Guidelines for Metals and Metalloids in Ambient ... - ARCHIVE: Defra

Expert Panel on Air Quality Standards
296. The measurements made in this study were of ‘Cr(VI) as CrO 3 ’.
Expressed as Cr(VI) the guideline value above must be multiplied by a
factor of 0.52, producing a figure of 0.2 ng/m 3 .
5.5.1 Sensitivity to method of derivation
297. Unit risk approach. There are three choices of exposure response for
determining an acceptable level for public protection: 1) USEPA, based
on the Ohio chromate production workers; 2) WHO based on a hybrid
of Baltimore chromate production workers and Norwegian ferrochrome
workers; and 3) Park et al. (2004) analysis of Baltimore chromate
production workers. Our opinion is that we should use the last of these
since it appears to use the best data and to be best analysed.
298. Park et al. (2004) estimated that 1mg/m 3 .year of cumulative exposure
to Cr(VI) (as CrO 3 ) with a lag of five years had a relative rate of 2.44
(95% CI 1.54 to 3.83). This was used to estimate the unit risk for lung
cancer per µg/m 3 over a life-time using the formula in WHO (2000):
• UR = P 0 (RR-1)/life time exposure
• P 0 = 0.04 (as in WHO 2000)
• RR-1 per mg/m 3 = 1.44 (from Park et al., 2004)
• Life-time average exposure = 8/24x240/365x1/70 = 0.003131
• Unit risk = (0.04x1.44)/(8/24x240/365x1/70) = 18.40 per mg/m 3
• = 0.0184 per µg/m 3 (1.8 x 10 -2 )
299. This is close to the unit risks estimated by the USEPA from different
data, and WHO using a combination of Baltimore and Norwegian
data (see earlier).
300. The risks of lung cancer associated with life-time exposures to
different levels are: 0.05 ng/m 3 =1 in 10 -6 (10 -6 /1.84 x 10 -5 ); 0.5 ng/m 3 =
I in 10 -5 ; 5.0 ng/m 3 = 1 in 10 -4 .
301. The guideline value of 0.35 ng/m 3 as CrO 3 derived using the customary
EPAQS method above equates to a lifetime risk of 7 in one million
people. This gives confidence that the EPAQS procedure yields a
guideline value consistent with that that would be generated by other
procedures such as the unit risk method.
302. At current upper UK urban levels of chromium of around 15 ng/m 3
containing an estimated 4 ng/m 3 of Cr(VI), the increased risk of lung
cancer would amount to a little under 1 in 10,000 which is comparable
to the rate of death from lung cancer in non-smokers derived from a
20 year follow-up of male British doctors.
303. Particulate matter may be more potent as any effect may be extended
in time and effectively localised. However, particulate matter will be
largely Cr(III) and a standard must take account of this.
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