Predicting Aspergillus fumigatus exposure from composting facilities using a dispersion model: A conditional calibration and validation.

Bioaerosols are released in elevated quantities from composting facilities and are associated with negative health effects, although dose-response relationships are unclear. Exposure levels are difficult to quantify as established sampling methods are costly, time-consuming and current data provide limited temporal and spatial information. Confidence in dispersion model outputs in this context would be advantageous to provide a more detailed exposure assessment. We present the calibration and validation of a recognised atmospheric dispersion model (ADMS) for bioaerosol exposure assessments. The model was calibrated by a trial and error optimisation of observed Aspergillus fumigatus concentrations at different locations around a composting site. Validation was performed using a second dataset of measured concentrations for a different site. The best fit between modelled and measured data was achieved when emissions were represented as a single area source, with a temperature of 29°C. Predicted bioaerosol concentrations were within an order of magnitude of measured values (1000-10,000CFU/m3) at the validation site, once minor adjustments were made to reflect local differences between the sites (r2>0.7 at 150, 300, 500 and 600m downwind of source). Results suggest that calibrated dispersion modelling can be applied to make reasonable predictions of bioaerosol exposures at multiple sites and may be used to inform site regulation and operational management.

Evaluation of inflammatory effects of airborne endotoxin emitted from composting sources.

Because of the lack of effective methodology, the biological effects of environmental endotoxin have not been assessed. Here we have collected and measured airborne endotoxin at different locations around composting sites. Increased endotoxin concentrations were observed close to composting activities and also at nearby boundary areas. Analysis of proinflammatory effects of the environmental endotoxin on interleukin (IL)-8 and IL-6 release from human D562 pharyngeal epithelial and MM6 monocytic cell cultures showed an association between endotoxin level and cytokine induction. The cytokine-inducing effect of bioaerosol extracts was inhibited by polymyxin B, indicating that endotoxin was the cause of cytokine responses we found. The environmental endotoxin was also more active for stimulating cytokines in airway epithelial cells than commercially purified Escherichia coli endotoxin. Our results suggest that these in vitro inflammatory cell models may contribute to the assessment of health impacts of environmental endotoxin.

The importance of domestic water quality management in the context of faecal-oral disease transmission.

The deterioration of drinking water quality following its collection from a community well or standpipe and during storage in the home has been well documented. However, there is a view that post-supply contamination is of little public health consequence. This paper explores the potential health risk from consuming re-contaminated drinking water. A conceptual framework of principal factors that determine the pathogen load in household drinking water is proposed. Using this framework a series of hypotheses are developed in relation to the risk of disease transmission from re-contaminated drinking water and examined in the light of current literature and detailed field observation in rural Honduran communities. It is shown that considerable evidence of disease transmission from re-contaminated drinking water exists. In particular the type of storage container and hand contact with stored drinking water has been associated with increased incidence of diarrhoeal disease. There is also circumstantial evidence linking such factors as the sanitary conditions in the domestic environment, cultural norms and poverty with the pathogen load of household stored drinking water and hence the risk of disease transmission. In conclusion it is found that re-contaminated drinking water represents a significant health risk especially to infants, and also to those with secondary immunodeficiency.

Mechanisms leading to post-supply water quality deterioration in rural Honduran communities.

Drinking water can become contaminated following its collection from communal sources such as wells and tap stands, as well as during its storage in the home. However, the mechanisms leading to contamination between the points of supply and consumption have not been well documented. This study carried out field-based experiments in three rural Honduran communities to investigate the potential for contamination through hand contact, method used to draw water, and dirty collection containers. The possibility of bacterial growth occurring in stored water was also considered. Hand-water contact was observed frequently during the collection and drawing of drinking water. Faecal contamination was present on 44% of women's fingertips tested during normal household activities, and this faecal material was easily transferred to water. An immediate deterioration in water quality was observed on filling collection containers. Faecal material was detected on cups and beakers used for drawing stored drinking water. Evidence was produced indicating that thermotolerant coliforms remain attached to the inner surface of clay storage containers after rinsing. Drinking-water quality deteriorates during collection and storage as a result of multiple factors linked to hygiene practices and circumstances. However, hands have the greatest potential to introduce contamination because of the constant risk of contact during household water management.