Sediment toxic factor

Comparison of the relative sediment toxicity of different SPs can be difficult as there are a variety of different test methods and endpoints evaluated, in addition to other confounding factors relating to sediment quality. Amweg et al. [28] determined the toxicity of six SPs to //. azteca in 10-day studies at 23 °C in natural sediments containing 1-6% OC. Toxicity data were reported as bulk sediment concentrations and normalized to the organic carbon content (Table 5). The results indicated that normalization removed some, but not all, of the variability between sediments. Other factors such as sediment texture may also affect bioavailability and hence apparent toxicity in sediment studies. 

Ankley, G. T., Benoit, D. A., Balogh, J. C., Reynoldson, T. B., Day, K. E. and Hoke, R. A. (1994) Evaluation of potential confounding factors in sediment toxicity tests with three freshwater benthic invertebrates, Environmental Toxicology and Chemistry 13 (4), 627-635. 

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). 

As discussed in previous sections, there are numerous factors that can modify the toxicity of materials. The prediction of the toxicity of mixtures is also difficult. One of the best attempts at toxicity prediction has been formulated by Swartz et al. (1995) and predicts the sediment toxicity of polynuclear aromatic hydrocarbons. The model is based on the concentration of 13 PAHs in collected sediments, the predicted concentration in the sediment pore water, and the toxicity of these concentrations as determined by a large toxicity data set. 

To illustrate the WoE approach we will apply it to the evaluation of toxicity as a cause or risk factor in the alteration of benthic community structure in a waterway (Figure 12.11). Extensive data on chemical concentrations in sediments are obtained at the site under investigation (A). Data on the chemical contaminants are matched with laboratory tests of sediment toxicity to the chemicals (B). A comparison of the chemical concentrations to the toxicity data indicates that the materials are toxic under laboratory conditions (C). A hypothesis is then generated that identifies the sediment under consideration as likely to be toxic. Sediment bioassays of the sediment can confirm the hypothesis (D). Since the assessment endpoint is the preservation of benthos, measurements are made of the benthic community structure in the region (E). Chemical concentrations and toxicity results are also compared to measures of benthic community structure. Chemicals that are positively associated... 

Chemicals, which are persistent, toxic and liable to bioaccumulation, are called PTBs. They have primarily local effects. Persistence is the evidence that the substances half-life is greater than two months in water and greater than sue months in soil or sediment. Toxicity is the potential to adversely affect human health and/or the environment. Bioaccumulation is the evidence that the Bio-Accumulation Factor (BAF) is greater than 5000. Up to 1995, there was no clear definition of which products belong to this class [394]. Heavy metals, such as mercury and POPs fall into this category. 

In summary, the bioavailability and observed toxicity of synthetic pyrethroids in sediment-water systems is influenced by a number of physicochemical factors, including the quantity and type of organic and inorganic matter in sediment and in water, as well as by temperature. The use of equilibrium partitioning calculations can be a useful tool for estimating the dissolved and potentially bioavailable fraction of pyrethroids. 

Similarly, the reductions in toxicity observed in laboratory toxicity tests where exposure is modified (either through the addition of sediment or by removal to clean water) are also apparent in the field. Field effect concentrations are generally observed to occur at concentrations around three to ten times above those based on standard laboratory data. Dissipation and degradation are therefore clearly the critical factors in mitigating effects of pyrethroids under field conditions. This provides reassurance that preliminary ecological risk assessments based on... 

POCs proportions and content of POCs in river waters compared with maximum permissible concentration (MPC, for DDT, HCH and PCB, are equal to 100,20 and 1 ppb correspondingly for water and 100,100 and 100 for bottom sediments) behavior of toxic compounds in the water body factors promoting an increase of the ecological risk of polluted riverine input into the Caspian Sea (Figure 4). 

Generally, slow sorption or desorption has made complete remediation technology difficult. However, there have recently been legitimate questions raised by some researchers [163,187] about whether we even need to be concerned about residues that desorb so slowly and thus are apparently largely bio-unavailable. At a minimum, it is important that we understand the factors which govern slow sorption/desorption rates, their kinetics and causes at the intra-particle level of different solid phase materials (e.g., surface/subsurface and aquatic sediment particles), and how these phenomena can relate to contaminant transport, bioavailability, toxicity, remediation, and risk assessment modeling. 

Metal profiles for two sediment cores from the Elizabeth River, VA, USA. Land use along the shores adjacent to collection site PC-1 (Paradise Creek) is primarily industrial and includes oil terminals, shipyard installations, coal transfer facilities, petroleum distribution and shipment operations, and wood treatment facilities. It has been identified as a toxic hot spot by the U.S. EPA. Land-use adjacent to WB-2 (Western Branch) is primarily residential. Excess lopb and profiles for (a) PC-1 and (b) WB-2 profiles. These were used to determine accumulation rates (1.1 to 2.3cm/y at PC-1 and <0.5cm/y at WB-2). Trace metal enrichment factor profiles (see Eq. 28.1 in text) are presented in profiles (c-g) in groups determined by the depth and shape of their concentration peaks. Source From Conrad, C. R, et al. (2007). Marine Pollution Bulletin 54, 385-395. 

Bioavailability from Environmental Media. Toxicity studies in animals indicate that absorption of hexachlorobutadiene through the gastrointestinal tract, respiratory tract, and skin can occur. Studies which identify the relationship between absorption and the matrix of soils, sediments, and foods would be useful in establishing whether or not absorption is significantly affected by such factors. 

The in vitro bioassay for dioxins with cleaned sediment extracts (DR-CALUX) proved to comply with the QA/QC criteria needed to guarantee the reliability of data in an inter- and intralaboratory study (Besselink et al., 2004). The chemical stability of dioxins makes it possible to apply destructive clean-up procedures which remove all matrix factors. Sample extraction and cleanup for other in vitro bioassays for specific mechanisms of toxicity require further development to make sure that the chemicals of interest are not lost or unwanted chemicals included in the sediment extract to be tested. Table 4 summarizes possible bioassays that could be performed in addition to chemical analyses with the dredged sediment in a licensing system. 

Table 7 Example application of process in Box B to evaluate the risk of dioxins in Dutch sediments. No observed effect (NOEC) concentrations for chronic toxicity of dioxins in vertebrates (immune, reproductive and developmental toxicity) expressed as internal concentration (ng TEQ/g Iw). The sediment to fish bioconcentration factor is set at 4 (ng TEQ/g Organic Carbon to ng/g lipid weight in fish) based on Traas et al. (2001). Based on a species-specific biomagnification factor (BMP) from fish to animal (ng TEQ/g Iw) the internal NOEC is extrapolated to a NOEC in sediment. These data are used to construct the SSDs in Figures 5 and 6.

---