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6. Conclusions and recommendations

Analyses of emissions data from the National Pollutant Inventory (NPI), has shown that several tonnes of heavy metals were emitted into the atmosphere from industries and area-based sources. For example from 1998 to 1999 the major estimated metals emissions from NPI reporting facilities were: 90 tonnes of arsenic and compounds, 1 tonne of cadmium and compounds, 10 tonnes of chromium(VI) compounds, 8 tonnes of cobalt and compounds, 1 tonne of copper and compounds, 39 tonnes of lead and compounds, 343 tonnes of manganese and compounds, 2 tonnes of mercury and compounds, 9 tonnes of nickel and compounds and 3 tonnes of zinc and compounds. For that same year, estimated major emissions from area-based emission activities were: 602 tonnes of lead and compounds, 2 tonnes of arsenic and compounds, 3 tonnes of chromium(VI) compounds, 4 tonnes of manganese and compounds, 1 tonne of mercury and compounds, 8 tonnes of nickel and compounds and 347 tonnes of zinc and compounds. These metals were associated with particulate matter in air.

Lead emissions from motor vehicles and petroleum services (in several cities), manganese (from a mining operation in the Northern Territory), zinc (from domestic solid fuel burning in Tasmania) and arsenic (from a copper mining operation SA) featured strongly in the total heavy metals emissions. Although there were limitations to the accuracy of the 1998/1999 emissions data, being the first year of reporting, this NPI database served as a useful screening tool for identifying metal emissions worth considering in future ambient studies. More accurate NPI emissions data should emerge in the future.

There were large amounts of data on the ambient concentrations of heavy metals measured in particulate matter from studies conducted in Melbourne, Sydney-Wollongong-Newcastle, Perth, Brisbane, Adelaide, Canberra, Tasmania, the Northern Territory and other towns in Australia. Available ambient metals data did not appear to be consistent with some of the NPI reported emissions for 1998/1999.

Lead was the most measured metal since it is a criteria air pollutant, ubiquitous and was present at high concentrations in ambient air until the phase-out of leaded petrol. Measurement of ambient lead levels started before 1990 in several Australian cities and towns.

There were six major studies in Australia on the elemental composition of airborne particulate matter. These studies were performed to determine the contributions of identified pollutant emission sources to particulate matter concentration in ambient air. They were source apportionment studies, and required the measurement of metals and other non-metal compounds such as carbon. The studies found metal profiles or 'fingerprints' in emissions from motor vehicles, coal combustion, industries, smoke, soil and sea spray, and subsequently used to determined sources of emissions. Studies of several elements, which included heavy metals, were completed between 1992 and 2000.

The procedures used for sampling particulate matter for the determination of their metals content were consistent with that used for the determination of particulate lead, which was sampled according to the Australian Standard Method AS2800 (1985). However, the frequency of sampling and the duration of sampling for metals were not consistent between studies. Also, different particle sizes, PM₁, PM_2.5, PM₁₀ and TSP were collected for metal analysis.

The Particle Induced X-ray Emission (PIXE) spectroscopy technique was the most commonly used analytical method by the Australian studies for determining the concentrations of several metals in particulate matter. This technique was sensitive, fast, accurate, and less expensive since it could measure several metals simultaneously. Only a few Australian studies used other methods such as Inductively Coupled Plasma spectroscopy or Atomic Absorption Spectroscopy techniques for determining multiple metals in particulate matter. Since there was no Australian standard method for multiple metals determination in particulate matter, samples were not analysed or results reported in a consistent way that would have enhanced easy data comparison across all the jurisdictions.

Table 12: Comparison of maximum annual average metals concentrations in TSP with available WHO health guideline values

Metals	Maximum annual average concentration (µg m-3)	Place and year was measured	Data source	WHO annual average guideline (µg m-3)
Arsenic*	na	-	-	-
Cadmium	na	-	-	0.005
Chromium(VI)*	0.008	Tas, 1997	AFP	-
Lead	0.259	SA, 1997	AFP	0.5
Manganese	0.075	Tas, 1997	AFP	0.15
Mercury	na	-	-	1.0
Nickel*	0.198	Qld, 1996	AFP	-
Vanadium	0.005**	NSW, 1996 ACT, 1997	AFP	1.0**

Notes:
na: annual average data not available
* These compounds are classified as carcinogens by WHO (unit risk factors are provided)
** 24-h concentration
AFP: Australian Fine Particles Study (Ayers et al., 1998)

The most abundant metals measured in ambient air, with concentrations normally greater than 0.1 µg/m³, were sodium, aluminium, silicon, potassium, calcium, iron, lead, and zinc. Currently reported ambient lead concentrations in several Australian cities were below the NEPM lead standard of 0.5 µg/m³ annual average, being attributable to lead reduction programs for motor vehicle emissions enforced in Australia over the years. There are no Australian ambient air quality standards to compare the concentrations of the other measured metals. The World Health Organisation (WHO) ambient air quality health guidelines were available for a few metals; arsenic, cadmium, chromium(VI), lead, manganese, mercury, nickel and vanadium (WHO, 1987). The maximum annual average metal concentrations in TSP, measured in Australian cities are compared to WHO Air Quality Guideline values for the corresponding metals in Table 12. Ambient lead, manganese and vanadium concentrations in the table are below the WHO guideline values. Annual average data were not available for arsenic, cadmium or mercury in any of the Australian cities, although the WHO has Air Quality Standards for them. Arsenic, chromium(VI) and nickel are classified as carcinogens by the WHO, since they do not appear to have thresholds for the onset of health effects, hence the WHO provide unit risk factors (health risk-concentration relationships) for them (WHO, 1987).

No statistical long-term trend analysis could be performed on the data from the studies on multiple metals, since insufficient samples were collected at any particular sites. This was due to the fact that most of the studies were done over short periods. For example, during the Australian Fine Particle study, data were collected from six cities, but only for very brief periods (1-2 months). The longitudinal data available were limited to Queensland and the Northern Territory, but were still insufficient for long-term statistical trend analysis of ambient metal concentrations. However, seasonal differences were observed in the Queensland data. From that data, the concentrations of aluminium and potassium showed statistically significant seasonalities from 1996 to1998, and for calcium, titanium and phosphorus, from 1997 to 1999. Lead, iron and silicon showed statistically significant seasonal differences in 1996, 1997 and 1999. In general, winter concentrations were observed to be higher than summer concentrations for the metals that depicted significant seasonal differences.

The metals reported in the NPI, with the exception of beryllium, cadmium, mercury and antimony, have also been determined in most of the ambient air studies. The available ambient metals data were not comprehensive; in particular there were no data on mercury and little data on cadmium and arsenic concentrations in several Australian cities. However, the NPI database showed several tonnes of these metals and lead were emitted into the atmosphere annually.

From the review of the data available on heavy metals analysis in ambient air in Australia, the author wishes to make the following observations/recommendations:

• There is a need for an Australian standard method for determining multiple metals in particulate matter from ambient air, to allow consistent measurement and reporting of their concentrations.
• Long-term trend monitoring should be conducted for mercury and cadmium, alongside lead monitoring; these metals can be toxic at levels that are only moderately above background levels, and their emissions are being regulated in other industrialised countries. This report shows that there are currently few ambient data on cadmium and mercury in Australia.
• The methods used for the collection and analysis of the heavy metals cadmium, mercury, arsenic, antimony, beryllium and selenium should be verified. Data from the NPI showed that industries and diffuse sources emitted these metals, but there are very little ambient available data on them, and the reported concentrations were very low. In particular, it should be ascertained if current collection and analyses techniques are suitable for them, or whether they should be complemented with other techniques. For example, there is a potential for the volatile compounds of these metals, including lead, to be lost from the filter paper during sampling. There is a need for the efficiencies of their collection to be determined and reported with the concentration data.
• Inter-laboratory sample analysis of heavy metals in particulate matter should be encouraged between Australian laboratories, irrespective of analytical techniques used for their determination.
• Analytical techniques such as Neutron Activation Analysis (NAA) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) or other techniques, which can determine isotopic ratios, should be used more extensively for determining metals concentrations in particulate matter in order to differentiate sources of emissions.
• For any future multiple metals studies, the six-day (24 hour) cycle should be used as a minimum for collecting particulate matter, and synchronised to occur on the same days as lead monitoring. In addition to this cycle of monitoring, attempts should be made to collect samples when pollution events occur, since the Perth Haze study showed that combustion sources, for example, dominated these events.
• Since there is a distribution of the different metal types in the various particle size ranges, both PM₁₀ and PM_2.5 samples should be collected. The use of a dichotomous sampler or similar sampler enables the collection of both types of particles.

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