Occupational Lead Poisoning

With respect to airborne lead, the DHSS Working Party recommends that the average concentration to which any person is exposed should not exceed 2 ~g/m3 in any year, whereas the NHMRC recommends that this should not exceed 1. 5 ~g/m3 in any three-month period. The DHSS Working Party estimates that most urban dwellers in the United Kingdom are exposed to annual concentrations of less than O. 5 ~g/m3, with only a few exposed to concentrations greater than 1 ~g/m3 and perhaps a very few in "hot spots" exposed to concentrations which may be as high as 6 ~g/m3. The Working Party gives high priority to the identification of local "hot spots" and to quantification of the resulting increase in blood lead levels. The NHMRC recommendation is more demanding than that of the Working Party, in respect of both the average concentration, which is somewhat lower, and the averaging period, which is considerably shorter. The shorter averaging period is more demanding because urban air lead levels fluctuate considerably with the season, so that the average for some three-monthly periods exceeds the yearly average by a considerable margin. When this factor is taken into account, the difference in the limits set by the two authorities becomes so large (a factor of two at least) that both cannot be acceptable. It is to be hoped that the NHMRC will carefully evaluate the scientific evidence presented by the DHSS Working Party in the light of this divergence in standards. The laying down of a limit for environmental airborne lead implies that this is the maximum average concentration to which any person should be exposed over a long period. To mean any more than this, the limit needs to be tied to a standard monitoring procedure which can be used to test for compliance. The laying down of such a monitoring procedure is beset with tremendous difficulties. It is well known that air lead concentrations are highest at the kerbside of busy roads and fall rapidly as the distance from the kerbside increases. Given the great variation in human occupancy in respect of distance from roads, it is not possible to nominate a standard distance from a kerbside that will adequately reflect human exposure. The DHSS Working Party seems to be aware ofthis problem when it strongly recommends closer attention to "hot spots" and omits any reference to a monitoring procedure. The NHMRC offers some details of monitoring procedure, stating that the level should be calculated on the basis of 15x24-hour samples collected over a three-month period taken at six-day intervals, and thereby implies that monitoring is a practical proposition; but it entirely neglects to state anything about the site at which the samples should be taken. This aspect of the NHMRC statement is likely to lead to considerable confusion. In respect to blood lead levels, the NHMRC has recommended that a level of 30 ~g/1 00 mL (1 . 45 ~mol/L) "be taken to represent a level of concern"; whereas the DHSS Working Party has recommended a slightly higher level of 35 ~g/dL (1 . 69 ~mol/L) as one worthy of a follow-up to identify the source of lead. The more pragmatic approach of the Working Party is preferable to the emotive terminology of the NHMRC which gives a "level of concern" without defining what the concern should be about and without defining an appropriate course of action when the level is found to be exceeded. For those aware of the difficulties involved in achieving accuracy in blood lead estimations, the differences in these two levels will not seem great. The difference is of the same order as that between two competent laboratories analysing the one sample. Laboratories not especially competent are likely to overestimate levels by much greater amounts. The DHSS Working Party obviously appreciates these difficulties. It talks of accuracy to "within ± 1 0% providing quality control is meticulous". It refers to the strictly monitored international quality control scheme applying to the laboratories whose results it reports. There is no such quality control scheme available in Australia and there are only a few laboratories in Australia which have proved themselves competent in this field. Until a quality control scheme is available here, there is likely to be much unnecessary investigation and many people unnecessarily worried by spuriously high blood lead levels reported from laboratories lacking experience in blood lead determinations. OCCUPATIONAL LEAD POISONING