Air Sampling Artefacts

3 Biological Relevance of Samples Within-room/building Spatial and Temporal Variability of Contamination 

As discussed earher, it is also important to evaluate whether a single spot measurement of contaminant concentration in air and/or dust from a given microenvironment represents a biologically relevant sample. Where not aU of the surface area of a room is sampled to obtain 

In addition to within-room spatial variability, within-room temporal variability in both air and dust contamination has been the subject of several recent studies. For air, Hazrati and Harrad (2006) reported appreciable (but not always statistically significant) seasonal variation in concentrations of PCBs and tri-hexa-PBDEs in four homes and four offices. The seasonal variability was less pronounced than observed widely for PCBs in outdoor air (e.g. Currado and Harrad, 2000 Hillery et al, 1997). This was attributed to (a) the narrower temperature range indoors and (b) the mitigation of summer peaks in concentration due to 

The temporal variability in concentrations of PBDEs in dust samples taken at monthly intervals in the same three home microenvironments over a 9-10 month period was monitored by Harrad et al. (2008b). The variability in the entire dataset of 9-10 monthly samples within each room expressed as the relative standard deviations (RSDs) of concentrations (ng EBDE/g) ranged between 58 and 166%, indicating at least moderate temporal variability. This was underlined further by the fact that in the three rooms studied, the maximum Etri-hexa-BDE concentration (ng/g) exceeded the minimum by a factor of 50, 3.5, and 5.5 in the three homes studied, while for BDE-209, the corresponding figures were 7.5, 400, and 35. 

Harrad, Abdallah, and Covaci (2009) conducted a similar examination of the temporal variation in concentrations of HBCDs in dust from the same three rooms as those characterised for PBDEs by Harrad et al. (2008b). RSDs of concentrations of ZHBCDs in these samples (27-190%) were broadly in line with those for PBDEs. Furthermore, the maximum concentration (ng EHBCDs/g) exceeded the minimum by a factor of2.6,224, and 4.0 in the studied rooms. Clearly, substantial variation in estimates of exposure is possible, depending when a given room is sampled. In both papers, the authors were able to attribute most of the temporal variability to changes in the contents of the rooms studied for example, the temporary removal and reintroduction to one room of a TV shown elsewhere in the study to be a substantial source of HBCDs was demonstrated to coincide with significant changes in concentrations of HBCDs in dust. 

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