I am an environmental organic chemist whose current research focuses on the fate and transport of current-use pesticides and other organic contaminants in aquatic and terrestrial environments.
Much of my research is focused on pesticides but also includes other organic contaminants. I direct a research laboratory that is focused on developing new methods to measure pesticides and their degradates in water, sediment, and biota. My laboratory specializes in small samples sizes, complex matrices, and non-standard procedues. Additionally, I also work on developing methods and measuring disinfection by-products in treated water (especially those that are not-currently regulated and are understudied) with a focus on wastewater discharges.
Professional Experience
Research Chemist, USGS, California Water Science Center, Sacramento, 2006 to present
Chemist, USGS, California Water Science Center, Sacramento, 2005-2006
Graduate Fellow/Research and Teaching Assistant, Deparment of Geography and Environmental Engineering, Johns Hopkins University, 1999-2005
Undergraduate Research Summer Institute, Department of Chemistry, Vassar College, 1997,1998
Undergraduate Research and Teaching Assistant, Department of Chemistry, Vassar College ,1997,1998
Education and Certifications
Ph.D. 2005, Environmental Engineering and Chemistry, Johns Hopkins University, Baltimore, Maryland
B.A. 1999, Chemistry, Vassar College, Poughkeepsie, New York
Science and Products
Collaborative Science Provides Understanding of Contaminants in Bottled Water-an Increasingly Common Alternate Drinking Water Source
Wild Prairie Grouse Diet and Microbiomes Vary Between Cropland and Grassland Habitats
Pesticides Detected in Bees, Flowers, Soil, and Air within Pollinator-Attractive Row-Crop Border Plantings
Science to Understand Low-Level Exposures to Neonicotinoid Pesticides, their Metabolites, and Chlorinated Byproducts in Drinking Water
Clothianidin Exposure Associated with Changes in Tadpole Behavior
Costs and Benefits of Nitrapyrin
Dysbiosis, immunomodulation, and health effects of agricultural pesticides in wild prairie grouse
Environmental Management of Vector-borne Diseases
Water-Quality Inventory Pesticides in the Golden Gate National Recreation Area
Organic Chemistry Research — Sacramento, California
Pesticide Fate Research Group (PFRG)
Scientists Examined Native Pollinator Exposure Risk to Neonicotinoids in Native Prairie Strips
Multiresidue extraction of current-use pesticides from complex solid matrices using energized dispersive extraction with analysis by gas and liquid chromatography tandem mass spectroscopy
Pesticide Concentrations in American Bullfrog (Lithobates catesbeianus) Tadpoles Collected from Ponds and Reservoirs near Mead, Nebraska
Target-Chemical Concentrations and Microbiological Results for Assessment of Mixed Contaminant and Biological Exposures in Bottled Water, 2020
Pesticide residues in passive samplers and bee tissue from Conservation Reserve Program fields across an agricultural gradient in eastern Iowa, USA, 2019
Pesticide concentrations in bees and other matrices collected from sunflower fields (with and without a neonicotinoid seed treatment) near Sacramento, California
Naled and dichlorvos in water and aquatic organisms from a canal and rice fields near Sacramento, California
Current-use pesticides, nutrients, chloride, and metals in ponds and stormwater basins of the New Jersey Pinelands, 2018-20
Water-quality results from a wastewater reuse study: Inorganic and organic compositions of wastewater effluent and select urban and agricultural water types during rain-induced runoff, Chickasha, Oklahoma, 2018-2019
Characterizing microbiota, virulome, and resistome of wild prairie grouse in crop producing and uncultivated areas of Nebraska
Pesticide Concentrations Measured in Zooplankton Samples Collected from the Sacramento River and Yolo Bypass, California, 2017-2020
Concentrations of organic and inorganic constituents in tapwater samples from California in 2020-21 (ver. 3, September 2022)
Concentrations of pesticides in multiple matrices to measure exposure of wild bees visiting pollinator hedgerows in northern California
Multiresidue extraction of current-use pesticides from complex solid matrices using energized dispersive guided extraction with analysis by gas and liquid chromatography tandem mass spectroscopy
Field assessment of Naled and its primary degradation product (dichlorvos) in aquatic ecosystems following aerial ultra-low volume application for mosquito control
Assessing the presence of current-use pesticides in mid-elevation Sierra Nevada streams using passive samplers, California, 2018–19
Juxtaposition of intensive agriculture, vulnerable aquifers, and mixed chemical/microbial exposures in private-well tapwater in northeast Iowa
Contaminant exposure and transport from three potential reuse waters within a single watershed
Wild bee exposure to pesticides in conservation grasslands increases along an agricultural gradient: A tale of two sample types
Pesticide prioritization by potential biological effects in tributaries of the Laurentian Great Lakes
Bottled water contaminant exposures and potential human effects
Comparative behavioral ecotoxicology of Inland Silverside larvae exposed to pyrethroids across a salinity gradient
Comparing imidacloprid, clothianidin, and azoxystrobin runoff from lettuce fields using a soil drench or treated seeds in the Salinas Valley, California
Tapwater exposures, effects potential, and residential risk management in Northern Plains Nations
Potential health effects of contaminant mixtures from point and nonpoint sources on fish and frogs in the New Jersey Pinelands
Science and Products
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Collaborative Science Provides Understanding of Contaminants in Bottled Water-an Increasingly Common Alternate Drinking Water Source
U.S. Geological Survey researchers and public health experts collaborated to determine what contaminants occur in bottled water, which is an increasingly common alternate drinking water source, to broaden their understanding of human exposure to contaminants in drinking water supply chains. Bottled water, like public-supply and private-well tap water supply chains, contained multiple organic...Wild Prairie Grouse Diet and Microbiomes Vary Between Cropland and Grassland Habitats
Wild prairie grouse residing in croplands had altered diets and gut microbiome imbalances characterized by a greater abundance of pathogenic bacteria and antibiotic-resistance genes in comparison to those residing in grasslands. Similar gut microbiome imbalances are rarely associated with lethal outcomes, but rather linked to sublethal health effects including growth, development, behavior, immune...Pesticides Detected in Bees, Flowers, Soil, and Air within Pollinator-Attractive Row-Crop Border Plantings
Field study in California describes the potential for pollinator-attractive field borders in agricultural areas to become a pesticide exposure pathway to bees through soil, air, and plants.Science to Understand Low-Level Exposures to Neonicotinoid Pesticides, their Metabolites, and Chlorinated Byproducts in Drinking Water
Scientists reported the discovery of three neonicotinoid pesticides in drinking water and their potential for transformation and removal during water treatment. The research provides new insights into the persistence of neonicotinoids and their potential for transformation during water treatment and distribution, while also identifying granulated activated carbon as a potentially effective...Clothianidin Exposure Associated with Changes in Tadpole Behavior
During a laboratory exposure study, tadpole movement decreased with increased concentrations of clothianidin, a neonicotinoid pesticide. Decreased movement could affect a tadpole’s ability to forage, escape predation, and metamorphose before ponds dry.Costs and Benefits of Nitrapyrin
In December 2020, our research group (as part of the Food Integrated Science Team) published a review of nitrapyrin costs and benefits in the journal Environmental Science & Technology.Dysbiosis, immunomodulation, and health effects of agricultural pesticides in wild prairie grouse
Agrochemical pollution poses a severe threat to biodiversity. Agrochemicals can detrimentally affect wildlife growth, development, survival, reproduction, and immune responses, which facilitates emergence and spread of infectious diseases that may cause unusually high mortality. Animal microbiota plays a fundamental role in host’s food detoxification and defense against pathogens, regulates...Environmental Management of Vector-borne Diseases
Effective management programs for vector-borne pathogens, such as West Nile Virus and the Lyme disease spirochete, are necessary to protect public health. However, some vector control methods, such as landscape manipulations and pesticide applications, can also adversely affect nontarget species and environmentally sensitive natural systems. Efficient targeting and integration of vector control...Water-Quality Inventory Pesticides in the Golden Gate National Recreation Area
In 1998, all urban creeks in the San Francisco Bay Area were added to the Clean Water Act Section 303d list due to known or suspected diazinon impairment. Diazinon is an organophosphorus insecticide used on lawns, and fruit and vegetables. This pesticide has since been "phased out" and has not been available for purchase since late 2004. Diazinon use is declining and is being replaced by other...Organic Chemistry Research — Sacramento, California
About the ResearchThe Environmental Health Program collaborates with chemists and hydrologists at the Organic Chemistry Research Laboratory (OCRL) to develop targeted analytical methods for the quantitation of chemicals that can impact the health of organisms and humans. The scientists have developed methods in a wide variety of environmental media; in addition to water and sediment, they also...Pesticide Fate Research Group (PFRG)
Pesticides are applied in agricultural and urban areas to control weeds, insects, fungus, and other pests. Applied pesticides and their degradates can be transported off-site through a variety of mechanisms; these pesticides can then be found in non-target areas. Pesticide transport can occur through the atmosphere, in the aqueous phase (surface and groundwater) and associated with soil/sediment...Scientists Examined Native Pollinator Exposure Risk to Neonicotinoids in Native Prairie Strips
Neonicotinoids were not detected in native prairie plants placed next to agricultural fields several years after discontinuation of neonicotinoid seed treatment. In addition, neonicotinoid concentrations were lower or absent in soils and runoff at sites with the native prairie strips. - Data
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Multiresidue extraction of current-use pesticides from complex solid matrices using energized dispersive extraction with analysis by gas and liquid chromatography tandem mass spectroscopy
A multiresidue method for solids (i.e., soil, sediment, sludge) was developed and evaluated for the analysis of pesticides and pesticide degradates. Initially, a well characterized soil was used to determine the recovery of target compounds using an Energized Dispersive Guided Extraction (EDGE) system with two extraction solvents, acetonitrile and 1:1 (v/v) hexane:acetone. Extracts were cleaned usPesticide Concentrations in American Bullfrog (Lithobates catesbeianus) Tadpoles Collected from Ponds and Reservoirs near Mead, Nebraska
To evaluate the potential uptake and accumulation of pesticides in amphibians, American bullfrog (Lithobates catesbeianus) tadpoles were collected from surface water sites (four ponds and one reservoir) in 2021 near Mead, Nebraska. Sites were located in the landscape surrounding the AltEn ethanol plant, a plant which had previously received pesticide treated (coated) seeds. Tadpoles were collectedTarget-Chemical Concentrations and Microbiological Results for Assessment of Mixed Contaminant and Biological Exposures in Bottled Water, 2020
This data release contains concentration and quality-assurance results for inorganic, organic analytes and microbiological pathogens collected from 30 different commercial bottled water sources. Samples were processed on July 20 and August 17, 2020 at the New Jersey Water Science Center and analyzed at various U.S. Geological Survey laboratories. Samples were analyzed for nutrients, cations and anPesticide residues in passive samplers and bee tissue from Conservation Reserve Program fields across an agricultural gradient in eastern Iowa, USA, 2019
This data release includes sampling location, pesticide concentrations in passive samplers (silicone bands) and bees foraging in Conservation Reserve Program fields. Sampling took place during July and August of 2019. Fields were located on private land managed for the U.S. Department of Agriculture Conservation Reserve Program in eastern central Iowa, U.S.A.Pesticide concentrations in bees and other matrices collected from sunflower fields (with and without a neonicotinoid seed treatment) near Sacramento, California
Hybrid sunflower production occurs near Sacramento in Northern California where seed treatments are commonly used. In this study, four locations were sampled in 2016 as matched pairs; half of each field was sown with thiamethoxam treated seed and half without. In addition to the thiamethoxam seed treatment, all seeds were coated with two fungicides, fludioxonil and mefenoxam/metalaxyl. Both wild bNaled and dichlorvos in water and aquatic organisms from a canal and rice fields near Sacramento, California
Ultra-low volumes of naled are applied by aircraft over rice fields and canals to reduce adult mosquito populations near Sacramento, California. Each summer, the pesticide is applied approximately 7-10 times between July and October. Naled and its major degradate (dichlorvos) were quantified in water, biofilm, and invertebrates following aerial applications. In 2020, samples were collected beforeCurrent-use pesticides, nutrients, chloride, and metals in ponds and stormwater basins of the New Jersey Pinelands, 2018-20
The data presented in this data release include concentrations of current-use pesticides, nutrients, chloride, and metals in surface water collected from 60 wetlands including natural ponds, excavated ponds (Xponds), and stormwater basins in the New Jersey Pinelands, 2018-20. Site information, basic water-quality parameters, and method information also are included.Water-quality results from a wastewater reuse study: Inorganic and organic compositions of wastewater effluent and select urban and agricultural water types during rain-induced runoff, Chickasha, Oklahoma, 2018-2019
Oklahoma State University South-Central Research Station (SCRS) was used to conduct research to understand the chemical composition of various water types and their potential environmental and human health effects. The study area provided the opportunity to study five water types: (1) receiving surface water (Washita River), (2) urban stormwater, (3) wastewater treatment plant effluent used for irCharacterizing microbiota, virulome, and resistome of wild prairie grouse in crop producing and uncultivated areas of Nebraska
Chart listing the geographic locations, NCBI numbers, voucher numbers, and microbiome characteristics of specimens collected for publicationPesticide Concentrations Measured in Zooplankton Samples Collected from the Sacramento River and Yolo Bypass, California, 2017-2020
Zooplankton samples were collected at a site in the Yolo Bypass in Northern California and at a comparison site on the Sacramento River below the city of Sacramento and analyzed for a large suite of current-use pesticides and degradates. Samples were collected biweekly in the summer/fall 2017 and 2018, and from May 2019-March 2020. Samples were collected by towing a 150-micron conical plankton netConcentrations of organic and inorganic constituents in tapwater samples from California in 2020-21 (ver. 3, September 2022)
This dataset contains the trace elements, cations, anions, disinfection by-products, per- and polyfluoroalkyl substances (PFAS), pharmaceutical and pesticide concentration results for the tapwater study conducted in California, November, 2020 through May, 2021. Trace elements, cations and anions were analyzed at the U.S. Geological Survey Redox Chemistry Laboratory in Boulder, Colorado. The disiConcentrations of pesticides in multiple matrices to measure exposure of wild bees visiting pollinator hedgerows in northern California
To better understand the exposure of wild bees to pesticides in an agricultural landscape, samples were collected from fields in northern California. Hedgerows are known to provide habitat for wild bees, but these bees may also be exposed to pesticides from nearby agricultural fields. The study included eight hedgerow sites located in an intensively managed agricultural landscape that includes alm - Multimedia
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Multiresidue extraction of current-use pesticides from complex solid matrices using energized dispersive guided extraction with analysis by gas and liquid chromatography tandem mass spectroscopy
The development of sample processing techniques that recover a broad suite of pesticides from solid matrices, while mitigating coextracted matrix interferences, and reducing processing time is beneficial for high throughput analyses. The objective of this study was to evaluate the effectiveness of an automated extraction system for pesticide analyses in solid environmental samples. An Energized DiAuthorsGabrielle Pecora Black, Emily Woodward, Corey Sanders, Michael S. Gross, Michelle HladikField assessment of Naled and its primary degradation product (dichlorvos) in aquatic ecosystems following aerial ultra-low volume application for mosquito control
Naled, an organophosphate insecticide, is applied aerially at ultra-low volumes over aquatic ecosystems near Sacramento, California, USA, during summer months for mosquito control. Two ecosystem types (rice fields and a flowing canal) were sampled in 2020 and 2021. Naled and its primary degradation product (dichlorvos) were measured in water, biofilm, grazer macroinvertebrates, and omnivore/predatAuthorsCassandra Smith, Michelle Hladik, Kathryn Kuivila, Ian R. WaiteAssessing the presence of current-use pesticides in mid-elevation Sierra Nevada streams using passive samplers, California, 2018–19
Passive sampler devices were deployed in six northern California streams five times between November 2018 and December 2019 to measure the presence or absence of current-use pesticides in surface water. In the targeted areas, there are reported pesticide uses for agriculture, commercial forestry, and rights of way maintenance along with unreported pesticide use at private residences and cannabis gAuthorsMatthew D. De Parsia, James L. Orlando, Michelle L. HladikJuxtaposition of intensive agriculture, vulnerable aquifers, and mixed chemical/microbial exposures in private-well tapwater in northeast Iowa
In the United States and globally, contaminant exposure in unregulated private-well point-of-use tapwater (TW) is a recognized public-health data gap and an obstacle to both risk-management and homeowner decision making. To help address the lack of data on broad contaminant exposures in private-well TW from hydrologically-vulnerable (alluvial, karst) aquifers in agriculturally-intensive landscapesAuthorsPaul Bradley, Dana W. Kolpin, Darrin A. Thompson, Kristin Romanok, Kelly Smalling, Sara Breitmeyer, Mary C. Cardon, David M. Cwiertny, Nicola Evans, R. William Field, Michael J. Focazio, Laura E. Beane Freeman, Carrie E Givens, James L. Gray, Gordon L. Hager, Michelle Hladik, Jonathan N. Hoffman, Rena R. Jones, Leslie K. Kanagy, Rachael F. Lane, R. Blaine McCleskey, Danielle Medgyesi, Elizabeth Medlock-Kakaley, Shannon M. Meppelink, Michael T. Meyer, Diana A. Stavreva, Mary H. WardContaminant exposure and transport from three potential reuse waters within a single watershed
Global demand for safe and sustainable water supplies necessitates a better understanding of contaminant exposures in potential reuse waters. In this study, we compared exposures and load contributions to surface water from the discharge of three reuse waters (wastewater effluent, urban stormwater, and agricultural runoff). Results document substantial and varying organic-chemical contribution toAuthorsJason R. Masoner, Dana W. Kolpin, Isabelle M. Cozzarelli, Paul Bradley, Brian Arnall, Kenneth J. Forshay, James L. Gray, Justin F. Groves, Michelle Hladik, Laura E. Hubbard, Luke R. Iwanowicz, Jeanne B. Jaeschke, Rachael F. Lane, R. Blaine McCleskey, Bridgette F. Polite, David A. Roth, Michael Pettijohn, Michaelah C. WilsonByWater Resources Mission Area, Environmental Health Program, Colorado Water Science Center, California Water Science Center, Central Midwest Water Science Center, Geology, Energy & Minerals Science Center, Kansas Water Science Center, Oklahoma-Texas Water Science Center, South Atlantic Water Science Center (SAWSC), Upper Midwest Water Science Center, Reston Biogeochemical Processes in Groundwater LaboratoryWild bee exposure to pesticides in conservation grasslands increases along an agricultural gradient: A tale of two sample types
Conservation efforts have been implemented in agroecosystems to enhance pollinator diversity by creating grassland habitat, but little is known about the exposure of bees to pesticides while foraging in these grassland fields. Pesticide exposure was assessed in 24 conservation grassland fields along an agricultural gradient at two time points (July and August) using silicone band passive samplersAuthorsMichelle Hladik, Johanna M. Kraus, Cassandra Smith, Mark W. Vandever, Dana W. Kolpin, Carrie E Givens, Kelly SmallingPesticide prioritization by potential biological effects in tributaries of the Laurentian Great Lakes
Watersheds of the Great Lakes Basin (USA/Canada) are highly modified and impacted by human activities including pesticide use. Despite labeling restrictions intended to minimize risks to nontarget organisms, concerns remain that environmental exposures to pesticides may be occurring at levels negatively impacting nontarget organisms. We used a combination of organismal-level toxicity estimates (inAuthorsSamantha K. Oliver, Steven R. Corsi, Austin K. Baldwin, Michelle A. Nott, Gerald T. Ankley, Brett R. Blackwell, Daniel L. Villeneuve, Michelle Hladik, Dana W. Kolpin, Luke C. Loken, Laura A. DeCicco, Michael T. Meyer, Keith LoftinBottled water contaminant exposures and potential human effects
Bottled water (BW) consumption in the United States and globally has increased amidst heightened concern about environmental contaminant exposures and health risks in drinking water supplies, despite a paucity of directly comparable, environmentally-relevant contaminant exposure data for BW. This study provides insight into exposures and cumulative risks to human health from inorganic/organic/micrAuthorsPaul Bradley, Kristin Romanok, Kelly Smalling, Michael J. Focazio, Nicola Evans, Suzanne C. Fitzpatrick, Carrie E Givens, Stephanie Gordon, James L. Gray, Emily M. Green, Dale W. Griffin, Michelle Hladik, Leslie K. Kanagy, John T. Lisle, Keith Loftin, R. Blaine McCleskey, Elizabeth Medlock-Kakaley, Ana Navas-Acien, David A. Roth, Paul F. South, Christopher P. WeisComparative behavioral ecotoxicology of Inland Silverside larvae exposed to pyrethroids across a salinity gradient
Pyrethroids, a class of commonly used insecticides, are frequently detected in aquatic environments, including estuaries. The influence that salinity has on organism physiology and the partitioning of hydrophobic chemicals, such as pyrethroids, has driven interest in how toxicity changes in saltwater compared to freshwater. Early life exposures in fish to pyrethroids cause toxicity at environmentaAuthorsSara Hutton, Samreen Siddiqui, Emily Pedersen, Christopher Markgraf, Amelie Segarra, Michelle Hladik, Richard E Connon, Susanne M. BranderComparing imidacloprid, clothianidin, and azoxystrobin runoff from lettuce fields using a soil drench or treated seeds in the Salinas Valley, California
Neonicotinoid insecticide use has increased over the last decade, including as agricultural seed treatments (application of chemical in a coating to the seed prior to planting). In California, multiple crops, including lettuce, can be grown using neonicotinoid treated seeds or receive a direct neonicotinoid soil application (drenching) at planting. Using research plots, this study compared pesticiAuthorsEmily Woodward, Michelle Hladik, Anson Main, Michael Cahn, James Orlando, Jennifer TeerlinkTapwater exposures, effects potential, and residential risk management in Northern Plains Nations
In the United States (US), private-supply tapwater (TW) is rarely monitored. This data gap undermines individual/community risk-management decision-making, leading to an increased probability of unrecognized contaminant exposures in rural and remote locations that rely on private wells. We assessed point-of-use (POU) TW in three northern plains Tribal Nations, where ongoing TW arsenic (As) interveAuthorsPaul Bradley, Kristin Romanok, Kelly Smalling, Michael J. Focazio, Robert Charboneau, Christine Marie George, Ana Navas-Acien, Marcia O'Leary, Reno Red Cloud, Tracy Zacher, Sara Breitmeyer, Mary C. Cardon, Christa K. Cuny, Guthrie Ducheneaux, Kendra Enright, Nicola Evans, James L. Gray, David E. Harvey, Michelle Hladik, Leslie K. Kanagy, Keith Loftin, R. Blaine McCleskey, Elizabeth Medlock-Kakaley, Shannon M. Meppelink, Joshua F. Valder, Christopher P. WeisPotential health effects of contaminant mixtures from point and nonpoint sources on fish and frogs in the New Jersey Pinelands
Aquatic ecosystems convey complex contaminant mixtures from anthropogenic pollution on a global scale. Point (e.g., municipal wastewater) and nonpoint sources (e.g., stormwater runoff) are both drivers of contaminant mixtures in aquatic habitats. The objectives of this study were to identify the contaminant mixtures present in surface waters impacted by both point and nonpoint sources, to determinAuthorsSara Breitmeyer, Heather L. Walsh, Vicki S. Blazer, John F. Bunnell, Patrick M. Burritt, Jeff Dragon, Michelle Hladik, Paul Bradley, Kristin Romanok, Kelly Smalling - News