Washington state officials for years have been trying to figure out exactly what toxic chemicals reach rivers and streams, where they come from, and how much ends up in the waters.

A new state analysis released Thursday finds there isn't one source: the tens of thousands of toxic chemicals that get washed into Puget Sound each year come from many, diffused sources, including leaking oil from cars, zinc from rooftops, copper in boat paint, and polycyclic aromatic hydrocarbons (PAHs) from creosote-treated wood pilings and woodstoves.

"Most toxic chemicals are used in some way by all of us. They are in our homes and gardens. They're produced when we develop land without adequate runoff controls, when we burn wood, when we drive and park our cars," said Ecology Director Ted Sturdevant.

"If we want to protect Puget Sound, we need to find and use less toxic alternatives as we do our business and live our lives," he added.

Thursday's report ties together a multi-year effort to quantify and understand the chemical threats in Puget Sound. The Puget Sound Partnership plans to use the results of the assessment to come up with new strategies to reduce the contaminants and clean up Puget Sound.

"It's wonderful to have these reports because we need to be able to say definitively what the problems are," said Heather Trim, policy director with the nonprofit group, People for Puget Sound. It was much more challenging before such quantitative data was available, she said.

The report recommends working to control petroleum releases from motor oil leaks and refueling operations, pursuing efforts to reduce wood smoke and vehicle emissions, increasing efforts to remove creosote-treated wood pilings in marine waters, and evaluating how many toxic chemicals are leaching from roofs. It also suggests routine inspections for businesses that handle large amounts of the chemicals.

Researchers found that the chemicals are released from scattered sources, mostly in urban, developed areas, and reach Puget Sound mainly through surface runoff from parking lots, rooftops, driveways and other hard surfaces. Some chemicals also reach Puget Sound by falling directly on marine waters, or being discharged from wastewater treatment plants.

The study focused on 17 toxic chemicals, such as arsenic, flame retardants and phthalates, because of their potential to harm people, fish, and the Puget Sound ecosystem.

Scientists recently found that adult coho salmon returning from the ocean to spawn in the Puget Sound region have been prematurely dying at high rates in the last decade. Although they don't know precisely what is causing the die-offs, "the likely explanation is toxic chemicals in stormwater runoff," said Jay Davis, an environmental toxicologist for the U.S. Fish & Wildlife Service.

Other studies by government scientists have also shown that copper at the low levels that have been found in waterways harms young coho salmon's sense of smell and reduces their ability to escape from predators. Ecology officials estimate that 61,000 to 140,000 pounds of copper enter the Puget Sound each year. State legislators have already passed laws phasing out copper in brake pads and copper-based boat paint. Thursday's report estimates that one-third of the copper entering Puget Sound may come from urban and homeowner use pesticides and fertilizers containing copper. The report suggests learning more about pesticide use.

The state estimates that about 710,000 to 800,000 pounds of petroleum enters the Puget Sound each year - much smaller than previous estimates. Thursday's report showed that two-thirds of the petroleum comes from motor oil drips and leaks on vehicles and roads.

About 250,000 to 300,000 pounds of zinc and 300 to 600 pounds of polycyclic aromatic hydrocarbons (PAHs) are also getting into streams.

Todd Myers, an environmental analyst with the Washington Policy Center, a business-oriented think tank, said the most recent study, as well as others, don't help people understand what do to with this information.

"The next study that really needs to be done is to get a better handle on what this means," he said.

Myers said state and local government could then determine how to best spend limited resources.

"This was a baby step, not a big step," he said.