The study cited in the Canberra Times article as a "trick" is a far more honest study than the lead industry graph. The 1976-80 NHANES (National Health And Nutrition Examination Survey) US study measured blood lead levels in nearly 10,000 people, this is nearly twice the total number of people blood lead tested in all 13 of the pre-1970 studies put together, for the ILZRO graph. Because so many people were involved in the NHANES study, numbers in most of the sub-groups are large enough to make the results statistically significant. Over the four years of the survey, the levels of lead in people's blood dropped significantly and almost exactly in step with the decline in the amount of lead added to petrol, following initiatives to encourage cars to run on unleaded petrol begun in 1975.

As opposed to the industry graph, the NHANES evidence is especially reliable and convincing since the correlation between lead levels in people's blood and the amount of lead added to petrol is very close and the correlation held in almost every case when the sample was sub-divided into groups defined by age, sex, race, family income, season, region and type (urban or rural) of residence.

Also, a careful control programme showed that the trends were not due to changes in laboratory practice. Throughout the four years of the survey, there were no chronological trends in blind controls that were analysed.

To put paid to the suggestion "that airborne lead from car emissions was not a major source of lead in human blood" the NHANES follow-up to the 1976-80 study provides compelling evidence of the huge impact of lead from petrol, as the following list of results indicates (Pirkle et al, 1994):

The NHANES follow-up study estimated as of July, 1994 that 210,000 children under age six in the United States had levels of 20 ug/dL or higher [twice the Australian goal], which is a 96 % drop from the 4.7 million estimate from 1980. The Centers for Disease Control has attributed the drop to the elimination of lead from gasoline and solder on food cans (Brown, 1996).

In 1996 the national blood lead survey estimated that there were 75,000 1-4 year old children in Australia above the Australian blood lead goal (Donovan, 1996; Gilchrist and Beale 1996). Unfortunately for all children, there is no safe level of exposure to lead as no threshold level has been found. Changes in blood enzymes and disruption to children's neurobehaviour and IQ are evident at levels below the Australian goal. In the US, recent research into the effects of lead at even lower levels has prompted a call to halve the "acceptable" level to 5 µg/dL. The renowned lead researcher, Professor Herbert Needleman, (Professor of Pediatrics and Psychiatry at the University of Pittsburgh) has demonstrated a strong correlation between the levels of lead in the bones of youths and their delinquent behaviour. Moss et al (1999) used NHANES data to conclude that for every 5 ug/dL increase in blood lead level, children show an 80% increase in the number of dental caries. The social implications of effects of lead on behaviour may be even more profound than those on intelligence. New York researchers, Mendelsohn et al, in 1998 demonstrated adverse behaviour changes in 1 to 3 year olds with "low" blood lead levels, when compared to children with very low levels. And Lanphear found cognitive impairment, affecting maths ability and especially affecting reading ability, in children with levels as low as 2.5 µg/dL (Tanner, 2000).

During the slow lumbering phase-out of leaded petrol in Australia, air lead levels have been gradually reduced and blood lead levels have fallen as a result. Isotopic research in the early and late nineteen-nineties determined that the contribution from petrol to lead in air in Sydney and Melbourne remained constant at 90%, but the air lead level had been reduced by 75% in that time (Chiaradia et al, 1997). It is expected therefore that there are no longer 75,000 lead poisoned pre-schoolers and the government appears to be so confident of this that there is no intention to carry out the planned follow-up to the national blood lead survey of children.

The Grose article refers to an ad hoc 1993 Victorian study, which supposedly indicated that only 3 children were above the Australian goal of 10 µg/dL. In fact the study states that over 8% of the under 5’s, the highest risk category, had a lead level above the Australian goal. The researchers in this study also acknowledged that the reduction in lead levels seen since 1979 was attributable to better food processing and the reduction of lead in petrol in Victoria. Victorian petrol has since 1983 had the lowest lead content of any petrol in Australia.

In reality it happens rarely if at all, that a study has the capacity to show blood lead levels in the same population (the general population) under the influence of just one variable - lead from petrol. It happened once in Italy, according to New Scientist: "In [an] Italian study (in Turin and Piedmont), lead from the Broken Hill mine in Australia was put in petrol sold in the area for almost two years between 1977 and 1979. This lead has a different ratio of the isotopes lead-206 and lead-207 from lead from other sources. So researchers could find out how much of the lead in people's bodies came from this source merely by measuring changes in the isotopic ratios of the lead in their blood. They found that the ratio characteristic of Broken Hill lead dropped by 30% for people in Turin after 1979, suggesting that lead from petrol makes up a similar percentage of the total burden of lead in the body."

It should be noted that the above estimate as to the contribution of lead from petrol to lead in blood was made in an era where many other sources of lead were less controlled than they are now in people's workplaces, hobbies and homes. A more recent analysis by Thomas et al (1999) of blood lead studies in 17 locations on 5 continents which compared population blood lead levels before and after changes in use of petrol has concluded that:-

In 1993, Julian Cribb reported an estimate that reducing lead in petrol would save more people's lives (from fatal heart attacks and strokes) than the road toll each year.

It is sobering to consider that 55 countries will have eliminated lead from petrol before Australia does by 1st January 2002.

PDF version of this file: New strategies needed to cut lead pollution