Larry B. Barber

Molecularly imprinted polymer−electrochemical sensors (MIP-ES) are a promising approach for detecting less electrochemically active contaminants, such as per- and polyfluoroalkyl substances (PFAS). However, exposure of poly(o-phenylenediamine) [poly(o-PD)]-based MIP films to strongly acidic conditions can alter the polymer environment and complicate the interpretation of electron mediator based electrochemical readout. In this study, we examined how low pH exposure influences the response of the anionic perfluorooctanoic acid (PFOA) templated poly(o-PD) MIP-ES by comparing four commonly used electron mediators with different charge states: ferrocenemethanol, ferrocyanide, ferricyanide, and hexaammineruthenium(III). Apparent association constants (KA) and maximum PFOA-dependent current differences (Δimax) derived from a fractional response two-parameter Langmuir binding isotherm model, together with ratiometric comparisons of normalized current differences, showed that mediator-dependent trends changed after acidic pH exposure of the polymer. The anionic mediators, ferrocyanide and ferricyanide, exhibited the largest increases in apparent KA and Δimax, whereas the neutral mediator, ferrocenemethanol, retained a similar apparent KA but exhibited a lower fitted response amplitude. Hexaammineruthenium(III) produced substantial variability that limited Langmuir isotherm interpretation. These results are consistent with the interpretation that changes in the protonation state of the poly(o-PD) film influence mediator access and interactions within the sensing environment, thereby biasing the mediator-based current response. Overall, this work highlights that mediator choice can strongly affect the apparent performance of poly(o-PD)-based MIP-ES after exposure to low pH and should be considered carefully when interpreting sensor response under challenging conditions.

Per- and polyfluoroalkyl substances (PFAS) occur as complex mixtures, yet mixture-dependent biological effects under environmentally realistic exposure conditions remain poorly understood. We conducted multiyear (2018, 2019, 2021) continuous-flow, field-based exposures of male fathead minnows (Pimephales promelas) using a low-PFAS reference well (REF; total PFAS (∑PFAS) 0.1–0.2 μg L^–1) and PFAS-contaminated groundwater from a fire-training area (FTA) at Joint Base Cape Cod, Massachusetts. Dilution treatments enabled separation of concentration and mixture effects. Groundwater from well FTA1 was perfluorooctanesulfonate (PFOS) dominated (∑PFAS 10–31 μg L^–1), whereas groundwater from well FTA2 had higher concentrations and was enriched in perfluorooctanoate (PFOA) and diverse precursors (∑PFAS ∼ 80 μg L^–1). Despite comparable plasma ∑PFAS and PFOS in FTA1–100% and FTA2–50% on day-7, cumulative mortality reached approximately 35% in FTA2–50% and 17% in FTA2–100%, and secondary sex trait expression was reduced by approximately 65–80% relative to REF, whereas sperm motility effects were mixture- and time-dependent. Plasma PFAS profiles were dominated by perfluorohexanesulfonate (PFHxS), PFOS, and sulfonamide precursors. Liver transcriptomics from REF-acclimated fish revealed robust disruption of metabolic, mitochondrial, and endocrine pathways that link PFAS mixture chemistry and internal exposure profiles to organismal outcomes, and testis transcriptomics provided complementary insight into reproductive impairment. These results indicate that PFAS mixture composition and internal exposure profiles, including precursor-associated differences, are important determinants of ecotoxicological outcomes under field-realistic conditions.

Imidacloprid, a neonicotinoid insecticide, is used for agricultural and nonagricultural purposes and is toxic to nontarget organisms at low concentrations in aquatic ecosystems. A total of 12,547 water samples were collected from 2013 to 2022 from 77 rivers across the United States (U.S.) and were analyzed to evaluate detections and temporal trends in imidacloprid concentrations. Imidacloprid was detected in 44% of all samples, and the mean concentration, adjusted for nondetect samples, of 24.9 ng/L (median = 11.9 ng/L) was more than twice the chronic benchmark for freshwater invertebrates (10 ng/L). This potential hazard to aquatic life was persistent, with 44% of the sites having a median concentration exceeding the chronic benchmark. Half of the sites (n = 38) had increasing trends, including large river sites along the Mississippi River. The mean increase was 10.6 ng/L over the past decade, while only six sites indicated decreasing trends. The estimated total loading of imidacloprid delivered to the Gulf of America from 2013 to 2022 was 129,489 kg (142.7 U.S. ton). The extensive presence of imidacloprid in U.S. waterways, the high percentage of sites with trends of increasing concentrations, and the prevalence of concentrations exceeding chronic benchmarks suggest widespread persistent risks to ecosystem health.

Per- and polyfluoroalkylsubstances (PFAS) are established environmental micropollutants that need a rapid and robust sensor as a first line of defense. Molecularly imprinted polymer (MIP)-based sensors have shown great promise in electrochemically detecting PFAS. However, like all binding-based sensors, they suffer from interferent effects, especially in the absence of the target of interest. Here, we address this challenge by proposing a ratiometric sensing method. This method uses MIP-modified electrodes in two different compartments: a compartment in which we know there is no perfluorooctanesulfonate (PFOS) or perfluorooctanoic acid (PFOA), and a compartment in which we add PFOS or PFOA. A sample with the absence of PFOS or PFOA results in a ratio of electrochemical signals of ~ 1. A sample that contains PFOS or PFOA results in a ratio different from 1. We demonstrate the principle in controlled samples of lab water and Wabash River water (West Lafayette, IN). Further application is explored through the application of these molecularly imprinted polymer – electrochemical sensors (MIP-ES) in both ground water and surface water samples collected from Joint Base Cape Cod (Cape Cod, MA). The MIP-ES showed great promise in identifying PFAS containing samples down to concentrations of ~200 ppt (~0.4nM for PFOS and ~0.5nM for PFOA) for ground water and surface water sample matrices. The blank samples, not containing analyte but mimicking the sample matrices, were provided through our partnership with the United States Geological Survey (USGS). This method in both lab-controlled samples and field relevant samples is now established as a way to address interferent effects when applying MIP-ES PFAS sensing in complex sample matrices.

Molecularly imprinted polymer - electrochemical sensors (MIP-ES) rely on selective binding at templated sites within the molecularly imprinted polymer (MIP) matrix to enable accurate analyte detection. However, this selectivity can be disrupted when the ortho-phenylenediamine (o-PD) polymer surface becomes protonated under low pH sample matrix conditions, altering both the binding affinity of analytes and the accessibility of electron mediators to the binding sites. Such effects introduce potential biases in the electrochemical performance of MIP-ES. In this study, we investigated the electrochemical sensitivity of MIP-ES by evaluating binding affinity constants (K _A ) derived from Langmuir isotherm models and analyzing normalized current responses across varying sample conditions. The electron mediators studied include ferrocenemethanol, ferrocyanide, ferricyanide, and ruthenium (III) hexamine. Under protonated polymer conditions, the neutrally charged ferrocenemethanol exhibited a reduced K _A value of 8.62 x 10^11, while negatively charged ferrocyanide and ferricyanide showed increased K _A values of 9.50 x 10^12 and 2.14 x 10^13, respectively, compared to non-protonated K _A values of 8.35 x 10^12 and 4.94 x 10^12. Ratiometric comparisons indicated a loss of sensitivity for ferrocyanide, ferricyanide, and ruthenium (III) hexamine under protonated conditions. However, calibration curves for ruthenium (III) hexamine deviated from predictable trends when fit with a Langmuir isotherm model. Notably, ferrocenemethanol demonstrated superior electrochemical robustness, retaining sensor sensitivity even under protonated polymer surface conditions while in the presence of perfluorooctanoic acid (PFOA) as the analyte. These findings provide insights into the influence of polymer surface protonation on electron mediator performance, as well as MIP-ES sensor sensitivity, and highlight ferrocenemethanol as a reliable electron mediator for MIP-ES applications. Figure 1

Managing per- and polyfluoroalkyl substances (PFAS) in water resources requires a basin-scale approach. Predicted environmental concentrations (PEC) and stream-vulnerability scores for PFAS were determined for the Potomac River watershed in the eastern United States. Approximately 15% of stream reaches contained municipal and/or industrial wastewater treatment plant (WWTP) discharges that are presumptive PFAS sources, comprising from 90% of streamflow. Mean annual PEC, based on the summed concentrations of eight PFAS detected in WWTP effluents (ΣPFAS_PEC), for all stream reaches in the watershed was 3.8 ng L^-1, and stream reaches impacted by WWTP had perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) PEC of 0.39 and 0.14 ng L^-1. For locations where measured-environmental concentrations (MEC) were determined, municipal and industrial WWTP contributed 7.8% (0 to 65%) of the total annual streamflow and MEC were greater than PEC in 99% of the samples, indicating additional potential PFAS sources. The mean ΣPFAS_PEC was 9.1 ng L^-1 compared to a mean sum of PFAS MEC of 34 ng L^-1. Under mean-August low-flow, 17% and 9.4% of the water-supply intakes had maximum PFOA and PFOS PEC exceeding drinking water maximum contaminant levels.

The Chesapeake Bay Partnership is implementing conservation practices (CPs) throughout the Chesapeake Bay watershed to reduce nutrient and sediment delivery to the Bay. This study intends to provide an integrated and detailed understanding of how local streams respond to these CP-driven management efforts.Key issue: To what extent do CPs positively affect the health of local streams in the nontidal watershed (cobenefits)?Critical unknown: How do CPs change water quality and the stressors that affect stream aquatic life? Which CPs improve stream health more effectively?Critical knowledge to be delivered to stakeholders includes—the effects of CPs on local water-quality conditions,the degree to which these same CPs also provide local stream-ecosystem benefits, anda deeper understanding of local stream-ecosystems, including stressors and CPs, to guide the selection of management efforts that enhance both water quality and overall stream-ecosystem health.

Evidence of the widespread occurrence of microplastics throughout our environment and exposure to humans and other organisms over the past decade has led to questions about the possibility of health hazards and mitigation of exposures. This document discusses nanoplastics as well as microplastics (referred to solely as microplastics); the microplastics have a range from 1 micrometer to 5 millimeters (1 μm–5 mm) in length, whereas the nanoplastics are less than 1 μm in length (sidebar ES1).A myriad of environmental exposure pathways with microplastics to humans and wildlife, including ingestion, inhalation, and bodily absorption, are likely to exist. A growing body of evidence has documented bioaccumulation of microplastics in tissues and organs of humans and wildlife, benthic community effects, and potential nutritional and reproductive effects in some wildlife species. Understanding if or when environmental exposures pose a health risk is complicated by the diversity of microplastic sizes, morphologies, polymer types, and chemicals added during manufacturing or sorbed from the environment; ongoing challenges in analytical methods used to detect, quantify, and characterize microplastics and associated chemicals in our ecosystems; and the fact that ecotoxicological studies regarding microplastics are still in their infancy. Therefore, the study of environmental exposures and potential related health hazards of microplastics to the public and wildlife is a One Health (sidebar ES2) research topic that necessitates integrated science approaches.A better understanding of the sources, pathways, fate, and biological effects of microplastics has become a priority of the Federal Government, State governments, Tribes, stakeholders, and the public. Examples of Federal and State microplasticfocused legislation and programs to prioritize microplastic research and reduction include the Federal Microbead-Free Waters Act of 2015, California Senate Bills 1422 and 1263 (2018), the U.S. Environmental Protection Agency (EPA) Trash Free Waters Program, the National Institute of Standards and Technology’s Microplastic and Nanoplastic Metrology project, and Minnesota’s microplastic project. With its unique expertise and capabilities, the U.S. Geological Survey (USGS) is well positioned to help fill some of the most important microplastic science gaps.This strategic science vision document for microplastics identifies current (2023) microplastic science gaps and prioritizes research relevant to the mission, expertise, and capabilities of the USGS. It is intended for USGS scientists and stakeholders to use as a starting point for planning, prioritizing, and designing collaborative environmental microplastic science. Many of the microplastic science gaps and priorities are scalable, from local to national, and thus, can be made commensurate with available funding and evolving analytical and field tools, laboratory capacity, and stakeholder needs. Current (2023) or future research by academia and other Federal or State agencies, and Tribes may be aimed at some of the same microplastic science gaps identified in this document. Therefore, this document can be used as an information resource to maximize strengths and capabilities and minimize redundancy in communication and collaboration.