A report on lead in Port Pirie by the SAHC (South Australian Health Commission) in August 1983 is the first place known to me where lead in ceiling dust is mentioned. Anecdotal evidence suggests that collapses of ceilings in both Broken Hill and Port Pirie under the sheer weight of ceiling dust have been known for at least the last 30 to 40 years.

Ceiling dusts in Broken Hill readily amount to 2-5 cm and more deep and 40 to 100 kilograms per square metre in older mine-houses close to the line of lode. (ie the ore body).

Ceiling dusts preserve the history of fugitive dust fallout and accumulation in our communities. From the days of dusty roads and horse drawn carts, ubiquitous coal and wood burning to the advent of the motor car and the rapidly growing use of leaded petrol from the 1930’s the settled dusts in the ceiling space of older houses may preserve an amazing stratigraphy. They are artefacts of historical air pollution and surface dust emissions. For the biologist there is a rich collection of pollens for example. In industrial suburbs there will be accumulations from foundries, coal-gas works, brick works, battery factories, pigment factories and other industries that have long since closed down or moved elsewhere.

Ceiling dusts are an excellent media for assessing the geographic extent and magnitude of dust emissions in residential settings. Ceiling dusts can be long-term accumulations over the age of a building, or preserve the chemical fingerprint of a short-term episode of local particulate emissions. Chemical species in emitted dusts have a good chance of being preserved intact in the absence of moisture and mechanical abrasion once trapped in the confines of a ceiling space. The processes of degradation of toxic compounds that may take place in soils for example may be unlikely to take place to the same extent in ceiling dusts.

The scientific value of ceiling dust as a long term deposit gauge analogue is important. Direct human exposure to ceiling dust cannot be underestimated. Pathways of exposure can be many and varied; the risks of exposure to ceiling dust are not well understood as ceiling dusts have not been comprehensively characterised. Lead in ceiling dust is one issue among many. It is assumed by many that the community is not exposed to ceiling dusts.

Broken Hill

I first sampled ceiling dusts while working as a geologist in Broken Hill in 1989-90 and living in the former "British Mine" manager's house ON the line of lode north of Blackwoods Open cut. On windy days dust visibly blew / trickled through vents linking the ceiling space and the house living space. In order to seal the vents hundreds of kilograms of dust were removed. Out of curiosity I had the dust tested. Over subsequent months I collected and analysed samples from 21 locations. This work was reported by letter to government, industry and other authorities and then later in the ‘Barrier Daily Truth’, on the 20^th of March 1991.

The geometric mean lead concentration in Broken Hill ceiling dust from 21 locations was ~ 0.6% Pb [lead] or 6000 mg/kg, with Pb > 1.0 wt % (on a whole sample basis) for 8 locations either adjacent to the line of lode or in Broken Hill South.

These data were evidence of the high mobility of Pb in dusts in Broken Hill and the probable penetration of Pb dusts into the living space as well as ceiling space. Comparison with the Port Pirie ceiling dust data available from Peter Body [of Royal Australian Chemicals Institute and SA Dept. of Planning and Environment] suggested that community-wide Pb dust mobility in Broken Hill had at least been at a high magnitude at some time and would be reflected in elevated child PbB [lead in blood]. The particular design of ceilings in Broken Hill with vents commonly linking the ceiling space and living space was recognised as being problematic. Ceiling dust was not suggested to be THE source of child Pb exposure but was proffered as evidence of widespread residential Pb contamination. The need for a child PbB survey was now very clear.

A subsequent child blood lead testing survey in 1991 established the nature of child lead exposure in Broken Hill and in time the community has come to both accept and deal with the Pb issue. Broken Hill as a location and community maintains its standing as a wonderful jewel in the NSW outback. Some without local knowledge state that the Broken Hill child lead issue was recognised as a result of the Pb poisoning of dogs in Broken Hill. Curious indeed given that key health figures were not aware of a publication on dog Pb poisoning by Koh and Babidge (1986) in the Australian Veterinary Journal (Barrier Daily Truth, 24 April 1992).

Levels of Pb in ceiling dust > 1% reported in early 1991 were critical in getting the extent, magnitude and implications of dust contamination in Broken Hill recognised. This was the public information that exposed the extent of Pb dust in homes in Broken Hill. The blood lead testing of Dr Don Howarth in late 1990 and the many letters of residents written to NSW politicians complaining about dust emissions, and the local residents action group were also important. The subsequent NSW Government ‘political response’ to Pb appeared to be catalysed by emerging findings and political sensitivity to the Broken Hill issue and was substantially founded on readily available findings from Port Kembla, Boolaroo (particularly post-earthquake), Glebe, Mort Bay and Summer Hill. Lead advocacy in NSW is also the strongest of any Australian State. Responses included the Interdepartmental Lead Taskforce, and Select Committee upon Lead Pollution. Today New South Wales has the most proactive approach to community wide child lead exposure of any Australian State.

At 1% Pb in Broken Hill ceiling dust, (based on my 1991 data) there is 1.5% Zn [zinc] ; 200 mg/kg Cu [copper]; ~ 60 to 120 mg/kg As [arsenic]; 60 mg/kg Cd [cadmium] and 20 mg/kg Ag [silver] (2/3 of an ounce of silver per tonne of ceiling dust) this reflects classic Broken Hill ore body elemental ratios.

To find SILVER near two ounces per tonne in ceiling dust from one house for example indicates unambiguously the ore body origin of the metals in ceiling dusts of the Silver City [Broken Hill].

Adelaide Data

To get the gravimetric ceiling dust loading value you need to sample a measured area. Accumulations of <100 micron fraction ceiling dust in 11 houses in an older non-industrial Adelaide suburb averaged 430 g/m², (s.d.=370) while in an inner-city industrial setting 10 houses had dust accumulations of 1640 g/m² (s.d.=1130). A maximum value of 3.6 kg/m² of ceiling dust was encountered.

Galvanised Iron

What are the influences of roof material on the character of ceiling dusts? Galvanised iron roof materials fail at the overlapping sheet margins with age and white accumulations of ZnO and ZnCl appear at the laps. If you look carefully at the ceiling dust in an old house with a deteriorating galvanised iron roof you will see parallel white bands of Zn rich powder in the ceiling dust (readily 4% Zn). Check whether the white bands match the position of edges of the current roof iron sheets. If you are interested in nearby industrial emissions I could advise that samples be taken between these bands but more usefully don’t choose houses with galvanised iron roofs for testing for Zn and Cd in dusts. However, in Broken Hill and Port Pirie the galvanised iron effect may be swamped by the high levels of Zn in depositing dusts.

For 12 non-galv. roofed houses in non-industrial settings, in Adelaide, the mean Zn in ceiling dust level was 600 mg/kg (s.d. = 234); whereas in 21 galv roofed houses the level was 4870 mg/kg (s.d.=1570). For a representative sample of the ceiling dust, for exposure investigation purposes, a representative area or transect sample type is appropriate, not a point grab sample. Where houses have been re-roofed, paint chips can be seen at iron sheet boundaries. The sieving of ceiling dust can limit the impact of "non-dust" materials and is recommended for research purposes when preparing ceiling dust samples. Paint Pb does not appear to be a major component of ceiling dust relative to motor vehicle Pb.

Terracotta Tiles

There is much fine-grained red-orange ceramic chips and dust material in ceiling dust in houses with terracotta tile roofs. One of the elemental curiosities of ceiling dusts from such houses in Adelaide is elevated levels of Vanadium (eg 94 mg/kg compared to 28 mg/kg in houses not tiled with terracotta).

Cement Tiles

The particle size distribution for ceiling dusts associated with terracotta tiles, cement tiles and slate will reflect a contribution of coarse material from the roof material. Ceiling dust associated with cement tiles can have a high proportion of sand sized particles from abrading cement.

Gross dust accumulation rates

Dust accumulation rates determined in Adelaide range from as low as 1 gram per square metre per year from newer houses in distant settings to some 60 grams per square metre per year for houses in industrial settings. It is clear that prior to the 1950’s and 1960’s, dust deposition rates were substantially greater than they are now.

Motor Vehicle Lead in Ceiling Dust

For houses in non-industrial settings there is a strong linear relationship between lead and bromine in ceiling dust that reflects the ratio of these elements in leaded petrol. The presence of industrial Pb can be separated from motor vehicle lead.

In industrial settings the Pb -Br [lead - bromine] relationship breaks down due to the presence of non-motor vehicle Pb emissions.

A simple traffic proximity index that is a sum of the traffic flow divided by distance to the road for all roads within 400 metres can be easily developed. Additional functions for prevailing winds and complex deposition decay functions with distance could be used. An added dimension to the index is the historical and current traffic count data. Using a traffic proximity index the lead loading in ceiling dust (mg Pb/m²) can be seen to be strongly related to a simple traffic proximity index.

The upshot is that hot-spots for high lead loadings from motor vehicles in ceiling dust can be predicted.

Miscellaneous Observations

I mention the stratigraphy of dusts - look carefully for colour changes layer by layer when gently scraping down through dusts. Within 1 metre of the eaves of the roof (if the eaves are relatively open and the house exposed to the wind) you can see sometimes ‘sand ripples’ that are evidence of high speed winds across the dust surface. This disturbance is limited in extent.

Re-roofing and laying insulation can variously tend to preserve further or destroy the scientific integrity of ceiling dust accumulations. Brilliant historical snapshots are available from houses that are regularly extended with new rooms. The age of a house, room or ceiling needs to be known so as to interpret the deposition rate of dust or lead for example. In addition, if you collect samples from under insulation you need to know when the insulation was installed.

Ardeer Battery Factory Melbourne; Vic EPA

Lead in ceiling dusts was analysed with a view to evaluating the extent of Pb contamination adjoining a former lead-acid battery factory in Melbourne. This is another example of using ceiling dust as a long term deposit gauge to determine the extent and magnitude of a point source emission problem. (The Age, 20/7/92, p.10). Samples > 2000 mg Pb /kg were encountered in this investigation.

ICI Dulux, Concord, Sydney; Woodward-Clyde

The investigations at Concord, Sydney are another example of using ceiling dust as a means of drawing a line around an area subject to potentially heavy air fall contamination.

Summary

Risk assessment associated with ceiling dust, and the characterisation of ceiling dust is in its infancy. However the technique of using ceiling dust as an analogue for dust deposition gauges is showing much promise. Concentrations and loadings of contaminants in ceiling dust can be used to readily delineate areas subject to various degrees of impact of near-by industries, polluting activities and road emissions for example.