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Nanoparticles

Lemnos meeting 11 September 2003

Nuclei or accumulation mode - which particles are most significant from a health

point of view?

Urban WassVolvo Technology [email protected]


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Heavy-duty Engines

1,00E+10

1,00E+11

1,00E+12

1,00E+13

1,00E+14

1,00E+15

1,00E+16

1 10 100 1000

Particle diameter (nm)

Part

icle

num

ber p

er k

W/h

Euro I, D1

Euro III, D2

Euro III+CRT, D5

50

”Semi-volatile”+ solidnanoparticles

Solidnanoparticles


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Accumulation Mode Particles (Soot)

• A core of elemental carbon and adsorbed organic compounds

• A number of potentially toxicologically-relevant organic compounds, such as PAHs, nitro-PAHs, and oxidized PAH derivatives

• Small amounts of sulfate, nitrate, metals, and other trace elements

• Well-proven toxicity in animal studies• Potential health risks in humans:

• Long-term: lung cancer, other lung damage• Short-term: Irritation and inflammatory symptoms of

a transient nature


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Nucleation Mode Particles

• ”Semi volatile”• Formed from nucleation of sulphuric acid and water,

followed by particle growth by condensation of organic species

• Unburned fuel and lubricating oil are probably a major source of the organic matter

• Typically only a few percent or less of particulate mass• Limited lifetime in the atmosphere (?)


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Adverse Health Effects fromHeavy Hydrocarbon Exposure

• Oil fog (mist) *• Rats, 3.5 h/week, 4 days/w, 4 or 13 weeks• 0, 0,5, 1,5 g/m3

• Inflammation only at the highest exposure level• Raw Jet Fuel**

• Rats• Moderate inflammation at 1 g/m3

• Exposures more than a million times the maximum exposures in polluted cities, yet little effect

• Nucleation mode particles are likely to de dissolved or dispersed in the lung lining fluid

*) Selgrade et al. J Toxicol. Environ. Health. 1987;21:173-185.Selgrade et al. Toxicol. Ind. Health. 1990;6:123-143.

**) Wang S et al. Toxicol. Ind. Health. 2001;17:23-29


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Adverse Health Effects fromSulphuric Acid Droplets

• Mild effects of sulphuric acid at exposure of about 100 µg/m3 *• One study failed to show any effect on lung function at 3

mg/m3, either as 6 µm or 0.3 µm aerosols **• There are no studies of effects from exposures at such low

concentrations of sulphuric acid that would result from ambient diesel engine exhaust

• Theory indicates that very small sulphuric acid droplets may be less toxic than larger ones, and that they may be neutralized by endogenous NH3 ***

• Experimental studies have not demonstrated any consistent differences between sulphuric aerosols of different sizes.

*) Frampton et al. Environ Res 1995;69:1-14. **) Aris R et al. Am Rev Resp Dis 1991;142:744-750***) Jarvholm B, Rappaport S. Int J Occup Environ Health 1995;1:311-314


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Mass

• Particulate mass is the only metric for which health-based air quality guidelines have been established

• ”Although uncertainty exists as to whether DPM [Diesel particulate matter mass, µg/m3] is the most appropriate parameter to correlate with human health effects, it is considered a reasonable choice until more definitive information about the mechanisms of toxicity or mode(s) of action of DE [Diesel Exhaust] becomes available”The Health Assessment Document for Diesel Engine Exhaust (DE). US EPA May 2003


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Reflections

• One can never prove the null hypothesis (that is, that certain particles pose no danger)

• It is prudent to put more weight on a risk factor that has been “proven” in well-conducted studies than on a factor that has been claimed to pose a risk but where data to back up this assumption are lacking


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Conclusions

• No convincing evidence that particles in the nucleation mode would be more toxic than particles in the accumulation mode The situation appears to be rather the opposite The carbonaceous accumulation mode is likely to be the most

important from a health perspective It seems unlikely that ambient levels of nucleation mode

particles would pose any significant health risk if they consist of heavy hydrocarbons [from lubrication oil] and sulphuric acid

• Absence of evidence of risk is not evidence for absence of risk

• The ”precautionary principle” warrants further studies of the ”nucleation phenomena”

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