|
Lead pollution and
the human environment
by Ted Floyd
Ted Floyd has been an environmentalist for 20 years
and a campaigner with Friends of the Earth for the last five years. Can
you tell when he wrote this article?
One of the by-products of the industrial and
technological revolutions that have occurred in the last couple of
hundred years has been the increase of chemicals in the environment.
Many of these chemicals are dangerous to human and animal health.
Many thinking people were shocked when Rachel
Carson published her book "Silent Spring" in 1962. This book
clearly showed the hazards of the continual use of pesticides. Because
of the initial work of Rachel Carson most people are now aware of the
dangers of pesticides, but pesticides are still being used
indiscriminately.
There is one chemical, lead, which is being
continually released into the environment and which is potentially more
dangerous to humans than the total impact of pesticides. Studies on lead
are showing that it is very toxic and is affecting many people
especially in motorised, urban environments.
The toxicity of lead to humans has been a problem
for many years. For example, some historians partially attribute the
downfall of the ruling classes of Rome to lead poisoning. Lead was used
in plumbing, for wine storage, in drinking and eating utensils and
cosmetics. Even today, cases of lead poisoning have been attributed to
improperly lead glazed pottery. One possible cause of lead poisoning, is
pica, or the eating of non-food items, which occurs as a normal phase in
a young child's development and becomes abnormal if it persists beyond
the age of around 18 months. Children or adults can be lead poisoned by
eating chips of paint containing lead (which often occurs in old
houses), contaminated soil, bullets, fishing sinkers, lead shot, etc.
Industries where lead is used were a common source
of lead poisoning. However, in most countries regulations are now in
force which control lead in paint and help protect workers in industry,
but cases of industrial lead poisoning still occur.
Health hazards of lead
Lead poisoning occurs when a human being absorbs,
through the air he breathes or the food or other material he ingests,
substantially more lead than his body can excrete. Absorbed lead enters
the blood stream and accumulates in body tissue, particularly the
kidneys, bones and nervous system. The foetus, infant and child are
especially vulnerable. Lead is a cumulative poison and once absorbed it
remains in the body for months or years.
At high blood lead levels, obvious clinical
symptoms often occur, but recent research has found that at lower levels
less obvious, hard to detect, i.e. subclinical symptoms can occur.
Lead has an adverse effect on many enzyme systems
causing metabolic disturbances. Lead can disrupt the orderly function of
some trace elements such as copper and zinc. Metabolic disturbances
occur above about 20 micrograms. Subclinical lead exposure can have
effects on behaviour and intelligence. Evidence is accumulating that
prolonged low-grade exposure to lead may cause hyperactivity in
children, learning difficulties and impaired brain function.
Lead poisoning in children occurs at lower blood
lead levels than in adults. The age range of 1-5 years is the most
critical. The pregnant woman and her foetus are highly susceptible to
lead poisoning. Chronic exposure to lead can cause miscarriages and
stillbirths. During conditions of abnormally high calcium metabolism
such as fever or cortisone therapy, lead can be mobilised from bones and
then transported via the blood to other organs to wreak damage once
again.
Lead, petrol and pollution
Lead is added to petrol in the form of tetra ethyl
and tetra methyl lead. These compounds increase the octane rating of the
petrol.
Many studies have shown that the lead content of
air increases in areas close to roads, and falls dramatically with
distance from a road. Usually within 50m of a road over 50% of the lead
has settled out. More lead is found on the downwind side of a road and
the lead content of the air or the soil near a road increases with
traffic density. In cities with tall buildings there can be a problem of
poor ventilation which can result in very high lead content in both
street dusts and air at street level.
Lead is transferred from the atmosphere to the soil
and vegetation by sedimentation and precipitation. Most lead that enters
the soil forms insoluble compounds and this results in most soil lead
being found in the surface soil. Soils near roadsides can contain 30
times as much lead as virgin soils.
Plants growing near roads are contaminated with
lead, mainly on their above-ground external surfaces. Vegetables near
roads contain 5-20 times more lead than other vegetables.
Though the most serious levels of petrol lead
pollution are in the vicinity of roads, studies of lead levels in areas
remote from pollution sources, such as Northern Greenland and Cape Grim
in Tasmania, demonstrate that lead from petrol is polluting the whole
earth.
Summary
The lead and petrol industries claim that general
air lead levels have little effect, while recent overseas studies show
that lead levels once thought to be safe can be detrimental to health.
Current legislation in NSW restricts petrol content
of lead (in Sydney, Newcastle and Wollongong) to 0.45 grams per litre
(g/L). This restriction is to be lowered to 0.40 g/L by 1st Jan 1980. Is
this legislation sufficient? Are children who live near expressways
safe from lead?
This article was written over 14 years ago and
lists all the reasons that every other OECD country has legislated
nationally to curb lead pollution from petrol and other sources.
Australia is the only developed country with different legislated petrol
lead limits for each state and Greece is the only other OECD country
which, like Australia, allows more lead in country petrol than in city
petrol. Australian country lead in petrol limits and the lead limits for
three of our capital cities remain higher than in any other OECD city or
country.
|
