The approximately one billion gallons of used oil generated in the United States each year comes primarily from lubricating oils -- motor and transmission oils -- and from hydraulic and cutting oils used in industry.
The researchers found that selling untreated used oil as an inexpensive fuel, the most common method of managing used oil in the United States, causes significant emissions of heavy metals like lead and zinc.
There are three primary ways of managing used oil: About 14 percent of old oil is re-refined; 11 percent is treated and recycled for heating fuel; and 75 percent is resold, without treatment, as fuel oil to industrial consumers. It's the latter that presents the biggest problem, according to the authors of the new study.
"We have the oil changed in our cars, but what happens after that [oil] is out of sight and out of mind?" asks Bob Boughton, a researcher with the California Department of Toxic Substances Control and lead author of the paper. "Only 10 percent of the more than 100 million gallons of used oil generated each year in California is recycled to produce useful lubricants, just as paper is recycled to produce paper again."
Boughton, along with Arpad Horvath, Ph.D., from the University of California, Berkeley, compared the environmental impacts from each of the three ways of managing used oil, focusing on used oil data from California in 2002.
They found that, while the three ways of handling used oil were equal in their effects on ozone depletion and global warming, emissions from the untreated used oil fuel contained significantly higher levels of zinc, lead, copper and cadmium -- heavy metals that can threaten both human health and the environment.
The total emission of heavy metals from used oil fuel in 2002 was potentially on the same scale as the combined emissions from all of California's large stationary pollution sources, such as refineries and other manufacturing plants. These staggering results suggest that Californians -- and others in the United States -- should support recycling and re-refining programs to reduce this environmental burden, according to Boughton.
The study's results are representative of the nation, Boughton says.
Because of its stringent air quality standards, the majority of California's untreated used oil is sold to out-of-state and overseas customers.
In terms of total mass, zinc was by far the most abundant metal in the study, with emissions of about 136 metric tons from California's used oil in 2002. Copper and lead weighed in at 6.5 and 5.2 metric tons respectively.
But total mass alone does not address the potential threat to human health or the environment, so the researchers used a weighting method to compare the impacts. Each metal was assigned a value for its potential toxicity to both humans and terrestrial ecosystems, based on its known behavior in the environment. Compared to lead, for example, zinc is more toxic to wildlife and ecosystems, but much less toxic to humans.
After adjusting for each metal's relative toxicity and adding the results together, the researchers compared the effects of untreated used oil as fuel to both re-refining and distillation. In both comparisons, the toxicity potential of untreated oil was 150 times greater for terrestrial ecosystems, and more than five times greater for humans. Zinc and cadmium posed the greatest threat to ecosystems; lead and chromium drove the human health effects.
The results provide further incentive for citizens and policymakers to encourage alternative used oil management strategies, possibly through incentives for treatment and by supporting markets for processed oil products, according to Boughton. But he is quick to point out what he considers the best option of all: use less oil in the first place.
One way to accomplish this would be extending oil change intervals from the national average 4,500 miles to more than 9,000 miles. "The bottom line is that motor oil quality has continually improved, but the oil filters have stayed basically the same for the last 30 years," Boughton says. Most filters are made of a paper element that gets clogged after 5,000 miles, so the oil needs to be changed simply because it gets dirty. Yet high efficiency filters exist now and are available to the public. "If the auto manufacturers put these on new cars and called for these at each oil change, the used oil volume could be reduced by half from the transportation sector," Boughton says.
-- Jason Gorss
The online version of the research paper cited above was initially published Dec. 12 on the journal's Web site. Journalists can arrange access to this site by sending an e-mail to firstname.lastname@example.org or calling the contact person for this release.