James River at Richmond, VA

Semi-Permeable Membrane Devices (SPMD’s) for Sampling Dissolved Organic Substances from Surface Waters Don Smith Virginia Department of Environmental Quality

Dissolved Organic Substances The U.S. EPA has defined criteria and the States have developed water quality standards (WQS) for numerous organic substances which are either toxic or are otherwise of environmental concern. However, these standards, as well as the concentrations typically observed in ambient surface waters, have generally been well below the minimum levels of detection permitted by established analytical methods!

Biological Magnification The uptake of low-level dissolved organic substances by living organisms often results in the accumulation of much higher concentrations in animal tissues - “bioconcentration”! (Organic compounds are much more soluble in natural fats and oils than in water!) Fish-tissue analyses and “screening values” for human health concerns (related to fish consumption) have consequently been used to evaluate water quality, but...

Fish and other aquatic organisms are mobile… source of contamination often in question! Different organisms may uptake and depurate (metabolize or excrete) various organic compounds at quite different rates… Whether fish-tissue concentrations are representative of local water quality conditions is uncertain… Thus, true concentrations in the water column remain unknown…cannot be ‘back-calculated’! and assessment of the water body for other designated uses would still be questionable!

Research scientists from the United States Geological Survey (USGS), at the Columbia Environmental Research Center (CERC), Columbia, Missouri, developed an artificial sampling device that mimics the parts of animals that cause “bioconcentration”! (mid 1980’s through early 1990’s) More recent studies have improved this technology and provided a powerful tool for measuring the average concentrations of dissolved organic compounds in ambient surface waters over extended periods of time. Semi-Permeable Membrane Devices

SPMDs have been described as “Virtual Fish” Consist of purified ‘triolein’ oil (a natural fat found in aquatic organisms) sealed within a flat, tubular membrane of thin, low-density polyethylene (LDPE) The LDPE mimics a biological membrane by allowing selective diffusion of organic compounds from the water into the triolein. The organic compounds are highly soluble in triolein and become concentrated there! SPMDs are sensitive - they can sample from air, water or soil!

Examples of Contaminants that are Concentrated in Triolein- Containing SPMDs (not all-inclusive)

SPMD Elizabet h River

Uptake Rates of Organic Compounds are Initially Linear < Linear uptake for up to 30 days or more!

When exposed over a reasonable time period (up to 30 days in the field), the concentrations of organic substances within the triolein become high enough to be measured directly, and are in direct proportion to the average concentrations within the environment ( in this case ambient surface water)! Subsequent extraction and analysis of the organic compounds yields a direct measure of the average environmental concentrations, and a reliable assessment may be performed using well-established Water Quality Standards!

< Transported frozen to USGS/CERC, Columbia, MO

Very Sensitive, Very Accurate, Very Expensive! Field enclosure(s) - –USGS - loaned, but if you lose them, –you buy them! –(3 x $550 per site, if lost!) $1650 –(DEQ - 1 x $20, disposable) $ 20 Unit Cost, USGS contract $4500 –(including SPMD, sample extraction and analysis) Total Cost (50 Units) ~$225,000

Further Information on SPMDs Basic information, Glossary, Overview, Tutorial, Frequently asked questions, References, USGS SPMD research activities, etc.