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Metals
The metallic elements lead (Pb), cadmium (Cd), arsenic (As), nickel (Ni) and mercury (Hg) have the potential to cause adverse health effects in humans. Cadmium, arsenic, and nickel occur as pollutant emissions from coal burning, heavy fuel oil burning, waste incineration and some industrial processes. Mercury is emitted from waste incineration, industrial processes using mercury cells, some non-ferrous metal processes and coal combustion. The major source of ambient lead is vehicles using lead-containing fuel. Emissions of cadmium, arsenic, nickel and mercury in the UK have all fallen by more than 80% since 1970, as a result of reduced coal and oil combustion, and better emission controls on industrial processes and waste incineration plant. Emissions of lead have been reduced by 93% since 1970, by a substantial reduction of the permitted lead content of petrol in 1986, followed by the phasing out of leaded petrol in 1999. Concentrations of these metallic elements in ambient air are expressed in microgrammes (i.e. 10-6 grammes) per cubic metre (µg m-3 ) or nanogrammes (i.e. 10-9 grammes) per cubic metre (ngm-3). The metals lead (Pb), cadmium (Cd), arsenic (As), nickel (Ni), and mercury (Hg) were monitored at three sites in Northern Ireland over a twelve month period, December 1999 to November 2000. This monitoring was carried out by Casella Stanger on behalf of the Department of Environment, Transport and the Regions (now Defra), as part of a study investigating ambient concentrations of these metals around industrial emission sources. The three sites were all located near to power stations or large industrial plant. Table 9.1 shows the locations of these monitoring sites. At these sites, particulate phase ambient concentrations were measured using gravimetric PM10 measurement apparatus. The duration of each sample period was one week. One site, Whitehead, also monitored the metal vanadium. Table 9.1 Metals
Monitoring Sites
Lead The 1st Daughter Directive, (1999/30/EC) and the Air Quality Strategy contain limit values and objectives for annual mean lead. These are shown in Table 9.2. Table 9.2 Limit
Values and Objectives for Lead
At present, lead is the only metallic pollutant to be covered by the Air Quality Strategy. Other Metals The metals As, Cd, Hg and Ni in ambient air are to be covered by a fourth Daughter Directive, currently at the draft stage. This Directive proposes “target values” (rather than limits) for As, Cd and Ni, which are shown in Table 9.3; however, it should be noted that these have not been finalised and may change. Table 9.3 Proposed
EC Directive Target Values for As, Cd and Ni.
For As, Cd and Ni the target values apply to the total As, Cd or Ni concentration in the PM10 fraction. No target value has been set for Hg. Table 9.4 shows the metals monitoring results for all three sites in Northern Ireland, from the study1 carried out over the 12 months December 1999 to November 2000. Annual mean Pb concentrations at all three sites were well
within the EC Directive limit value 0.5 µg m-3 (500 ng m-3). They were also well within the lower
AQS objective of 0.25 µg m-3
(250 ng m-3): thus all three sites already meet the AQS objective for this metal, set for the end of 2008. Annual means of As, Cd and Ni were well within the proposed EC Directive target values at all three sites. Table 9.4 Results of Metals
Monitoring Study
On the basis of this one-year study, it was concluded that levels of metallic pollutants at these three sites in Northern Ireland were low. As the duration of this study was just one year, it is not possible to assess trends. Overall UK trends for all these metals are decreasing. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
