Study finds Catalyst Metal Emissions Substantial, Allergy, Asthma link seen

Diesel Fuel News, Jan 7, 2002 by Jack Peckham

A study at University of Notre Dame (UND) on the emissions of platinum-group metals (PGM) from vehicle catalytic converters along U.S. roadsides suggests a potential link between the startling rise in allergies and asthma in the U.S. and the co-incident introduction of exhaust catalysts 26 years ago.

In recent years, many health advocacy groups and some U.S. EPA officials have often linked diesel exhaust and asthma, justifying pushes for alternative fuels, much to the dismay of clean-diesel technology defenders.

On the other hand, some U.S. Department of Energy officials at the Diesel Engine Emissions Reduction (DEER) workshops in recent years have suggested that the evidence for diesel exhaust causing asthma is rather slim, whereas some researchers see a possible link between gasoline vehicle catalyst particle emissions and the co-incident rise in asthma (see Diesel Fuel News 9/17/2001, p7).

Now, the UND study shows that so much platinum (Pt), palladium (Pd) and rhodium (Rd) - common materials in 3-way catalysts on hundreds of millions of U.S. gasoline vehicles - are attriting from catalysts as fine particulate matter (PM) along roadways that it may be possible to "mine" roadsides profitably for precious-metal recovery.

Catalyst fine particles are so extensive that it's likely that humans near the source emissions are breathing-in or otherwise taking-in some amount of PGM and catalyst alumina substrate, with possible health implications, the researchers suggested, citing other studies.

However, the UND study didn't investigate or compare the relative contribution of catalyst particle emissions to possible health effects. Over the same three decades since exhaust catalysts debuted, total gasoline and diesel combustion likewise has increased -- by tens of billions of gallons -- causing considerable increase in various exhaust particles including nitrates (from nitrogen oxide emissions) and sulfates (from sulfur oxide), along with increases in hydrocarbons, elemental carbon and other particles.

Over the decades, combustion emissions sources can account for billions of pounds of combustion products -- some of them relatively benign, such as CO2, but others not so benign. Example: U.S. EPA estimates that diesel PM emissions were 500,000 tons in 1996.

By contrast, total platinum consumption for vehicle catalysts in North America was 600,000 ounces last year, while total palladium for catalysts was 2.8 million ounces, according to a recent Johnson-Matthey report.

It's estimated that between 1 to 5% of PGM would be emitted by catalytic converters over the vehicle life, according to Clean Diesel Technologies (CDT), makers of a platinum/cerium diesel fuel additive that reduces diesel emissions and promotes PM filter regeneration.

"That's just ounces of metal emitted from catalysts, compared to tons of diesel PM" emissions, points out CDT official Jim Valentine.

Likewise, Association for Emissions Control by Catalyst (AECC) and Manufacturers of Emission Control Association (MECA) contend that exhaust catalyst emissions are "tiny amounts of material . . . in the form of small particles of inert metal," which are "not allergenic." Recent German roadside catalyst emission studies show that most of the catalyst particles settle out close to roadside (within 7 meters), with levels 10 meters away at background levels, AECC said.

The UND news release describing the study findings says that "potentially harmful levels of platinum-group elements are being dispersed on roadsides," and says that "platinum is highly allergenic and consistent exposure to it at even low levels can lead to asthma, sensitive skin or other symptoms."

* Doubts On Health Threat

However, CDT points out that the platinum health threat suggestions can be misleading or exaggerated.

"There is no allergenic response to platinum metal (used in jewelry) or platinum oxide emissions and no known toxicity," CDT's Valentine told us. "Response is to chlorinated or halogenated ionic platinum compounds which cause a response in some platinum refinery workers. These compounds are no longer used in catalytic converters and are not used in our fuel additive. Diesel oxidation catalysts also emit small amounts of platinum. So if they found chlorinated platinum compounds [in the UND study] they might have a point, but if it's platinum metal, then they should pick it up."

Platinum is also being taken up in the cells of some roadside plants, possibly pointing toward human ingestion of PGM from crops grown near highways, the UND study found. Whether this poses any health threat isn't yet known, they said.

The UND study is the first-ever in the U.S., although studies in Europe earlier spotted similar catalyst attrition trends and raised questions about possible health effects. The UND study now confirms that PGM attrition roadside abundance in the U.S. is comparable to that found in European studies.

"The amount and rate of [PGM] release from catalytic converters is affected by the speed of the automobile, type of engine, type and age of catalyst, and type of fuel additives," the UND researchers reported, citing other studies. They also noted that "higher speeds and catalyst temperatures enhanced attrition and emissions of PGMs.