Which is environmentally friendlier? Gasoline or diesel?

Dear EarthTalk: I’ve been hearing about the great gas mileage for Volkswagens that use diesel fuel. But is it better for the environment to use diesel or unleaded gasoline?

K. Cronk

Bay City, Mich.

In the past, diesel fuel was always considered dirtier than gasoline. But newer standards regulating sulfur content and improved technology in diesel engines have made diesel somewhat kinder to the environment. Many eco-advocates now tout diesel as a viable and preferable alternative to regular unleaded gasoline.

Where diesel fuel really shines over gasoline is improved fuel economy thanks to its higher “energy densityâ€: Diesel contains more power per liter than gasoline. Today’s diesel engines have 20 to 40 percent better fuel economy than their gasoline counterparts, which some say more than makes up for the fact that they also produce about 15 percent more greenhouse gases. This greater efficiency means that diesel engines emit less carbon monoxide and carbon dioxide and fewer hydrocarbons than gasoline engines.

Diesel’s downside is that it emits larger amounts of nitrogen compounds and particulate matter (soot) that can cause respiratory problems and even cancer. The California Air Resources Board (CARB) attributes 70 percent of that state’s cancer risk from airborne toxins to soot from diesel cars and trucks. Nationwide, studies have shown a 26-percent mortality increase for those living in soot-polluted areas.

But diesel’s dark side is getting a little brighter, thanks to new technologies such as Mercedes-Benz’s BlueTEC system (now used in many VW, Audi and Chrysler diesel models) that filters particulates while improving overall engine performance. The Diesel Technology Forum (DTF), a trade association of carmakers, engine builders and petroleum distributors, reports that technologies now commonplace in new diesel engines reduce the tailpipe output of particulate matter by as much as 90 percent and nitrogen oxides by some 50 percent compared to diesel engines on the road just a decade ago.

“The industry has made significant strides in recent years to develop diesel systems that are cleaner and more efficient than ever before,†reports DTF. “Thanks to state-of-the-art engines, cleaner-burning fuels, effective emissions-control systems, and advancements in the fuel injection system, it would take 60 trucks sold today to equal the soot emissions of one 1988 truck.†U.S. Environmental Protection Agency (EPA) data shows that airborne diesel particulate levels fell by more than 37 percent during the 1990s.

Meanwhile, continually improving fuel efficiency standards in the European Union (where the majority of new cars purchased in many member countries use diesel fuel) are forcing carmakers to design more fuel-efficient, less polluting vehicles around the world. After all, there’s no sense in designing better engines for one region with high standards and another for areas with less stringent rules.

Another green benefit of diesel-powered engines is their ability to run on plant-derived biodiesel instead of petroleum-based diesel. And in the near future consumers may be able to shop for new diesel-electric hybrid cars now on the drawing boards of major automakers around the world.

For now, consumers looking to buy a new or used car — diesel or otherwise — can see how different models stack up in regard to efficiency and emissions via the FuelEconomy.gov website, a joint effort of the EPA and the U.S. Department of Energy.

CONTACTS: CARB, arb.ca.gov; Mercedes-Benz’s BlueTEC, mbusa.com/bluetec; Diesel Technology Forum, dieselforum.org; FuelEconomy.gov, fueleconomy.gov.

Dear EarthTalk: What are the differences between farmed versus wild salmon when it comes to human and environmental health?

Greg Diamond

Nashville, Tenn.

Salmon farming, which involves raising salmon in containers placed underwater near shore, began in Norway about 50 years ago and has since caught on in the United States, Ireland, Canada, Chile and the United Kingdom. Due to the large decline in wild fish from overfishing, many experts see the farming of salmon and other fish as the future of the industry. On the flip side, many marine biologists and ocean advocates fear such a future, citing serious health and ecological implications with so-called “aquaculture.â€

George Mateljan, founder of Health Valley Foods, says that farmed fish are “far inferior†to their wild counterparts. “Despite being much fattier, farmed fish provide less usable beneficial omega 3 fats than wild fish,†he says.

Indeed, U.S. Department of Agriculture research bears out that the fat content of farmed salmon is 30 to 35 percent by weight while wild salmons’ fat content is some 20 percent lower, though with a protein content about 20 percent higher. And farm-raised fish contain higher amounts of pro-inflammatory omega 6 fats instead of the preponderance of healthier omega 3s found in wild fish.

“Due to the feedlot conditions of aquafarming, farm-raised fish are doused with antibiotics and exposed to more concentrated pesticides than their wild kin,†reports Mateljan. He adds that farmed salmon are given a salmon-colored dye in their feed “without which their flesh would be an unappetizing grey color.â€

Some aquaculture proponents claim that fish farming eases pressure on wild fish populations, but most ocean advocates disagree. To wit, one National Academy of Sciences study found that sea lice from fish farming operations killed up to 95 percent of juvenile wild salmon migrating past them. And two other studies — one in western Canada and the other in England — found that farmed salmon accumulate more cancer-causing PCBs and dioxins than wild salmon due to pesticides circulating in the ocean that get absorbed by the sardines, anchovies and other fish that are ground up as feed for the fish farms. A recent survey of U.S. grocery stores found that farmed salmon typically contains 16 times the PCBs found in wild salmon; other studies in Canada, Ireland and Great Britain reached similar conclusions.

Another problem with fish farms is the liberal use of drugs and antibiotics to control bacterial outbreaks and parasites. These primarily synthetic chemicals spread out into marine ecosystems just from drifting in the water column as well as from fish feces. In addition, millions of farmed fish escape fish farms every year around the world and mix into wild populations, spreading contaminants and disease accordingly.

Ocean advocates would like to end fish farming and instead put resources into reviving wild fish populations. But given the size of the industry, improving conditions would be a start.

Noted Canadian environmentalist David Suzuki says that aquaculture operations could use fully enclosed systems that trap waste and do not allow farmed fish to escape into the wild ocean.

As for what consumers can do, Suzuki recommends buying only wild-caught salmon and other fish. Whole Foods and other natural foods and high-end grocers, as well as concerned restaurants, will stock wild salmon from Alaska and elsewhere.

CONTACTS: Health Valley Foods, healthvalley.com; USDA, usda.gov; David Suzuki Foundation, davidsuzuki.org.

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