Toxicity interstitial water

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. 

Polychaete worms belonging to the genera Nereis and Scolecolepides have extensive metabolic potential. Nereis virens is able to metabolize PCBs (McElroy and Means 1988) and a nnmber of PAHs (McElroy 1990), while N. diversicolor and Scolecolepides viridis are able to metabolize benzo[a]pyrene (Driscoll and McElroy 1996). It is worth noting that apart from excretion of the toxicant, polar, and mnch more water-soluble metabolites such as the glycosides formed from pyrene by Porcellio sp. (Larsen et al. 1998) may be mobile in the interstitial water of the sediment phase. 

Copper concentrations in sediment interstitial pore waters correlate positively with concentrations of dissolved copper in the overlying water column and are now used to predict the toxicity of test sediments to freshwater amphipods (Ankley et al. 1993). Sediment-bound copper is available to deposit-feeding clams, especially from relatively uncontaminated anoxic sediments of low pH (Bryan and Langston 1992). The bioavailability of copper from marine sediments, as judged by increased copper in sediment interstitial waters, is altered by increased acid volatile sulfide (AYS)... 

One aspect to be addressed in order to obtain a realistic vision of the toxicity of these kinds of compounds is their environmental behaviour. Surfactants tend to be adsorbed on particulate matter and thus subsequently to sediment. Consequently, the highest surfactant concentrations are found in sediments, although their distribution is dependent on the partitioning equilibrium between the substrate and interstitial water. This results in two possible routes for uptake (bioaccumulation) and effect. The relative importance of each of these routes depends on the special habits of each benthic organism. 

J. M. and Boothman, W.S. (1996) Predicting the toxicity of metal-spiked laboratory sediments using acid-volatile sulfide and interstitial water normalizations, Environmental Toxicology and Chemistry 15, 2067-2079. 

Future predictions are improved by the inclusion of TIE and CBR analyses. TIEs have been and continue to be used to establish causality based on the toxicity of sediment interstitial pore waters (Ankley and Schubauer-Berigan, 1995 Stronkhorst et al., 2003). However, because interstitial water testing may overestimate toxicity of non-persistent, readily water soluble substances (e.g., ammonia) and underestimate toxicity of persistent, poorly water soluble substances, the focus of TIEs is shifting to studies of whole sediments (Burgess et al., 2000, 2003 Ho et al., 2002). TIEs have been used as part of the SQT to determine causation (Hunt et al., 2001). The information provided regarding specific contaminants responsible for observed toxicity provides additional information for predictions related to changes in loadings of contaminants such as metals, which are not metabolized. 

Schubauer-Berigan MK, Ankley GT. 1991. The contribution of ammonia, metals and nonpolar organic compounds to the toxicity of sediment interstitial water from an Illinois River tributary. Environ Toxicol Chem 10 925-939. 

An informative paper by Di Toro et al. (1991), on predicting the acute toxicity of Cd and Ni in sediments by assessing the acid volatile suflide (AVS), illustrates that the sediment properties that determine the concentration (activity) of the sediment in the interstitial water determine the fraction of the metal that is bioavailable and potentially toxic. The study of Di Toro et al. is based on measurements of acute toxicity to benthic organisms (amphipodes, oligo-chaetes, and snails). It is shown that this toxicity is essentially related to the free metal ions in solubility equilibrium with the solid metal sulfides present. 

Most sediment toxicity tests have been conducted in the laboratory with single species of freshwater and marine benthic organisms such as amphipods and midges, but in some cases planktonic species also have been used. Most tests conducted to date have been acute and have been of 10 days duration or less. Sediment toxicity tests are conducted with the solid phase or the pore water (interstitial water). Methods have been published describing the collection and preparation techniques. 

The IPAH model incorporated a number of factors that can modify the toxicity of the sediment-borne PAHs. Equilibrium partitioning was used to estimate the concentration of each PAH in the pore water of the sediment. The assumption was that the pore water material is the fraction that is bioavail-able. QSAR was also used to estimate the interstitial water concentration based on the octanol-water partition coefficient of several PAHs. Amphipods were used as the test organism to represent environmental toxicity. A toxic unit (TU) approach was used and the toxicity is assumed to be additive. The assumption of additivity is justified since each of the PAHs has a similar mode of action. Finally, a concentration-response model was formulated using existing toxicity data to estimate the probability of toxicity. 

A flowchart for estimating sediment toxicity is presented in Figure 6.2. First, a bulk sediment sample is taken and the PAH concentration and total organic carbon are measured. The equilibrium partitioning model is run to predict the concentration of each PAH in the interstitial water of the sediment. The predicted PAH concentrations are then converted to toxic units (TUs) using the 10-d amphipod LC50 as the toxicity benchmark. The TUs are then added up and processed through the concentration response model. The expected mortality is then converted to nontoxic, uncertain, and toxic predictions. 

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... 

Berry, W.J., Hansen, D.J., Boothman, W.S., Mahoney, J.D., Robson, D.L., DiToro, D.M., Shipley, B.P., Rodgers, B. and Corbin, J.M. (1996) Predicting the toxicity of metal-spiked laboratory sediments using acid-volatile sulfide and interstitial water normalizations. Environ. Toxicol. Chem., 15, 2067-2079. 

It is important to take into account the different modes of exposure to the toxicant this may take place directly from the aqueous phase, from interstitial water, or via food to which the toxicant is bound. The whole issue of partition must, therefore, be taken into account. In addition, the issue of true tissue levels and the role of metabolism and elimination, for example, by fish must be assessed. This has already been discussed in Chapter 3, Section 3.1.5. 

In every form of heavy metals, the acid soluble phase is the most active. It controls the distribution of heavy metals in sediments-pore waters and their availability. The difference between acid-volatile sulfide and simultaneous extracted metals (AVS-SEM) was investigated to explain the biological toxicity of zinc in the sediments to benthic organisms (Han et al., 2003). When the molar difference between SEM and AVS (i.e., SEMzn-AVS) was <0 pmol/g, the concentration of zinc in the sediment interstitial water was low and few toxic effects were observed. Conversely, when SEM n-AVS exceeded 0 pmol/g, a dose-dependent increase in the relative concentration of zinc in the pore water was detected and apparent toxic effects in the organisms were observed. 

Bioavailability and toxicity of copper to aquatic orgaiusms depend on the total concentration of copper and its speciation. Both availability and toxicity are significantly reduced by increased loadings of suspended solids and natural orgaiuc chelators and increased water hardness. Toxicity to aquatic life is primarily related to the dissolved cupric ion (Cu+ ) and possibly to some hydroxyl complexes. Cupric copper (Cu+ ) is the most readily available and toxic inorgaiuc species of copper in freshwater, seawater, and sediment interstitial waters. Cupric ion accounts for about 1 % of the total dissolved copper in seawater and less than 1% in freshwater. In freshwater, cupric copper... 

Keywords Identification Interstitial waters Sediments TIE Toxicity ... 

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