Bad air a 'genetic risk' - Mac shows mutated genes hereditary

Bad air a 'genetic risk' - Mac shows mutated genes hereditary

By Eric McGuinness

McMaster University research is the first in the world to show that urban air pollution causes gene damage which animals pass from one generation to the next.

Biologists Jim Quinn and Chris Somers have demonstrated that male laboratory mice exposed to Hamilton steel-mill emissions transfer mutated genes to their young. And they warn the same thing could be happening in humans.

While gene mutations may increase risk of cancer and birth defects, the McMaster scientists say they can't make a direct comparison to human health.

At the same time, they say there's every reason to believe human genes react the same way.

That creates an urgent need to investigate the genetic consequences of chemical pollution in urban air, especially in places such as Hamilton, where there are integrated steel-making complexes.

Quinn and Somers placed one colony of laboratory mice downwind of the Stelco and Dofasco mills and another in rural Freelton for 10 weeks in the fall of 1999.

They then allowed the mice to breed and tested tail tissue for gene damage.

They found far more mutations in the city mice, mutations that were inherited by baby mice almost entirely from their fathers.

The results appear in the current issue of a respected U.S. research journal, Proceedings of the National Academy of Sciences.

Quinn and Somers blame the genetic damage mainly on polycyclic aromatic hydrocarbons or PAHs -- toxic chemical compounds that attach themselves to microscopic, breathable particles of soot and dust. They say PAHs are among the most genotoxic or gene-damaging urban air pollutants and that steel mills are a major source.

PAHs in the body are thought to attach to strands of DNA, the carriers of genetic information, and are suspected of playing a role in formation of cancerous tumours.

The Mac scientists say their discovery means people working in or living around integrated steel-making complexes -- ones that produce steel from iron ore rather than just recycling scrap -- may be at higher risk of genetic mutations induced by the air they breathe.

"Globally, hundreds of thousands of humans live or work in industrial areas near steel mills and are incidentally exposed to airborne emissions. These populations may be at risk of increased heritable mutation frequency through exposed fathers."

Health Canada experts who co-authored the research paper previously found mutations in herring gulls nesting downwind of the Hamilton mills, but couldn't separate the effects of air and water pollution, so mice were chosen for a followup study.

Although the city mice and country mice were fed identical diets, the mutation rate in city mice was 1.5 to two times than that of their rural counterparts. The city mice also had smaller litters. Quinn and Somers attribute the differences to air quality.

While cars, diesel engines and other industries also emit PAHs, the researchers point to steel mills as the culprit because they produce high levels of the toxic substances and because the earlier gull studies showed birds in Hamilton had more mutations than those in Toronto, a larger city with lots of traffic but no integrated steel-making complexes.

Quinn, 49, is an associate professor of biology. Somers, 28, is a PhD candidate who carried out most of the work with the mice.

Somers says one way to reduce the risk from steel mills would be to better filter their air emissions to remove the tiny particles that carry PAHs. To test that theory, he and Quinn have already conducted a second experiment in which two colonies of mice were placed on Pier 25 on the Beach Strip, half exposed to the air outdoors, half breathing filtered air. Results of those tests should be available early next year.

The genes being studied are prone to mutations and not ones that would directly result in birth defects, but Somers says there's every reason to believe other genes are similarly affected, though at a much lower rate.

Quinn compares the mice with canaries once used to warn coal miners of dangerous gases. The research paper says, "The use of sentinel laboratory animals exposed in situ is a powerful experimental approach for assessing air pollution hazards because it combines the controlled elements of laboratory studies with direct exposure to ambient pollution levels."

Before this, elevated mutation rates were found in human families living near sites of radioactive contamination in Belarus and other former Soviet republics as well as in barn swallows near the nuclear reactor accident site in Chernobyl. But the herring gull and mouse studies in Hamilton are so far the only ones showing chemicals can cause mutations that are inherited.

Source: The Hamilton Spectator (Canada - December 10 2002)