SEATTLE — A study of sediments taken from Tacoma’s Commencement Bay showed reduced levels of toxic metals and other chemicals, but also found higher levels of newer contaminants, the state Department of Ecology said today.
Researchers collected sediment samples in 2008 and compared them to ones taken in the same 30 locations in 1999 as part of a larger Urban Waters Initiative.
The study of Commencement Bay found improvements in the environmental health of sediments, an indicator of an overall healthy ecosystem.
“The sediments show us what kinds of pollution people are sending downstream into urban bays,” said Rob Duff, manager of the department’s environmental assessment program.
Researchers found reduced levels of toxic metals such as arsenic, copper, lead, mercury, nickel, silver, tin and zinc, and lower levels of some polycyclic aromatic hydrocarbons, or PAHs. PAHs have been linked to cancer and are formed by the incomplete burning of coal, oil, gas and other organic substances.
In much of the bay, the study showed healthier populations of bottom-dwelling invertebrates, such as worms, clams and small crustaceans. These animals form the base of the aquatic food web.
But researchers found increased levels of plasticizers, or phthalates. These chemicals are used to make plastics flexible and are pervasive in everyday items such as toys, pharmaceuticals and personal care products.
The contaminants may present concerns for marine life, Duff said.
The study found no change in metals such as cadmium and chromium, polychlorinated biphenyls — or PCBs — and some types of PAHs. PCBs have been shown to cause cancer.
“Things are definitely looking better,” said lead scientist Valerie Partridge, adding that there had been tremendous work done to clean up pollution “but Commencement Bay has had a lot of insult and injury. We still have ways to go.”
The city of Tacoma also released results of an eight-year storm water study on Friday. That report found lower concentrations of suspended solids, lead and PAHs.
Contaminants end up in sediment from air pollution and storm water runoff.
Industries, sewer plants and internal combustion engines also add to the pollution.
Although pollution from industries, sewer and shipping has decreased, new pollutants from sources that are hard to trace still threaten the bay, ecology officials said. Storm water runoff is the leading source of pollution for urban waters in the state.
The state ecology department is also studying sediment quality in the waters off Bainbridge Island, Bellingham, Olympia and Everett. Last year, officials found improvements in sediment collected from Seattle’s Elliott Bay.
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