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Chemical contaminants and potential toxicity of extracts from semipermeable membrane devices (SPMDs):

Overview:
. Semipermeable membrane devices (SPMDs) are passive samplers that concentrate trace levels of hydrophobic (not capable of uniting with or absorbing water) organic contaminants in aquatic systems. The samplers are designed to mimic the bioaccumulation of organic contaminants in the fatty tissues of aquatic organisms. The SPMDs were constructed from low-density, polyethylene (LDPE) tubing filled with a thin film of purified lipid triolein (fat found in most aquatic organisms) that simulates the exposure to and passive uptake of highly lipid-soluble organic compounds by biological membranes (Huckins and others, 1993). The LDPE tubing only allows dissolved bioavailable organic contaminants to diffuse or pass through the membrane to be concentrated in the lipid. Because SPMDs integrate chemical conditions over an extended period of time and flow conditions (low-flow and high-flow), they may offer a more complete representation of potential chemical exposure of organism to contaminants than water samples collected at one point in time (Huckins and others, 1993). Among the organic contaminants that may be concentrated by the SPMDs are polychlorinated dioxins and furans, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine insecticides, and pyrethroid insecticides. The chemicals concentrated in the SPMDs were analyzed for both concentration and potential toxicity. In this study, SPMDs were deployed to compare chemistry and potential toxicity of SPMD extracts at sites along a gradient of urban intensity from low to high and to determine the relation to other physical, chemical, and biological factors.

What we measured:
. SPMD extracts were analyzed for hydrophobic organic contaminants, such as polychlorinated dioxins and furans, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine insecticides, and pyrethroid insecticides.

. SPMD extracts were analyzed for potential toxicity using three bioassays, an ultraviolet (UV) fluorescence scan to screen for PAHs, Microtox® bioassay, and P450RGS assay.

When we sampled:
. SPMDs were placed at each site during low flow for a period of 4 to 6 weeks prior to collection of invertebrate and algae samples for studies that sampled in 2003 and 2004.

. Six-inch (15 cm) SPMDs were housed inside a protective cover for placement in the stream. Each SPMD was placed in a shipping canister to prevent atmospheric contamination during shipment. SPMDs were suspended in the stream by attaching the protective cover to a metal rod that was pounded into the stream channel.

. SPMDs were deployed for a period of 4 to 6 weeks.

. At the end of the deployment period, the SPMDs were placed back in the shipping canister and sent to Environmental Sampling Technologies (EST), in St. Joseph, Missouri for processing.

Laboratory analyses:
. At the end of the deployment period, contaminants concentrated in the SPMDs were extracted (separated) from the lipid by dialysis in an organic solvent at Environmental Sampling Technologies (EST), in St. Joseph, Missouri, by using methods described in Huckins and others (1990).

. Two assays were run on the extract at the USGS Columbia Environmental Research Center (CERC) in Columbia, Missouri - an ultraviolet (UV) fluorescence scan (Johnson and others, 2004) and a Microtox® bioassay (Johnson, 1998).

o The UV fluorescence scan provided a semi-quantitative screen for PAHs, which fluoresce under UV light. A standard curve was developed by using various concentrations of pyrene (a specific PAH compound) under a specific wavelength of UV light. The SPMD extracts were then exposed to same conditions and the resulting florescence was reported as a pyrene index in milligrams per SPMD extract.

o The Microtox® bioassay measured the light production of photo-luminescent bacteria when exposed to the SPMD extracts; the biochemical pathway for light production is lowered by a wide range of compounds concentrated by the SPMDs. Results were reported as EC50, the concentration of the SPMD extract that caused a 50 percent decrease in light production.

. An additional assay, the P450RGS test, was run by the U.S. Army Corp of Engineers Environmental Laboratory in Vicksburg, Mississippi (Murk and others, 1996). The P450RGS assay provides a rapid screen for aryl hydrocarbon receptor (AhR) type compounds that include PCBs, PAHs, dioxins, and furans. All vertebrates produce detoxifying enzymes upon exposure to AhR compounds; the amount of enzymes produced is directly proportional to the concentration of the compounds. Quantifying one of these enzymes (the gene CYP1A1) serves as a measure of dioxin activity. The concentration of AhR compounds in the SPMD extract that induce CYP1A1 production is expressed as the amount of dioxin, in toxic equivalents (TEQs), that would induce the same response.

. A portion of each SPMD extract was sent to the U.S. Geological Survey's National Water Quality Lab for chemical analyses using gas chromatography/mass spectrometry (GC/MS) analysis (Tom Leiker, U.S. Geological Survey, written communication, 2005).

Quality control:
. Quality-control samples for the SPMDs included dialysis, solvent, and trip blanks. During processing in the laboratory, dialysis blanks and solvent blanks were collected to monitor for possible manufacturing and laboratory contamination. Trip blanks were collected in the field by exposing a SPMD to the air for the amount of time it took to remove a SPMD from the canister and place it in the stream, and then to remove the same SPMD from the stream and place it back into the canister. With the trip blank, however, the SPMD was left in the canister while the field-SPMDs were deployed in the stream. In this way, the trip blank mimicked exposure to airborne chemical contamination that field-deployed SPMDs experienced during deployment and retrieval. In addition to the trip blanks, replicate SPMDs were deployed at a subset of sites.

What these samples represent:
. SPMDs integrate chemical conditions over an extended period of time and flow conditions (low flow and high flow) and represent the potential chemical exposure of organism to contaminants better than water samples collected at one point in time.

. Chemical analyses of SPMD extracts include additional organic compounds not analyzed in water samples.

. Chemical Analyses of SPMD extracts provides information on specific hydrophobic contaminants present in the SPMD extract that complements the bioassay results.

. The bioassays represent the potential toxicity of specific groups of organic contaminants concentrated in the SPMDs.

Reference:
Huckins, J.N., Manuweera, G.K., Petty, J.D., Mackay, Donald, and Lebo, J.A., 1993, Lipid-containing semipermeable membrane devices for monitoring organic contaminants in water: Environmental Science and Technology, v. 27, p. 2489-2496.

Huckins, J.N., Tubergen, M.W., and Manuweera, G.K., 1990, Semipermeable membrane devices containing model lipid - A new approach to monitoring the availability of lipophilic contaminants and estimating their bioconcentration potential: Chemosphere, v. 20, p. 533-552.

Johnson, B.T., Petty, J.D., Huckins, J.N., Lee, Ken, Gauthier, Joanne, 2004, Hazard assessment of a simulated oil spill on intertidal areas of the St. Lawrence River with SPMD-TOX: Environmental Toxicology, v. 19, p. 329-335 Johnson BT. 1998. Microtox toxicity test system - New developments and application, in Microscale testing in aquatic toxicology: Advances, techniques and practice, PG Wells, K Lee and C Blaise, eds.: Boca Raton, Florida, CRC Lewis Publishers, p. 201-218.

Murk, A.J., Legler, J., Penison, M.S., Giesy, J.P., Vande Guchte, C., and Brouwer, A., 1996, Chemical activated luciferase gene expression (calux): A novel in vitro bioassay for AH receptor active compounds in sediment and pore water: Fundamental and Applied Toxicology, v.33, p.149-160.

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