Encyclopedia of Puget Sound

Removal of creosote-treated pilings may assist herring recovery

Researchers are analyzing the harmful effects of creosote-treated wood pilings on Pacific herring and shellfish in Puget Sound. Studies show that piling removal projects can ease the impacts, but only if carefully done. 

Creosote removal project in Puget Sound. Photo courtesy of the Washington State Department of Natural Resources.
Creosote removal project in Puget Sound. Photo courtesy of the Washington State Department of Natural Resources.


Thousands of abandoned wood pilings — the ghosts of piers and docks past — are located throughout Puget Sound. Most of them are treated with creosote, a toxic chemical used to preserve wood that contains polycyclic aromatic hydrocarbons (PAHs), a class of chemicals that are also associated with oil spills and burning of fossil fuels.

While creosote-treated pilings are used less for construction of new piers, scientists at the Washington State Department of Ecology and the Washington Department of Fish and Wildlife are now studying the impacts of existing pilings on herring and shellfish populations along with the effectiveness of removal projects. 

In 2017 about 8,500 old pilings in Port Gamble were removed along with tens of thousands of cubic yards of sediment. Prior to the cleanup, researchers at the state agencies conducted a herring embryo mortality study to understand the impacts of the cleanup on herring populations.

That study showed that prior to cleanup herring embryos were at highest risk of elevated PAH contamination in areas near mill sites with high piling density. Similar research found elevated PAH and PCB concentrations in bay mussels at the same locations. Preliminary work in 2018 has demonstrated a reduction of PAHs in shellfish since cleanup, and researchers are optimistic the cleanup will yield similar results for herring embryos now being analyzed.

While the Port Gamble cleanup has yielded promising results so far, not all cleanup projects are created equal. In Quilcene Bay, herring embryos were studied before piling removal, just after the removal project, and one year after removal. Embryos incubated before removal contained five times the amount of PAHs than those from control sites but did not exceed health effects thresholds. During removal, pilings were cut at the sea floor leaving debris and freshly exposed surfaces of the pilings. PAH concentrations during and after the removal were 25 to 85 times higher than reference embryos and many exceeded health effects thresholds. 

Researchers say these studies demonstrate creosote-treated pilings have health effects for herring embryos, and piling removal projects have the potential for reducing PAH concentrations during this critical life stage. However, removal projects must adhere to strict protocols to ensure they do not increase contaminant loads rather than reduce them.

About the Author: 
Megan Feddern is a graduate student at the University of Washington School of Aquatic and Fishery Sciences.