Bio-Kaffee, der Geschmack von Mexiko
5.2.3 AGENTE BROKER
There are two approaches to the investigation of negative health effects associated with exposure to particles by inhalation. First, to investigate the long-term influence of habitual inhalation of poor quality air on morbidity and mortality. Second, to examine the short-term sequelae of exposure to high particulate aerosol loading in poor air.
Most epidemiological studies that have been performed on large popula-tions have used PM10as the index of exposure. There is now widely accepted evidence that chronic exposure to typical urban levels of PM10 damages health. Studies which have examined the prevalence or incidence of disease, in relation to the levels of particulate pollution, while controlling for confounding factors, have shown associations between exposure and increased premature mortality, chronic respiratory disease and reduced lung function
(Dockery et al, 1989, 1993; Abbey et al, 1995; Pope et al, 1995; Raizenne et al, 1996; Ackermann-Liebriche et al, 1997; Kunzli et al, 2000). The ‘six city study’
in the USA found a differential mortality between the most and the least polluted cities of approximately 15 per cent, after controlling for confounding factors. The study concluded that around 3 per cent of all deaths in the USA were associated with inhalation of particles. The study by Kunzli et al (2000) concluded that up to 6 per cent of all deaths, in the parts of Europe included in the study, could be associated with particle inhalation. The pathogenic mechanism is not clear, but a large proportion of the increase in pathology in the populations studied is associated with cardiovascular disease, which is similar to the pattern of disease in tobacco smokers and suggests that there may be a common aetiology. The observations of Seaton et al (1995) may be of considerable relevance.
With respect to acute mortality and exposure to particulate aerosols, there is another body of evidence which supports the hypothesis that they can be the cause of ‘deaths brought forward’. Figure 13.1 shows the results of
–2 –1 0 1 2 3 4 London, UK
Aphea (8 cities) Los Angeles, CA Chicago, IL Erfurt, Germany Santiago, Chile Amsterdam, NL Steubenville, OH Santa Clara, CA Brisbane Athens, Greece Detroit, MI Birmingham, AL Cincinnati, OH Philadelphia, PA Sau Paulo, Brazil Utah Valley, UT St Louis, MO Kingston, TN
Differential epidemiology of ambient aerosols
% increase in mortality
Figure 13.1 PM10and daily mortality from cities around the world. Expressed as a percentage change in daily mortality associated with a 10m3increase in PM10
(Anderson, 2000).
Nanotechnology and Nanoparticle Toxicity: A Case for Precaution 161
studies on daily mortality performed in 19 cities around the globe. The percent increase in mortality for an associated increase of 10mm3 in PM10 is shown. Although not all the studies reached statistical significance, they do all point in the same direction. This is strongly indicative of a causal relationship.
The increase in mortality is expressed through respiratory failure and cardiovascular events, such as myocardial infarctions and strokes. In general, the temporal trend is predicable, the respiratory deaths occurring within the first 24 hours after the onset of poor air quality, while some studies show that the cardiovascular events peak with a lag of about 4 days after the onset of poor air quality. This is indicated in Figure 13.2.
Discussion
While acknowledging the potential benefits of nanotechnology, the main aspect of concern in the immediate future is the manufacture and release into the environment of free nanoparticles in the size range 1–100nm. The literature that exists on the health effects of nanoparticles indicates that a precautionary stance should be adopted, particularly because the relevant risk assessments have not yet been completed and the hazard characterizations have yet to
1.22
1.11
1.00
0.90 4 4 1 1
total cv re other
4 4 1 1
total
UP ‘PM2.5’
cv re other
Figure 13.2 Effects of ultrafine particles (UFP) and fine particles (PM2:5) on mortality for prevalent diseases (total, cardiovascular, respiratory, others). Best day-lag model. There seems to be a stronger immediate effect (lag 0 or 1 day) on respiratory causes and a stronger delayed effect (lag 4 or 5 days) on cardiovascular
causes (Wichman and Peters, 2000).
reach consensus. Direct research on nanoparticles, though still relatively scarce, supports such a cautious approach. Most of our current knowledge on the effects of nanoparticles on humans has come from the study of ambient aerosols of pollutants.
Populations living in urban locations are routinely exposed to ambient levels of particulate aerosols that did not exist throughout evolution. There is strong evidence that our respiratory systems are not well adapted to cope with the smaller size fractions such as aerosols. In particular, the ultrafine fraction tends to be preferentially deposited in the alveolar portion of the lung, beyond the mucociliary escalator. In the alveolar region the alveolar macrophages, the final defence mechanism before particle internalization occurs, have difficulty recognizing the smallest particles and in addition they are easily overloaded by the numbers of particles arriving. Once internalized, insoluble particles appear to have the ability to translocate to other body compartments.
The influence of the size of particles on their toxicity is currently the subject of increasing research. The indication from current research is that there is a general tendency for acute toxicity, expressed through an ability to induce inflammation, to increase as the particle size decreases, particularly below 100nm diameter. The precise mechanism of this effect remains unknown but there are indications that it is associated with changes in the surface chemistry, possibly through an ability to produce free radicals. There are parallels with the action of heterogeneous catalysts.
Although many countries continue to use PM10as the standard metric for assessing particle exposure, some countries are changing to the use of PM2:5. There is a debate within the scientific community concerning which fraction of PM10is responsible for its toxicity. CAFE´, a European scientific committee studying the effects of air pollution on health has recently recommended that the EU adopt a PM2:5regulatory standard.
What appears to be beyond dispute is that health effects at the population level have been associated with both chronic and acute particulate aerosol exposure. The science is widely accepted and recognized to be of a high standard, despite some reservations from certain industries (HEI, 2000).
The positive aspect of this problem is that particulate aerosols are short lived and, unlike some other forms of pollution, do not persist in the environment. The associated health problems are therefore open to remedia-tion. It is simply a matter of political willpower being sufficient for policy implementation to take place.
The negative aspect is that the ultrafine fraction of particulate aerosols, arguably the most hazardous part, is the most stubbornly resistant to abatement through regulation (Wichmann and Peters, 2000). Additionally, the major source of particulate emissions in cities is vehicular traffic. Exclusion of vehicles from areas of high population density is currently a difficult political problem.
However, reduction in particulate aerosol concentrations would definitely lead to tangible health benefits in the relatively short term, and therefore should be actively pursued.
Nanotechnology and Nanoparticle Toxicity: A Case for Precaution 163
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