Methane emissions from trees planted on a closed landfill site.

Trees have morphological adaptations that allow methane (CH4) generated below ground to bypass oxidation in aerobic surface soils. This natural phenomenon however has not been measured in a landfill context where planted trees may alter the composition and magnitude of CH4 fluxes from the surface. To address this research gap, we measured tree stem and soil greenhouse gas (GHG) emissions (CH4 and CO2) from a closed UK landfill and comparable natural site, using an off-axis integrated cavity output spectroscopy analyser and flux chambers. Analyses showed average CH4 stem fluxes from the landfill and non-landfill sites were 31.8 ± 24.4 µg m-2 h-1 and -0.3 ± 0.2 µg m-2 h-1, respectively. The landfill site showed seasonal patterns in CH4 and CO2 stem emissions, but no significant patterns were observed in CH4 and CO2 fluxes at different stem heights or between tree species. Tree stem emissions accounted for 39% of the total CH4 surface flux (7% of the CO2); a previously unknown contribution that should be included in future carbon assessments.

Scoping studies to establish the capability and utility of a real-time bioaerosol sensor to characterise emissions from environmental sources.

A novel dual excitation wavelength based bioaerosol sensor with multiple fluorescence bands called Spectral Intensity Bioaerosol Sensor (SIBS) has been assessed across five contrasting outdoor environments. The mean concentrations of total and fluorescent particles across the sites were highly variable being the highest at the agricultural farm (2.6 cm-3 and 0.48 cm-3, respectively) and the composting site (2.32 cm-3 and 0.46 cm-3, respectively) and the lowest at the dairy farm (1.03 cm-3 and 0.24 cm-3, respectively) and the sewage treatment works (1.03 cm-3 and 0.25 cm-3, respectively). In contrast, the number-weighted fluorescent fraction was lowest at the agricultural site (0.18) in comparison to the other sites indicating high variability in nature and magnitude of emissions from environmental sources. The fluorescence emissions data demonstrated that the spectra at different sites were multimodal with intensity differences largely at wavelengths located in secondary emission peaks for λex 280 and λex 370. This finding suggests differences in the molecular composition of emissions at these sites which can help to identify distinct fluorescence signature of different environmental sources. Overall this study demonstrated that SIBS provides additional spectral information compared to existing instruments and capability to resolve spectrally integrated signals from relevant biological fluorophores could improve selectivity and thus enhance discrimination and classification strategies for real-time characterisation of bioaerosols from environmental sources. However, detailed lab-based measurements in conjunction with real-world studies and improved numerical methods are required to optimise and validate these highly resolved spectral signatures with respect to the diverse atmospherically relevant biological fluorophores.

A study of the potential release of bioaerosols from containers as a result of reduced frequency residual waste collections.

Microorganisms have the potential to grow within waste containers if waste is stored for longer periods as a result of an extended residual waste collection cycle. Release of microorganisms as bioaerosols during waste collection and processing may be an occupational risk to workers within the industry. There may be many constituents of the bioaerosol that may be of concern, however, there are currently only workplace exposure limits proposed for endotoxin (90EUm-3). A field-scale trial was established to determine the concentration of mesophilic bacteria, Gram-negative bacteria, Listeria monocytogenes, thermotolerant fungi, Aspergillus fumigatus, and endotoxin and (1→3)-ß-d-glucan in air within bins containing either bagged or loose residual waste, in warm (23°C) or cold (7°C) conditions, to simulate an extended collection cycle. Fresh waste was added during the first four weeks, with an additional 'missed collection' phase of a further four weeks where no more waste was added. A second trial examined the microbiological components of bioaerosols associated with 'tipping' the bins, simulating the moment when bins are emptied into waste collection vehicles. The majority of mesophilic bacteria, fungi and A. fumigatus concentrations were recorded when fresh material was added to the bins, with only mesophilic bacteria recorded up to week 6 during the 'missed collection' phase. (1→3)-ß-D-glucan concentrations were variable throughout the first trial, (geometric mean range 0.4-13.8ngm-3). Perhaps the bioaerosol component of most interest was endotoxin (geometric mean range 0.52-1288EUm-3). Elevated endotoxin concentrations were recorded during the 'missed collection' phase of the extended collection cycle and during 'tipping'. This data demonstrates significant concentrations of bioaerosols and particularly endotoxin can be generated during prolonged residual waste storage and collection. As endotoxin is a bioaerosol component of concern it can be concluded there is the potential for workplace exposure hence identifying key areas for risk assessment.

Organic dust exposure and work-related effects among recycling workers.

OBJECTIVE: Organic dust exposure and work-related symptoms and effects among household waste recycling workers in Materials Recovery Facilities (MRFs) are a concern. MRFs are a central operation where source-segregated, dry, recyclable materials (paper, plastics, cans, etc.) are sorted, mechanically or manually, to market specifications for processing into secondary materials. METHODS: One hundred and fifty-nine MRF workers (91%) from nine MRFs participated. Measurements of airborne total dust, endotoxin, (1-->3)-beta-D-glucan, and a questionnaire survey were carried out. Blood data was restricted to MRFs 3, 6, and 9 (45 workers). Blood sampling investigated differential cell counts, erythrocyte sedimentation rate (ESR), and immunoglobulin (Ig)E. RESULTS: Workers exposed to higher amounts of endotoxin and (1-->3)-beta-D-glucan had an increased risk for respiratory symptoms as compared to those with lower exposure. Stomach problems was associated to higher (1-->3)-beta-D-glucan exposure. MRF 3 had a higher (1-->3)-beta-d-glucan exposure compared to 6 and 9, and respiratory symptoms, unusual tiredness, and vomiting were reported more often in MRF 3. Monocyte numbers and ESR were significantly decreased in MRF 3 compared to MRF 6 and 9, but all measured values were within normal ranges. CONCLUSIONS: The results suggest that MRF workers exposed to higher levels of endotoxin and (1-->3)-beta-D-glucan at their work sites exhibit various work-related symptoms, and that the longer a worker is in the MRF environment, the more likely he is to become affected by various respiratory and gastrointestinal symptoms.