Effects of lead in petrol are well-known however a recent additive to petrol manganese may be just as toxic

Apr 7 2004

The disastrous environmental and health effects of lead in petrol are well-known, and western countries have been phasing it out for many years now. However, a recent additive to petrol - manganese - may be just as toxic. A Macquarie University study aims to find out.

The study, to be funded by the Australian Research Council over the next four years, is led by Macquarie geochemist and toxicologist Professor Brian Gulson of the Graduate School of the Environment. Gulson's previous research has linked lead poisoning to osteoporosis in the elderly, and has proven that lead can be passed from mother to child via breastmilk.

As well as Gulson and Macquarie psychologist Dr Alan Taylor who will provide statistical analysis, the research will also involve two divisions of the CSIRO, the Australian Government Analytical Laboratories and the US Environmental Protection Agency, all of whom provided seed funding for the study along with Macquarie.

Over the next three years, Gulson will periodically measure the levels of heavy metals found in more than 100 children, currently aged between six and 18 months, living across Sydney. The intensive effort of recruitment and retention of this cohort has been the work of colleague Karen Mizon.

"We've stratified the cohort into people who live within 300 metres of a main road and those who live further away," Gulson says. "We'll take samples from the children every six months to see how much gets into the blood and how much is excreted through urine. We'll also take environmental samples from a range of sources such as food, house dust, soil, hand wipes, and the air using the NSW Environmental Protection Authority's high volume air filters.

"Incidentally, one of the staggering things we found when we were looking to recruit kids at long day care centres was that about 80 per cent of them are on main roads or near traffic lights where you get a big spurt of emissions from the car's tailpipe."

Preliminary testing has already identified that a few of the children have dangerously high blood lead levels, probably caused by exposure to lead-based house paint. However, the most interesting facet of the study - and the reason for the US EPA's involvement - is its ability to test for exposure to the controversial petrol additive methyl-cyclopentadienyl manganese tricarbonyl (MMT).

MMT is produced by the same US company, Ethyl Corporation, that previously introduced the toxic petrol ingredient tetraethyl lead to the world. MMT is now used in 24 countries, including many developing South American nations.

Throughout Canada and in some US states, MMT has been used as a major petrol component over the past 30 years, despite car manufacturers' claims that it interferes with their catalytic converters. However, while US and Canadian authorities also have reservations about the health and environmental effects of MMT, it still has an official clean bill of health due to inconclusive medical testing.

One of the reasons for this, says Gulson, is that manganese is found naturally everywhere in our environment, particularly in soil and rocks. It's also an essential part of the human diet, being involved in around 300 enzyme reactions, in the mitochondria, and as a powerful antioxidant.

"So we're also looking at lead and a selection of other metals with the intention of deriving a geochemical signature that will distinguish the manganese that comes out of an exhaust pipe from the manganese that's in the environment already," Gulson says.

In countries where people have already been exposed to MMT for some time, like the US, Canada and Britain, health researchers would be unable to pinpoint the source of manganese found in children. However, as MMT was only introduced to New South Wales last year, and will only be used for another year or so, Gulson has been provided with an excellent opportunity to study manganese levels before, during and after MMT introduction.

Despite the lack of conclusive medical evidence linking MMT to ill health, scientific and anecdotal information on health problems experienced by workers at manganese mines in Groote Eylandt, Peru, Chile and India is starting to mount up.

"In the US they're also starting to worry about manganese steel welders exposed to vapours," Gulson adds. "All of a sudden there's a lot of concern about the potential health effects because workers are experiencing symptoms similar to Parkinson's Disease. Most of the available data indicates that inhalation is the most toxic pathway, apparently the manganese in vapour just goes straight to the brain after it's inhaled."

The main reason for using young children in his study, explains Gulson, is because of the so-called 'homeostatic mechanism'.

"Most of the manganese we take into our adult bodies comes from our diet, and approximately 97 per cent of that is excreted in urine and faeces regulated by the homeostatic mechanism," he says. "Because manganese is so critical in the body, like calcium, potassium or sodium, it is highly regulated, so too much manganese is potentially going to cause problems because it finishes up in the brain. But in young children we don't even know for sure when the homeostatic mechanism kicks in for manganese, though it's thought to not come in until 18 months or two years."

The Canadian Parliament had enough concerns about the health and environmental effects of MMT to legislate against its import and interprovincial transport in 1997. However, Ethyl Corporation subsequently filed a lawsuit against the Canadian government under the North American Free Trade Agreement for US$251 million to cover losses resulting from the 'expropriation' of both its MMT production plant and its 'good reputation'. In an embarrassing backdown, the Canadian government paid Ethyl Corporation US$13 million and revoked its legislation banning MMT.

But while the US, Canadian and Australian governments, international toxicologists and the giant Ethyl Corporation continue to keep tabs on Gulson's research, he warns that the results may not be conclusive either way.

"In New South Wales, MMT is only currently used in Lead Replacement Petrol and only by some petrol companies, unlike in Canada where it's used in all gasoline," Gulson says.

"I hate to be negative to begin with, but that's why we may not come up with an answer - it's used only in a small way compared to, say, Canada. Nevertheless, I wouldn't have a clear conscience if in ten years time people suddenly said 'my God, chronic exposure to manganese even at low levels has an effect on young children' and nobody had done the study. Is this the leaded petrol situation all over again?"