As part of an ambient monitoring program being conducted for the Puget Sound Naval Shipyard & Intermediate Maintenance Facility in Sinclair and Dyes Inlets of the Puget Sound, receiving waters of the Inlets are routinely monitored for trace metals and toxicity to assess water quality status, track progress in achieving water quality goals, and demonstrate protection of aquatic life. Recently, aqueous metal bioavailability using diffusive gradient thin-film (DGT) passive samplers has been incorporated into the monitoring program. The DGT samplers allow for the measurement of trace metal concentrations integrated over time via in situ chelation of labile metals. The DGT samplers are selective for free and weakly complexed metal species, allowing uptake to mimic diffusion limited bioavailability. This provides a monitoring solution by which episodic events are captured that provides a better representation of the potential for biological effects. A combination of laboratory performance tests and field deployed DGTs have been used to assess the reliability of the method to accurately measure labile concentrations Cu, Pb, and Zn under baseline and episodic storm events. Based on the results from DGTs deployed over different intervals spanning continuous deployments of 1-56 days and rainfall events of 0.4 – 3.2 inches/24 hr, reproducibility was affected by the presence of partially labile complexes, mass loading rate (time to equilibrium) which is proportional to free ion concentration, and variation in resin blank values. Best results were obtained for 3-7 day DGT deployments which showed high resolution of labile metal concentrations over varying spatial and temporal scales. The ability to conduct constant surveillance of metal bioavailable for a variety of freshwater and nearshore marine environments under varying environmental conditions greatly improves the assessment of potential ecological effects from exposure to metals
