Sediment-dwelling organisms

Sediment Toxicity. Because of their low solubiUty ia water and lipophilic nature, phthalates tend to be found ia sediments. Unfortunately httle work has previously been carried out on the toxicity of phthalates to sediment dwelling organisms. Eor this reason ECPI has commissioned some sediment toxicity studies designed to measure the effect of DEHP and DIDP ia a natural river sediment on the emergence of the larvae of the midge, Chironomus riparius. 

Sediment dwelling organism toxicity study (e.g., Chironomus riparius)... 

It is interesting to compare these observed BSAFi]ipoc values (Table 10.3) with values reported for other sediment-dwelling organisms and/or locations. Tracey and Hansen (1996) have compiled numerous BSAFaipoc data for PCBs and some data for polycyclic aromatic hydrocarbons (PAHs). The reported BSAF,ripoc values for PCBs... 

Table 10.3 Estimated Equilibrium (tf, ipw, A",lipoc) versus Measured Lipid-Normalized Bioaccumulation Factors BAFm) and Biota-Sediment Bioaccumulation Factors (BSAFilipoc) for Three PCB Congeners in Phytoplankton and Various Sediment-Dwelling Organisms in Western Lake Erie0...

For example, when we are interested in the accumulation of SOCs in earthworms, we may adopt a similar approach as we used for sediment-dwelling organisms. Since earthworms have a significant lipid content (ca. 5%, Table 10.1) and we are interested in relatively hydrophobic substances, we use lipid- and organic carbon-normalized biota-soil accumulation partition coefficients CK, jpoC) and bioaccumulation factors (BSAFnipoc). These correspond exactly to the biota-sediment accumulation partition coefficients and factors defined by Eqs. 10-21 and 10-24 (for an application see Problem P 10.2),... 

The biota-sediment bioaccumulation factor describes bioaccumulation in sediment dwelling organisms and fish relative to chemical concentrations in sediment. It is the ratio of chemical concentration in an organism to that in the sediments in which the organism resides. This ratio is usually expressed in one of two ways ... 

Hylland, K., M. Skold, J.S. Gunnarsson, and J. Skei. 1997. Interactions between Eutrophication and contaminants. IV. Effects on sediment-dwelling organisms. Mar. Pollut. Bull. 33 90-99. 

Plant-, soil-, and sediment-dwelling organisms have other potential routes of exposure that may be used in toxicity testing. Plants are often exposed through the soil or to an atmospheric deposition. Soil invertebrates are often placed in a standardized soil laced with a particular concentration of the test substance. Sediment tests are usually with contaminated sediments or with a material added to a standardized sediment. 

For sediment-dwelling organisms, one important factor that determines the degree of exposure to xenobiotics in the sediment phase is the partitioning from the true sediment phase into interstitial water from which the xeno-biotic may then be accumulated by biota. Exposure of sediment biota to xenobiotics is, however, a complex process, since uptake may proceed either via particulate material or via interstitial water, or by both routes. In the equilibrium partition model the concentration of a xenobiotic in the interstitial water (Ciw) is given by the following relation ... 

After deposition into sediments, particulate-associated xenobiotics may be desorbed into sediment interstitial water and thereby mediate exposure of the xenobiotic to sediment-dwelling organisms such as oligochaetes, amphipods, or chironomids and thence into higher organisms in the food chain this has been discussed in Section 3.3.2. It is important to appreciate that such processes may occur at sites remote from those at which the initial sorption to the particulate matter took place, and that their extent will depend both on hydrological conditions in the water mass as well as on the specific nature of the association. 

Sediment-dwelling organisms and water column organisms are equally sensitive to the substance. 

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