Diffusive gradient thin-films in seawater: time integrated technique for aqueous trace metal monitoring in impacted waterways

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

Assessing 21st century contaminants of concern using integrative passive sampling devices to obtain more meaningful and cost effective data on impacts from stormwater runoff

In many cases stormwater compliance monitoring is labor intensive, expensive, and largely unsuccessful in providing the data needed to support stormwater management goals. In addition, data from manual grab sampling and automated composite sampling are rarely collected in a manner that provides the information required to identify sources of contamination, evaluate the effectiveness of Best Management Practices, and inform effective decision making. Furthermore, monitoring is often driven by the need to meet low concentration benchmarks for metals and other constituents that do not take into account loading into the receiving waters, resulting in arbitrary monitoring requirements (monthly or seasonally) that are not tied to the driving forces within the watershed such as hydrology (flow regime), weather (storm events and antecedent dry periods), and upland land use and cover. To help address these issues, passive sampling devices including Diffusive Gradients in Thin films (DGT) for metals and Polar Organic Chemical Integrative Samples (POCIS) for a wide range of household, personal care, pharmaceutical, and endocrine disrupting compounds are being used to monitor stormwater runoff. In the Puget Sound a network of monitoring stations was established in Sinclair and Dyes Inlets to assess runoff from industrial areas of Naval Base Kitsap as well as commercial, residential, and rural areas within the watershed. Passive samplers were co-located with autosamplers to provide a direct comparison with grab and composite sampling. Preliminary results from multiple DGT deployments showed that time-dependent variability in stormwater impacts on ambient metal concentrations could be detected on small time scales, as well as over multiple days of rainfall. The POCIS samplers showed that a wide range of organic compounds could be reliably detected from the surveillance monitoring which should prove very useful for finger printing likely sources of contamination in stormwater runoff in the areas monitored