7 The New Zealand Dioxin Inventory

7.1 Basis of the 1998 inventory

The total annual estimate for emissions to air in New Zealand was between 14 and 51 g I-TEQ per year. The secondary metals sector was estimated to contribute between 0.126 and 3.16 g I-TEQ per year. The categories used were secondary steel, non-ferrous metals and secondary aluminium production. Table 17 summarises the data used to estimate total annual emissions for 1998.

Table 17: PCDD and PCDF estimates from secondary metals, 1998

Source: Ministry for the Environment, 2000.

The secondary metal sector was identified as a reasonably significant contributor to the national emissions from industrial sources, but there was a large uncertainty associated with the estimates due to uncertainty in both the emission factors and the activity statistics.

The emission estimate for secondary steel was based on one plant with an EAF processing steel scrap with a rated capacity of 170,000 tonnes per year, which represented 90% of New Zealand's iron and steel production at the time. This site was excluded from the present study, as discussed elsewhere. Six samples from the plant over a six-month period gave emissions in the range 0.0064 to 0.239 ng I-TEQ/Nm³ with a mean of 0.0127 ng I-TEQ. This corresponded to an emission factor of 0.098-0.37 µg I-TEQ tonne^-1. The activity statistic and emission factors were both rated as having high certainty. The estimates for total PCDD and PCDF from the 1998 inventory did not include iron and steel foundries.

Non-ferrous metal production estimates from the 1998 inventory included brass, copper, bronze and lead. Non-ferrous metal foundries in New Zealand were estimated to produce between 0.5 and 30 tonnes per day. The large number of small operators in the sector was identified as a limiting factor in being able to predict accurate production data. Information was used from the Metal Casting Industry Association and the number of employees in the sector to estimate total production at between 20,000 and 36,000 tonnes per year. This figure is similar to the survey results from the present study (see section 4) of 23,200 tonnes per annum, noting that one large secondary copper operation has recently ceased operation.

In 1988 no emission data were available for non-ferrous metals other than tests on a secondary lead smelter (described below), and activity data were extrapolated. An emission factor range of 5 to 35 µg I-TEQ tonne^-1 was used, sourced from the UK inventory (Her Majesty's Inspectorate of Pollution, 1995).

A factor for New Zealand lead smelting was derived from New Zealand emission testing of 0.45 µg I-TEQ tonne^-1, consistent with US emission factors for lead. The operation used a gas-fired rotary kiln with fabric filtration. Lead smelting has not been revised as part of this study due to the availability of specific test data, although this site was not accounted for separately in the 1998 inventory.

The 1998 inventory identified that there were four main sites in New Zealand processing secondary aluminium. The total aluminium production from these sites was estimated at 35,000 tonnes per year. No estimate was made for production from small aluminium foundry operations. The survey estimate from the present study, which includes all New Zealand operations, gave 47,000 tonnes, suggesting the 1998 estimates were reasonable and there has been no significant change.

For secondary aluminium production an emission factor range of 0.26-52.2 µg I-TEQ tonne^-1 was used, which was based on the data reported in the US inventory (US EPA, 1998). The activity statistic was rated as having medium certainty and the emission factor was rated as low certainty.

7.2 Revised dioxin inventory 2002

The inventory previously included emissions from one secondary iron and steel plant, which has a capacity to produce 170,000 tonnes per year. Other ferrous metal plants, particularly foundries, were investigated in the current study. Secondary iron and steel production was found to involve an additional 21,000 tonnes per year.

Table 18: Updated PCDD and PCDF estimates for the secondary metals sector, 2002/03

a Taken as the geometric mean of the measured data.

b Data from 1998 dioxin inventory.

A comparison of data in Tables 17 and 18 shows that tonnes of metal melted have not changed significantly from the estimates in the 1998 inventory. The emission factors developed from the emission-testing programme in New Zealand are similar to those used in 1998, and this is offset by the additional metal production estimates.

While the 2002 estimates span a larger range of values when compared to 1998, the reliability of the data has improved. In 1998 the estimates for the secondary ferrous industry were rated as high. However, production estimates and emission factors for the secondary aluminium industry were rated as having a medium and low certainty respectively, while both the production and emission factors were rated as low for the non-ferrous industry. The new data allows the production estimates and emission factors for ferrous, aluminium and non-ferrous industries all to be given at least medium or high certainty ratings.

Emissions calculated using the geometric mean of the results, as reported in Table 18, are low at 0.012 g I-TEQ per year. Including secondary steel, this gives a range for annual emissions of 0.029 to 0.075 g I-TEQ. But care is needed with this type of estimate because some of the large sites had high emissions, which are effectively ignored by this type of averaging.

An important observation from the measurement programme is that larger sites contribute the major portion of dioxin because they process the majority of the metal. The smaller sites do not appear to contribute a disproportionate amount of dioxin relative to their size and/or production levels. While the flue gases are not always as well controlled as in large plants, it appears that the majority of the poor-quality scrap is confined to the larger sites.