Diesel exhaust is listed as the most significant cancer-causing air pollutant in each of New England’s six states.

In fact, two counties in Rhode Island — Providence and Newport — are in the worst 20 percent nationwide when it comes to health risks from diesel pollution, according to Nicole Poepping, Clean Water Action Rhode Island’s new diesel campaign organizer.

“It’s a huge health issue,” said Poepping, the former project manager for Building a Healthy Newport Environment Coalition. “The city of Newport is actually taking more of a burden than that 20 percent.”

The streets of Little Compton and Jamestown, for instance, don’t feature nearly the same volume of diesel-powered tour buses and construction equipment.

Last year, two bills designed to curb the amount of toxic diesel exhaust spewed into Rhode Island’s air were submitted to the General Assembly. Both received much resistance from the construction industry, and both failed to gain lawmaker support.

A 16-member commission, though, was formed to “study the impact of and solutions for addressing diesel emission pollution from heavy duty vehicles.” The commission’s findings are expected in early February.

Health effects associated with diesel pollution are the worst in densely populated urban areas, such as Providence County, where proximity to such concentrated emissions sources as busy intersections, bus stops, highways and construction sites make the problem more pronounced.

Each year in Rhode Island, 50 premature deaths, 80 heart attacks and nearly 1,000 asthma attacks are linked diesel pollution exposure, according to Clean Water Action. All six New England states have childhood asthma rates higher than 10 percent.

Much of the diesel exhaust now spewed into the air is a toxic concoction of sooty particles and about 40 known poisonous substances, such as arsenic, benzene, formaldehyde and nickel. The Environmental Protection Agency determined seven years ago that diesel exhaust is a likely cancer-causing agent.

In fact, the black carbon soot released from a diesel engine is nearly eight times more carcinogenic than all 133 air toxics tracked by the EPA combined.

According to the Clean Air Task Force, 21,000 people die annually from illnesses linked to diesel exhaust particles. The microscopic size of these particles makes them an efficient means of delivering chemicals into bodies.

Diesel exhaust is easily inhaled deep into the lungs, which inflames tissue and increases the plaque that forms in arteries, contributing to heart and lung disease.

The Environment Defense Fund calls diesel exhaust one of the most dangerous and pervasive forms of air pollution. The EPA says reducing emissions from diesel engines is one of the most important air quality challenges currently facing the country.

Yet there are about 11 million diesel-powered pieces of machinery, including more than 2 million pieces of construction equipment, in the United States building communities, transporting food and taking us to and from work that lack pollution controls, according to the Boston-based nonprofit, Clean Air Task Force.

In Rhode Island, construction equipment is the No. 1 source of toxic diesel emissions — a problem, Poepping said, the state needs to solve.

Federal, state and local governments have taken some steps in the past few years to lower harmful diesel emissions.

Since 2007, federal standards have required new diesel engines to be fitted with filters that make them run 90 percent cleaner. But many of the 11 million or so diesel engines at work in the United States don’t feature such filters.

The same technology that makes 90 percent fewer emissions possible in post-2006 engines can be retrofitted on diesel engines built after 1993. The problem, however, is that because construction equipment is sturdy and reliable, it is typically in use for decades and there is a low rate of vehicle turnover.

Federal officials also are phasing in a less-polluting low-sulfur diesel fuel for on-road vehicles.

In Rhode Island, a 2006 law, which is less-than-rigorously enforced, was passed that prohibits diesel vehicles from idling for longer than five minutes. A year later, the Diesel Emissions Reduction Act was passed, which mandates that by 2010 all Rhode Island school buses must be equipped with advanced pollution control technology.

The Rhode Island Public Transit Authority already has retrofitted 50 percent of its diesel bus fleet with particulate filters.

Providence received a $565,000 federal stimulus grant this year to equip 42 city trucks with diesel pollution controls. Last year, Newport, Pawtucket, Providence and Warwick passed ordinances seeking greater enforcement of the state’s anti-idling law and calling on the state to regulate diesel emissions even further.

“School buses are well on their way to running much cleaner,” Poepping said. “Our concerns now are construction and municipal diesel fleets.”