Pore water sampling

Booij et al. (2003b) made an effort to model contaminant uptake by buried passive samplers. The major assumptions underlying this model are that the sampler can be regarded as an infinite sink for target contaminants, that the depletion of the bulk sediment phase is insignificant, and that the contaminant desorption kinetics are not rate-limiting. 

Since the right hand side of Eq. 3.59 would typically approximate 1, a Vs/wtoc ratio of 0.05 mL g seems to be a safe choice. 

For compounds that do not reach a significant degree of equilibrium during the exposure, the absorption rate by the SPMD should be much smaller than the desorption rate by the sediment (Booij et al., 2003b) 

When groundwater sampling is essentially equivalent to the exposure 

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As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

Shipboard analysis for the sampling of trace metals in seawater has been discussed by Schuessler and Kremling [2] and Dunn et al. [3]. Teasdale et al. have reviewed methods for collection of sediment pore-waters using in situ dialysis samples [4]. Bufflap and Allen [5] compared centrifugation, squeezing, vacuum filtration, and dialysis methods for sediment pore-water sampling. 

External precision is the ability to demonstrate analytical repeatability with multiple preparations and analyses of a material over a long period of time. The MC-ICP-MS techniques and the more widespread TIMS methods either demonstrate or claim external precisions in the range 0.5 to 1.0%o (2ct). The stated precision for most TIMS methods is estimated from the reproducibility of the L-SVEC standard. In many cases the analysis of individual samples prepared multiple times yields precisions poorer than this estimate. This is in part due to the heterogeneity of natural samples and in part due to effects introduced during preparation and analysis that are not experienced by the standard. Zhang et al. (1998) cite reproducibility of the L-SVEC standard of <1.0%o (2ct), but their duplicate measurements of individual pore water samples vary from 0.1 %o to 6.1 %o (mean 2.3%o all 2cj). Later studies using refined TIMS procedures appear to achieve superior replicate precision (e.g., 0.4%o to 1. l%o for multiple replicates in Chan et al. 2002c). 

In the solar evaporation ponds, salinities in the cores reached almost four times oceanic values. In these cores the concentration profile of bimane sulfide with depth also tracked that of methylene blue sulfide and bimane total reduced sulfur tracked DTNB. However, the difference between the bimane method and the other two methods is unacceptably large and suggests that there was some inhibition of the bimane reaction. Pore water samples which were diluted to normal seawater salinity with 200 mM HEPES buffer pH 8 were not inhibited. Dilution will of course lead to a loss of sensitivity for trace thiols. Another factor which can effect the yield of the bimane reaction is the unusual... 

EH s that are often encountered in sediment pore waters. Cores from Mono ake (not shown) had extremely alkaline pH s of 9.8 to 10.1. This high a pH definitely has an effect on the bimane reaction. Pore water samples adjusted to pH 8 gave much higher results which were similar to those obtained from the methylene blue and DTNB method (data not shown). Thiosulfate and sulfite were present in micromolar quantities in cores from all habitats. Thiosulfate was highest in the salt pond cores where it occasionally was more abundant than sulfide. While methane thiol, glutathione, and other organic thiols can be detected by the bimane method, they were not abundant (< 10 mM) in the core samples we chose to analyze. 

For the soil pore water sampling, the procedure described by Knight et al. (1998) and Tye et al., (2003) can be normally followed. Samplers are inserted into soil containers and soil pore water extracted by connecting a syringe to each sampler and applying a suction. 

Bufflap, S. E., and Allen, H. E. (1995b). Comparison of pore water sampling techniques for trace metals. Water Res. 29(9), 2051—2054. 

Morrison, R., and Szecsody, J. (1985). Sleeve and casing lysimeters for soil pore water sampling. Soil Sci. 139(5), 446-451. 

Falter, J. L., and Sansone, F. J. (2000). Shallow pore water sampling in reef sediments. Coral Reefs 19, 93-97. 

Bender M., Martin W., Hess J., Sayles F., Ball L., and Lambert C. (1987) A whole-core squeezer for interstitial pore-water sampling. Limnol. Oceanogr. 32(6), 1214-1225. 

Water samples were stored In precleaned glass carboys and returned to the laboratory where they were filtered and extracted within 18 hours of sampling. Filters were Soxhlet extracted with hexane/acetone (1 1) for 24 hours and again with fresh hexane/ace-tone for an additional 24 hours. Water and pore water samples were extracted three times with CH2CI2 In a separatory funnel. Extracts were dried over Na2S04, concentrated to near dryness, and hexane was added with further concentration by rotary evaporation under vacuum until hexane replaced the CH2CI2. 

The pore water samples of the sediment layers close to the surface of both samples, TKWA and TKS, were characterised by DOC values between 16 and 60 mg/L. The maximum values were obtained in the top layer of the TKS sample. The results of the inorganic analyses revealed concentrations of copper and zinc within a range between 1 to 14 mg/L and 0,02 to 0,1 mg/L, respectively. For the TKS samples the highest values were determined in the top layer. The concentrations of lead and cadmium were below the detection limit in all samples investigated. 

Carignan, R., Rapin, F. Tessier, A. (1985) Sediment pore water sampling for metal analysis A comparison of techniques. Geochim. Cosmochim. Acta 49., 2493-2497. 

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