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Adolescence is a critical stage in the development of an individual's physical activity (PA) habits and preferences. Adolescents' perceptions of PA can influence their motivation to engage in PA and, consequently, their overall level of PA. Thus, our primary aim was to investigate whether Czech adolescents misperceive their peers' PA. Our dataset comprised cross-sectional data on 1289 adolescents aged 11-15 years. PA was measured using self-reported items used in the HBSC study. To describe the gender and school grade differences in VPA, independent samples T, ANOVA, Mann-Whitney U, and Kruskal-Wallis H tests were performed. To analyze the effect of gender, school grade, school, and participants' own PA on the underestimation of PA, binomial regression models were used. Our study points out that there is a discrepancy between self-perceived levels of PA and the perceived descriptive norms of peers' PA. Adolescents underestimate the prevalence of sufficient PA, and thus perceived descriptive norms in PA as being worse than levels of own PA. These findings indicate room for targeted interventions based on social-norms-based approaches to increase the PA of adolescents or at least strengthen their actual positive behavior.
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Background/objective: The holistic concept of physical literacy (PL) embraces different person-centered qualities (physical, cognitive, affective/psychological) necessary to lead physically active lifestyles. PL has recently gained increasing attention globally and Europe is no exception. However, scientific endeavors summarizing the current state of PL in Europe are lacking. Therefore, the goal of this study was to comprehensively assess and compare the implementation of PL in research, policy, and practice across the continent. Methods: We assembled a panel of experts representing 25 European countries. Employing a complementary mixed-methods design, the experts first prepared reviews about the current state of PL in their countries (categories: research, practice/policy). The reviews underwent comparative document analysis, ensuring a transnational four-eyes principle. For re-validation purposes, the representatives completed a quantitative survey with questions reflecting the inductive themes from the document analysis. Results: The document analysis resulted in ten disjunct themes (related to "concept", "research", "practice/policy", "future/prospect") and yielded a heterogenous PL situation in Europe. The implementation state was strongly linked to conceptual discussions (e.g., existence of competing approaches), linguistic issues (e.g., translations), and country-specific traditions. Despite growing scholarly attention, PL hesitantly permeates practice and policy in most countries. Nevertheless, the experts largely anticipate increasing popularity of PL for the future. Conclusion: Despite the heterogeneous situation across Europe, the analysis has uncovered similarities among the countries, such as the presence of established yet not identical concepts. Research should intensify academic activities (conceptual-linguistic elaborations, empirical work) before PL may gain further access into practical and political spheres in the long term.
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Background/Objective: The second edition of the Czech Republic's Report Card on Physical Activity for Children and Youth was released in 2022. This paper describes the development of the Report Card and presents a comprehensive summary of the main findings. Methods: The multi-level search strategy was developed by the national expert panel to identify the available sources that provide data related to the physical activity of Czech children and adolescents. The data were used to assign grades to ten core and two additional indicators. Results: A total of 28 sources provided data that allowed grades to be assigned to 11 out of the 12 indicators. Grade B was assigned to six indicators (School: B+, Community and Environment: B, Organized Sport and Physical Activity: B-, Active Transportation: B-, Family and Peers: B-, Sleep: B-), grade C to three indicators (Overall Physical Activity: C+, Active Play: C, Physical Literacy: C), and grade D to two indicators (Government: D+, Sedentary Behaviors: D). No grade for the "Physical Fitness" indicator could be assigned due to a lack of data collected in the reference period 2018-2019. Conclusions: Although the family, school, and built environment provided a variety of opportunities to be physically active, a high proportion of children and adolescents did not meet the current physical activity guideline and were exposed to excessive sedentary behavior. A multisectoral and multidisciplinary response is required to reduce the health and economic burden of physical inactivity and excessive sedentary behavior among Czech children and adolescents.
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Drug efficacy determined in preclinical research is difficult to transfer to clinical practice. This is mainly due to the use of oversimplified models omitting the effect of the tumor microenvironment and the presence of various cell types participating in the formation of tumors in vivo. In this study, we used robust three-dimensional models including spheroids grown from colon cancer cell lines and organotypic cultures prepared from the colorectal carcinoma tissue to test novel therapeutic strategies. We developed a multi-modal approach combining brightfield and fluorescence microscopy for evaluating drug effects on organotypic cultures. Combined treatment with 5-fluorouracil and disulfiram/copper efficiently eliminated cancer cells in these 3D models. Moreover, disulfiram/copper down-regulated the expression of markers associated with 5-fluorouracil resistance, such as thymidylate synthase and CD133/CD44. Thus, we propose combined therapy of 5-fluorouracil and disulfiram/copper for further testing as a treatment for colorectal carcinoma. In addition, we show that organotypic cultures are suitable models for anti-cancer drug testing.
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Neoplasias Colorretais , Fluoruracila , Linhagem Celular Tumoral , Neoplasias Colorretais/tratamento farmacológico , Neoplasias Colorretais/patologia , Cobre/farmacologia , Cobre/uso terapêutico , Dissulfiram/farmacologia , Fluoruracila/farmacologia , Fluoruracila/uso terapêutico , Humanos , Esferoides Celulares/patologia , Microambiente TumoralRESUMO
The role of supportive environments on health, wellbeing, and longevity has been widely recognized. However, there is no strong empirical evidence on the association between health literacy (HL) as a particular health-related competence and neighbourhoods. Therefore, the aim of the study was to assess the association between the features of neighbourhoods and the level of HL competencies of young people from three countries (Czech Republic, Poland, Slovakia). Self-reported data from an international sample of 11,521 students aged 13-15 years participating in the Health Behaviour in School-aged Children Study (HBSC) in the year 2018 were included in the analyses. The level of HL shows a strong positive relationship with family wealth, and a significant relationship is maintained in all studied countries. Both social and structural features of neighbourhoods turned out to have an impact on students' HL. However, HL is most clearly explained by the school environment. This study confirms the school effect on higher levels of HL competences in adolescents. This indicates the need to invest in schools located in less affluent areas to generally improve the level of education, implement modern health education combined with HL, and strengthen the social and health competencies of students.
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Letramento em Saúde , Adolescente , Saúde do Adolescente , Criança , República Tcheca , Humanos , Polônia , Instituições Acadêmicas , EslováquiaRESUMO
Pesticides pose a serious risk to ecosystems. In this study, we used European Food Safety Authority methods, such as risk quotient (RQ) and toxicity exposure ratios (TER), to assess the potential ecological risks of 15 pesticide residues detected in agricultural soils in the Gaidahawa Rural Municipality of Nepal. The mean and maximum concentrations of the detected pesticide residues in the soil were used for risk characterization related to soil organisms. RQmean, TERmean and RQmaximum, TERmaximum were used to determine general and the worst-case scenarios, respectively. Of all the detected pesticides in soils, the no observed effect concentration (NOEC) for 27% of the pesticides was not available in literature for the tested soil organisms and their TER and RQ could not be calculated. RQ threshold value of ≥1 indicates high risk for organisms. Similarly, TER threshold value of ≥5, which is acceptable trigger point value for chronic exposure, indicates an acceptable risk. The results showed that the worst-case scenario (RQmaximum) indicated a high risk for soil organisms from chlorpyrifos [RQmaximum > 9 at depths (cm) of 0-5, 15-20 and 35-40 soil layer]; imidacloprid (1.78 in the 35-40 cm soil layer) and profenofos (3.37 in the 0-5 cm and 1.09 in the 35-40 cm soil layer). Likewise, for all the soil depths, the calculated TER for both the general and worst-case scenarios for chlorpyrifos ranged from 0.37 to 3.22, indicating chronic toxicity to F. candida. Furthermore, the risk of organophosphate pesticides for soil organisms in the sampling sites was mainly due to chlorpyrifos, except for two study sites where the risk was from profenofos. Ecological risk assessment (EcoRA) of the pesticide use in the study area indicated that the EFSA soil organisms were at risk at some of the localities where farmers practiced conventional farming.
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Resíduos de Praguicidas , Praguicidas , Poluentes do Solo , Ecossistema , Nepal , Resíduos de Praguicidas/análise , Resíduos de Praguicidas/toxicidade , Praguicidas/análise , Praguicidas/toxicidade , Medição de Risco , Solo , Poluentes do Solo/análise , Poluentes do Solo/toxicidade , VerdurasRESUMO
The current social, health, and educational changes in society require an adequate response in school-based physical activity (PA), including physical education (PE) lessons. The objective of this study was to identify the real average step counts of Czech and Polish adolescents during PE lessons, and propose recommendations for improving PE programs. This research was carried out in 143 Czech and 99 Polish schools. In the research, a total of 4911 adolescents aged 12-18 years were analyzed as part of teaching practice and 1827 in the context of habitual school practice. Steps were monitored using pedometers. The average step count per PE lesson was 2390 in Czech and Polish boys, while girls achieved 1851 steps. In both countries, boys were subject to greater physical strain in PE lessons compared to girls, both in teaching practice (F(4088,3) = 154.49, p < 0.001, ηp2 = 0.102) and school practice (F(1552,3) = 70.66, p < 0.001, ηp2 = 0.103). Therefore, the priority in PE lessons is to increase the amount of PA for girls, achieve the objectives of PE during PA, and use wearables to improve awareness of PA and improve physical literacy, as well as to support hybrid and online PE as a complement to traditional PE.
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Exercício Físico , Educação Física e Treinamento , Actigrafia , Adolescente , Criança , Feminino , Humanos , Masculino , Polônia , Instituições AcadêmicasRESUMO
To achieve a healthy lifestyle, adolescents must be physically active and meet physical activity (PA) guidelines. One of the most natural ways of increasing the amount of PA is active commuting (AC) to school. Recent reviews suggest that peer norms have the potential to shape PA during adolescence in particular. Thus, our primary aim was to investigate whether Czech adolescents misperceive their peers' AC behaviors and attitudes towards AC. Our dataset comprised cross-sectional data on 1586 adolescents aged 11-15 years. Basic descriptive statistics, chi-square tests, and correlation analyses were used to analyze the data. Regarding traveling to school, 68% of the Czech adolescents in this study are daily active commuters (walking, cycling, or riding a scooter or skateboard). Less than half of the respondents believed that most of their classmates were commuting to school actively almost daily. The students who believed that most of their classmates commuted to school actively had significantly higher chances of being regular active commuters themselves. The results showed that most of the Czech adolescents misperceived the AC norms of their peers. Thus, there could be potential in using a social norms approach aimed at increasing the level of AC in Czech adolescents through targeted interventions.
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Ciclismo , Meios de Transporte , Adolescente , Atitude Frente a Saúde , Criança , Estudos Transversais , República Tcheca , Humanos , Instituições Acadêmicas , CaminhadaRESUMO
BACKGROUND: Regular physical activity and doing well in school are important for growing adolescents. In this study, the associations between physical activity and perceived school performance (PSP) are examined together. METHODS: Young adolescents from 42 countries (n = 193,949) in Europe and Canada were examined for associations between self-reported moderate to vigorous physical activity (MVPA) and PSP. Multinominal analyses were conducted with 0 to 2 days of MVPA and below average PSP as reference categories. Adjusted odds ratios and 95% confidence intervals were reported for pooled data and individual countries after controlling for family affluence scale. RESULTS: Girls had better PSP than boys, yet more boys participated in daily MVPA than girls. The associations between PSP and MVPA were inverted U shaped. The strongest association for very good PSP was among young adolescents who reported 5 to 6 days MVPA (odds ratios = 2.3; 95% confidence interval, 2.1-2.4) after controlling for family affluence scale. CONCLUSIONS: Young adolescents with average or better PSP took part in at least 3 days of MVPA in a week, suggesting that participating in some MVPA was positively associated with PSP. More days of MVPA in a week, especially for young adolescents with below average PSP, would be beneficial for health and school performance.
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Exercício Físico , Instituições Acadêmicas , Adolescente , Criança , Estudos Transversais , Feminino , Comportamentos Relacionados com a Saúde , Humanos , Masculino , AutorrelatoRESUMO
Currently used pesticides (CUPs) represent one of the largest intentional inputs of potentially hazardous compounds into agricultural soils. Subsequently, pesticide residues (PRs) and their transformation products (TPs) persist in agricultural soils, occurring in diverse mixtures of compounds in various concentrations. In this study, measured environmental concentrations (MECs) of CUP residues and TPs, originated from previous growing seasons in agricultural soils of the Czech Republic, were used to characterize the environmental risk for agroecosystems. Toxicity exposure ratios (TERs) were calculated using predicted no-effect concentrations (PNECs) and MECs in order to identify single pesticide residues risk to in-soil invertebrates and microorganisms. Ecological risk assessment (ERA) for the mixtures of pesticide residues at each monitored site was assessed using a risk quotient (RQ) method and considering concentration addition among components in the mixtures. The compilation of ecotoxicity data to derived PNECs for in-soil organisms clearly showed data gaps mainly for triazine and chloroacetanilide TPs. In addition, chronic toxicity data for in-soil invertebrates at different trophic levels are not available for 30% of monitored CUPs. The ERA revealed that pesticide residues in soil pose a risk at 35% of the sites (RQâ¯≥â¯1). Among measured pesticides, epoxiconazole, atrazine-2-hydroxy, carbendazim, dimoxystrobin, terbuthylazine and difenoconazole were the main contributors to the overall pesticide mixture toxicity. The measured levels of epoxiconazole together with the frequent presence in soils represent a risk for the agroecosystems. Further assessment of higher tiers of ERA should be considered and prioritized in the pesticides risk management.
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Resíduos de Praguicidas/química , Praguicidas/química , Solo/química , República Tcheca , Resíduos de Praguicidas/análise , Praguicidas/análise , Medição de RiscoRESUMO
The dissipation, partitioning dynamics and biouptake was measured for selected hazardous current-used pesticides (conazole fungicides: epoxiconazole, flusilazole, tebuconazole; prochloraz, chlorpyrifos, pendimethalin) and for a transformation product (2-hydroxyatrazine) in agricultural soil and quartz sand as representatives of a real and a worst-case scenario. Dissipation, uptake to Lactuca sativa and the freely dissolved concentration along with the organic carbon-normalized sorption coefficients (Koc) were determined on days 12, 40, and 90 following the application of compounds at three fortification levels (0.1-1.0-10â¯mg/kg). Conazole fungicides showed similar dissipation patterns and were more persistent in soil than prochloraz, chlorpyrifos and pendimethalin. 2-Hydroxyatrazine showed a concentration-depended decrease in persistency in soil. Lettuce roots were shown to accumulate higher amounts than shoots where the extent of root uptake was driven by compound partitioning. This was evidenced by the ability of freely dissolved concentration (Cfree) to reliably (r2â¯=â¯0.94) predict root uptake. Concentration in leaves did not exceed the maximum residue levels (MRLs) for lettuce, which was likely given by the low root-to-shoot translocation factors (TFs) of the tested compounds varying between 0.007 and 0.14. Koc values were in the range of literature values. Sorption to soil was higher than to sand for all compounds, yet following the Koc dynamics compounds did not appear to be sequestered in soil with increasing residence time. From these results, it follows that the tested compounds may persist in soil but since they did not accumulate in lettuce above MRLs, contamination of the food web is unlikely.
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Atrazina/análogos & derivados , Lactuca/metabolismo , Praguicidas/farmacocinética , Poluentes do Solo/análise , Atrazina/análise , Atrazina/farmacocinética , Fungicidas Industriais/análise , Fungicidas Industriais/farmacocinética , Praguicidas/análise , Folhas de Planta/metabolismo , Raízes de Plantas/metabolismoRESUMO
Although large amounts of pesticides are used annually and a majority enters the soil to form short- or long-term residues, extensive soil surveys for currently used pesticides (CUPs) are scarce. To determine the status of CUPs' occurrence in arable land in Central Europe, 51 CUPs and 9 transformation products (TPs) were analysed in 75 arable soils in the Czech Republic (CR) several months after the last pesticide application. Moreover, two banned triazines (simazine and atrazine) and their TPs were analysed because of their frequent detection in CR waters. Multi-residue pesticide analysis on LC-MS/MS after soil QuEChERS extraction was used. The soils contained multiple pesticide residues frequently (e.g. 51% soils with ≥5 pesticides). The levels were also noticeable (e.g. 36% soils with ≥3 pesticides exceeding the threshold of 0.01mg/kg). After triazine herbicides (89% soils), conazole fungicides showed the second most frequent occurrence (73% soils) and also high levels (53% soils with total conazoles above 0.01mg/kg). Frequent occurrence was found also for chloroacetanilide TPs (25% of soils), fenpropidin (20%) and diflufenican (17%). With the exception of triazines' negative correlation to soil pH, no clear relationships were found between pesticide occurrence and soil properties. Association of simazine TPs with terbuthylazine and its target crops proved the frequent residues of this banned compound originate from terbuthylazine impurities. In contrast, frequent atrazine-2-hydroxy residue is probably a legacy of high atrazine usage in the past. The occurrence and levels of compounds were closely associated with their solubility, hydrophobicity and half-life. The results showed links to CR water-monitoring findings. This study represents the first extensive survey of multiple pesticide residues in Central European arable soils, including an insight into their relationships to site and pesticide properties.
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Although respiratory muscle functions can influence swimming performance, respiratory muscle training (RMT) is not routinely used for improving fin-swimmers´ performance. The aim of our study was to verify the benefit of a one month of RMT in young fin-swimmers. We assessed the effect of this training on respiratory muscles and on maximal underwater swimming distance. 28 fin-swimmers were randomly divided into an experimental group (EG) and a control group (CG). The study finished with 20 fin-swimmers (EG: n = 12; average age 12.0; weight 47.4 kg; height 1.58 m; CG: n = 8; age 11.5; weight 49.6 kg; height 1.53 m). Both group performed regular swimming training, during which the EG used Threshold PEP (positive expiratory pressure) and IMT (inspiratory muscle trainer) for RMT for one month. After one-month washout period, the CG also performed RMT. RMT showed significant improvement of inspiratory muscles in both groups (Z = <1.96; 2.59>; p < 0.05). Significant improvement was observed also in apnoea (AP) max (ZCG = 2.03; p < 0.05; ZEG=2.93; p < 0.01). A long-term effect was observed in the respiratory muscle strength and AP max in the EG (ZEG = 2.52; p < 0.05). RMT in fin-swimmers improves both respiratory muscle strength and the performance in AP max.
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OBJECTIVE: School is a place where students spend most of their daytime hours. Previous studies indicate that the class climate significantly affects students in both positive and negative ways. The aim of our study is to describe the trends in the psychosocial school environment based on four surveyed years in the Czech Republic. METHODS: The trends in perception of school were assessed by the standardised self-reported HBSC questionnaire from data collected in 2002, 2006, 2010, and 2014. The overall sample included 8,530 girls and 8,087 boys. Data was analysed separately by gender and three age categories 11, 13, and 15 years. Trends were calculated using descriptive categories and percentages. To identify factors influencing school likeness we used binominal logistic regression. RESULTS: Results showed that school satisfaction declines with age both in boys and girls in each of four surveyed periods. Students who do not feel a high level of support from the teacher are more prone to negative perceptions of school. School duties in both genders were perceived to be greater and more stressful in 2014 than in 2002. CONCLUSIONS: Interventions to support the perception of psychosocial school environment via the educational system should, therefore, take the aforementioned variation into account.
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Comportamentos Relacionados com a Saúde , Inquéritos Epidemiológicos , Instituições Acadêmicas , Meio Social , Estudantes/psicologia , Adolescente , Criança , Estudos Transversais , República Tcheca , Feminino , Humanos , Estudos Longitudinais , Masculino , Satisfação Pessoal , Apoio SocialRESUMO
OBJECTIVE: The aim of the article is to examine trends in tobacco consumption among the Czech school-age population. METHODS: For the analysis, data from the Czech Health Behaviour in School-aged Children project, conducted between 1994 and 2014 were used. Trends in tobacco smoking were determined separately for boys and girls, applying the binary logistic regression with survey period as an independent variable for the smoking status. RESULTS: The analysis showed that there have been significant changes in adolescent tobacco smoking for the recent 20 years. While the share of current school-aged smokers was continuously increasing since the mid-1990s, the trend reached its peak in the mid-2000s. CONCLUSION: In recent years, the prevalence of adolescent smokers has significantly declined in the Czech Republic. Despite this recent decline, adolescent smoking remains a major challenge for the national health policy.
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Comportamentos Relacionados com a Saúde , Inquéritos Epidemiológicos , Fumar/epidemiologia , Adolescente , Criança , Estudos Transversais , República Tcheca/epidemiologia , Feminino , Humanos , Estudos Longitudinais , Masculino , PrevalênciaRESUMO
OBJECTIVE: Good parent-child communication is associated with adolescent well-being. The aim of the present study was to report time trends in parent-adolescent communication in biological and stepfamilies in the Czech Republic between 2002 and 2014 and to assess gender and age differences. METHODS: The research sample consisted of 16,160 adolescents aged 11, 13, and 15 years (48.1% of boys) who participated in the 2002, 2006, 2010 and 2014 surveys within the Health Behaviour in School-aged Children (HBSC) study in the Czech Republic. The trends in family communication were evaluated using logistic regression. RESULTS: Compared with 2002, a significant increase in the ease of communication with biological parents was observed in 2014. On the other hand, the adolescents' perception of communication with stepparents did not change in this period. Compared with the girls, a higher rate of boys reported communication with their father or stepfather as being easy throughout the study period. The ease of talking to biological parents decreased with age. CONCLUSION: The growing positive trend demonstrated an improvement in communication in intact families at the beginning of the 21st century, while communication with stepparents remained unchanged from 2002 to 2014. The increase in rates of ease of communication with biological fathers was reported by both genders. However, the ease of talking to biological mothers grew mainly among boys.
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Comunicação , Comportamentos Relacionados com a Saúde , Inquéritos Epidemiológicos , Relações Pais-Filho , Adolescente , Criança , Estudos Transversais , República Tcheca , Feminino , Humanos , Estudos Longitudinais , MasculinoRESUMO
OBJECTIVE: Brushing one's teeth twice a day is the main self-care method to prevent the most prevalent non-communicable diseases. The aim of the study is to describe the trends in brushing teeth in 11-, 13-, and 15-year-old Czech children between 1994 and 2014. METHODS: One question about oral health from the HBSC study protocol was used in the six surveys (1994, 1998, 2002, 2006, 2010, and 2014). Altogether, 21,170 answers from boys and girls were analyzed using statistical description and binominal logistic regression. RESULTS: The findings showed that the prevalence of brushing their teeth more than once a day increased throughout the twenty years, more so in boys, but a preventive programme is still needed to educate the 21-38% of those who brush their teeth less than twice a day. CONCLUSION: Although the recommended frequency of brushing their teeth has increased among Czech school-aged children, it still lags far behind the recommended twice-a-day regularity, especially among boys.
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Comportamentos Relacionados com a Saúde , Inquéritos Epidemiológicos , Escovação Dentária/tendências , Adolescente , Criança , Estudos Transversais , República Tcheca , Feminino , Humanos , Estudos Longitudinais , MasculinoRESUMO
A fast, selective, and sensitive method for the determination of three monosaccharide anhydrides (galactosan, mannosan, levoglucosan), based on hydrophilic interaction chromatography and Fourier transform mass spectrometry, was successfully developed. The simple experimental stationary phase and mass spectrometry performance screening allowed the selection of the best available chromatographic and mass spectrometry conditions. Thus, the chromatographic separation was performed on a highly selective stationary phase containing a zwitterionic phosphorylcholine group and the monosaccharide anhydrides were detected as [M+HCOO]- adduct in the negative mode. The method showed accuracy in the range of 84-111 and 89-102% with interbatch precision expressed as relative standard deviations of 5.6-15.4 and 5.0-9.0% for the aerosol extract and snow samples, respectively. The limit of quantification in absolute values ranged from 10 to 30 pg, the limit of quantification, expressed as concentration, ranged was 0.3-0.9 ng/m3 for aerosol and 10-20 ng/mL for snow samples. The method was successfully applied for the determination of monosaccharide anhydrides in aerosol and snow samples.
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Sludge coming from remediation of groundwater contaminated by industry is usually managed as hazardous waste despite it might be considered for further processing as a source of nutrients. The ecotoxicity of phosphorus rich sludge contaminated with arsenic was evaluated after mixing with soil and cultivation with Sinapis alba, and supplementation into composting and vermicomposting processes. The Enchytraeus crypticus and Folsomia candida reproduction tests and the Lactuca sativa root growth test were used. Invertebrate bioassays reacted sensitively to arsenic presence in soil-sludge mixtures. The root elongation of L. sativa was not sensitive and showed variable results. In general, the relationship between invertebrate tests results and arsenic mobile concentration was indicated in majority endpoints. Nevertheless, significant portion of the results still cannot be satisfactorily explained by As chemistry data. Composted and vermicomposted sludge mixtures showed surprisingly high toxicity on all three tested organisms despite the decrease in arsenic mobility, probably due to toxic metabolites of bacteria and earthworms produced during these processes. The results from the study indicated the inability of chemical methods to predict the effects of complex mixtures on living organisms with respect to ecotoxicity bioassays.