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Controlling and minimising background contamination is crucial for maintaining a high quality of samples in human biomonitoring targeting organic chemicals. We assessed the contamination of three previous types and one newly introduced medical-grade type of sample tubes used for storing human body fluids at the German Environmental Specimen Bank. Aqueous extracts from these tubes were analysed by non-targeted liquid chromatography-high resolution mass spectrometry (LC-HRMS) before and after a dedicated cleaning procedure. After peak detection using MZmine, Bayesian hypothesis testing was used to group peaks into those originating either from instrumental and laboratory background contamination, or actual tube contaminants, based on if their peak height was reduced, increased or not affected by the cleaning procedure. For all four tube types 80–90% of the 2475 peaks (1549 in positive and 926 in negative mode) were assigned to laboratory/instrumental background, which we have to consider as potential sample tube contaminants. Among the tube contaminants, results suggest a considerable difference in the contaminant peak inventory and the absolute level of contamination among the different sample tube types. The cleaning procedure did not affect the largest fraction of peaks (50–70%). For the medical grade tubes, the removal of contaminants by the cleaning procedure was strongest compared to the previous tubes, but in all cases a small fraction increased in intensity after cleaning, probably due to a release of oligomers or additives. The identified laboratory background contaminants were mainly semi-volatile polymer additives such as phthalates and phosphate esters. A few compounds could be assigned solely as tube-specific contaminants, such as N,N-dibutylformamide and several constituents of the oligomeric light stabiliser Tinuvin-622. A cleaning procedure before use is an effective way to standardise the used sample tubes and minimises the background contamination, and therefore increases sample quality and therewith analytical results.

Nonylphenol (NP), nonylphenol monoethoxylate (NP1EO), and nonylphenol diethoxylate (NP2EO) are widely used in various daily products and have been cataloged as endocrine-disrupting chemicals. Due to their high lipophilicity and low biodegradability, these compounds remain in the environment and enter the human body through the food chain. Growing concerns regarding the potential negative effects of NP, NP1EO, and NP2EO on human health have raised the need for biomonitoring to investigate human exposure to these compounds. In this study, a simultaneous analysis method using solid-phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC–MS) was established by controlling the background contamination of NP, NP1EO, and NP2EO, which are ubiquitous in laboratory environments. The proposed method showed proper linearity of over 0.999 and a recovery greater than 85.8% for all analytes. Accuracy and precision were verified in ranges of 92.97–116.30% and 0.65–9.29%, respectively. The detection limits for NP, NP1EO, and NP2EO were 0.0363 μg L−1, 0.0401 μg L−1, and 0.0364 μg L−1, respectively, which were suitable for determining the trace analytes in human urine. Therefore, this simple and integrated analytical method was applied to measure the free and total forms of the target analytes in 25 human urine samples collected in Korea. Overall, free NP, NP1EO, and NP2EO were detected with average contents of 3.94 ± 4.14 μg L−1, 4.63 ± 2.62 μg L−1, and 0.293 ± 0.638 μg L−1, respectively, and with total NP, NP1EO, and NP2EO contents of 6.14 ± 8.24 μg L−1, 5.99 ± 2.91 μg L−1, and 0.806 ± 1.10 μg L−1, respectively. These data showed that these compounds are prevalent in human urine, and indicate the need for further studies. [ABSTRACT FROM AUTHOR]

Potential sources of a specific and considerable contamination with bisphenol A (BPA) via biological sample testing were investigated. Determination of BPA in animal plasma, collected in a commercially provided vacuum tube, revealed a significant contamination of 6 ng/ml of BPA in the tested sample, while blood serum from the same animal collected in a glass tube contained 0.37 ng/ml of BPA. Further investigation proved that the origin of the contamination was the separator gel in the vacuum collection tube, which contained, without any declaration from the producer, BPA at a mean ± SD concentration of 2046 ± 75 ng/g. However, the BPA concentrations found in the separator gel of the two batches of the vacuum tubes were varied by sevenfold. The problem with contaminated vacuum tubes was fixed with the further use of glass tubes without a separator gel. The second BPA contamination case reports on significant leaching of BPA out of rubber HPLC vial septa. Within eight consecutive injections using the same septum, the BPA concentration in the vial progressively increased from a value of zero at the first injection to 7.8 ng/ml at the eighth injection, while the septa itself contained BPA at average ± SD of 3386 ± 699 ng/g. The problem with contaminated HPLC vial septa was fixed with the further use of more chemically inert septa materials, e.g. silicone/PTFE. [ABSTRACT FROM AUTHOR]

Micro and nanosized plastics (MNPs), and a range of associated additive chemicals, have become pervasive contaminants that humans and the environment are exposed to everyday. However, one of the principal challenges in their analysis is adequate strategies to minimise background contamination. Here a blueprint for a specialised plastics and additive-minimised clean room laboratory built for this purpose is presented. Common laboratory construction materials (n = 23) were tested, including acoustic baffles, ceiling materials, floor materials, glazing rubber, and silicone sealant. The % polymer content ranged from 2–76% w/w while the sum concentration of six phthalates ranged from 0.81 (0.73–0.86) to 21000 (15000–27000) mg/kg, assigning many of these materials as inappropriate for use in a clean room environment. The final design of the laboratory consisted of three interconnected rooms, operated under positive pressure with the inner rooms constructed almost entirely of stainless steel. Background concentrations of MNPs and phthalates in the new laboratory were compared to two Physical Containment Level 2 (PC2) laboratory environments, with concentrations of MNPs reduced by > 100 times and phthalates reduced by up to 120 times. This study reports the first known clean room of its kind and provides a blueprint for reference and use by future plastics research. [Display omitted] • Design, testing and build of a plastics and additive chemicals minimised laboratory. • 23 construction materials contained 2-76% polymers and 0.8-21000 mg/kg phthalates. • Using stainless steel can reduce phthalate introduction by 250–650 times. • Background levels of MNP and phthalates were > 100 lower compared to a PC2 laboratory. [ABSTRACT FROM AUTHOR]

Metagenomics-based high-throughput sequencing (HTS) enables comprehensive detection of all species comprised in a sample with a single assay and is becoming a standard method for outbreak investigation. However, unlike real-time PCR or serological assays, HTS datasets generated for pathogen detection do not easily provide yes/no answers. Rather, results of the taxonomic read assignment need to be assessed by trained personnel to gain information thereof. Proficiency tests are important instruments of validation, harmonization, and standardization. Within the European Union funded project COMPARE [COllaborative Management Platform for detection and Analyses of (Re-) emerging and foodborne outbreaks in Europe], we conducted a proficiency test to scrutinize the ability to assess diagnostic metagenomics data. An artificial dataset resembling shotgun sequencing of RNA from a sample of contaminated trout was provided to 12 participants with the request to provide a table with per-read taxonomic assignments at species level and a report with a summary and assessment of their findings, considering different categories like pathogen, background, or contaminations. Analysis of the read assignment tables showed that the software used reliably classified the reads taxonomically overall. However, usage of incomplete reference databases or inappropriate data pre-processing caused difficulties. From the combination of the participants’ reports with their read assignments, we conclude that, although most species were detected, a number of important taxa were not or not correctly categorized. This implies that knowledge of and awareness for potentially dangerous species and contaminations need to be improved, hence, capacity building for the interpretation of diagnostic metagenomics datasets is necessary.

Abstract Background Culture-independent sequencing methods are increasingly used to investigate the microbiota associated with human mucosal surfaces, including sites that have low bacterial load in healthy individuals (e.g. the lungs). Standard microbiota methods developed for analysis of high bacterial load specimens (e.g. stool) may require modification when bacterial load is low, as background contamination derived from sterile laboratory reagents and kits can dominate sequence data when few bacteria are present. Main body Bacterial load in respiratory specimens may vary depending on the specimen type, specimen volume, the anatomic site sampled and clinical parameters. This review discusses methodological issues inherent to analysis of low bacterial load specimens and recommends strategies for successful respiratory microbiota studies. The range of methods currently used to process DNA from low bacterial load specimens, and the strategies used to identify and exclude background contamination are also discussed. Conclusion Microbiota studies that include low bacterial load specimens require additional tests to ensure that background contamination does not bias the results or interpretation. Several methods are currently used to analyse the microbiota in low bacterial load respiratory specimens; however, there is scant literature comparing the effectiveness and biases of different methods. Further research is needed to define optimal methods for analysing the microbiota in low bacterial load specimens.

Metagenomics-based high-throughput sequencing (HTS) enables comprehensive detection of all species comprised in a sample with a single assay and is becoming a standard method for outbreak investigation. However, unlike real-time PCR or serological assays, HTS datasets generated for pathogen detection do not easily provide yes/no answers. Rather, results of the taxonomic read assignment need to be assessed by trained personnel to gain information thereof. Proficiency tests are important instruments of validation, harmonization, and standardization. Within the European Union funded project COMPARE [COllaborative Management Platform for detection and Analyses of (Re-) emerging and foodborne outbreaks in Europe], we conducted a proficiency test to scrutinize the ability to assess diagnostic metagenomics data. An artificial dataset resembling shotgun sequencing of RNA from a sample of contaminated trout was provided to 12 participants with the request to provide a table with per-read taxonomic assignments at species level and a report with a summary and assessment of their findings, considering different categories like pathogen, background, or contaminations. Analysis of the read assignment tables showed that the software used reliably classified the reads taxonomically overall. However, usage of incomplete reference databases or inappropriate data pre-processing caused difficulties. From the combination of the participants' reports with their read assignments, we conclude that, although most species were detected, a number of important taxa were not or not correctly categorized. This implies that knowledge of and awareness for potentially dangerous species and contaminations need to be improved, hence, capacity building for the interpretation of diagnostic metagenomics datasets is necessary. [ABSTRACT FROM AUTHOR]

Controlling and minimising background contamination is crucial for maintaining a high quality of samples in human biomonitoring targeting organic chemicals. We assessed the contamination of three previous types and one newly introduced medical-grade type of sample tubes used for storing human body fluids at the German Environmental Specimen Bank. Aqueous extracts from these tubes were analysed by non-targeted liquid chromatography-high resolution mass spectrometry (LC-HRMS) before and after a dedicated cleaning procedure. After peak detection using MZmine, Bayesian hypothesis testing was used to group peaks into those originating either from instrumental and laboratory background contamination, or actual tube contaminants, based on if their peak height was reduced, increased or not affected by the cleaning procedure. For all four tube types 80-90% of the 2475 peaks (1549 in positive and 926 in negative mode) were assigned to laboratory/instrumental background, which we have to consider as potential sample tube contaminants. Among the tube contaminants, results suggest a considerable difference in the contaminant peak inventory and the absolute level of contamination among the different sample tube types. The cleaning procedure did not affect the largest fraction of peaks (50-70%). For the medical grade tubes, the removal of contaminants by the cleaning procedure was strongest compared to the previous tubes, but in all cases a small fraction increased in intensity after cleaning, probably due to a release of oligomers or additives. The identified laboratory background contaminants were mainly semi-volatile polymer additives such as phthalates and phosphate esters. A few compounds could be assigned solely as tube-specific contaminants, such as N,N-dibutylformamide and several constituents of the oligomeric light stabiliser Tinuvin-622. A cleaning procedure before use is an effective way to standardise the used sample tubes and minimises the background contamination, and therefore increases sample quality and therewith analytical results., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Murine models of Salmonella enterica serovar Typhimurium infection are one of the commonest tools to study host-pathogen interactions during bacterial infections. Critically, the outcome of S. Typhimurium infection is impacted by the genetic background of the mouse strain used, with macrophages from C57BL/6 and BALB/c mice lacking the capacity to control intracellular bacterial replication. For this reason, the use of congenic strains, which mix the genetic backgrounds of naturally protected mouse strains with those of susceptible strains, has the capacity to significantly alter results and interpretation of S. Typhimurium infection studies. Here, we describe how macrophage knockout cell lines generated by CRISPR/Cas9 gene editing can help determine the contribution of background contaminations in the phenotypes of primary macrophages from congenic mice, on the outcome of S. Typhimurium infection studies. Our own experience illustrates how the CRISPR/Cas9 technology can be used to complement pre-existing knockout models, and shows that there is great merit in performing concurrent studies with both genetic models, to exclude unanticipated side-effects on host-pathogen interactions.

Aim. We analysed current environmental state of the Dagestan coast of the Caspian Sea. Data on the spatial variability of contaminants in the coastal areas of the Dagestan segment of the Caspian Sea from the northern districts (Lopatin) to the central (Sulak coastal land) and, further, to the southern district (within Russian subsoil management) confirm that it is caused by irregular contamination of the sea by above-ground sources. Location. Dagestan coastal area of the Caspian SeaMethods. Concentration analysis of background contamination of chemical agents in the Dagestan coastal water from northern districts (Lopatin) to southern (Sulak coastal land) during the period between 2004 and 2007.Results. Data on the spatial variability of contaminants in the coastal areas of the Dagestan segment of the Caspian Sea from the northern districts (Lopatin) to the central (Sulak coastal land) and, further, to the southern district (within Russian subsoil management) confirm that it is caused by irregular contamination of the sea by above-ground sources.Main conclusions. The envisaged large-scale hydrocarbon resource development requires regular monitoring of sea currents on Makhachkala, Izberbash and Derbent roads.

In the present study, a quick and sensitive method was developed for simultaneous determination of nonylphenol ethoxylates (NP x EOs) and octylphenol ethoxylates (OP x EOs) ( x = 2–20) in three leafy vegetables, including cabbage, lettuce, and spinach using a modified “QuEChERS” method and ultra-high performance supercritical fluid chromatography–tandem mass spectrometry (UHPSFC-MS/MS) with scheduled multiple reaction monitoring (MRM). Under optimized conditions, the 38 target analytes were analyzed within a short period of time (5 min). The linearities of the matrix-matched standard calibrations were satisfactory with coefficients of determination ( R 2 ) > 0.99 and the limits of detection (LOD) and quantification (LOQ) were in between 0.02–0.27 and 0.18–1.75 μg kg −1 , respectively. The recovery of all target analytes spiked at three (low, medium, and high) fortification levels in various leafy vegetables were ranged from 72.8–122.6% with relative standard deviation (RSD) ≤18.3%. The method was successfully applied to market samples and the target analytes were found in all monitored samples, with total concentrations of 0–8.67 μg kg −1 and 15.75–95.75 μg kg −1 for OP x EOs and NP x EOs ( x = 2–20), respectively. In conclusion, the newly developed UHPSFC-ESI–MS/MS method is rapid and versatile and could be extrapolated for qualitative and quantitative analysis of AP x EOs in other leafy vegetables. [ABSTRACT FROM AUTHOR]

Perfluorinated compounds (PFCs) have potential health risk to human. In this paper, human serum samples collected from Jiading District, Shanghai aged from 23 to 87 years old (12 male and 33 female) were analyzed for 17 perfluorinated compounds (PFCs). A novel method for the elimination of background contamination of perfluorooctanoic acid (PFOA) generated from instrument by the modification of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) has also been developed and validated. The limit of detection (LOD) for all monitored PFCs range from 0.02 to 0.18 ng mL −1 . The limit of quantitation (LOQ) for PFOS and PFOA was 2.23 and 1.60 ng mL −1 , respectively, and for other PFCs it ranged from 0.04 to 0.88 ng mL −1 . Of the 17 PFCs analyzed in Shanghai serum, eleven were found. The dominating PFCs in all samples were perfluorooctanesulfonate (PFOS) and PFOA with a fraction of 49.5%, 34.2%, respectively. The median total concentration of each serum samples was 53.43 ng mL −1 with a range from

Research studies on the effects of microlitter on marine biota have become more and more frequent the last few years. However, there is strong evidence that scientific results based on microlitter analyses can be biased by contamination from air transported fibres. This study demonstrates a low cost and easy to apply methodology to minimize the background contamination and thus to increase results validity. The contamination during the gastrointestinal content analysis of 400 fishes was tested for several sample processing steps of high risk airborne contamination (e.g. dissection, stereomicroscopic analysis, and chemical digestion treatment for microlitter extraction). It was demonstrated that, using our methodology based on hermetic enclosure devices, isolating the working areas during the various processing steps, airborne contamination reduced by 95.3%. The simplicity and low cost of this methodology provide the benefit that it could be applied not only to laboratory but also to field or on board work. [ABSTRACT FROM AUTHOR]

Although significant headway has been achieved regarding method harmonisation for the analysis of microplastics, analysis and interpretation of control data has largely been overlooked. There is currently no consensus on the best method to utilise data generated from controls, and consequently many methods are arbitrarily employed. This study identified 6 commonly implemented strategies: a) No correction; b) Subtraction; c) Mean Subtraction; d) Spectral Similarity; e) Limits of detection/ limits of quantification (LOD/LOQ) or f) Statistical analysis, of which many variations are possible. Here, the 6 core methods and 45 variant methods (n = 51) thereof were used to correct a dummy dataset using control data. Most of the methods tested were too inflexible to account for the inherent variation present in microplastic data. Only 7 of the 51 methods tested (six LOD/LOQ methods and one statistical method) showed promise, removing between 96.3 % and 100 % of the contamination data from the dummy set. The remaining 44 methods resulted in deficient corrections for background contamination due to the heterogeneity of microplastics. These methods should be avoided in the future to avoid skewed results, especially in low abundance samples. Overall, LOD/LOQ methods or statistical analysis comparing means are recommended for future use in microplastic studies. [Display omitted] • Microplastic research has not reached a consensus on how to analyse control data. • We tested 51 correction methods to find if currently used methods are valid. • Only 7 of the 51 methods were found suitable for analysis of microplastic data. • LOD/LOQ methods are the most reliable for microplastics data. [ABSTRACT FROM AUTHOR]

The efficient and rapid production of a high-quality, pure beam of highly charged ions is at the heart of any radioactive ion beam facility. Whether an electron cyclotron resonance (ECR) ion source or an electron beam ion source (EBIS) is used to produce these highly charged ions, their operating characteristics will set the boundaries on the range of experiments which can be performed. In addition, time structure and duty cycle have to be considered when defining the operating parameters of the accelerator system as a whole. At Argonne National Laboratory (ANL), an ECR charge breeder was developed as part of the Californium Rare Ion Breeder Upgrade (CARIBU) program. The charge breeding efficiency and high charge state production of the source is at the forefront of ECR charge breeders, but its overall performance as part of the accelerator system is limited by pervasive background and relatively long breeding times. As such, an EBIS charge breeder has been developed and is running in an off-line configuration. It has already demonstrated good breeding efficiencies, shorter residence times, and reduced background and is scheduled to replace the ECR charge breeder in late 2015. The resultant change in duty cycle and time structure necessitates changes to the overall operation of the facility. The experiences with these breeders, as well as from several other facilities which already utilize an ECR or EBIS for charge breeding, help to define the operational characteristics of each technology – their strengths, their weaknesses, and the possible paths to improvement. [ABSTRACT FROM AUTHOR]

Determination of trace amounts of bisphenol A (BPA) may cause problems mainly related to the presence of BPA in solvents (even in LC-MS grade), laboratory vessels, and plastic equipment used for sample preparation. Variable and sometimes significant amounts of BPA present in the background cause problems in obtaining good repeatability of measurements at the ultra-trace levels. Such observations (i.e., poor repeatability of results) were made during development of the LC-MS/MS method for determination of BPA in human serum samples. The method included gradient separation of the sample's constituents. The BPA peak was present in the chromatograms not only when procedural blanks were injected but also when void injections were made. One of the possible ways to eliminate background contamination is to change the source of solvents, use a different water purification system, and introduce rigorous equipment cleaning procedures. However, despite the use of these recommended guidelines, the peak of BPA was still present in the system blank. It was observed that the intensity of the BPA peak was proportional to the time of column conditioning. It was concluded that BPA, present in the components of the mobile phase, is being enriched in the front of the separation column during its conditioning (i.e., when mobile phase elution strength was low). This paper describes effects of gradient and isocratic elution conditions on LC-MS/MS system blank. The problem of spurious BPA peak, originating from the mobile phase, was solved by replacing gradient with isocratic elution mode. The use of isocratic elution conditions with the mobile phase of relatively high elution strength (50 % of acetonitrile) allowed elimination of the peak of BPA coming from the mobile phase and significantly improved the precision of determination of BPA at low concentration levels. [ABSTRACT FROM AUTHOR]

Using information from a variety of published studies, a data set was assembled with approximately 200 surface soil samples collected from urban locations across New York State (NYS) not directly influenced by known sources of contamination. Statistical characteristics for 17 polycyclic aromatic hydrocarbon (PAH) compounds were examined and compared with draft NYS soil cleanup objectives that had been developed using risk-based and rural background considerations. For the carcinogenic PAH compounds, approximately 12-40% of samples exceeded cleanup objectives proposed for residential land use, but few samples exceeded the less stringent standards proposed for commercial and industrial properties. Qualitative comparisons with a recent study of NYS rural soils indicated substantial differences in background PAH levels between urban and rural locations. These findings motivate further research into the best manner for incorporating background information into soil cleanup objectives for urban areas. [ABSTRACT FROM AUTHOR]

Data on E. coli incidence in drinking water samples have been evaluated for 4 European countries. Within the EC project MicroRisk, large volume sampling was done in the United Kingdom (with disinfectant residual), the Netherlands (mainly without disinfectant residual) and Germany (without disinfectant residual). No E. coli were found and very low background concentrations (< 10-4 per L) were calculated. Furthermore, data of 280,000 water samples collected in France (with disinfectant residual), the Netherlands and Germany (both with and without disinfectant residual) were evaluated for E. coli incidence. In total, similar results were obtained for Germany and the Netherlands. In France, significantly higher incidences occurred as more small rural supply systems were included. The detailed data evaluation revealed a slight increase of mean E. coli concentrations during distribution in Germany and the Netherlands, for both disinfected and non-disinfected supply zones. This suggests that, if technical measures are taken to avoid contamination during distribution, non-disinfected supply zones can be regarded as being as safe as disinfected supply zones. Furthermore, the indicator principle of E. coli for faecal contaminations is valid in non-disinfected supply zones. In chlorinated systems, on-line-monitoring of chlorine residuals represents a good means to detect ingress of organic material. [ABSTRACT FROM AUTHOR]

Research conducted so far on the presence of microplastics in the environment shows that these items are ubiquitous pollutants and therefore constitute an inherent part of our lives. This constitutes a significant problem in many aspects, and one of them is the correct identification of microplastics in environmental samples. Environmental samples can be easily contaminated by plastic microparticles from other sources if proper precautions are not taken during sampling and analysis. The consequence of not taking this cross-contamination into account when analysing the results may be their significant overestimation. This review aims to draw attention to the problem of cross-contamination that accompanies the collection and analysis of samples for the presence of microplastics, and to discuss this issue in a comprehensive manner. The article indicates potential sources of cross-contamination, lists the mitigation methods, and describes the possibilities of assessing this type of contamination. Moreover, the review examines how cross-contamination control appears in practice, based on the available literature data. [ABSTRACT FROM AUTHOR]

Hormesis is an intriguing phenomenon characterized by low-dose stimulation and high-dose inhibition. The hormetic phenomena have been frequently reported in the past decades, but the researches on the biphasic responses of soil enzymes are still limited. The main objective of this study is to explore dose response of alkaline phosphatase (ALP) to Cd (0, 0.003, 0.03, 0.3, 3.0 and 30 mg/kg) in the presence of different levels of background Cd contamination (bulk soil with no added Cd, BS; low background Cd, LB; medium background Cd, MB; and high background Cd, HB). ALP activity at 0.003–0.3 mg Cd/kg was 13–39% higher than that of the control (0 mg Cd/kg) for HB after 7 d. Similarly, the enzyme activities at 0.003–0.03 mg Cd/kg were 2–25% and 14–17% higher than those of the controls for MB and HB after 60 d. After 90 d, ALP activities at 0.3–3.0 mg Cd/kg increased by 11–17% for LB. The dose-response curves had the shape of an inverted U, showing biphasic responses at days 7 (HB), 60 (MB and HB) and 90 (LB). After 60 days of exposure, total operational taxonomic units (OTU) numbers and unique species exposed to Cd stress displayed hormetic-response curve for MB. The relative abundances of Agrobacterium , Salinimicrobiums , Bacilllus , and Oceanobacillus displayed significantly positive correlations with ALP activity. This suggested that bacterial communities potentially contribute to ALP's hormesis. This study further provides new insights into the ecological mechanisms of pollutant-induced hormesis, and substantially contributes to the ecological risk assessment of Cd pollution. Unlabelled Image • Cd can induce biphasic responses of alkaline phosphatase (ALP). • Biphasic response occurs at low background doses with extended exposure time. • Biphasic response originates from quorum sensing of soil bacterial populations. • Biphasic response should be incorporated into the processes of Cd risk assessment. [ABSTRACT FROM AUTHOR]

There is a growing understanding of how oil pollution can affect aquatic ecosystems, including physical and chemical effects. One of the biggest challenges with detecting the effects of oil-related contaminants on biota from resource development is understanding the background levels and potential effects of the exposure of biota to contaminants from various natural and anthropogenic sources prior to large scale oil and gas operations. Seabirds are effective indicators of pollution, and can be useful for tracking oil-related contaminants in the marine environment. We sampled four seabird species (black guillemot, Cepphus grylle ; thick-billed murre, Uria lomvia ; black-legged kittiwake, Rissa tridactyla ; and northern fulmar, Fulmarus glacialis) in the Baffin Bay-Davis Strait region of the Northwest Atlantic and Arctic oceans, an area where natural oil and gas seeps are present but lacking any large-scale oil and gas projects. We found detectable levels of PACs and several trace elements in all species examined. Alkylated PAC levels were higher than parent compounds in all four seabird species examined, with fulmars and murres having the highest levels detected; mean hepatic concentrations of ∑ 16 PAC were 99.05, 46.42, 12.78 and 9.57 ng/g lw, respectively, for guillemots, murres, fulmars and kittiwakes. Overall, PAC concentrations in the seabird species examined were similar to PAC concentrations measured in other bird species in regions with more industrialization. These findings provide data which can be used to assess the current oil-related contaminant exposure of biota in the region. As well, they provide background levels for the region at a time when shipping activity is relatively low, which can used for future comparisons following expected increases in shipping and oil and gas activities in the region. Unlabelled Image • Petrogenic and pyrogenic polycyclic aromatic compounds (PAC) were detected in 4 seabird species. • Natural oil and gas seeps offshore of Baffin Island contribute to seabird PAC concentrations. • Concentrations and composition of PACs and trace elements significantly differed between the species. • The species that fed most coastally had higher levels of pyrogenic PACs compared to offshore feeders. • Concentrations of PACs in the four species were similar to levels detected in other industrialized areas. [ABSTRACT FROM AUTHOR]

Murine models of Salmonella enterica serovar Typhimurium infection are one of the commonest tools to study host-pathogen interactions during bacterial infections. Critically, the outcome of S . Typhimurium infection is impacted by the genetic background of the mouse strain used, with macrophages from C57BL/6 and BALB/c mice lacking the capacity to control intracellular bacterial replication. For this reason, the use of congenic strains, which mix the genetic backgrounds of naturally protected mouse strains with those of susceptible strains, has the capacity to significantly alter results and interpretation of S . Typhimurium infection studies. Here, we describe how macrophage knockout cell lines generated by CRISPR/Cas9 gene editing can help determine the contribution of background contaminations in the phenotypes of primary macrophages from congenic mice, on the outcome of S . Typhimurium infection studies. Our own experience illustrates how the CRISPR/Cas9 technology can be used to complement pre-existing knockout models, and shows that there is great merit in performing concurrent studies with both genetic models, to exclude unanticipated side-effects on host-pathogen interactions.