Biodiesel, a cleaner-burning renewable fuel, is used to power trucks, buses and trains.

This summer, it will get its first local use in commercial boating on Salem Sound.

Mid-Harbor Launch Inc. of Marblehead has been testing various biodiesel blends on a partner company's research vessel, The Stellwagen.

"We want to lead by example," said Eric Loftus, Mid-Harbor's sales and marketing manager.

It's an example others are setting as well, from an initiative to stop boaters from dumping sewage into the water to a program monitoring shellfish habitat.

Mid-Harbor Launch plans to begin using a mixture called B20, and possibly higher mixes, on three or four of its new launches for the upcoming boating season.

The fuel will be delivered in early May to Mid-Harbor's 500-gallon capacity work boat, Loftus said, and the launches will be fueled from there.

Upon delivery, it will be the first commercial marine use on the North Shore, according to Ed Burke, chairman of the board at Dennis K. Burke Inc., the first major fuel distributor in the Boston area to offer B20 and B5 biodiesel blends.

Pure biodiesel — B100 — is biodegradable, renewable and nontoxic, according to literature provided by Burke.

Burning biodiesel offers huge reductions in hydrocarbon exhaust, a global warming contributor, and also offers reduced particulate matter, sulfur, carbon monoxide and other carcinogenic and compromising exhausts.

"The pollution benefits are astronomical," Burke said.

However, in some cases, nitrogen oxide — another major contributor to global warming — actually increases with biodiesel.

There are other downsides.

Biodiesel can degrade natural rubber in older engines. Its organic components — fatty acid esters — can form sediment when in contact with some metals, such as brass, copper and lead, clogging some fuel filters.

According to materials provided by Burke, more efficient processing procedures are needed to minimize fuel filter plugging.

Another factor may be a lack of federal regulation and state specifications for biodiesel.

While biodiesel may help reduce global warming impacts at the consumer level, some environmentalists are concerned about its sources. In other parts of the world, such as Malaysia, Indonesia and Brazil, large tracts of rain forest and agricultural lands are being cleared to grow palm oil and soybean plants in order to produce biofuels, according to Greenpeace.

If this trend were to explode in response to a large market demand, environmentalists fear a major spike in global warming — as deforestation contributes to accelerated climate change.

Though Burke declined to name the company's supplier, he said all of his company's biodiesel is "American-made," and is manufactured in Cincinnati, Ohio, and Florida. Sources include virgin soybeans and recycled cooking oil, according to company literature posted on Burke's Web site and other materials provided.

"We're dedicated to it," he said.

Locally, use of biodiesel may help improve air quality and to reduce Salem Sound's carbon footprint.

"We're trying to improve the area we're working in," said Loftus.

No dumping, and other initiatives

A survey in 2005 by Salem Sound Coastwatch found that 15 percent of boats in Salem Sound dump sewage into the water.

Untreated sewage and land-based runoff are responsible for the bacteria and fecal coliform levels that close beaches.

As a result, Coastwatch has applied for Salem Sound to be a state-designated, federally approved No Discharge Area, which means sewage cannot be dumped within approximately a 3-mile zone of the shoreline.

Coastwatch has long been targeting land-based runoff, "which is probably still the largest pollution source in Salem Sound," according to Barbara Warren, executive director of SSCW and the applicant's author.

"But even though we will continue to work on what's coming off the land, we need to reduce marine waste," she said.

It is expected that by midsummer, Salem Sound will be an official No Discharge Area. To achieve that status, applicants must prove that there are enough pump-out facilities available and enough outreach, education and resources so the boating community knows why and how to pump out.

It also enables harbormasters to enforce no discharge laws.

Other environmental initiatives in Salem Sound include:

r Salem Sound Coastwatch and the state Division of Marine Fisheries are monitoring water quality to assess the condition of shellfish habitat.

r Monitoring invasive species and salt marshes.

r A sea grass monitoring program by the Division of Marine Fisheries. These delicate beds are an important habitat for fish, and are easily harmed by sewage and other water pollution.

For a map of the proposed Salem Sound No Discharge Area and more information, go to www.salemsound.org.