that intrinsic uncertainty cannot be eliminated from experimental work, a revision of the criteria used to identify the proper input data and a thorough revision of the actual groundwater modelling is recommended.

Pesticides in surface freshwater: a critical review.

The objective of this study was to critically review studies published up to November 2021 that investigated the presence of pesticides in surface freshwater to answer three questions: (1) in which countries were the studies conducted? (2) which pesticides are most evaluated and detected? and (3) which pesticides have the highest concentrations? Using the Prisma protocol, 146 articles published from 1976 to November 2021 were included in this analysis: 127 studies used grab sampling, 10 used passive sampling, and 9 used both sampling techniques. In the 45-year historical series, the USA, China, and Spain were the countries that conducted the highest number of studies. Atrazine was the most evaluated pesticide (56% of the studies), detected in 43% of the studies using grab sampling, and the most detected in passive sampling studies (68%). The compounds with the highest maximum and mean concentrations in the grab sampling were molinate (211.38µg/L) and bentazone (53µg/L), respectively, and in passive sampling, they were oxyfluorfen (16.8µg/L) and atrazine (4.8μg/L), respectively. The levels found for atrazine, p,p'-DDD, and heptachlor in Brazil were higher than the regulatory levels for superficial water in the country. The concentrations exceeded the toxicological endpoint for at least 11 pesticides, including atrazine (Daphnia LC50 and fish NOAEC), cypermethrin (algae EC50, Daphnia and fish LC50; fish NOAEC), and chlorpyrifos (Daphnia and fish LC50; fish NOAEC). These results can be used for planning pesticide monitoring programs in surface freshwater, at regional and global levels, and for establishing or updating water quality regulations.

Determination of 72 Chemical Pesticides and Estimation of Measurement of Uncertainty in Rice Using LC-MS/MS and GC-MS/MS

A multi-residue method was developed and validated for the simultaneous determination of 39 and 33 chemical pesticides in rice using LC-MS/MS and GC-MS/MS, respectively. The coefficient of determination was 0.994 to 0.999 over the linear concentration range of 0.01 to 0.1 μg mL-1. The LOD and LOQ were in the range of 0.31 to 3.35 and 1.04 to 10.06 μgkg-1, repsectively. The mean recoveries at 0.01, 0.05, and 0.1 mgkg-1 were found within the range 70 to 120% with satisfactory precision (RSD < 15%). Measurement uncertainty (Uexp) values estimated at 0.05 mgkg-1 spiking level were found lower than 20 μgkg-1 for all tested pesticides. A rice and wheat powder check samples under the proficiency test were analyzed using a standardized method, and the Z score recorded within the acceptable range of −2 to +2. The proposed method was applied to analyze the pesticides in real samples collected from the market and quantified the residues. The developed method could be useful for monitoring 72 chemical pesticides in rice matrices and can be adopted for the pesticide monitoring program.

Cumulative dietary risk assessment of chronic acetylcholinesterase inhibition by residues of pesticides.

A retrospective cumulative risk assessment of dietary exposure to pesticide residues was conducted for chronic inhibition of acetylcholinesterase. The pesticides considered in this assessment were identified and characterised in a previous scientific report on the establishment of cumulative assessment groups of pesticides for their effects on the nervous system. The exposure assessments used monitoring data collected by Member States under their official pesticide monitoring programmes in 2016, 2017 and 2018, and individual food consumption data from 10 populations of consumers from different countries and from different age groups. Exposure estimates were obtained by means of a two‐dimensional probabilistic model, which was implemented in SAS ® software. The characterisation of cumulative risk was supported by an uncertainty analysis based on expert knowledge elicitation. For each of the 10 populations, it is concluded with varying degrees of certainty that cumulative exposure to pesticides contributing to the chronic inhibition of acetylcholinesterase does not exceed the threshold for regulatory consideration established by risk managers.

Comparison of cumulative dietary exposure to pesticide residues for the reference periods 2014-2016 and 2016-2018.

Retrospective dietary exposure assessments were conducted for pesticides that have chronic effects on the thyroid and pesticides that have acute effects on the nervous system. Exposure assessments were performed using monitoring data collected by Member States under their official pesticide monitoring programmes in 2016, 2017 and 2018. Exposure estimates were obtained for 10 populations of consumers (i.e. from different countries and from different age groups) by means of a two‐dimensional probabilistic model. Results were compared to those previously obtained for the years 2014, 2015 and 2016, and exposure did not change significantly over time. However, an increase of the sampling uncertainty was identified for one pesticide in a specific food commodity. Strategies are therefore recommended to reduce the sampling uncertainty and to anticipate potential problems before initiating a cumulative risk assessment.

4 Agrochemical Residues, Product Quality, and Safety of Beef Fed Cotton Ginning and Other Byproduct Feeds

Abstract Most commodity crops undergo milling, husking, ginning or other processing procedures before use as human food or fiber. Byproduct nutrient density varies with the type of grain or oil seed processed and use typically varies with nutrient needs of specific production situations. Drought or high grain prices may increase the use of byproducts; regionally available, low-cost ingredients such as cotton ginning byproduct may be used extensively by beef producers to replace forage. Doubt associated with the use of such byproducts is not typically related to nutritional value but with uncertainties about the presence of residual pesticides, herbicides, or harvest-aid chemicals. Potential chemical residues in consumer products and the concomitant financial and reputational losses borne by the industry provide an impetus for concern. Negative experiences with contaminated Australian beef established a long-lived suspicion of “cotton trash” that continues to impact the industry today. The purpose of this review is to discuss sources, amounts, and risks of chemical residues associated with byproduct feeds used in the southern United States with cotton ginning byproducts as a major focus. The use patterns of specific crop protection and harvest-aid chemicals will be discussed in context with chemical tolerances established by the U.S. EPA. In addition, U.S. pesticide monitoring programs in beef will be discussed. Although data describing the transmission of chemical residues from byproduct feeds into beef products are limited, the available data suggest some best practices could be adopted to mitigate concerns and minimize possible agrochemical residue contamination of beef.

Pesticide Monitoring Program: Re‐allocation of number of samples considering population changes

Pesticide Monitoring Program: Re‐allocation of number of samples considering population changes

Pesticide residue levels in vegetables and surface waters at the Central Rift Valley (CRV) of Ethiopia

Seven pesticides, profenofos, metalaxyl, λ-cyhalothrin, 4,4′-DDT, 4,4′-DDE, and α- and β-endosulfan, were determined in vegetables (tomato, onion) from 20 locations and surface waters from 12 locations in the Central Rift Valley (CRV) of Ethiopia. Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) and solid phase extraction (SPE) methods were used for the vegetables and water, respectively. In 2.5% of the tomato samples, profenofos was detected above European maximum residue limits (MRLs), in 12.5% of the samples metalaxyl, and in 2.5% α- and β-endosulfan. In 5% of the onion samples, profenofos was detected above European MRLs, in 7.5% of the onion samples metalaxyl, and in 5% λ-cyhalothrin. In surface water, profenofos was detected at the highest concentration of 2300 μg/L in the Bulbula River, 890 μg/L near the agricultural land north of Lake Ziway (ANLZ-1), 1700 μg/L in the floriculture effluent (FE-1), and 900 μg/L in tap water at the Batu Drinking Water (BDW) supply. These results show that the levels of pesticides are in several cases substantially elevated, and emphasize the need of regular pesticide monitoring programs for surface waters and vegetables in the Ethiopian CRV.

Cumulative dietary risk characterisation of pesticides that have acute effects on the nervous system.

A retrospective acute cumulative risk assessment of dietary exposure to pesticide residues, supported by an uncertainty analysis based on expert knowledge elicitation, was conducted for two effects on the nervous system: brain and/or erythrocyte acetylcholinesterase inhibition, and functional alterations of the motor division. The pesticides considered in this assessment were identified and characterised in the scientific report on the establishment of cumulative assessment groups of pesticides for their effects on the nervous system. Cumulative exposure assessments were conducted through probabilistic modelling by EFSA and the Dutch National Institute for Public Health and the Environment (RIVM) using two different software tools and reported separately. These exposure assessments used monitoring data collected by Member States under their official pesticide monitoring programmes in 2014, 2015 and 2016 and individual consumption data from 10 populations of consumers from different countries and different age groups. This report completes the characterisation of cumulative risk, taking account of the available data and the uncertainties involved. For each of the 10 populations, it is concluded with varying degrees of certainty that cumulative exposure to pesticides that have the acute effects on the nervous system mentioned above does not exceed the threshold for regulatory consideration established by risk managers.

Cumulative dietary risk characterisation of pesticides that have chronic effects on the thyroid.

A retrospective chronic cumulative risk assessment of dietary exposure to pesticide residues, supported by an uncertainty analysis based on expert knowledge elicitation, was conducted for two effects on the thyroid, hypothyroidism and parafollicular cell (C‐cell) hypertrophy, hyperplasia and neoplasia. The pesticides considered in this assessment were identified and characterised in the scientific report on the establishment of cumulative assessment groups of pesticides for their effects on the thyroid. Cumulative exposure assessments were conducted through probabilistic modelling by EFSA and the Dutch National Institute for Public Health and the Environment (RIVM) using two different software tools and reported separately. These exposure assessments used monitoring data collected by Member States under their official pesticide monitoring programmes in 2014, 2015 and 2016 and individual consumption data from 10 populations of consumers from different countries and different age groups. This report completes the characterisation of cumulative risk, taking account of the available data and the uncertainties involved. For each of the 10 populations, it is concluded with varying degrees of certainty that cumulative exposure to pesticides that have the chronic effects on the thyroid mentioned above does not exceed the threshold for regulatory consideration established by risk managers.

Spatio-temporal distribution and ecological risk assessment of pesticides in the water resources of Abou Ali River, Northern Lebanon.

The objective of this study is to assess the occurrence, spatial, and temporal distribution of forty-eight multiclass pesticides in surface and groundwater samples of the Abou Ali River, located in the North of Lebanon. A 3-year monitoring program (six batches from August 2015 to March 2017) was implemented, and thirty sampling points were selected along the river for analysis. The analysis was executed using a previously developed and optimized solid-phase micro-extraction (SPME) gas-chromatography-mass spectrometry (GC-MS) method. Statistical analysis, using Kolmogorov-Smirnov, Kruskal-Wallis, and Dunnet T3 multiple comparison tests, was applied to compare mean concentrations of pesticides between the different sampling sites and the batches taken. The pesticides that had the highest frequency of detection in the surface and groundwater samples were alachlor, α-endosulfan, and methomyl. For surface water samples, high mean concentrations were perceived for two stations in the upper stream (S5 and S7), two stations (S11 and S14) in the middle stream, and one station (S16) in the lower stream of the river. The highest mean concentrations were observed in October 2015 and August 2016, the time of the year which correlates with the period of pesticide application. Considering groundwater samples, high mean concentrations of pesticides were detected in sites G4, G9, G10, and G12 and during October 2015 and March 2016, following the rainy season. Ecotoxicological risk assessment using the risk quotient (RQ) methodology revealed high risk for five pesticides under average conditions and fourteen under extreme conditions. This study presents, for the first time, a statistical analysis showing the quantification of pesticides in the water resources of the Abou Ali River. In conclusion, it reveals the need to apply a complete pesticide monitoring program, not only for the Abou Ali River but for all the water resources in Lebanon.

Indices of Water Quality and Pesticide Monitoring Survey in Lake of Western Co?te d’Ivoire and Its Human Risk Assessment

The aims of the work were to study the current quality of the water in Lake DOHOU used for drinking water supply through several physical, chemical analyses and using water quality indices (WQI). In addition, the question was whether the populations are at risk after drinking water of lake following a reduction of 50% and 75% in the median and maximum values of pesticides. Thus, the results of the pesticide monitoring program were incorporated into probabilistic human health risk assessment exercises. Water samples were collected over a period of one year. Pesticides were subjected to solid phase extraction and then analyzed using gas chromatography coupled to tandem mass spectroscopy. The other parameters were measured according to conventional methods. The results showed that the most frequently detected pesticides were aldicarb (79%), simazine (79%) and monolinuron (44%). They also showed the mean values of concentrations exceeding 1.5 μg/L. Metoxuron detected at a frequency of 29% showed the maximum average concentration (13.46 μg/L). Nearly 98% of the sampling points had at least one substance with an average concentration above the quality standard (0.1 μg/L) and 80% did not meet the total concentration standards. Cumulative risk quotient estimates after 50% or 75% abatement for frequently identified pesticides were greater than unity when extreme values for adults and children were considered. To determine the suitability of water for aquatic life, drinking water consumption and drinking water production, the water quality index (WQI), the heavy metal pollution (HPI) and the heavy metal evaluation (HEI) were calculated. The poor quality of the water was mainly related to pesticides, organic matter and microbiological parameters. Most of the nutrients and metals studied were often below the standards of drinking water and aquatic life. The Water Quality Index (WQI) has shown that water quality is degrading for these three modes of use and ranges from poor to marginal. The coupling of monitoring data with probabilistic estimates of human risks could be used by the Ivorian authorities to propose effective pollution management plans.

Cumulative dietary exposure assessment of pesticides that have chronic effects on the thyroid using SAS® software.

Retrospective dietary exposure assessments were conducted for two groups of pesticides that have chronic effects on the thyroid: hypertrophy, hyperplasia and neoplasia of C‐cells, and hypothyroidism. The pesticides considered in this assessment were identified and characterised in the scientific report on the establishment of cumulative assessment groups of pesticides for their effects on the thyroid. The exposure assessments used monitoring data collected by Member States under their official pesticide monitoring programmes in 2014, 2015 and 2016, and individual food consumption data from 10 populations of consumers from different countries and from different age groups. Exposure estimates were obtained for each group of pesticides by means of a 2‐dimensional probabilistic model, which was implemented in SAS ® software. Results were validated against exposure estimates obtained by the Dutch National Institute for Public Health and the Environment (RIVM) using the Monte Carlo Risk Assessment (MCRA) software. Both tools produced nearly identical results and minor differences were mainly attributed to the random effect of probabilistic modelling. The exposure estimates obtained in this report are used in the final scientific report on the cumulative dietary risk characterisation of pesticides that have chronic effects on the thyroid. The latter combines the hazard assessment and exposure assessment into a consolidated risk characterisation including all uncertainties.

Cumulative dietary exposure assessment of pesticides that have acute effects on the nervous system using SAS® software.

Retrospective dietary exposure assessments were conducted for two groups of pesticides that have acute effects on the nervous system: brain and/or erythrocyte acetylcholinesterase inhibition, and functional alterations of the motor division. The pesticides considered in this assessment were identified and characterised in the scientific report on the establishment of cumulative assessment groups of pesticides for their effects on the nervous system. The exposure assessments used monitoring data collected by Member States under their official pesticide monitoring programmes in 2014, 2015 and 2016 and individual food consumption data from 10 populations of consumers from different countries and from different age groups. Exposure estimates were obtained for each group of pesticides by means of a 2‐dimensional Monte Carlo simulation, which was implemented in SAS ® software. Results were validated against exposure estimates obtained by the Dutch National Institute for Public Health and the Environment (RIVM) using the Monte Carlo Risk Assessment (MCRA) software. Both tools produced nearly identical results and minor differences were mainly attributed to the random effect of probabilistic modelling. The exposure estimates obtained in this report are used in the final scientific report on the cumulative dietary risk characterisation of pesticides that have acute effects on the nervous system. The latter combines the hazard assessment and exposure assessment into a consolidated risk characterisation including all related uncertainties.

Characterization of MS/MS Product Ions for the Differentiation of Structurally Isomeric Pesticides by High-Resolution Mass Spectrometry.

Structural isomeric pesticides are used in agriculture and may be challenging to differentiate for accurate identification in pesticide monitoring programs. Due to structural similarity, isomeric pesticides are difficult to separate chromatographically, and thus, their accurate identification may rely solely on mass spectrometric analysis (MS). In this study, we challenged the ability of high-resolution quadrupole-orbitrap (Q-Orbitrap) mass spectrometry to produce and evaluate the tandem mass spectrometry (MS/MS) product ions for the selected five pairs of isomeric pesticides from different classes: Pebulate and vernolate, methiocarb and ethiofencarb, uniconazole and cyproconazole, sebuthylazine and terbuthylazine, and orbencarb and thiobencarb. The use of Q-Orbitrap instrument with a mass error <3 ppm allowed proposed elucidation of the product ion structures with consideration of the ion formulae, data interpretation, and literature searches. Product ions unique to pebulate, vernolate, methiocarb, ethiofencarb, and uniconazole were observed. Elucidation of the observed MS/MS product ion structures was conducted, and the fragmentation pathways were proposed. This information is valuable to increase selectivity in MS/MS analysis and differentiate isomeric pesticides, and thereby reduce the rates of false positives in pesticide monitoring programs.