Pore water assessments

Pore water assessments evaluate the toxicity of the interstitial water of the sediment to the aquatic organism (Mayer, 1993). The interstitial water is removed from the sediment by sediment compression or centrifugation. The advantage of this assessment is that the equilibrium of the sediment/water interface is more closely evaluated toxicologically, which allows more confidence in the bioavailability assessment. However, toxicity artifacts such as ammonia and sulfide... 

As is the case with assessments of the toxicity of dissolved trace metals, the development of sediment quality criteria (SQC) must be based on the fraction of sediment-associated metal that is bioavailable. Bulk sediments consist of a variety of phases including sediment solids in the silt and clay size fractions, and sediment pore water. Swartz et al. (1985) demonstrated that the bioavailable fraction of cadmium in sediments is correlated with interstitial water cadmium concentrations. More recent work (e.g., Di Toro et al, 1990 Allen et al., 1993 Hansen et al, 1996 Ankley et ai, 1996, and references therein) has demonstrated that the interstitial water concentrations of a suite of trace metals is regulated by an extractable fraction of iron sulfides. 

Free-phase NAPL refers to NAPL that exists as an independent phase, not as a dissolved component in the pore water or pore atmosphere. The environmental concerns associated with sites affected with free-phase NAPLs revolve around hydrocarbon-impacted soil (residual hydrocarbon), the NAPL itself (which can serve as a continued source for groundwater contamination), dissolved hydrocarbon constituents in groundwater, and hydrocarbon vapors. The detection of free-phase NAPLs in the subsurface presents many challenges. Two questions frequently arise at sites impacted by NAPLs how much is there and how long will it take to clean up. Before one can address these two questions, assessments of the type and subsurface distri-... 

The bioavailability of contaminants to wildlife and humans is also an area of critical importance, where contaminants can be taken up in pore water and by dermal contact, particle ingestion, or particle inhalation. The dynamics of sorption/desorption are not currently incorporated into exposure and risk assessment models for organic compounds, where availability, in most cases, is assumed to be 100% [224]. Recently, the following have been demonstrated and reported ... 

In the past few years the use of rotifers in ecotoxicological studies has substantially increased. The main endpoints used are mortality, reproduction, behavior, cellular biomarkers, mesocosms, and species diversity in natural populations [126]. Several workers have used Brachionus calyciflorus for various types of toxicity assessments. Thus, comprehensive evaluation of approximately 400 environmental samples for the toxicity assessment of solid waste elutriates, monitoring wells, effluents, sediment pore water, and sewage sludge was carried out by Persoone and Janssen [127]. The mortality of rotifers hatched from cysts is evaluated after 24 hours exposure. This microbiotest has been commercialized in a Rotoxkit F [128,129]. 

P 9.7 Assessing the Speciation of a PCB-Congener in a Sediment-Pore Water... 

The distribution of Hg within seepage lakes is a net result of the processes that control Hg transport between the atmosphere, water column, seston, sediments, and groundwater. This discussion focuses on the processes that control the exchange of Hg between the sediments and lake water. We first present data on spatial and temporal concentrations in the water column, sediments, pore water, and groundwater. These data set the context for a subsequent discussion of the chemical and physical processes responsible for the transport of mercury across the sediment-water interface and are necessary for assessing transport rates. 

Harkey, G.A., Landrum, P.F. and Klaine, S.J. (1994) Comparison of whole-sediment, elutriate and pore-water exposures for use in assessing sediment-associated organic contaminants in bioassays, Environmental Toxicology and Chemistry 13 (8), 1315-1329. 

The pT-method can be used to assess the toxic potential of both treated and untreated wastewater, surface water (receiving streams), groundwater, pore water, elutriates and chemical extracts of sediments. This paper deals with wastewater, the application of the pT-method to sediments is described in Chapter 9 of this volume. The method can be applied universally and is user-friendly. Any number of aquatic... 

Wenholz, M. and Crunkilton, R. (1995) Use of toxicity identification evaluation procedures in the assessment of sediment pore water toxicity from an urban stormwater retention pond in Madison, Wisconsin, Bulletin of Environmental Contamination and Toxicology 54, 676-682. 

The case study presented here was conducted by the Environmental Research Centre, CIMA, Faculty of Sciences, of the University of La Plata. The more frequently applied tests were those conducted with the Lactuca sativa seed germination assay, followed by the Hydra, Daphnia and Selenastrum tests. They were used for the assessment of toxicity from hazardous wastes and waste leachates, sediment pore water and sediment leachates, surface waters and groundwater. An additional test based on (3-galactosidase (in vitro-free enzyme test) inhibition, known for its sensitivity to metals (Apartin and Ronco, 2001), was also incorporated in the battery. 

Table 5. Results of applying the EDAR index for hazard assessment of waste samples, sediment extracts or pore water and pure compounds using the reduced battery of tests.

The first study was designed to assess the suitability of various microscale bioassays and recommend an appropriate testing strategy for sediment toxicity assessment (Cote et al., 1998a,b). The recommended test batteries included seven micro-scale laboratory assays conducted on bacteria (Vibrio fischeri), cnidarians (Hydra attenuata), micro-crustaceans (Thamnocephalus platyurus), and benthic macroinvertebrates (Hyalella azteca and Chironomus riparius), and involved two phases of exposure (pore water and whole sediment). A total of 16 stations were included in the toxicity assessment scheme. 

In many references that describe the relationship between the concentration of a contaminant in the pore water and the total concentration in soil, the kind of pore water concentration assessed (inclusive or exclusive of organic and inorganic metal complexes) is not mentioned. 

To assess the environmental bioavailability, mobility and geochemical cycling of trace elements in soil, analyses of soil pore water composition are frequendy more instructive than those from whole soil or soil extracts. The validity of this concept... 

One method for assessing bioavailability is via pore-water concentrations. Pore-water concentrations are arguably better overall predictors of bioavailability and effects on the terrestrial ecosystem than measurements of total soil concentrations of contaminants. Peijnenburg et al. (1997) showed that for several substances risks... 

Bioavailability of organic chemicals is strongly dependent on aqueous solubility. The equilibrium partitioning theory has been applied to sediment toxicity studies, and it was concluded that uptake from sediment as well as from (pore) water is possible at the same time however, the exposure route in equilibrium is not necessarily important. For substances with log /< W < 5, the equilibrium partitioning theory is considered acceptable to assess the risk. For substances with log Kov/ > 5, a safety factor of 10 is applied, in order to include the additional uptake by sediment ingestion (Loonen et al. 1997). 

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