In January, an official inventory suggested that British Steel could be by far the UK's largest source of dioxins. Emissions from its sintering plants were put at 80-2,220 grams per year - expressed as the toxic equivalent (TEQ) of the most toxic dioxin, 2,3,7,8-TCDD - compared to a total UK release to air of 590-3,700g TEQ (ENDS Report 240, pp 4-5 ).
The estimates were based on variable data from overseas studies. Dioxin emission concentrations of 24-68ng/m3 have been reported at one German sintering plant, with lower levels of 5-10ng/m3 on other units.
However, no monitoring data were available for UK sintering plant. British Steel's failure to carry out any dioxin tests was particularly surprising because it had known of the German studies for some time and was on the point of applying to HMIP for authorisations under integrated pollution control (ENDS Report 240, pp 3-4 ).
The company eventually carried out emission tests in April. Consultants Symonds Travers Morgan took a dozen samples which were analysed for dioxins by Scientific Analysis Laboratories (SAL).
The two sintering units at the Llanwern works showed the highest concentrations, with emissions of 2.0 and 3.4 ng/m3 recorded on one unit and 1.4 and 2.4ng/m3 on the other. Emissions at Port Talbot were found to be 1.6, 0.9 and 0.6ng/m3, while those at the Teesside works were put at 1.7 and 1.0ng/m3. Releases from the two units at Scunthorpe, which share a common stack, were below 1ng/m3.
British Steel says that these results indicate that annual dioxin releases from the four sites amount to some 40g TEQ. The company links the higher emissions recorded overseas to the practice of returning process wastes contaminated with organochlorines to sintering plant, and says that it phased out the main contaminants, chlorinated cutting oils, in the late 1980s.
Nevertheless, British Steel's assertion that "each sinter plant is only a very minor contributor to local background levels of dioxin" should be viewed with some caution. Dispersion modelling, for instance, has been carried out only at the Scunthorpe plant. Analysis by SAL of six soil samples from around the Llanwern plant found levels of 1-11ng TEQ per kg of dry soil - "well within the average for rural sites and significantly less than for urban sites", according to British Steel. However, samples were taken on or close to the works rather than at the site of predicted maximum deposition.
HMIP is now assessing the results of emission tests carried out by its own contractors. Even if these confirm British Steel's findings, steelworks have now been firmly identified as potentially significant local dioxin sources.
On British Steel's estimates, mass emissions are similar to those from an old municipal waste incinerator (ENDS Report 241, pp 13-14 ). HMIP says that by 1997, when new emission rules bite, dioxin releases from incinerators will fall to less than 15g TEQ. But British Steel's mass emissions will remain little changed even if HMIP applies the 1ng/m3 new plant standard because of the very high gas volumes released.