Vehicular Exhaust and Air Pollution

Introduction

Individual tailpipe emissions

Transport and fate in the environment

Measuring exposures

Prevention and control of exposure

Exposure Pathway

Risk assessment

Adverse effects


Harmful Effects

Dose Response

Absorption, Metabolism and Molecular Mechanisms of Action

Organ Sites of Toxicity

Biomarkers

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Ozone and Particulate Matter:

There are two main organ site of toxicity associated with ground level ozone and particulate matter, the respiratory tract and the cardiovascular system. The main evidence for this comes from the fact that people with impaired respiratory systems are primarily affected. High levels of asthma have been associated with elevated levels of air pollution, particularly in ozone and particulate matter (PM), in urban centers. Although children, and people with pre-existing respiratory problems are primarily affected, healthy people are at risk as well. Exposure to ozone for 6 to 7 hours, even at relatively low concentrations, significantly reduces lung function and induces respiratory inflammation in normal, healthy people. It can be accompanied by symptoms such as chest pain, coughing, nausea, and pulmonary congestion. Studies in animals and evidence from humans has shown that repeated exposure to high levels of ozone can produce permanent structural damage to the lungs. The cardiovascular system is another lesser known target of particulate matter and ozone. Elevated levels of these two pollutants have been associated with increased heart related deaths.

Respiratory System

Here is a sample of some studies done showing an association between ozone and particulate matter with impaired respiratory function:

Journal 1

An experiment done in Mexico City in the mid 1990’s looked at the effects of the general non-hospitalized population with increasing ozone concentrations.

They found that ozone increments (10ppb) were associated with upper respiratory symptoms and ocular symptoms. During emergency episodes, symptoms increased sharply when ozone reached 281 ppb, a finding that resulted in a change in the ozone criteria for emergency declaration from 294 to 281 ppb.

Sanchez-Carrillo CI, Ceron-Mireles P, Rojas-Martinez MR, Medoza-Alvarado L, Olaiz-Fernandez G, Borja-Aburto VH. Surveillance of acute health effects of air pollution in Mexico City. Epidemiology. 2003 Sep;14(5):536-44.

Journal 2

Another study was done to show that exposure of healthy subjects and asthmatics to ozone levels comparable to those measured in ambient air during hot summer days can generate respiratory symptoms, neutrophilic airways inflammation and lung function impairment.

The study found that lung function does change following ozone exposure and is more pronounced in asthmatics. They also found that the airway epithelial cell layer is likely to play a pivotal role in initiating the inflammatory process following ozone exposure.

Kleis S, Louis R, Bartsch P. Ozone exposure and asthma. Rev Med Liege. 2003 Mar;58(3):132-8.

Cardiovascular

Particulate Matter and ozone have been associated with varying degrees of cardiac autonomic dysfunction. They appear to lower the human heart’s ability to vary it’s speed, resulting in increased heart attacks and heart related deaths. Particulate matter and ozone also thicken the blood and increases coagulation, thereby raising the risk for a stroke.

Journal 3

A study was conducted in a nursing home in Mexico to determine the association between heart rate variability and air pollution. Heart rate variability was measured every other day for three months. They also took daily measurements of indoor and outdoor air quality. PM 2.5 levels averaged 50ug/m3 , while daily 1-hour maximum ozone levels ranged from 47 to 228 ppb. Their results suggested that ambient levels of PM2.5 and ozone can reduce the high-frequency component of heart rate variability and that subjects with underlying hypertension are particularly susceptible to this effect.

Holguin F, Tellez-Rojo MM, Hernandez M, Cortez M, Chow JC, Watson JG, Mannino D, Romieu I.Air pollution and heart rate variability among the elderly in Mexico City. City. Epidemiology. 2003 Sep;14(5):521-7

Journal 4

A study in Taiwan showed that admissions for strokes go up significantly on days when air pollution is bad, PM 2.5 and ozone appear to be the most dangerous. Air pollution had the strongest affect on burst blood vessels in the brain but also showed an effect on blood clots blocking blood flow to the brain. They claimed that air pollution thickens the blood and may cause clots to break loose and enter circulation thereby increasing the risk of a stroke. They also found that air pollution irritated and inflamed small structures deep inside the long. This caused an increase in blood coagulation making clots more likely. The particulate matter also caused blood vessels to constrict and narrow which poses a great danger to people with pre-existing conditions.

Tsai SS, Goggins WB, Chiu HF, Yang CY. Evidence for an association between air pollution and daily stroke admissions in Kaohsiung, Taiwan. Stroke. 2003 Nov;34(11):2612-6. Epub 2003 Oct 09