Environ. Sci. Technol. 1997, 31, 2960-2965
Semipermeable Membrane Devices as Passive Samplers To Determine Organochlorine Pollutants in Compost BO STRANDBERG,* NADJA WÅGMAN, PER-ANDERS BERGQVIST, PETER HAGLUND, AND CHRISTOFFER RAPPE Institute of Environmental Chemistry, Umeå University, S-901 87 Umeå, Sweden
Semipermeable membrane devices (SPMDs) are polymeric membranes enclosing a thin film (1 mL) of a synthetic lipid. Herein, SPMDs are used to sample bioavailable persistent organochlorine contaminants, viz. PCBs, DDTs, chlordanes, lindane, chlorobenzenes, and dieldrin, in composts. The study comprises three different indoor household composts and one fortified compost. The contaminant levels in the composts range between 0.2 and 444 ng/g of dry weight. SPMDs were applied inside the compost (S/solid) and above the surface inside a closed container (S/air). After a sampling time of 28 days, the amount of PCBs accumulated from the natural household composts were 440-11000 and 72-470 ng/SPMD for S/solid and S/air, respectively. The concentration of the pesticides ranged between 4 and 300 ng/SPMD for both sample types. The amount accumulated in the S/solid correlates with the results obtained in a traditional compost analysis. Furthermore, the S/air analysis reveals the fugitive properties of the technical mixtures and individual congeners, evaporating from the compost surfaces. Thus, the SPMDs provide a simple and efficient way to sample, and clean up, pollutants in compost, as well as substances evaporating from the soil surface. The SPMD methodology will be a useful tool, although of semiquantitative character, for soil and solid surface monitoring studies and for studies aiming at the fate of organochlorine contaminants.
Introduction The first to use membranes as passive samplers of lipophilic contaminants in the environment was So¨dergren (1). He used a hydrophilic dialysis bag filled with hexane to trap dissolved organic compounds in water. Huckins et al. (2) used semipermeable membrane devices (SPMDs) consisting of a neutral lipid (triolein) inside a hydrophobic polyethylene layflat tube for passive in situ monitoring of aquatic contaminants. Following these pioneering works SPMDs have been applied in various environmental applications (3-8). Petty et al. demonstrated, for instance, that these devices also could be used as highly efficient passive air samplers (9, 10). Interestingly, the SPMDs can sample the truly gaseous phase, i.e., the fraction of a compound that is not absorbed on particles. Petty et al. estimated the sampling rate for PCBs in indoor air to be roughly 5 m3 per day and SPMD. * Author to whom correspondence should be addressed. Telephone: +46 90-165672; fax: +46 90-186155; e-mail: Bo.Strandberg@ chem.umu.se.
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 10, 1997
The SPMD theory and performance have been thoroughly described by Huckins et al. (2, 5). Briefly, the polyethylene film has transient pores with a diameter of approximately 10 Å. Lipophilic chemicals with a cross-sectional diameter of this size or smaller can permeate the thin wall of the tubing and partition into the lipid. Contaminants larger than this size limit or adsorbed on particles are not able to pass into the lipid in the SPMD. Sampling rate in water is largely controlled by the membrane/water partitioning coefficient and the cross-sectional diameter of the compound and also by the temperature. The capacity of a SPMD to concentrate a compound can be approximated by the octanol-water partition coefficient (Kow) value. To estimate the ambient concentrations of pollutants, the SPMDs are typically allowed to sample during several weeks, resulting in a time-integrated value. However, this time has to be shorter than the time to reach saturation for each compound. Organochlorine compounds such as PCBs, DDT and its metabolites (DDTs), chlordane substances (CHLs), hexachlorobenzene (HCBz), lindane, and dieldrin are persistent ubiquitous environmental contaminants. These chemicals are released to the environment at the location of production or usage. Although they have a low vapor pressure and a low water solubility, they still evaporate and can be spread worldwide by long-range air transport (11, 12). The impact of these contaminants on ecosystems and humans is of great concern (13, 14). Hence, there is a clear need for simple and cost-efficient tools to study their fate in and between the different environmental compartments. An advantage with the SPMDs as passive samplers for water and air is that these devices sample the bioavailable, non-particle-bound, fraction of contaminants and thus mimic the uptake of pollutants through gill membranes in fish (2) and lung alveoli in mammals. SPMDs applied inside a solid, such as soil or compost, will sample low molecular weight compounds. The uptake will reflect the relative composition and concentration of pollutants in the matrix. If SPMDs also are placed above the surface of the solid, volatiles will be sampled as well. This methodology could be a valuable tool for soil surface monitoring studies, since it can give an estimate of the exposure of the terrestrial ecosystem, and for studies aiming at the fate of contaminants in the environment. The objective with this work was to elucidate the potential of the SPMD technique to semiquantitatively determine the relative bioavailable amount of pollutants in, and evaporating from, a solid material. This paper describes how the SPMD methodology can be used to sample organochlorines in composts and in air above the composts.
Experimental Procedures Materials and Chemicals. All solvents used were of glassdistilled grade from Burdick and Jackson (Muskegon, MI). The glassware was of high quality, machine-washed with alkaline detergent and solvent rinsed, prior to use. The lowdensity polyethylene dialysis tubing (25 mm wide, 85-90 µm wall thickness) was from EST (St. Joseph, MO). Triolein (1,2,3tri[cis-9-octadecenoyl]glycerol) of 95% purity was purchased from Sigma Chemical Co. (St. Louis, MI). All PCBs are numbered according to IUPAC rules (15). The technical PCB products, Aroclor 1232, 1242, 1248, and 1260, originated from Monsanto Industrial Co. (St. Louis, MO). Hexachlorobenzene (HCBz), technical chlordane (CHL), lindane, dieldrin, and DDT were obtained from Alltech Associates (Deerfield, IL). The internal standards octachloronaphthalene, and 13Clabeled PCB 80, PCB 101, PCB 153, lindane, HCBz, p,p′-DDT,
S0013-936X(97)00236-8 CCC: $14.00
1997 American Chemical Society
TABLE 1. Amount of Contaminants (ng/SPMD) after a 28 Day SPMD Sampling of Three Household Composts (C1, C2, and C3) and a Compost (F) Fortified with PCBs, DDTs, Chlordanes, Hexachlorobenzene, and Dieldrina S/ambient S/air S/air S/air S/air S/solid S/solid S/solid S/solid CMA/ CMA CMA CMA prep/ mean C1 C2 C3 mean F mean C1 C2 C3 mean F mean blank C1 C2 C3 blank (n ) 2) (n ) 1) (n ) 1) (n ) 2) (n ) 2) (n ) 1) (n ) 1) (n ) 2) (n ) 2) (n ) 1) (n ) 1) (n ) 1) (n ) 1) (n ) 1) lindane PCBz HCBz ∑DDD/DDT ∑DDE DDTs HCHLep ∑octa-CHL ∑nona-CHL CHLs dieldrin ∑tri-PCB ∑tetra-PCB ∑penta-PCB ∑hexa-PCB ∑hepta-PCB ∑octa-PCB nona-PCB deca-PCB PCBs wet wt (g) dry wt (g) loss of ignc (%) H2O content (%)
30 3.7 15
