Environmental Risk Assessment of Antibiotics: Investigations into Cyanobacteria Interspecies Sensitivities and Establishing Appropriate Protection Limits

Antibiotics have been described as a ‘wonder drug’ that have transformed medicine since their discovery at the beginning of the 20th century and are used globally in safeguarding human and animal health. Environmental risk assessment (ERA) aims to ensure their environmental safety by setting protection limits that seek to prevent adverse effects upon populations and ecosystem function. In the case of antibiotics however, there is concern that ERA may not be fully protective of bacterial populations. This thesis examines the ERA of antibiotics and highlights that protection limits may in some cases be under-protective or over-protective for bacteria populations (including cyanobacteria), depending on the antibiotic mode of action and the species on which the protection limit is based. The first section of the thesis contains a systematic review including a meta-analysis of all publicly available aquatic ecotoxicity data. The results illustrate that generally bacteria are the most sensitive taxa to antibiotics compared with eukaryotes but that interspecies variability in sensitivity among bacteria can range by up to five orders of magnitude. This far exceeds the assessment factor of 10 used to account for such uncertainty in protection limits. It also shows that the costly testing on fish may not be required and in accordance with the principle of the 3Rs could be excluded from the ERA of antibiotics, as they are not likely to drive the protection limit. Further, it demonstrates that protection limits established for antimicrobial resistance (AMR) may not always be protective of environmental health and that both protection limits should be determined in ERA. Next, the thesis reports on the development and validation of a microplate assay for the rapid screening of chemical effects (here antibiotics) on cyanobacteria. The microplate assay is optimised to allow for the direct comparison of species sensitivity, ensuring consistent test conditions and thus limiting differences in antibiotic behaviour between assays. Reference toxicity testing with potassium dichromate demonstrates reproducibility over time and comparability with the standard shake flask test used in ERA. The microplate assay is then used to experimentally confirm the findings of the meta-analysis. In this work, interspecies sensitivity across eight cyanobacteria species was demonstrated to vary by up to 70 fold following exposure to β-lactam antibiotics but only by an order of magnitude for macrolides. Cyanobacteria were not sensitive to sulfonamides and thus are not likely to be suitable for the setting of protection limits for this antibiotic class. Finally in this thesis, species sensitivity distributions were created to examine how effective the protection limit currently derived in ERA is for antibiotics. For cephalosporins, there was a higher probability of under-protection whilst the protection limits were over-protective for classes of antibiotics with less interspecies differences in sensitivity, such as macrolides. Further, a probabilistic ecological risk assessment suggested that 60 to 100% of cyanobacteria species might be adversely affected at the higher measured environmental concentrations in the literature, while no significant risk was found at average concentrations. The findings from this thesis illustrate that protection limits, as currently determined in ERA for antibiotics, may not be suitable for the adequate protection of cyanobacteria populations and most likely other bacterial taxa. The thesis proposes several approaches for improving ERA, including incorporating greater bacterial diversity in ecotoxicity testing, the inclusion of functional and/or community testing and the use of probabilistic methods to derive protection limits

Diagnostics for specific PAHs in the far-IR: searching neutral naphthalene and anthracene in the Red Rectangle

Context. In the framework of the interstellar polycyclic aromatic hydrocarbons (PAHs) hypothesis, far-IR skeletal bands are expected to be a fingerprint of single species in this class. Aims. We address the question of detectability of low energy PAH vibrational bands, with respect to spectral contrast and intensity ratio with ``classical'' Aromatic Infrared Bands (AIBs). Methods. We extend our extablished Monte-Carlo model of the photophysics of specific PAHs in astronomical environments, to include rotational and anharmonic band structure. The required molecular parameters were calculated in the framework of the Density Functional Theory. Results. We calculate the detailed spectral profiles of three low-energy vibrational bands of neutral naphthalene, and four low-energy vibrational bands of neutral anthracene. They are used to establish detectability constraints based on intensity ratios with ``classical'' AIBs. A general procedure is suggested to select promising diagnostics, and tested on available Infrared Space Observatory data for the Red Rectangle nebula. Conclusions. The search for single, specific PAHs in the far-IR is a challenging, but promising task, especially in view of the forthcoming launch of the Herschel Space Observatory.Comment: 13 pages, 13 figures, accepted for publication in A&

Integrating human and environmental health in antibiotic risk assessment: A critical analysis of protection goals, species sensitivity and antimicrobial resistance

This is the author accepted manuscriptAntibiotics are vital in the treatment of bacterial infectious diseases but when released into the environment they may impact non-target organisms that perform vital ecosystem services and enhance antimicrobial resistance development with significant consequences for human health. We evaluate whether the current environmental risk assessment regulatory guidance is protective of antibiotic impacts on the environment, protective of antimicrobial resistance, and propose science-based protection goals for antibiotic manufacturing discharges. A review and meta-analysis was conducted of aquatic ecotoxicity data for antibiotics and for minimum selective concentration data derived from clinically relevant bacteria. Relative species sensitivity was investigated applying general linear models, and predicted no effect concentrations were generated for toxicity to aquatic organisms and compared with predicted no effect concentrations for resistance development. Prokaryotes were most sensitive to antibiotics but the range of sensitivities spanned up to several orders of magnitude. We show reliance on one species of (cyano)bacteria and the ‘activated sludge respiration inhibition test’ is not sufficient to set protection levels for the environment. Individually, neither traditional aquatic predicted no effect concentrations nor predicted no effect concentrations suggested to safeguard for antimicrobial resistance, protect against environmental or human health effects (via antimicrobial resistance development). Including data from clinically relevant bacteria and also more species of environmentally relevant bacteria in the regulatory framework would help in defining safe discharge concentrations for antibiotics for patient use and manufacturing that would protect environmental and human health. It would also support ending unnecessary testing on metazoan species.AstraZeneca Global SHE Research Programm

HESFIRE: a global fire model to explore the role of anthropogenic and weather drivers

Vegetation fires are a major driver of ecosystem dynamics and greenhouse gas emissions. Anticipating potential changes in fire activity and their impacts relies first on a realistic model of fire activity (e.g., fire incidence and interannual variability) and second on a model accounting for fire impacts (e.g., mortality and emissions). In this paper, we focus on our understanding of fire activity and describe a new fire model, HESFIRE (Human–Earth System FIRE), which integrates the influence of weather, vegetation characteristics, and human activities on fires in a stand-alone framework. It was developed with a particular emphasis on allowing fires to spread over consecutive days given their major contribution to burned areas in many ecosystems. A subset of the model parameters was calibrated through an optimization procedure using observation data to enhance our knowledge of regional drivers of fire activity and improve the performance of the model on a global scale. Modeled fire activity showed reasonable agreement with observations of burned area, fire seasonality, and interannual variability in many regions, including for spatial and temporal domains not included in the optimization procedure. Significant discrepancies are investigated, most notably regarding fires in boreal regions and in xeric ecosystems and also fire size distribution. The sensitivity of fire activity to model parameters is analyzed to explore the dominance of specific drivers across regions and ecosystems. The characteristics of HESFIRE and the outcome of its evaluation provide insights into the influence of anthropogenic activities and weather, and their interactions, on fire activityinfo:eu-repo/semantics/publishedVersio

Hybrid Meson Decay Phenomenology

The phenomenology of a newly developed model of hybrid meson decay is developed. The decay mechanism is based on the heavy quark expansion of QCD and the strong coupling flux tube picture of nonperturbative glue. A comprehensive list of partial decay widths of a wide variety of light, $s\bar s$, $c\bar c$, and $b \bar b$ hybrid mesons is presented. Results which appear approximately universal are highlighted along with those which distinguish different hybrid decay models. Finally, we examine several interesting hybrid candidates in detail.Comment: 37 pages, 2 figures, 6 tables, Revte

Variability in cyanobacteria sensitivity to antibiotics and implications for environmental risk assessment

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record© 2019 Once released into the environment antibiotics can kill or inhibit the growth of bacteria, and in turn potentially have effects on bacterial community structure and ecosystem function. Environmental risk assessment (ERA) seeks to establish protection limits to minimise chemical impacts on the environment, but recent evidence suggests that the current regulatory approaches for ERA for antibiotics may not be adequate for protecting bacteria that have fundamental roles in ecosystem function. In this study we assess the differences in interspecies sensitivity of eight species of cyanobacteria to seven antibiotics (cefazolin, cefotaxime, ampicillin, sufamethazine, sulfadiazine, azithromycin and erythromycin) with three different modes of action. We found that variability in the sensitivity to these antibiotics between species was dependent on the mode of action and varied by up to 70 times for β-lactams. Probabilistic analysis using species sensitivity distributions suggest that the current predicted no effect concentration PNEC for the antibiotics may be either over or under protective of cyanobacteria dependent on the species on which it is based and the mode of action of the antibiotic; the PNECs derived for the macrolide antibiotics were over protective but PNECs for β-lactams were generally under protective. For some geographical locations we identify a significant risk to cyanobacteria populations based upon measured environmental concentrations of selected antibiotics. We conclude that protection limits, as determined according to current regulatory guidance, may not always be protective and might be better derived using SSDs and that including toxicity data for a wider range of (cyano-) bacteria would improve confidence for the ERA of antibiotics.AstraZeneca Global SHE Research ProGrammeMedical Research Council (MRC

A general model for the identification of specific PAHs in the far-IR

Context. In the framework of the interstellar PAH hypothesis, far-IR skeletal bands are expected to be a fingerprint of single species in this class. Aims. A detailed model of the photophysics of interstellar PAHs is required for such single-molecule identification of their far-IR features in the presently available Infrared Space Observatory data and in those of the forthcoming Herschel Space Observatory mission. Methods. We modelled the detailed photophysics of a vast sample of species in different radiation fields, using a compendium of Monte-Carlo techniques and quantum-chemical calculations. This enabled us to validate the use of purely theoretical data and assess the expected accuracy and reliability of the resulting synthetic far-IR emission spectra. Results. We produce positions and intensities of the expected far-IR features which ought to be emitted by each species in the sample in the considered radiation fields. A composite emission spectrum for our sample is computed for one of the most favourable sources for detection, namely the Red Rectangle nebula. The resulting spectrum is compared with the estimated dust emission in the same source, to assess the dependence of detectability on key molecular parameters. Conclusions. Identifying specific PAHs from their far-IR features is going to be a difficult feat in general, still it may well be possible under favourable conditions.Comment: 14 pages, 9 figures + 18 pages of online appendix. Accepted for publication in A&A (09/06/2006

Passive scalar convection in 2D long-range delta-correlated velocity field: Exact results

The letter presents new field-theoretical approach to 2D passive scalar problem. The Gaussian form of the distribution for the Lyapunov exponent is derived and its parameters are found explicitly.Comment: 11 pages, RevTex 3.0, IFUM-94/455/January-F

Interactive effects of inbreeding and endocrine disruption on reproduction in a model laboratory fish

This is the final version of the article. Available from Wiley via the DOI in this record.Inbreeding depression is expected to be more severe in stressful environments. However, the extent to which inbreeding affects the vulnerability of populations to environmental stressors, such as chemical exposure, remains unresolved. Here we report on the combined impacts of inbreeding and exposure to an endocrine disrupting chemical (the fungicide clotrimazole) on zebrafish (Danio rerio). We show that whilst inbreeding can negatively affect reproductive traits, not all traits are affected equally. Inbreeding depression frequently only became apparent when fish were additionally stressed by chemical exposure. Embryo viability was significantly reduced in inbred exposed fish and there was a tendency for inbred males to sire fewer offspring when in direct competition with outbred individuals. Levels of plasma 11-ketotestosterone, a key male sex hormone, showed substantial inbreeding depression that was unaffected by addition of the fungicide. In contrast, there was no effect of inbreeding or clotrimazole exposure on egg production. Overall, our data provide evidence that stress may amplify the effects of inbreeding on key reproductive traits, particularly those associated with male fitness. This may have important implications when considering the consequences of exposure to chemical pollutants on the fitness of wild populations.Thanks to NERC's Post Genomics & Proteomics Programme NE/F0077871/1 and AstraZeneca's Safety, Health and Environment Research Programme for funding this work. We thank Alexander Scott (11-ketotestosterone radioimmunoassay) at the Centre for Environment, Fisheries and Aquaculture Science, Jan Shears and Luanne Wilkes at University of Exeter, Gareth Readman, Vicki Cammack, Kate Hurd and Yohanna Glennon at Brixham Environmental Laboratory for their assistance