USGS: SPMD Data Collection:  Passive monitoring for organic contaminants in water using semipermeable membrane devices (SPMDs)

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Official Method Name
 Analysis of waterborne hydrophobic organic contaminants in water collected by semipermeable membrane devices
Current Revision
2008
Media
 WATER
Instrumentation
 Semipermeable Membrane Device (SPMD)
Method Subcategory
 Organic
Method Source
  USGS
Citation
 SPMD Technology Tutorial (3rd Edition), (Updated January 03, 2002), by James N. Huckins, J.D. Petty, Jon A. Lebo, Carl E. Orazio, Randal C. Clark, and Virginia L. Gibson, at URL http://wwwaux.cerc.cr.usgs.gov/spmd/SPMD-Tech_Tutorial.htm last accessed October 15, 2008
Brief Method Summary
 Lipid-containing SPMDs represent an innovative passive sampling technology for monitoring and assessing trace levels of hydrophobic organic contaminants. The SPMD is typically constructed from barefoot (no additives) layflat tubing of low-density polyethylene (LDPE). The thin-walled (<100 µm) LDPE tubing used in SPMDs is normally described as nonporous. However, random thermal motions of the polymer chains form transient cavities with maximum diameters of approximately 10 Å. Because these cavities are extremely small and dynamic, hydrophobic solutes are essentially solubilized by the polymer. The cross-sectional diameters of nearly all environmental contaminants are only slightly smaller than the polymeric cavities. Therefore, only dissolved (i.e., readily bioavailable) organic contaminants diffuse through the membrane and are concentrated through time. The sequestration media consist of both the thin film/plug of a large molecular weight (> 600 daltons) neutral lipid such as triolein and the LDPE membrane. Contaminant residues concentrated in SPMDs are simultaneously recovered and separated from the lipid in intact SPMDs (after carefully cleaning exterior surface of the membrane) by dialysis in an organic solvent.

SPMDs accomplish three tasks simultaneously:
  • Mimics the bioconcentration of organic contaminants in fatty tissues of organisms
  • Provides a highly reproducible passive in situ sampler for monitoring contaminant levels, which is largely unaffected by many environmental stressors that affect biomonitoring organisms
  • Enables in situ concentration of trace organic contaminant mixtures for toxicity assessments and toxicity identification evaluation (TIE)
Scope and Application
 The attributes of SPMDs include the following:
  • Non-mechanical, passive device which is easy to deploy and requires no maintenance
  • Mimics uptake of dissolved contaminants by biota, yet precision of concentration data is greater
  • SPMD matrices can conveniently be cleaned up prior to use, while extensive depuration periods may be required to reduce contaminant levels in the tissues of biomonitoring organisms
  • Readily concentrates contaminant residues such as PAHs that are metabolized by many aquatic organisms
  • Once prepared, SPMDs can be stored frozen until the most appropriate deployment time, while biomonitoring organisms require care and feeding, and may be subject to seasonal availability
  • Analytical cleanup of exposed SPMDs is generally less difficult than biomonitoring organism tissues or sediment samples
Applications for SPMDs:
  • Determination of pollutant sources and relative levels
  • Detection of episodic chemical releases
  • Measurement of TWA concentrations of dissolved or vapor phase chemical concentrations
  • Determination of the readily bioavailable fraction (dissolved or vapor phase) of a chemical in an environmental compartment for predicting transport, fate, and residue toxicity
  • Estimation of organism exposure and bioconcentration
  • In situ biomimetic extraction of environmental contaminants for bioassay and immunoassay
  • Dialytic separations (SPMD membrane) of target analyte interferences in various matrices
  • Tool for TIE procedures
Applicable Concentration Range
Interferences
  • Sampling rates can be affected by the physicochemical properties of the target compound (i.e., octanol-water or -air partition coefficient [KOW or KOA], polarity, molecular size/weight, and volatility) and environmental conditions of the exposure site (i.e., temperature, flow/turbulence, and biofouling level or the growth of a biofilm on the exterior membrane surface)
  • Temperature affects sampling rate, regardless of which step in the uptake process is rate limiting or has the most resistance to mass transfer
  • Given the wide range environmental exposure conditions, flow/turbulence effects are generally expected to have a greater impact on SPMD sampling rate than temperature or biofouling
Quality Control Requirements
 The exact level of QC required is determined during the development of the experimental design phase of a project and is dependent on project goals. At a minimum, QC samples should address: deployment, retrieval, storage, processing, fractionation, enrichment, and analysis. QC samples should represent 20 to 50-percent of the sample set and include SPMD-fabrication blanks, SPMD-process blanks, reagent blanks, field-blank SPMDs, permeability reference compound samples, SPMD spikes, and procedural spikes.
Sample Handling
  • Typically, SPMDs are stored and shipped in clean gas-tight metal cans of various sizes
  • Metal containment structures (storage cans and deployment devices) must be free of cutting oils or other potential interferences
  • Minimize use of plastic components, except Teflon and some types of PVC, due to the possible presence of leachable organic residues
  • The structural design of the deployment device should minimize abrasion of the membrane even in turbulent environments while baffling the very high flow/turbulence of some media
  • Current velocity/turbulence is also a concern in terms of tethering, especially during floods
  • If a loop design (SPMD) is used, the two sides should not make contact
  • If water turbidity is low, then a shading structure may be required for analytes such as PAHs that undergo photolysis (caution: estimated photolysis half-lives of PAHs in direct sunlight range from 0.1 h to 5 h)
  • For sampling PAHs from air, the deployment structure must reduce ambient sunlight levels to near zero
  • Unless permeability/performance reference compounds (PRCs) are used (see description of PRCs in subsequent section), the flow and temperature regime of exposure sites should be similar to facilitate inter-site comparisons
  • Because vandalism is always a potential problem in the field, the deployment structure should be amenable to hiding
  • Deployment structures are commercially available
Maximum Holding Time
 1. As soon as SPMDs are recovered from the environment, they should be sealed in the original can and placed on ice in a cooler for shipping (overnight shipping is recommended)

2. Some loss of SPMD-sequestered analytes with high
Relative Cost
 Greater than $400
Sample Preparation Methods
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