According to the National Atmospheric Emissions
Inventory of the United Kingdom, historically, it was just smoke in combination
with other pollutants that was known to cause health problems.
However, recent studies have linked
concentrations of particles in the atmosphere with human health effects.
Particles vary widely in size and composition. The PM10
are particles measuring 10Βμm or less. These are the particles which are likely
to be inhaled by humans, and have become the widely accepted measure of
particulate material in the atmosphere in the UK and in Europe.
In the 1970's, air pollution was mainly
dominated by the domestic coal combustion, but more recently, other sources
such as road transport (all road transport vehicles emit PM10
diesel vehicles emit a greater mass of particulate per vehicle kilometer) and
industrial processes (including bulk handling, construction, mining) account
for a large share.
Only a few studies have observed the
effects of exposure to particulate matter (pollution generated by traffic) on
risk to myocardial infarction or, in simpler words, a heart attack.
(A heart attack occurs when blood flow to a part of the heart is blocked for a long time,
eventually leading to death of that part of the heart muscle. In medical
language, such a condition is called "myocardial infarction")
A recent experimental study showed
adverse effects on heart within a few hours of controlled exposure to dilute
diesel exhaust fumes. This highlights the possibility of very short term (<1
day) exposure to traffic generated pollution or particulate matter affecting
The various pathways through which
pollution exposure may trigger myocardial infarction are:
Systemic inflammatory response
Increased or decreased heart rate
Increased blood viscosity or plasma
Increased blood pressure
recent study conducted by Krishnan Bhaskaran et al quantified the association
between the risk of myocardial infarction and exposure to PM10,
ozone, CO(carbon monoxide), NO2 (nitrogen dioxide), and SO2 (sulphur
dioxide) at hourly intervals
regarding heart attacks was collected from the Myocardial Ischaemia National
Audit Project, a register that maintains details regarding heart attacks in
England and Wales. Data on pollution was obtained from UK Air Quality Data and
Statistics Database. Other data, that is, data on temperature and circulating
viral infections were obtained from the British Atmospheric Data Centre and
Communicable Diseases Surveillance Centre at the Health Protection Agency
Results of the study suggested
that higher ambient levels of PM10 and NO2 are associated
with an increase in myocardial infarction risk just 1-6 hours following
are pollutants produced in urban areas largely by motor
vehicles and are therefore likely to be markers of traffic-related pollution.
there was no evidence of a net excess risk associated with any of the five
pollutants studied over a 72-hour period after exposure.
In brief, the immediate risk increases were followed
by reductions in risk at longer lags.
pattern of a positive association between pollutant and myocardial infarction
over 1-6 hours but then an inverse association at longer lags has shown to be consistent
with a "short term displacement (or "harvesting") effect of pollution" (Bringing forward by a
few hours a heart attack that would have happened anyway
Although numerous studies have
demonstrated that higher levels of air pollution are associated with increased
cardio respiratory mortality in urban settings in England and Wales, a similar
association was not found in this study.
Since no net increase in myocardial
infarction risk over a broader timescale was found, there may be limited
potential for reducing myocardial infarctions through reductions in pollution
alone. Findings therefore suggest that other, perhaps non-thrombotic,
mechanisms are more important causes of mortality increases associated with
higher pollution levels.
But again this finding cannot undermine
calls for action on air pollution, which has well-established associations with
broader health outcomes including overall, respiratory, and cardiovascular
study is of great importance as it stands the largest one till date to
investigate associations between the commonly measured pollutants and
myocardial infarction risk at an hourly temporal resolution.
the study, it was clearly seen that higher levels of the traffic-associated
were followed by a transiently
increased risk of myocardial infarction up to 6 hours later. After this time
period, there appeared to be subsequent reduction in risk at longer lags.
Thus, it is interpreted by
the researchers that this kind of a pattern could increase the chances of a
heart attack occurring much earlier in life than expected, in those prone to
1. The effects of hourly differences in air pollution on
the risk of myocardial infarction: case crossover analysis of the MINAP
database; Krishnan Bhaskaran et al; BMJ 2011; 343:d5531
3. National Atmospheric Emissions Inventory