Breathing Hong Kong's toxic cocktail of pollutants makes us stupid
Toxic heavy metals in the air have huge effect on our bodies and characters, even years after we leave highly polluted environments
Everyone knows that in Hong Kong we don't breathe air any more but a chemical soup which is bad for us. But understanding how it harms us requires the multidisciplinary skills of geologists, biologists, chemists and psychologists. Heavy metals, the most dangerously toxic pollutants, have resided undisturbed in the earth's crust since its formation five billion years ago. They came from first-generation exploded star debris.
During the first four billion years of life's evolution, only very small amounts of these elements found their way into the biosphere through volcanic eruption or leaching of rocks. Life emerged in a chemical soup largely lacking heavy metals, so most species failed to develop high levels of tolerance.
However, in the last 200 years, mining of coal and other minerals, together with oil drilling and manufacturing, released large amounts of heavy metals into our biosphere with results which scientists are only now beginning to understand.
Scientists have monitored our air and discovered a cocktail of toxic chemicals, each damaging us in a different way. The most damaging are heavy metals attached to PM2.5 particles of dust which are so small they can float right through our cell walls when we inhale them, lodging in our lungs, brain and other organs.
The most common heavy metal in our environment is lead, which can be found almost everywhere: in our air, water, paint, electric storage batteries, insecticides, car body shops, petrol, toys and seafood. It can have a dizzying number of effects on our bodies, including decreased intelligence and learning difficulties and attention deficit disorder. It can also impair our speech and cause violent behaviour, poor muscle coordination, decreased muscle and bone growth and kidney and hearing damage.
Other common toxic heavy metals include mercury, cadmium and zinc, which can alter our DNA. They are released by coal-burning power stations, ships and factories. The wind can carry them hundreds of kilometres.
Because lead mimics and inhibits the calcium which the body uses to build brain cells, it gets used in place of this element, breaking the neural networks which wire our brains. Once broken, the damage is permanent. The damage for adults is limited because adult brains are already fully formed. However, it is another story for children, whose brains grow rapidly from birth to the age of six. They absorb a large amount of environmental toxins in polluted environments and should therefore be regularly tested to monitor their exposure.
When you leave Hong Kong, you take a bit of our polluted air with you - in your bones.
Because lead is absorbed with calcium into our bones and then slowly released into our blood, people who move to less polluted environments continue to be affected. Thus a fetus conceived outside Hong Kong will be damaged by Hong Kong pollution even if the mother gives birth after leaving the city.
If your child does less well than expected at school, it may not be because he got unlucky in the gene pool or because you have been a bad parent. It could be the air we breathe.
The harmful effects of lead have been known for centuries, but recently scientists have discovered that even very small amounts of lead previously thought harmless can significantly and permanently reduce children's intelligence.
According to one US study, each microgram per decilitre increase in blood lead results in a 1 per cent drop in IQ. Richard Canfield, a senior researcher in Cornell's Division of Nutritional Sciences and senior author of a study in the journal said: "We found that the average IQ scores of children with blood level leads of only 5 to 10 micrograms were about five points lower than the IQ scores of children with less than five micrograms."
Other researchers have found that the impact is greater at the lowest levels. The world would have hundreds of thousands more geniuses were it not for the effects of lead.
According to recent research, levels of airborne heavy metal particles are 10-20 times higher on average in China than in the US. Children absorb more toxins from dirty air, partly because they breathe in more air, but more importantly because they tend to crawl around, get dust on their hands and then put them in their mouth.
Tainted food adds to the problem, especially for fish and rice eaters. Rice is grown in water which is often polluted, while heavy metals accumulate in the marine food chain.
Blood lead levels are usually measured in micrograms per litre in the US and in micrograms per decilitre in Hong Kong and China. There is no safe level for blood lead.
Governments set concern levels, which have been progressively lowered over the past decades, from 60 micrograms to five in the US. Hong Kong and China have levels of 10 micrograms - double the new US level.Governments around the world are slowly tightening legislation regulating air polluters, but enforcement lags regulation and is not enough to keep pace with the increase in pollution generated by economic growth. This means that things will get worse before they get better. And even when this happens, the damage will continue to be felt by future generations, whose DNA has been damaged by airborne zinc. It's a toxic gift for our descendents, which evolution will not help to solve.
Until now, human evolution has resulted in increasing intelligence, not because it allows more individuals to survive, but because of the sexual feedback-cycle which developed in the same way as the beautiful but useless peacock tail. High intelligence is not necessary for our survival and actually reduces our reproductive levels, as can be seen in the very low birth rates in cities like Hong Kong.
Children who through genetic mutation gain some tolerance of heavy metals and whose brains are thus less affected will be more intelligent, but their genes will not spread through the brain pool, because intelligence is correlated with lower rates of reproduction. So thanks to the destruction of our environment, we could end up seeing the survival of the stupidest.
