Review of data on heavy metals in ambient air in Australia

Technical Report No. 3
Environment Australia, May 2002
ISBN 0 6425 4781 5

Executive summary

Early during this review it was noted that a number of studies had been undertaken in Australia, in recent years, which measured the concentration of heavy metals associated with particulate matter in ambient air. It found that there has been no compilation of the data to determine the presence of heavy metals and the range of the concentrations observed across Australia. Nor had there been a review of the methods used for their sampling or analysis. Therefore this project sought to identify sources of information and studies on heavy metals in Australia, consolidate the available information, identify any gaps in knowledge on heavy metals measurement in ambient air, and where possible look at the trends in the concentrations. Another objective of the project was to identify the sources and determine the amount of heavy metals emitted in the States and Territories as reported in emissions inventories.

Results of the review showed that the major heavy metals emitted from NPI reporting facilities in Australia during 1998/1999 were: arsenic (As) and compounds (90 tonnes), cadmium (Cd) and compounds (1.4 tonnes), hexavalent chromium (Cr(VI)) compounds (10 tonnes), cobalt (Co) and compounds (8 tonnes), copper and compounds (1 tonne), lead (Pb) and compounds (39 tonnes), manganese (Mn) and compounds (343 tonnes), mercury (Hg) and compounds (2 tonnes), nickel (Ni) and compounds (9 tonnes) and zinc (Zn) and compounds (3 tonnes). Diffuse emission sources (area-based sources) such as motor vehicle exhausts, small-scale industrial activities and domestic fuel combustion were responsible for the emission of several tonnes of heavy metals in nine airsheds (Adelaide, Hobart, Kalgoorlie, Perth, Port Phillip Region, SE Queensland, Sydney-Wollongong-Newcastle, Alice Springs and Darwin). The major NPI area-based metal emissions for 1998/99 were found to be Pb and compounds (602 tonnes), As and compounds (2 tonnes), Cr(VI) compounds (3 tonnes), Mn and compounds (4 tonnes), Hg and compounds (1 tonne), Ni and compounds (8 tonnes) and Zn and compounds (347 tonnes). These metals and their compounds were emitted in the form of fine particulate matter. It was observed that on a national scale, heavy metals emissions were dominated by:

The review noted that the State and Territory environment authorities monitored lead in ambient air since it is one of the criteria pollutants under the National Environment Protection Measure (NEPM) for Ambient Air Quality. Lead was monitored according to Australian Standard Method AS2800 (1985), which involves the collection over 24-hours of total suspended particulate matter (TSP) or particulate matter with aerodynamic diameters less than 10 micrometres (PM10) onto filters, on a 6-day sampling cycle. This was followed by post-collection chemical analysis, usually by Atomic Absorption Spectroscopy methods. There were several years of data available for trends to be observed in the lead concentrations. Most of the Australian cities showed large decreases in ambient lead concentrations over the period 1990 to 2000, which was consistent with policies introduced over the years to reduce the lead-content of petrol. Seasonal variations were observed in ambient lead concentration.

Several major Australian studies have included, in addition to lead, the simultaneous determination of several other heavy metals in particulate matter. All conducted over the past ten years, these were the Melbourne Aerosol Study, the Perth Haze Study, the Australian Fine Particle Study (in Melbourne, Sydney, Brisbane, Adelaide, Launceston and Canberra), the Aerosol Sampling Program (in Sydney, Wollongong and Newcastle), the Charles Point Coarse and Fine Particle Study in the Northern Territory (NT), and the Queensland Particles Study. Most of these were source apportionment studies aimed at determining the contribution of identified pollutant sources to particulate matter concentration in ambient air. In this approach, source profiles were related to the ambient concentrations of the elements through multivariate analysis methods such as principal component analysis. Thus the studies involved the measurement of the concentration of metals and other non-metals, such as carbon, which occur in particulate matter. The studies identified the metal fingerprints of emissions from motor vehicles, coal combustion, industries, smoke, soil and sea spray, which can be used in the identification of sources.

In addition to compiling and consolidating the reported metal concentrations from the various studies, this project has reviewed the techniques applied for determining the concentrations of heavy metals, metalloids and other metals, such as sodium and potassium, in the six major studies and other Australian studies. The review found that the methods used for sample collection, analyses, and reporting were inconsistent between the studies. This was attributed to the absence of an Australian Standard Method for the determination of multiple elements in particulate matter. It was also observed that several different types of samplers were used for collecting airborne particulate matter on filters for analysis. Also, although there were several techniques available for determining the composition of suspended particulate matter for their heavy metals content, only a few had been applied in the Australian studies. For most of the Australian studies, particulate analysis was carried out using Particle Induced X-ray Emission spectroscopy (PIXE) at the Australian Nuclear Science and Technology Organisation. This technique provided data on the elemental concentration of the particles. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), which has the potential to determine the isotopic ratios and hence provide better information on the sources of metals and their compounds, was used in only a few studies.

A survey of the data from the multiple metals studies showed that most studied concentrations in PM10 and PM2.5. Other studies were based on PM1 and TSP. For PM10 the most abundant metals were observed to be sodium, aluminium, silicon, potassium, calcium, iron, lead, and zinc. Similar results were observed for PM2.5 data. Metals that were not measured consistently across most of the studies included arsenic, barium, cadmium, magnesium, bismuth, gallium, rubidium, strontium and yttrium. There were no NEPM ambient air quality guidelines for the ambient concentration of metals other than lead.

Long-term statistical trends in the data from the studies that measured several metals could not be determined, since most of the data were collected for only brief periods at the various sites. Only two studies, the Charles Point Study and the Queensland Particles Study measured the concentrations of several metals over three or more years. However, the data from these studies did not span four or more calendar years which is required for long-term statistical trend analysis. Seasonal variations were observed in the concentrations of some of the metals measured in the Queensland Particles Study, and statistically significant decreases were observed in the annual concentrations of lead, copper and iron. While decreases were observed in aluminium concentration, these were not statistically significant.

It was concluded that the suite of metals studied was not comprehensive; in particular, there were no ambient data on mercury and there were insufficient data on several heavy metals such as cadmium, arsenic and antimony. It was recommended that long-term monitoring of heavy metals in ambient air using a more comprehensive suite of metals should be conducted.

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