2. How does Particulate Matter (PM) affect human health?

2.1 Effects of long-term exposure to levels of PM observed currently in Europe
2.2 Is PM per se responsible for effects on health?
2.3 Which physical and chemical characteristics of PM are responsible for health effects?
2.4 Are health effects of PM influenced by the presence of other gaseous air pollutants?
2.5 Characteristics of individuals may influence how PM affects them
2.6 Is there a threshold below which nobody’s health is affected by PM?

2.1 Which effects can be expected of long-term exposure to levels of PM observed currently in Europe?

WHO states:

2.1.1 "Long-term ambient exposure to current ambient PM concentrations may lead to a marked reduction in life expectancy. The reduction in life expectancy is primarily due to increased cardio-pulmonary and lung cancer mortality.
Increases are likely in lower respiratory symptoms and reduced lung function in children, and chronic obstructive pulmonary disease and reduced lung function in adults." More...

2.1.2 "Cohort studies have suggested that life expectancy is decreased by long-term exposure to PM. This is supported by new analyses of time-series studies that have shown death being advanced by periods of at least a few months, for causes of death such as cardiovascular and chronic pulmonary disease." More...

Source & © : WHO Europe (2003)

2.2 Is PM per se responsible for effects on health?

2.2.1 WHO states: "Ambient PM per se is considered responsible for the health effects seen in the large multi-city epidemiological studies relating ambient PM to mortality and morbidity such as NMMAPS [National Morbidity, Mortality and Air Pollution study] and APHEA [Air Pollution and Health: A European Approach]. In the Six Cities and ACS [American Cancer Society] cohort studies, PM but not gaseous pollutants with the exception of sulfur dioxide was associated with mortality. That ambient PM is responsible per se for effects on health is substantiated by controlled human exposure studies, and to some extent by experimental findings in animals." More...

Source & © : WHO Europe (2003)

2.2.2 A large number of epidemiological studies show that PM₁₀ (which includes both fine and coarse particles) has adverse health effects. The fewer studies considering the fine particle fraction (PM_2.5) separately show that there are also health effects specifically from this fraction. Only recently have investigators begun to separately address health effects of coarse particles (PM_10-2.5).

Time series studies have assessed whether coarse particles are associated with health effects independently of the fine fraction (PM_2.5). They provide limited evidence for an association with mortality, as well as evidence for an association with specific health effects (morbidity endpoints) such as respiratory hospitalizations. One study that investigated the effect of long-term exposure to coarse particles did not show an impact on life expectancy.

Studies considering the way different particles deposit in the lungs, their chemical composition, and their toxicity provide further evidence of adverse health effects of coarse PM. For example, some effects that are seen with the coarse particles may be due to the presence of microbial structures and toxins which are less frequently found associated with fine particles. Therefore, there is sufficient concern about the health effects of coarse particles to justify their control. More...

2.3 Which of the physical and chemical characteristics of PM are responsible for health effects?

WHO states: "There is strong evidence to conclude that fine particles (< 2.5 µm, PM_2.5) are more hazardous than larger ones (coarse particles) in terms of mortality and cardiovascular and respiratory endpoints in panel studies. This does not imply that the coarse fraction of PM₁₀ is innocuous. In toxicological and controlled human exposure studies, several physical, biological and chemical characteristics of particles have been found to elicit cardiopulmonary responses. Amongst the characteristics found to be contributing to toxicity in epidemiological and controlled exposure studies are metal content, presence of PAHs, other organic components, endotoxin and both small (< 2.5 µm) and extremely small size (< 0.100 µm)." More...

Source & © : WHO Europe (2003)

2.4 Are health effects of PM influenced by the presence of other gaseous air pollutants?

WHO states: "Few epidemiological studies have addressed interactions of PM with other pollutants. Toxicological and controlled human exposure studies have shown additive and in some cases, more than additive effects, especially for combinations of PM and ozone, and of PM (especially diesel [exhaust] particles) and allergens. Finally, studies of atmospheric chemistry demonstrate that PM interacts with gases to alter its composition and hence its toxicity." More...

Source & © : WHO Europe (2003)

2.5 Which characteristics of individuals may influence how PM affects their health?

Are effects of PM dependent upon the subjects’ characteristics such as age, gender, underlying disease, smoking status, atopy, education etc? What are the critical characteristics?

In short-term studies, elderly people and those with pre-existing heart and lung disease were found to be more susceptible to effects of ambient PM on mortality and morbidity. In panel studies, asthmatics have also been shown to be more vulnerable to ambient PM compared to non-asthmatics. Responses of asthmatics to PM exposure include increased symptoms, larger lung function changes, and increased medication use.

In long-term studies, it has been suggested that socially disadvantaged and poorly educated populations respond more strongly in terms of mortality. PM exposure is also related to reduced lung growth in children.

In cohort studies, no consistent differences have been found between men and women nor between smokers and non-smokers in PM responses. More...

2.6 Is there a threshold below which nobody’s health is affected by PM?

"Epidemiological studies on large populations have been unable to identify a threshold concentration below which ambient PM has no effect on health. It is likely that within any large human population, there is such a wide range in susceptibility that some subjects are at risk even at the lowest end of the concentration range." More...

Source & © : WHO Europe (2003)

See also: General Issues and Recommendations on Air Pollutants:

• question 1.3 on uncertainties in defining thresholds
• question 3.1 recommendations regarding the concept of threshold