Half-lives bioaccumulation

Endosulfan does not bioaccumulate to high concentrations in terrestrial or aquatic ecosystems. In aquatic ecosystems, residue levels in fish generally peak within 7 days to 2 weeks of continuous exposure to endosulfan. Maximum bioconcentration factors (BCFs) are usually less than 3,000, and residues are eliminated within 2 weeks of transfer to clean water (NRCC 1975). A maximum BCE of 600 was reported for a-endosulfan in mussel tissue (Ernst 1977). In a similar study, endosulfan, isomers not specified, had a measured BCE of 22.5 in mussel tissue (Roberts 1972). Tissue concentrations of a-endosulfan fell rapidly upon transfer of the organisms to fresh seawater for example, a depuration half-life of 34 hours (Ernst 1977). Higher BCFs were reported for whole-body and edible tissues of striped mullet (maximum BCF=2,755) after 28 days of exposure to endosulfan in seawater (Schimmel et al. 1977). However, tissue concentrations decreased to undetectable levels 48 hours after the organisms were transferred to uncontaminated seawater. Similarly, a BCE of 2,650 was obtained for zebra fish exposed to 0.3 pg/L of endosulfan for 21 days in a flow-through aquarium (Toledo and Jonsson 1992). It was noted that endosulfan depuration by fish was rapid, with approximately 81% total endosulfan eliminated within 120 hours when the fish were placed in a tank of water containing no endosulfan. 

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. 

Food Chain Bioaccumulation. 1,2-Diphenylhydrazine reacts rapidly in water to form azobenzene and other oxidation products (half-life in wastewater is 60 minutes). Because of this and based upon the log octanol/water partition coefficient, no bioaccumulation is expected in any aquatic organism. 

Metabolism/Excretion- In healthy subjects, the half-life of pramlintide is approximately 48 minutes. Pramlintide is metabolized primarily by the kidneys. Des-lys pramlintide (2-37 pramlintide), the primary metabolite, has a similar half-life and is biologically active both in vitro and in vivo in rats. AUC values are relatively constant with repeat dosing, indicating no bioaccumulation. 

In the sections below, four different cases for converting biomonitoring data to exposure dose using pharmacokinetic modeling are considered lipid-soluble, bioaccumulative chemicals at steady state lipid-soluble, bioaccumulative chemicals not at steady state shorter-half-life chemicals at... 

A striking aspect of lead in the body is its very rapid transport to bone and storage there. Lead tends to undergo bioaccumulation in bone throughout life, and about 90% of the body burden of lead is in bone after long-term exposure. The half-life of lead in human bones is estimated to be around 20 years. Some workers exposed to lead in an industrial setting have as much as 500 mg of lead in their bones. Of the soft tissues, the liver and kidney tend to have somewhat elevated lead levels. 

TCDD on the soil surface range from 9 to 15 years, whereas the half-life in subsurface soil may range from 25 to 100 years (Paustenbach et al. 1992). CDDs have been shown to bioaccumulate in both aquatic and terrestrial biota. CDDs have a high affinity for lipids and, thus, will bioaccumulate to a greater extent in organisms with a high fat content. 

Half-life is a composite parameter dependent on the volume of distribution and the rate of clearance of the drug. This follows from the fact that it is only the drug presented to the eliminating organs that can be removed from the body. Optimization of the half-life of a new drug candidate is important as too long a half-life may result in bioaccumulation and toxic side effects, whereas... 

Indicates the rate at which a toxicant would be eliminated from the body affects its overall half-life Indicates for how long a compound would persist in the body and its potential for bioaccumulation, resulting in long-term adverse effects... 

The total U.S. airborne emission of volatile TDI is estimated by the International Isocyanate Institute (III) to be <25 t, or less than 0.005% of the annual U.S. production. Published data show that TDI has a 1/3 life of 8 s in air at 25°C and 50% rh, and a 0.5 s to 3 d half-life in water, depending on pH and agitation. Without agitation, isocyanates sink to the bottom of the water and react slowly at the interface. Because of this reactivity, there is no chance of bioaccumulation. 

Polonium is found in the natural environment, especially in uranium and thorium ores. Of seven natural radionuclides of polonium, Po is the most important. It is an alpha emitter with energy of 5.305 MeV and half-life of 138.376 days [24]. Polonium is a very radiotoxic element and undergoes strong bioaccumulation in land and aquatic organisms [1]. 

If released to ambient air, acetonitrile will remain in the vapor phase where it will be degraded through reaction with photochemically produced hydroxyl radicals. The half-life of acetonitrile in ambient air has been estimated to be 620 days. If released to soil, acetonitrile is expected to volatilize rapidly. Biodegradation in soil is not expected to be a major degradation pathway. If released to water, acetonitrile is not likely to adsorb to soil and sediment particles. Acetonitrile is expected to be removed from water bodies through volatilization as the chemical hydrolysis and bioaccumulation potential for this chemical are low. 

Benzene has a short half-life in surface water because it is so volatile. Detection of benzene in natural waters would therefore only be seen in areas adjacent to grossly contaminated waste sites. It would also tend not to bioaccumulate into fish tissue or biomagnify up the food chain. 

If released to acclimated water, biodegradation would be the dominant fate process (half-life 2.5-4 days). BPA may adsorb extensively to suspended solids and sediments (Kqc values range from 314 to 1524), and it may photolyze in the presence of sunlight. BPA is not expected to bioaccumulate significantly in aquatic organisms (BCF 5-68), volatilize, or undergo chemical hydrolysis. 

The half-life of dimethoate in river water is 8 days. It does not bioaccumulate in aquatic organisms, nor does it adsorb to suspended particles in water. Dimethoate undergoes significant hydrolysis, especially under alkaline conditions. However, losses by photolysis and evaporation from open waters are not expected to be significant. Dimethoate is not toxic to plants. 

Dioxane is a cyclic ether compound that is miscible with water in all proportions and is also moderately volatile. It is resistant to hydrolysis and microbial degradation, but may undergo photolysis at water and soil surfaces. An estimate of the half-life for abiotic degradation in water with addition of ozone was 60 h. The half-life for photo-oxidation in air was 3.4 h. 1,4-Dioxane has a low adsorption potential and a high mobility/leaching potential in soil/water systems. No bioaccumulation of this chemical is expected. 

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