Sorption processes bioconcentration

The ability to predict the behavior of a chemical substance in a biological or environmental system largely depends on knowledge of the physical-chemical properties and reactivity of that compound or closely related compounds. Chemical properties frequently used in environmental assessment include melting/boiling temperature, vapor pressure, various partition coefficients, water solubility, Henry s Law constant, sorption coefficient, bioconcentration factor, and diffusion properties. Reactivities by processes such as biodegradation, hydrolysis, photolysis, and oxidation/reduction are also critical determinants of environmental fate and such information may be needed for modeling. Unfortunately, measured values often are not available and, even if they are, the reported values may be inconsistent or of doubtful validity. In this situation it may be appropriate or even essential to use estimation methods. 

PROBABLE FATE photolysis, data not available oxidation oxidation by peroxy radicals or singlet oxygen is not expected to be important hydrolysis aquatic hydrolysis is not expected to be significant volatilization volatilization is not expected to be significant or important sorption if released to water, adsorption to sediments appears to be the important fate process biological processes bioconcentration is expected to be an important fate process if released to water... 

The dominant transport process from water is volatilization. Based on mathematical models developed by the EPA, the half-life for M-hexane in bodies of water with any degree of turbulent mixing (e.g., rivers) would be less than 3 hours. For standing bodies of water (e.g., small ponds), a half-life no longer than one week (6.8 days) is estimated (ASTER 1995 EPA 1987a). Based on the log octanol/water partition coefficient (i.e., log[Kow]) and the estimated log sorption coefficient (i.e., log[Koc]) (see Table 3-2), ii-hexane is not expected to become concentrated in biota (Swann et al. 1983). A calculated bioconcentration factor (BCF) of 453 for a fathead minnow (ASTER 1995) further suggests a low potential for -hcxanc to bioconcentrate or bioaccumulate in trophic food chains. 

Sorption is the dominant process controlling partitioning in water and movement in soil. Silver may leach from soil into groundwater acidic conditions and good drainage increase the leaching rate. Silver is bioconcentrated to a moderate extent in fish and invertebrates. 

DEHP is a widely used chemical that enters the environment predominantly through disposal of industrial and municipal wastes in landfills and, to a much lesser extent, volatilization into air (from industrial and end uses of DEHP), carried in waste water from industrial sources of DEHP, and within effluent from municipal waste water treatment plants. It tends to sorb strongly to soils and sediments and to bioconcentrate in aquatic organisms. Biodegradation is expected to occur under aerobic conditions. Sorption, bioaccumulation, and biodegradation are likely to be competing processes, with the dominant fate being determined by local environmental conditions. When DEHP is present in the environment, it is usually at very low levels. It is very difficult to determine these low levels accurately since DEHP is a ubiquitous laboratory contaminant, and laboratory contamination may cause false positives to be reported in the literature. 

The log -octanol-water partition coefficient (log Kow) is a measure of the lipophilicity of a substance. As such, log Kow is a key parameter in the assessment of environmental fate. Many distribution processes are driven by log Kow, e.g. sorption to soil and sediment and bioconcentration in organisms. 

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