Kristine H. Wammer

The presence of antibiotics in surface waters is a potential driver of antibiotic resistance and thus of concern to human and environmental health. Key factors driving the potential impact of antibiotics are their persistence and transport in rivers and lakes. The goal of this study was to describe the peer-reviewed published literature on the photolysis (direct and indirect), sorption, and biodegradation of a selected group of antibiotic compounds following a scoping review methodology. Primary research from 2000 to 2021 was surveyed to compile information on these processes for 25 antibiotics from 6 classes. After compilation and assessment of the available parameters, the results indicate that information is present to predict the rates of direct photolysis and reaction with hydroxyl radical (an indirect photolysis process) for most of the selected antibiotics. There is insufficient or inconsistent information for including other indirect photolysis processes, biodegradation, or removal via sorption to settling particles for most of the targeted antibiotic compounds. Future research should focus on collecting fundamental parameters such as quantum yields, second-order rate constants, normalized biodegradation rates, and organic carbon or surface area normalized sorption coefficients rather than pseudo-first order rate constants or sorption equilibrium constants that apply only to specific conditions/sites.
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•Quantitative information about antibiotic fate was assessed via a scoping review.•Data for direct photolysis and reaction with hydroxyl radical is robust.•There is limited data regarding biodegradation of antibiotics in aquatic systems.•Reported sorption equilibrium constants are often not normalized to organic carbon content.•Fundamental, generalizable data needed for robust models is limited.

This special issue honors them: Edward (Ed) Bouwer (1955-2019), Michael (Mike) Aitken (1956-2020), James (Jim) J. Morgan (1932-2020), Deborah (Deb) Swackhamer (1954-2021), and Philip (Phil) Singer (1942-2020). The 16 papers focus on the innovative microbial and chemical processes for addressing both classic problems (e.g., nutrient recovery and wastewater treatment) as well as emerging problems (e.g., biodiversity loss, plastic pollution, biotransformation of organic chemicals, cyanotoxins, and disinfection byproducts).

Dissolved organic matter (DOM) mediated indirect photodegradation can play an important role in the degradation of aquatic contaminants. Predicting the rate of this process requires knowledge of the photochemically produced reactive intermediates (PPRI) that react with the compound of interest, as well as the ability of individual DOM samples to produce PPRI. Key PPRI are typically identified using quencher studies, yet this approach often leads to results that are difficult to interpret. In this work, we analyze the indirect photodegradation of atorvastatin, carbamazepine, sulfadiazine, and benzotriazole using a diverse set of 48 waters from natural and engineered aquatic systems. We use this large data set to evaluate relationships between PPRI formation and indirect photodegradation rate constants, which are directly compared to results using standard quenching experiments. These data demonstrate that triplet state DOM (3DOM) and singlet oxygen (1O2) are critical PPRI for atorvastatin, carbamazepine, and sulfadiazine, while hydroxyl radical (OH) contributes to the indirect photodegradation of benzotriazole. We caution against relying on quenching studies because quenching of 3DOM limits the formation of 1O2 and all studied quenchers react with OH. Furthermore, we show that DOM composition directly influences indirect photodegradation and that low molecular weight, microbial-like DOM is positively correlated with the indirect photodegradation rates of carbamazepine, sulfadiazine, and benzotriazole.
This study highlights limitations in conventional approaches used to identify key photochemically produced intermediates involved in the indirect photodegradation of organic contaminants.

Predicting the formation of photochemically produced reactive intermediates (PPRI) during the irradiation of dissolved organic matter (DOM) has remained challenging given the complex nature of this material and differences in PPRI formation mechanisms. We investigate the role of DOM composition in photoreactivity using 48 samples that span the range of DOM in freshwater systems and wastewater. We relate quantum yields for excited triplet-state organic matter (f TMP), singlet oxygen (Φ 1O2 ), and hydroxylating species (Φ •OH) to DOM composition determined using spectroscopy, Fourier-transform ion cyclotron resonance mass spectrometry, and electron-donating capacity (EDC). f TMP and Φ 1O2 follow similar trends and are correlated with bulk properties derived from UV–vis spectra and EDC. In contrast, no individual bulk property can be used to predict Φ •OH. At the molecular level, the subset of DOM that is positively correlated to both Φ •OH and EDC is distinct from DOM formulas related to Φ 1O2 , demonstrating that •OH and 1O2 are formed from different DOM fractions. Multiple linear regressions are used to relate quantum yields of each PPRI to DOM composition parameters derived from multiple techniques, demonstrating that complementary methods are ideal for characterizing DOM because each technique only samples a subset of DOM.

This study investigated geospatial distributions of antibiotics and antibiotic resistance genes (ARGs) in surface waters and their associations with anthropogenic activities. During July-October 2020, the concentrations of antibiotics (water and sediment) and ARGs (sediment) were measured at 39 sites in the Twin-Cities metropolitan area (Minnesota) that experience a gradient of impacts related to human activities. For water samples, the number of antibiotics detected and the concentrations of certain antibiotics (e.g., sulfonamides) positively correlated with urbanization indicators (e.g., urban percentage, population density, number of wastewater discharge points; rho = 0.32-0.46, p = 0.003-0.04) and negatively correlated with undeveloped land indicators (e.g., forest; rho = -0.34 to -0.62, p = <0.00001-0.04). Antibiotics in sediments exhibited geospatial distribution different from that in corresponding water samples and exhibited no associations with anthropogenic factors. Relative abundances of ARGs were not associated with anthropogenic factors, but several ARGs (e.g., bla(oxa), mexB, and sul2) were inversely related to the organic content of sediments (rho = -0.38 to -0.44, p = 0.01-0.04). Strong correlations were found among relative abundances of various ARGs and intI1 (rho >= 0.67, p < 0.05), highlighting their co-occurrence in (sub)urban surface waters. These results identified promising anthropogenic/environmental factors for predicting antibiotic geospatial distributions and useful gene markers to monitor ARGs in surface waters.

•An overview of Dr Catherine A. Peters’ research which bridges environmental chemistry and hydrology, and her mentorship.•Development and application of novel tools for morphological and mineralogical characterizations of complex geomaterials.•Investigation of biogeochemical reaction mechanisms and rates for contaminant remediation and CO2 sequestration.•Upscaling of mineral reaction rates in heterogeneous porous media.•Improved understanding of the evolution of fractured porous media and their hydraulic properties, and the dependence on mineralogical complexity.
Dr. Catherine A. Peters’ research has advanced various topics in hydro-biogeochemistry. This paper highlights key research outputs across Dr. Peters’ career. Throughout her research endeavors, Dr. Peters has distinguished herself and her research portfolio via integration of experimental, theoretical and modeling approaches to tackle research questions at the intersection of hydrology and environmental geochemistry. Her work encompasses topics from mineralogical and morphological characterization of complex geomaterials, reactive transport of biogeochemical contaminants ranging from polycyclic aromatic hydrocarbons to arsenic and strontium, and reactive evolution of fractured and porous media with chemical and physical heterogeneities. Her work has advanced our fundamental understanding of complex geochemical reactions and their impacts on fracture alteration, the fate and transport of contaminants, and the stability of subsurface energy and resources systems. These findings have helped inform applications regarding bio-remediation, heavy metal removal by mineralization, and geological carbon storage. The methods and findings showcased here have broad scientific and engineering impacts and have benefitted other emerging research topics in hydrology and related topics (e.g., Earth’s critical zone). Along her scientific journey, Dr. Peters has uplifted and empowered many graduate and undergraduate students with her kindness, encouragement, and confidence in them. These students are now at different stages of their scientific careers and are following her steps in nurturing the next generation of scientists with diverse backgrounds in various types of institutions.

Antimicrobials may reach the soil environment from a variety of sources and pathways, including land application of human biosolids and animal manure. Once in soil, antimicrobials can affect the abundance and activity of soil microorganisms and exert selection pressures that enhance the emergence and spread of antimicrobial resistance (AMR). To mitigate the spread of AMR it is important to understand the spatial and temporal interactions between antimicrobials and soil. The goal of this study was to assess the vulnerability of Minnesota (U.S.) soil to contamination with specific antimicrobial compounds at temperatures experienced throughout the year. Soil contamination potential was estimated based upon specific antimicrobial drug binding and permanence, and average monthly temperature. Minnesota soil vulnerability was estimated by incorporating spatially explicit soil contamination potential, land cover type, and livestock density. Assessment of antimicrobials used in livestock production showed that soils are most vulnerable to antimicrobial contamination in southwestern Minnesota, to enrofloxacin, chlortetracycline, and oxytetracycline, and in the months of April and October. While the assessment herein was not based on actual on-farm antimicrobial use data and subsequent excretion of antimicrobial metabolites into the environment, this study provides an overview of the spatial and temporal potential for Minnesota soil to be contaminated by several antimicrobial drugs and demonstrates how specific vulnerability assessments might be conducted for geographic areas with known exposure (e.g., cropland fertilized with livestock manure and/or human biosolids). Such assessments might be used to identify best practices for mitigating antimicrobial exposure to soils and guide additional research to understand the role of environmental antimicrobial contamination in the problem of AMR.
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•The hypothetical soil contamination to antimicrobials (vulnerability) was assessed.•Spatiotemporally, southwestern Minnesota, April and October were most vulnerable.•Among antimicrobials, enrofloxacin and tetracyclines had the highest vulnerability.•These results may inform mitigation strategies of antimicrobial exposure to soil.

AbstractThe environment plays a key role in the spread and persistence of antimicrobial resistance (AMR). Antimicrobials and antimicrobial resistance genes (ARG) are released into the environment from sources such as wastewater treatment plants, and animal farms. This study describes an approach guided by spatial mapping to quantify and predict antimicrobials and ARG in Minnesota’s waterbodies in water and sediment at two spatial scales: macro, throughout the state, and micro, in specific waterbodies. At the macroscale, the highest concentrations across all antimicrobial classes were found near populated areas. Kernel interpolation provided an approximation of antimicrobial concentrations and ARG abundance at unsampled locations. However, there was high uncertainty in these predictions, due in part to low study power and large distances between sites. At the microscale, wastewater treatment plants had an effect on ARG abundance (sul1 and sul2 in water; blaSHV, intl1, mexB, and sul2 in sediment), but not on antimicrobial concentrations. Results from sediment reflected a long-term history, while water reflected a more transient record of antimicrobials and ARG. This study highlights the value of using spatial analyses, different spatial scales, and sampling matrices, to design an environmental monitoring approach to advance our understanding of AMR persistence and dissemination.

Background: Antibiotics and their metabolites released into aquatic and soil environments have the potential to affect their microbial communities and can be a selection pressure to drive antimicrobial resistance emergence and spread. However, data about the persistence of antibiotics and metabolites into the natural environment are still lacking. Objectives: The goal of this manuscript is to describe the protocol that will be used to conduct a formal scoping review of the current literature to address the following question: “What is known from the existing literature about degradation of a selected group of antibiotic compounds in water, sediment, and soil?”. Eligibility criteria: Eligible studies will be primary research, in English, from any geographic location, published between 2000-2020, include water, sediment, and/or soil samples, were conducted in natural systems and/or laboratory studies with relevant data applied to natural systems, include data related to transformation by sunlight, biodegradation, and/or sorption processes, and include data for any of the following compounds: i) sulfonamides: sulfachlorpyridazine, sulfadiazine, sulfadimethoxine, sulfamethazine, sulfamethoxazole, sulfapyridine; ii) macrolides: erythromycin, roxithromycin, tylosin, azithromycin; iii) tetracyclines: chlortetracycline, doxycycline, oxytetracycline, tetracycline; iv) fluoroquinlones: ciprofloxacin, enrofloxacin, norfloxacin, ofloxacin; v) beta-lactams: penicillins; vi) others: carbadox, trimethoprim, lincomycin.

Photolysis of trenbolone acetate (TBA) metabolites in the presence of various nitrogen-, sulfur-, or oxygen-containing nucleophiles (e.g., azide, ammonia, or thiosulfate, respectively) results in rapid (half-lives ∼20–60 min), photochemically induced nucleophile incorporation across the parent steroid’s trienone moiety. The formation of such nucleophile adducts limits formation of photohydrates, suggesting competition between the nucleophile and water for photochemical addition into the activated steroid structure. Analogous to previously reported photohydration outcomes, LC/MS analyses suggest that such photonucleophilic addition reactions are reversible, with more rapid elimination rates than thermal dehydration of photohydrates, and regenerate parent steroid structures. Beyond photonucleophilic addition pathways, we also found that hydroxylamine and presumed nucleophilic moieties in model dissolved organic matter (DOM; Fluka humic acid) can react via thermal substitution with TBA metabolite photohydrates, although this reaction with model DOM was only observed for photohydrates of trendione. Most nucleophile addition products [i.e., formed via (photo)­reaction with thiosulfate, hydroxylamine, and ammonia] are notably more polar relative to the parent metabolite and photohydration products. Thus, if present, both nucleophilic adducts and bound residues in organic matter will facilitate transport and help mask detection of TBA metabolites in surface waters and treatment systems.