Bioaccumulation experimental determination

Dichlorobenzene is expected to bioconcentrate in aquatic organisms. The high octanol-water partition coefficient (K, ) value of 2,455 (Leo et al. 1971) also suggests that 1,4-dichlorobenzene has a moderate to high potential for bioaccumulation. A calculated bioconcentration factor (BCF) of 267 was reported for the fathead minnow (Pimephales promelas) (ASTER 1995). Measured mean BCF values of 370 and 720 were experimentally determined for rainbow trout exposed to water concentrations of... 

Food Chain Bioaccumulation. No experimental data for the bioaccumulation potential of DNOC from water to aquatic organisms were located. However, according to one group of investigators, DNOC may bioaccumulate in terrestrial and aquatic organisms (Loehr and Krishnamoorthy 1988). An experimental determination of the bioaccumulation potential for DNOC in terrestrial or aquatic organisms would be helpful. Biomagnification potential for DNOC is unknown. 

The potential for bioaccumulation would normally be determined by using the octanol/water partition coefficient, usually reported as a log Kow determined by OECD Test Guideline 107 or 117. While this represents a potential to bioaccumulate, an experimentally determined Bioconcentration Factor (BCF) provides a better measure and should be used in preference when available. A BCF should be determined according to OECD Test Guideline 305. 

Poorly soluble substances for which no acute toxicity is recorded at levels up to the water solubility, and which are not rapidly degradable and have a log K w 4, indicating a potential to bioaccumulate, will be classified in this category unless other scientific evidence exists showing classification to be unnecessary. Such evidence would include an experimentally determined BCF < 500, or a chronic toxicity NOECs > 1 mg/1, or evidence of rapid degradation in the environment. ... 

The octanol-water partition coefficient for surfactants can not be determined using the shake-flask or slow stirring method because of the formation of emulsions. In addition, the surfactant molecules will exist in the water phase almost exclusively as ions, whereas they will have to pair with a counter-ion in order to be dissolved in octanol. Therefore, experimental determination of K w does not characterize the partition of ionic surfactants (Tolls, 1998). On the other hand, it has been shown that the bioconcentration of anionic and non-ionic surfactants increases with increasing lipophilicity (Tolls, 1998). Tolls (1998) showed that for some surfactants, an estimated log Kow value using LOGKOW could represent the bioaccumulation potential however, for other surfactants some correction to the estimated log Kow value using the method of Roberts (1989) was required. These results illustrate that the quality of the relationship between log Kow estimates and bioconcentration depends on the class and specific type of surfactants involved. Therefore, the classification of the bioconcentration potential based on log Kow values should be used with caution. 

Numerical quantities, experimentally determined or estimated by statistical or computational approaches, which measure the environmental behavior, fate, and toxicity of chemicals, are molecular descriptors usually referred to as environmental indices. The octanol-water partition coefficient (Kqw, log P) is the most well-known environmental index used as the measure of lipophilicity of compounds. Together with log P and the soil sorption partition coefficient (Koc) [Baker, Mihelcic et al, 2001 Uddameri and Kuchanur, 2004], other quantities have to be considered as relevant for environmental studies. Some of these have been defined to describe mobility, biodegradabUity, bioaccumulation, metabolism, partition, and toxicity of chemicals, thus becoming relevant to human health and environmental safety assessment. 

Bioaccumulation results when uptake of chemicals by dietary and nondietary pathways exceeds metabolism and excretion. Rates at which substances are absorbed, altered, and then excreted are relatively important. Bioaccumulation may involve sequestration mechanisms, such as the deposition of polychlorinated biphenyls (PCBs) in fat, or the incorporation of lead in the mineral portion of bone. Incorporation into fat is dependent on the lipophilicity of the compound. The most commonly performed test of lipophilicity involves experimental determination of the equilibrium partitioning of a test compound between octanol, a nonmiscible organic solvent, and water, often expressed as the log10 of the ratio or the octanol/ water partition coefficient (log K ). Organic compounds in which the log Kow value is less than 3.5 do not appreciably accumulate in the lipids of mammals [5], Because energetic compounds have relatively low log Kow values (Table 10.1), bioaccumulation cannot be explained solely by lipophilicity. 

Experimentally measured bioconcentration factors (BCFs), which provide an indication of the tendency of a chemical to partition to the fatty tissue of organisms, have been found to range between 10 and 100 for trichloroethylene in fish (Kawasaki 1980 Kenaga 1980 Neely et al. 1974 Veith et al. 1980). Barrows et al. (1980) estimated a value of 17 for bluegill sunfish. Somewhat lower BCFs were determined by Saisho et al. (1994) for blue mussel (4.52) and killifish (2.71). These numbers are suggestive of a low tendency to bioaccumulate. 

As seen above (equation (5)), the basis of the simple bioaccumulation models is that the metal forms a complex with a carrier or channel protein at the surface of the biological membrane prior to internalisation. In the case of trace metals, it is extremely difficult to determine thermodynamic stability or kinetic rate constants for the adsorption, since for living cells it is nearly impossible to experimentally isolate adsorption to the membrane internalisation sites (equation (3)) from the other processes occurring simultaneously (e.g. mass transport complexation adsorption to other nonspecific sites, Seen, (equation (31)) internalisation). 

A low BCF of hydrophobic compounds might also be related to a reduced bioavailability. In that case, however, the lower BCF is related to an experimental problem [49,50], and the apparently low bioaccumulation factor is a result of an overestimated concentration in the ambient environment. Usually the aqueous concentration is determined after liquid-liquid extraction of a water sample. The overestimation of the concentration in water results from analytical difficulties which fails to differentiate between available compounds and non-avail-able compounds that are, for example, associated to particles. 

A well-known subacute effect is the growth reduction in algae. Hitherto, only external effect concentrations have been reported for this type of subacute effect, since experimental problems make it difficult to determine those internal effect concentrations, and existing bioaccumulation models for, e. g., fish, do not apply to algae, e.g. [78]. It must be noted that algae and other small organisms are prone to diffusive uptake for contaminants from the ambient environment for which the link between bioconcentration and the internal effect concentration concept would be very promising. 

Most methods for experimental BCF determinations represent an assessment of the potential for accumulation. They do not account for specific environmental conditions, such as diflferences in the species exposed or the environmental bioavailability of the chemicals. The tests generally use fish as a model organism to serve as a predictor for bioconcentration in other aquatic species as well, and for bioaccumulation/biomagnification along aquatic foodwebs. Test guidelines for BCF in fish are available (e.g. OECD, 1981a), where the fish are exposed to the chemicals and from the concentrations in fish and water the BCF is obtained. The tests vary with respect to ... 

Figure 9.4 Risk assessment for an aquatic environment based on a probabilistic procedure into which the concept of varying sensitivity in multispecies communities is incorporated (Nendza, Volmer and Klein, 1990). Exposure and effects are determined separately from experimental or, if not available, QSAR data. Physico-chemical data and information on bioaccumulation and biotransformation are the input for computer simulations of transport and distribution processes that estimate the concentrations of a potential contaminant in a selected river scenario, using, for example, the EXAMS model (Bums, Cline and Lassiter, 1982). For the effects assessment, the log-normal sensitivity distribution is calculated from ecotoxicological data and the effective concentrations for the most sensitive species are determined. The exposure concentrations and toxicity data are then compared by analysis of variance to give a measure of risk for the environment. Modified from Nendza, Volmer and Klein (1990) with kind permission from Kluwer Academic Publishers, Dordrecht.

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