Geology topics

Landon M. Keele

Publications and source records attributed to Landon M. Keele.

5 recordsLinked to original sources

USGS2026

A review of extraction techniques for per- and polyfluoroalkyl substances in graminaceous plants

Per- and polyfluoroalkyl substances (PFAS) are a wide-ranging class of manufactured chemicals that are environmentally persistent. Due to their ubiquity and resistance to degradation, PFAS readily bioaccumulate in a variety of environmental matrices and elicit a range of toxicological impacts. Despite an increase in research into these compounds, there is a clear gap in consensus on extraction techniques to quantify many PFAS in certain environmental media, particularly at critical points in agricultural food systems such as pasture grasses and feedstocks. Developing methods for more comprehensive and accurate extraction of PFAS in plant tissues is crucial for the biomonitoring of PFAS contamination in these ecosystems. This review seeks to identify relevant information pertaining to the partitioning of PFAS in plant matrices and evaluate the performance of previously established methods for the extraction of PFAS in graminaceous plants. Evaluated methods varied widely in extraction techniques, limits of detection and accuracy. This review provides a framework for enhancing PFAS analysis by tailoring extraction and cleanup strategies to both complex plant matrices and diverse analyte properties. Standardizing these methodologies will provide the high-quality data essential for ecotoxicologists and policymakers to accurately map the metabolic fate and ecological risks of these pollutants across food webs.

Critical Reviews in Analytical Chemistry↗

USGS2026

Per- and polyfluoroalkyl substances and pesticides in black bears (Ursus americanus) and grizzly bears (Ursus arctos horribilis) from Montana's Cabinet-Yaak ecosystem: A baseline assessment of emerging and legacy contaminants

Per- and polyfluoroalkyl substances (PFAS) and pesticides are globally distributed contaminants that persist in terrestrial food webs, yet baseline data for large omnivores in the continental U.S. remain limited. This study quantified PFAS and pesticides in whole blood from free-ranging black bears ( Ursus americanus , n = 15) and grizzly bears ( Ursus arctos horribilis , n = 9) in the Cabinet-Yaak Ecosystem of northwestern Montana. Using high-resolution mass spectrometry-based methods (GC-MS/MS and LC-MS/MS), 52 PFAS and 186 pesticides were analyzed. PFAS were detected in all bears, with total PFAS concentrations ranging from 79.5 to 317 pg/mL. PFAS profiles were dominated by long-chain perfluoroalkyl carboxylic acids, particularly PFOA, PFDA, and PFUnDA, with minimal contribution from short-chain compounds. Species was the strongest ecological predictor of PFAS concentrations, although variability across age, sex, and capture location were observed. Only two pesticides, piperonyl butoxide and permethrin, were detected at quantifiable concentrations (2070–12,600 pg/mL), and no correlations were observed between pesticide and PFAS concentrations, indicating independent exposure pathways. The predominance of long-chain PFAS suggests diffuse environmental sources and bioaccumulation within terrestrial food webs. Although measured concentrations were generally low relative to other wildlife toxicological studies, the persistence and protein-binding properties of long-chain PFAS warrant continued monitoring, particularly for long-lived omnivores. These results establish baseline contaminant concentrations for two apex omnivores in a remote ecosystem and highlight the utility of large mammals as integrative sentinels of environmental contaminant exposure for regional monitoring and wildlife conservation. Continued monitoring in the Cabinet-Yaak and across western North America will be critical for assessing temporal trends, identifying new contaminant sources, and evaluating ecological health in bear populations.

Montana↗

USGS2026

A multi-state assessment of per- and polyfluoroalkyl substances (PFAS), pesticides, and antibiotic resistance genes in white-tailed deer (Odocoileus virginianus) of the United States

Sentinel species provide a vital One Health perspective on ecosystem contamination driven by rising global chemical production. We evaluated white-tailed deer ( Odocoileus virginianus ; n = 54, 24 states, six matrices) as nationwide bioindicators for PFAS, pesticides, antimicrobial resistance (AMR) genes, and microbiome diversity. PFAS were detected in 100% of deer samples (26 compounds identified overall; non-detect to 12.3 ng/g ww), with preferential accumulation in the liver, indicating widespread systemic exposure. Neither region, landscape, nor source proximity predicted liver PFAS concentrations, whereas landscape had a significant, albeit weak, effect on spleen concentrations. This overall absence of strong spatial drivers suggests ubiquitous background contamination rather than localized point-source exposure. Conversely, 13 pesticides/transformation products (ranging from non-detect to 88.6 ng/g ww; highest in scat) were detected in only 28% of samples, despite widespread national use. Since not all possible transformation products were measured, these data reflect the accumulation of the target compound rather than total pesticide exposure. Driven by the rapid metabolism and excretion of herbicides, persistent insecticides dominated tissue samples. Additionally, biological threats were prevalent with eight distinct AMR genes identified in WTD scat, frequently featuring the florfenicol resistance gene (flo st, 33%). The presence of synthetic compounds and AMRs in game meat and scat pose a direct One Health risk to the human food chain. These findings highlight the value of using a single, widely distributed sentinel species as an early warning system for the ecological and public health threats posed by global chemical pollution.

contiguous United States↗

USGS2026

Comparative evaluation of three extraction techniques: Validation of a novel approach for the determination of 51 Per- and Polyfluoroalkyl substances in Graminaceous plants

Per- and polyfluoroalkyl substances (PFAS) are a class of over 15,000 xenobiotic compounds that have permeated across the globe and are largely resistant to natural forms of degradation, resulting in their long-term environmental persistence. These compounds can bioaccumulate and cause toxicological effects in organisms living within PFAS contaminated ecosystems. Grasses and feedstocks grown on contaminated farmlands are intermediates in the transmission of PFAS from contaminated soil to livestock and humans and may provide a potential avenue for biomonitoring of PFAS as they permeate through agricultural food systems. However, extraction methods for these compounds in graminaceous plants are sparse, non-standardized and limited in analytical range of PFAS compounds. This study outlines the development of a novel method of extraction using an alkaline, methanol-based solid-liquid extraction technique for 51 PFAS in graminaceous plant material, including nine separate PFAS subclasses. In comparison to two other previously published methods, this alkaline, methanolic solid-liquid approach has statistically significantly improved analyte recoveries for 22 of the 51 tested PFAS, ranging from 64.7–139% recovery in previously unexposed prairie grass ( Panicum virgatum and Dactylis glomerata ). Method detection limits range from 0.091 – 53.7 parts per trillion across tested PFAS analytes, demonstrating increased precision and sensitivity when compared to two other tested extraction procedures. This method’s strategy of alkaline, methanolic SLE may serve as a foundation for further testing across new plant taxa and an increased range of PFAS analytes.

Journal of Hazardous Materials Advances↗

USGS2024

Guide to per- and polyfluoroalkyl substances (PFAS) sampling within Natural Resource Damage Assessment and Restoration

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals with a nondegradable fluorinated carbon backbone that have been incorporated in countless industrial and commercial applications. Because PFAS are nondegradable, they have been detected in all environmental media, indicating extensive global contamination. The unique physiochemical properties of PFAS and their complex interactions with environmental matrices create a great challenge for researchers when selecting site-specific sample matrices, sampling logistics, various analytical methods, and data interpretation. The widespread contamination and the potential toxicity of PFAS to human and environmental health have resulted in the proposed designation of two commonly used PFAS as hazardous substances, which may prompt new requirements for reporting, regulatory action, and site cleanup. For researchers involved in natural resource damage assessment efforts, understanding the multifaceted dynamics of the environmental fate and transport of PFAS will be essential for appropriate sample collections, analyses, and data interpretation. This guide aims to provide fundamental concepts and considerations involved with environmental sampling for PFAS during site assessments.

Open-File Report↗