Publication Summary

This report provides a synthesis of the Puget Sound Toxics Loading Analysis (PSTLA) which was conducted to provide scientific data to help develop an overall source control strategy for toxic chemicals in the Puget Sound basin. Release rates were estimated for 17 chemicals and chemical groups. Loads of these chemicals to Puget Sound through various pathways were also estimated, and an evaluation of their hazards was conducted.

Surface runoff was found to contribute the largest loads to Puget Sound for the majority of chemicals. Recommendations are provided to guide development of source control strategies, along with additional data needs.

The Washington State Department of Ecology and other agencies initiated a multi-phase project in 2006, the Puget Sound Toxics Loading Analysis (PSTLA), to evaluate sources of toxic chemicals entering Puget Sound. The analysis focused on an abbreviated list of chemicals that were known to, or threaten to, harm the Puget Sound Ecosystem. The study included an assessment of major delivery pathways such as surface water runoff, groundwater, publicly-owned treatment works (POTWs), and direct air deposition. An assessment of the relative hazards posed by target chemicals was also performed.

The overall goal of PSTLA is to provide technical information to help develop toxic chemical control strategies for the Puget Sound basin. This report is a synthesis of information generated on (1) chemical releases from human-caused sources, (2) the rates of chemical loading through various pathways, and (3) a basin-wide hazard evaluation for chemicals of concern.

For most of the chemicals addressed, the rate of loading to Puget Sound was estimated to be one to three orders of magnitude lower than the rate of release from human-caused sources. In most cases, surface runoff was found to contribute the largest loads to Puget Sound, typically accounting for more than one-half of the total loads from all environmental pathways combined. Loads delivered through POTWs were generally the smallest among the pathways assessed, typically accounting for less than 10% of the total loading for each of the chemicals addressed.

Results of the hazard evaluation suggest that the following chemicals are most likely to be found at concentrations where effects are documented or at levels above criteria used to protect aquatic organisms and consumers of aquatic organisms: