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An assessment of spatial and temporal variations (for dust and air) was conducted within selected indoor microenvironments. Spatial variations in indoor air concentrations were not monitored because of the general mixing and homogeneity of air within a room created by the ventilation, thermal mixing and turbulent mixing created by occupants in the room.

Currently, very little is understood regarding the variability of PFCs spatially and temporally. The presence of PFCs in the environment and within indoor environments (occupational and personal) has only been addressed within the last decade as a result of analytical instrumental improvements. There are still many unanswered questions relating to the behaviour and transformations of PFCs, and also their toxicity and exposure to humans. Estimates and generalisations of PFC behaviour can be assumed from the understanding of traits of other halogenated POPs, such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs). It is understood that PFCs share the same basic behavioural traits of other POPs, with movement in the environment towards cooler regions (Jones & de Voogt, 1999), with the pathway and movement dependent upon the volatility of the individual PFC and the ability to ‗hop‘ through the environment (Shoeib et al., 2006). However, the partitioning behaviour of PFCs varies from that of other POPs because of their differing physicochemical properties, (Arp et al., 2006).

The mechanisms of movement from treated goods into the indoor environment are not directly known, but are thought to include general wear and tear of products, leaching from and degradation of the products (as seen with brominated flame retardants, ATSDR 2004). The effects of wear and tear from walking and vacuuming treated carpets can result in 50 % loss of PFCs over a 9 year period (3M, 2000). Additional sources are known to occur directly from the use of PFC containing sprays (surfactant cleaning products, paints, stain repellent carpet sprays, etc). When such products are used, only 44 % reaches the intended surface and the rest is lost to air (3M, 2000). Moreover, a 73 % loss of PFCs from treated clothing is estimated over a 2 year period, with the loss primarily via washing of the garment (3M, 2000), suggesting that the perfluorinated compounds are easily removable and not chemically bound to the

garments. Sources of PFCs have been linked (in chapter 3) to the presence and activity of occupants in the room, but sources could also be related to the clothing of the occupant. Sources of contamination to a room are numerous for PFCs and they exist on stationary objects (such as furnishings and carpet), as well as on other transported objects (such as clothing, food packaging etc). People are more likely to be affected on an individual basis within a room depending upon their activity level and behaviour. This is different for other organohalogens, where exposure can be proportional to the proximity of certain fixed objects like a TV, and which is the case for hexabromocyclododecanes (HBCDs) (Harrad et al., 2009). Current research gaps noted by Harrad et al., (2010b) regarding the presence of PFCs indoors include the pathways of less volatile PFCs to indoor environments, the presence of localised ‗hot spots‘ occurring within rooms and the potential sources creating these, and emission rates from treated goods.

Due to the sampling format used for dust collection (point sampling), the impact of ‗hot spots‘ could produce an over- or under-estimate of the concentration from the whole room. It is unlikely that the dust ingested by the occupant will be derived from the whole room content, but more accordingly from a small region from within close proximity to the occupant. Therefore, a more accurate measure of the dust ingested by an occupant may be procured via sampling the dust from a well-frequented space, to correctly estimate the ‗biologically-relevant‘ (Allen et al., 2008) dust in the room. This dust is located in the area of the room that is used regularly and would be located where people spend a high proportion of their time.

Both spatial and temporal within-room variations in PFCs concentrations could significantly impact the output of the exposure assessment (which is conducted in chapter 4). Understanding the ability of the sample to provide a precise representation

of the ‗biologically relevant‘ dust concentration from the entire microenvironment will be determined by the significance of the variability (Harrad et al., 2010b).

Point sampling is a quick and relatively non-intrusive way of collecting a sample providing a snap shot of the internal environment (Harrad et al., 2010b). The sample is collected from a centrally, well frequented area of the room, where the dust is more likely to be ingested – making it ‗biologically relevant‘. Dust in other areas of a room may not be as likely to be ingested because of the lack of time spent in that area by occupants, hence contact with dust is reduced. Thus, inaccessible areas, such as corners, behind and under furniture were not sampled. Due to multiple uses of most rooms sampled, it is imperative to determine the relevance of this point sample for the entire room. Sampling of different areas of rooms, may also allow sources (contributing objects) to be identified.

There are many parameters within a room, which vary temporally, and are usually linked to seasonal variations including temperature, humidity, ventilation, and activity level. Human behaviour patterns also change with season; during warmer months (spring and summer) people tend to spend more time outdoors, rather than in their homes and this has been linked to more in-tread from shoes (Norra & Stuben, 2004). In addition, rooms are better ventilated during such periods. Changes to temperature, ventilation, humidity and use patterns of a room all vary seasonally, and can produce differences in source emissions, partitioning between particulate and gaseous phase and mixing within the room (Stock et al., 2005).

If within-room spatial variability of dust is significant, the possibility of one person receiving greater exposure than another is possible. This is of particular interest for young children, because of the amount of time they spend on the floor, and their rate of dust ingestion. Localised exposure can be created by short-range spatial differences

in sources of perfluorinated compounds, such as placement of furnishings and textiles, along with variations across the room caused by ventilation and drafts, heating and humidity, and general wear and tear rates of flooring. Variations in localised exposure are not only dependent upon the room characteristics, but also as a result of the occupant‘s activity and behaviour.

Temporal variations could also influence exposure estimates. Each sample represents a single period of time, and thus variations identified in indoor air concentrations (in chapter 3) associated with variations between microenvironments and buildings could in part be a result of variations in sampling collection dates.

Processes affecting concentrations within indoor environments include the cleaning processes employed and their frequency, room use and changes in use over the year, ventilation and draughts, and changes in room contents.

With respect to cleaning processes, the frequency and the type of cleaning applied will influence the dust loading within a room and, therefore, the amount of dust, and particle size that accrues. Washing floors and carpets is the most efficient technique to remove dust from indoor environments (Schneider et al., 1994, Svendsen et al., 2006), as vacuuming often re-suspends and leaves smaller particulates (Hunt et al., 2008), which go on to settle back down on sideboards and the floor.

Carpets are another source of variation within an indoor microenvironment, as they can act as dust reservoirs trapping dust particles within them (Roberts et al., 1999), therefore newer (less worn) carpets can achieve a higher retention and re-suspension of dust particles than worn and older carpets (Svendsen et al., 2006).