Basics.. Glossary.. Overview.. Tutorial .. FAQs.. References ..USGS/WRD SPMD Activities ..Other SPMD Links
By Tom Huff, George Mason University
Jacqueline Ganser, University of Minnesota
History of SPMD Technology
Summary of SPMD Technology
As part of their study of the bioavailability of hydrophobic organic chemicals to aquatic organisms, Jim Huckins and co-workers developed semipermeable membrane devices (SPMDs) at the Columbia Environmental Research Center, Columbia, MO (CERC, formerly the Midwest Science Center, then a part of the U.S Fish and Wildlife Service). (See J.N. Huckins.)
Two patents (owned by the U.S. Government) were obtained for this technology and an exclusive license eventually was sold to Environmental Sampling Technologies (St. Joseph, MO). Jim Huckins, Jim Petty, and co-workers have continued to develop and expand this technology at CERC, which is now a part of the U.S. Geological Survey's Biological Resources Division.
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For your convenience, a Glossary of terms related to SPMD technology is available.
Semipermeable membrane devices (SPMDs) are passive sampling devices consisting of a tubular layflat low-density polyethylene (LDPE) membrane containing a thin film of a high-molecular weight lipid (triolein). When placed in an aquatic environment, SPMDs passively accumulate hydrophobic organic compounds, such as PCBs, PAHs, and organochlorine pesticides.
The LDPE tubing mimics a biological membrane by allowing selective diffusion of organic compounds. Triolein is a major nonpolar lipid found in aquatic organisms. The passive sampling of the hydrophobic organic chemicals is driven by membrane- and lipid-water partitioning.
|Because bioconcentration of many organic compounds mainly results from partitioning between gill membranes and water, SPMDs can be used to estimate bioconcentration factors for respiratory uptake of organic compounds.|
|Studies of bioavailability and bioconcentration factors demonstrate that SPMDs are easier to use and less expensive than fish because they are more easily standardized than aquatic organisms and, for studies done at different sites or in different seasons, the data have better compatibility.|
|Because deployment of the SPMDs is over a long time period, the chemical concentrations in the SPMDs represent a time-weighted average.|
|SPMDs also eliminate many of the problems encountered when sampling biota. The SPMD sampling locations are fixed. The SPMDs are easily deployed and retrieved. Migration, mortality, metabolism, or selective-depuration (contaminants) problems, which are common in live biota samples, are nonexistent with SPMDs.|
|SPMDs are easy to use, can be standardized, and accumulated residues are representative of the thermodynamically dissolved organic phase in surface waters.|
|SPMDs can be deployed for long periods of time (days to months) and used to estimate the time-weighted mean concentrations of the hydrophobic organic compounds in the water body.|
|For a given nonionic organic chemical, an SPMD will effectively sample 0.5 to 10 L per day, depending on the chemical's hydrophobicity (as quantified by its water solubility or octanol-water partitioning coefficient, Kow) and other factors.|
|A compound with log Kow = 6 would need 200 days at an effective sampling rate of 10 L per day to reach ³ 90% of equilibrium. However, during the first 50 days, the uptake rate into the SPMD is linear.|
|The ambient "truly dissolved" water concentration (Cw) can be estimated based on the concentration in the SPMD (CSPMD), the volume of the SPMD, the effective sampling rate (Rs), and the time of deployment (t):|
Cw = CSPMD VSPMD/ (Rs*t)
The effective sampling rate (Rs) of many hydrophobic compounds has already been determined and more research is underway to expand the number of compounds.
After a typical deployment period of approximately 30 days, the SPMDs are removed from the aquatic environment and dialytically recovered with a nonpolar solvent such as hexane.
One of the problems encountered with deployment is the biofouling coating found on the membrane exterior. This biofouling layer can impede flux across the membrane, thus slowing the effective sampling rate (Rs). This impedance factor is specific to each SPMD at any given point in time. Impedance for a specific deployment can be quantified by measuring the loss of a surrogate compound (contained within the SPMD) during deployment.
SPMDs have also been used to passively sample air for hydrophobic organic chemicals.
Scientists interested in a more comprehensive explanation of SPMD technology should refer to the Tutorial section.
To review published papers, refer to the References section.
We have also answered 20 frequently asked questions (FAQs) about SPMD technology.
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Environmental Sampling Technologies (EST) holds the exclusive license for the two patents (U.S. Patent 5,098,573 and 5,395,426) for SPMD technology. SPMDs may be obtained only from EST and must be returned to them for dialysis (in preparation of the final analysis). Final analysis can be done by EST or another laboratory, such as the National Water Quality Assessment. The European source of SPMDs is ORIGO Hb, Trehorningen 34, S-922 66 Travelsjo, Sweden.
EST offers the following SPMD services:
1. Preparing custom-length SPMDs
2. Deployment devices
3. Dialysis separation from the SPMD
4. Gel permeation chromatography cleanup
5. Quantifying contaminants and priority pollutants
Use of trade names is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey (USGS).
Although this information is believed to be correct, there may be errors. If you see an error, please send an e-mail to firstname.lastname@example.org (Jim Huckins) with the correction. These pages are not an official publication of the USGS and should not be cited as such.
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If the reader has additional questions concerning SPMDs, contact Dave Alvarez: (573) 441-2970; e-mail: email@example.com
Basics ..Glossary .. Overview .. Tutorial ..FAQs .. References ..USGS/WRD SPMD Activities .. Other SPMD Links