PM health studies

[Guest guest]

University of Rochester has been doing a lot of this research.

www2.envmed.rochester.edu/envmed/PMC/anrep05.pdf

I spoke with another medical researcher (with UMDNJ-EOHSI) working on PM this week and was told that exposure studies done using pure elemental carbon (not from exhaust particles containing reactive oxidative species and other organics) showed that it is not the particle, per se, but the combustion product that causes the health effects. Even though all the talk is about PM10 and 2.5 respirable particles, it is not the particles themselves, but what they are comprised of, that should be of concern. So gravimetric analysis of ambient respirable particles is only a very indirect and inaccurate measure of what causes health effects - but evidently is what EPA intends to use for regulatory compliance purposes. They will be measuring pollen and mold spores but considering them to be diesel exhaust particles.

Comments?

Steve Temes

[Guest guest]

Steve,

It seems there would be a reactive component

for reactive particles.  But it also

seems likely that there is also an obstructive effect due to the fact that the

particle has mass and can physically obstruct gas exchange.  I would imagine that the finer the particle

the more efficient it would be at obstruction since it could enter deeper into

the lungs.  With fossil fuel combustion

products I would imagine that the reactive side would be more important, but

what about non-organic fine particles?

Mark Doughty

PM health

studies

University of Rochester has been doing a lot of this research.

www2.envmed.rochester.edu/envmed/PMC/anrep05.pdf

I spoke with another

medical researcher (with UMDNJ-EOHSI) working on PM this week and was told that

exposure studies done using pure elemental carbon (not from exhaust particles

containing reactive oxidative species and other organics) showed that it is not

the particle, per se, but the combustion product that causes the health

effects. Even though all the talk is about PM10 and 2.5 respirable

particles, it is not the particles themselves, but what they are comprised of,

that should be of concern. So gravimetric analysis of ambient respirable

particles is only a very indirect and inaccurate measure of what causes health

effects - but evidently is what EPA intends to use for regulatory compliance

purposes. They will be measuring pollen and mold spores but considering

them to be diesel exhaust particles.

Comments?

Steve Temes

[Guest guest]

A few comments below (if you have time).

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-----Original Message-----From: iequality [mailto:iequality ] On Behalf Of M. DydekSent: Friday, March 03, 2006 9:57 AMTo: iequality Subject: Re: PM health studies

Dear List:As a regulatory toxicologist, I have been involved with the issue of particulate matter (PM) toxicity for quite a while. Perhaps I can offer some insights.I agree with some earlier comments made in this forum that the total mass of PM is a crude measure of health risk. The advantage of using this parameter is that it is relatively easy to measure and fairly simple to explain to the lay public. As a toxicologist, though, I have always thought that it must be more than just the total mass or total number of particles that is most relevant to the human health risk assessment of PM exposure.In the latest EPA documentation (Air Quality Criteria for Particulate Matter), there is some discussion about chemical composition of the particles. The science is still inadequate in explaining what is really happening when a person is over-exposed to PM, but there is good evidence from epidemiological studies that some forms of PM are not associated with increased health risks. These are the so-called "crustal" particles, meaning PM that is from uncontaminated dust made up of materials common in the earth's crust (in other words, "just dirt").This make sense from an evolutionary biology point of view. Humans have been exposed to windblown dust for millions of years and have developed biological defense mechanisms to deal with those types of particles. Other types of PM, such as those from coal and oil combustion sources are relatively new in human history and we have not had time to adapt to these insults as yet.

Or from the opposing position, the earth's dust has been pretty much the same as it was intended and we screw it up more every day.

There are many conjectures about what might be the actual toxic agent(s) in PM that are the ones most likely to pose the highest health risk. Some say it's the metals content, others the acidity, others the polycyclic aromatic hydrocarbon (PAH) or other organic components of the PM. As I mentioned, at this point we don't really know what fractions or combination of fractions of PM are driving the health risks.

The surface area effect can be thought of in two ways:

1) Greater reactive area per volume (which must be tied to particle size and shape) for classical toxic mechanisms. Or, as in the case of polymorphs, a) greater dissolution in the blood or differing Gibbs free energy allowing differing cellular mutations or reactions to become more likely.

2) 3-D fit like a glove and hand necessary which (under certain cirmustances) can be correlated with effective surface area. [Expect more likely needed for immune (allergy)response]

I have some fractal dimension structural work on diesel particulate v health effects done by a colleague (now deceased) that indicates this relationship as a good correlation (or at least by fit of the model).So in conclusion, it can be said that not all particles are created equal (toxicologically). There is evidence that crustal particles are not as toxic as those produced by industrial sources, but beyond that there is much to be learned. For the time being, it appears that the relatively crude "total mass" measure will have to suffice for regulatory purposes.

This can be particularily useful when either a) the particles are generated sufficiently similar in charateristics of concern that the all act the same (except in unusual cases), and where general loading is an issue.

Consider the "weaponization" of bacillus anthracis causing inhalation anthrax recently compared to the 1950 inhalation cases in the US where b. anthracis spores were attached to goat/sheep hair - differing characteristics and different results.

Consider the fumed (spherical), particle (blocky), and "sponge" style lead and the electrical charge differences by each and the correlation to dissolution in the blood - better surface area as indicated by electrical charge conductance - the better the dissolution in the blood.

I hope this helps to shed some light on this interesting topic. DydekDydek Toxicology Consultingwww.tox-expert.com______________________________________________________________________________________Mark Doughty wrote:

Steve,

It seems there would be a reactive component for reactive particles. But it also seems likely that there is also an obstructive effect due to the fact that the particle has mass and can physically obstruct gas exchange. I would imagine that the finer the particle the more efficient it would be at obstruction since it could enter deeper into the lungs. With fossil fuel combustion products I would imagine that the reactive side would be more important, but what about non-organic fine particles?

Mark Doughty

-----Original Message-----From: iequality [mailto:iequality ] On Behalf Of AirwaysEnv@...Sent: Thursday, March 02, 2006 1:49 PMTo: iequality Subject: PM health studies

University of Rochester has been doing a lot of this research.www2.envmed.rochester.edu/envmed/PMC/anrep05.pdf I spoke with another medical researcher (with UMDNJ-EOHSI) working on PM this week and was told that exposure studies done using pure elemental carbon (not from exhaust particles containing reactive oxidative species and other organics) showed that it is not the particle, per se, but the combustion product that causes the health effects. Even though all the talk is about PM10 and 2.5 respirable particles, it is not the particles themselves, but what they are comprised of, that should be of concern. So gravimetric analysis of ambient respirable particles is only a very indirect and inaccurate measure of what causes health effects - but evidently is what EPA intends to use for regulatory compliance purposes. They will be measuring pollen and mold spores but considering them to be diesel exhaust particles.Comments?Steve Temes -- Dr. M. Dydek, Ph.D., D.A.B.T., P.E.

Chemical Toxicologist and Engineer

Dydek Toxicology Consulting

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