The Puget Sound Partnership tells us that "Human activities generate far more toxic chemicals than natural sources. People have typically released into our Puget Sound environment three to 30 times as much heavy metals -- such as copper, lead, (mercury) and zinc -- as flow naturally from regional streams and rivers. Some toxic chemicals that wash into the Sound come entirely from human activities, such as phthalates at a rate of about 100,000 pounds a year."
"Pollution from highways is complicated. Although a portion of some contaminants come directly from highways, roads act primarily as conduits for contaminated surface runoff to flow more quickly into Puget Sound."
Recently, the Washington State Department of Ecology released two new reports on human generated toxics and stormwater runoff from streets and highways.
For more information and to see full copies of the reports, visit Ecology’s Control of Toxic Chemicals website at www.ecy.wa.gov/programs/wq/pstoxics/index.html
Document Downloads: http://www.psp.wa.gov/documents.php