3. Psicología y salud
3.2. Modelos de Salud en Psicología
8.1.1
Evidence relating health effects to exposure to PM
from specific emission sources
Source apportionment applied to health outcome data
The methods used to apportion PM measured in ambient air to different sources are still evolving and it is a relatively new area of study. Due to the dynamic nature of atmospheric processes that affect the chemical and physical characteristics of emitted PM, source apportionment models are associated with an inherent amount of uncertainty. Furthermore, attribution of the identified emission profiles (or ‘factors’) to specific sources requires judgement and, therefore, includes inherent subjective uncertainty. This uncertainty is added to the uncertainty associated with the use of fixed-site monitors to estimate human exposure. Hence overall, the findings of studies linking specific sources to human health effects using source apportionment need to be interpreted with some caution.
Despite these limitations, source apportionment is a way of estimating the health impact of exposure to PM from a specific source in contrast to the total ambient PM mixture comprising PM from multiple sources.
Source apportionment studies suggest:
There is strong evidence that exposure to ambient PM from combustion emissions (particularly coal-fired power stations, diesel and, on-road vehicle emissions) is associated with adverse health outcomes.
Community-based cohort and cross-sectional studies
The health effects of PM emissions from coal mines and on-road vehicles have been investigated in communities that live close to these emission sources. A major limitation of these studies is that living in a particular location is invariably associated with a variety of factors that impact health and it can be difficult to find a directly comparable population with which to compare health outcomes. Nevertheless, these cohort and cross-sectional studies add to the evidence from source apportionment studies.
Community-based cohort studies show that:
living in close proximity to major roadways is associated with adverse health outcomes that are likely to be partially attributable to exposure to on-road vehicle PM emissions; living in close proximity to coal mines has been associated with adverse health outcomes
however there is insufficient evidence (due to study limitations and the small number of studies) to conclude that these health outcomes are specifically related to exposure to coal dust.
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Time-series studies
Time-series studies have investigated daily health outcomes associated with short-term exposure to increased ambient PM levels during bushfires, severe dust storms and periods of high use of wood - fuelled domestic heating. Many factors that affect population health change on a daily basis (e.g. air temperature) however, properly controlled time-series studies can show strong evidence of associations between ambient PM and daily health outcomes.
Time-series studies show that:
exposure to increased ambient PM mass during severe dust storms and bushfires is associated with adverse health effects, particularly in people with chronic respiratory disease;
exposure to ambient PM from wood-fired domestic heating is associated with an increase in respiratory disease symptoms and adverse respiratory events.
Intervention evaluation
There have been very few evaluations of the health impacts of interventions that have changed source-specific PM emissions. Interventions that have been evaluated include: a ban on coal sales in Dublin (Clancy et al. 2002), re-opening of a steel mill in Utah (Pope III 1989) and, reductions in the sulphur content of fuel oil for power stations and vehicles in Hong Kong (Hedley et al. 2002). Evaluations of interventions that have changed source-specific PM emissions suggest that:
exposures to PM emissions from combustion sources (domestic coal combustion, industrial combustion, power stations and vehicles) are associated with increased cardiovascular and respiratory mortality and morbidity.
Controlled human exposure (chamber) and toxicological studies
Controlled human exposure (chamber) and animal/cellular toxicological studies have been used to examine the biological effects of a variety of PM emissions, particularly diesel exhaust and wood smoke.
Controlled human exposure and animal/cellular toxicological studies demonstrate that:
exposure to diesel exhaust PM results in a variety of cardiovascular, respiratory, carcinogenic and developmental biological effects, many of which are consistent with the health effects associated with occupational exposure to diesel exhaust;
exposure to wood smoke PM results in compromised lung immune defence, oxidative stress responses and inflammation, effects that are consistent with adverse respiratory health endpoints in epidemiological studies.
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8.1.2
Evidence relating health effects to exposure to
ambient particle mass concentration and, PM of
specific size or chemical composition
Particle mass concentration
There is strong evidence from many large cohort studies and time -series studies that the ambient concentration of PM mass is associated with adverse health outcomes.
Long-term and short-term exposure to ambient PM mass is associated with adverse health outcomes, primarily related to respiratory and cardiovascular diseases but also including lung cancer, birth outcomes and developmental outcomes.
There is limited evidence related to the health impacts of low concentrations (<8 µg/m3) of ambient PM. There is no evidence of a concentration threshold below which ambient PM has no health effects, suggesting that improvements in population health will continue to occur as ambient mass concentrations of PM are reduced to “background levels”.
Particle size
There is strong evidence from cohort, time-series and toxicological studies that particle size influences the health effects associated with exposure to PM.
There is evidence that smaller particles have a greater impact on health than larger particles however some studies have indicated that larger (coarse) particles may preferentially affect the airways and lungs and cause more respiratory health effects than smaller particles.
Particle size is the basis on which PM is classified and has defined the study of exposure - response functions however particle composition is also important with regards to the health effects of PM.
Particle chemical composition
Ambient PM is recognised as a “mix” of many particles, with different compositions. The composition of PM is thought to influence the health impact of exposure.
There is evidence that metals and organic compounds within PM have toxic effects. There is evidence of health effects associated with sulphates and nitrates within PM but
this evidence is variable and generally effects are not greater than those associated with total PM2.5 mass.
179 Organic compounds in PM, particularly those emitted during the combustion of fossil fuels, are likely to cause health effects. However, the specific health impacts of organic compounds are unclear.
The evidence relating health effects to exposure of ambient concentrations of specific constituents of PM is still emerging. Presently, it is appropriate to continue to base emission reduction policies on minimising ambient particle mass rather than specific particle constituents.