Depuration half-life

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. 

Biota depuration half-life of 7.7 d in blue mussels (Gustafsson et al. 1999) ... 

Biota 24 < t,/, < 48 h depuration half-life in tissues of bluefill sunfish in 21 d-exposure experiment (Barrows etal. 1980 quoted, Howard 1989) ... 

BIOACCLMULATION BCF (bluegill, based on carbon 14 determinations, after 21 days exposure at a concentration of 9.73 mg/L) 663, depuration half life <2 days uptake efficiency (english sole gills, after 3 hr exposure at 20-250 mg/L concentrations) 42.2%... 

Species Xenobiotic Exposure time, other details Pre-depuration tissue cone. (fig g wet wt.) Depuration half-life" Long-term retention Reference... 

The formation of macromolecular adducts could be partly responsible for the increase in depuration half-life observed following increased periods of exposure of molluscs to the xenobiotic, particularly for PAH and other hydrocarbons (see Sect. 7.1). The process of adduct formation, and presumably excision and release, could therefore represent, or contribute to, the more stable cellular compartment with a lower rate of xenobiotic turnover postulated by Stegeman and Teal (1973). Similar considerations could contribute to, or explain, the observed tenfold excess in bis(tributyltin) oxide accumulation, compared to that predicted, in M. edulis (Laughlin et al 1986) the preferential retention of PCB with increasing degrees of chlorination (Sect. 7.1) and the higher BCF of PCB compared to those of PAH of similar n-octanol/water partition co-efficients (Pruell et al. 1986). 

When placed in pure water, the animals containing steady-state concentrations of PNA lost it at a rate of 9.4 ug/g/hr with a half-life (appearance in water) of 22 minutes when they were placed in a 5 mg/1 solution of unlabelled PNA, the rate of loss (turnover) of was similar to the depuration rate (Fig. 5). 

Similar to the case with fish, we are not aware of field studies with fluorene in plants. Figure 2 shows the very rapid depuration of label from duckweed in culture, resulting in the high K2 (Table III) and the short half-life (Table V). In view of the volatility of fluorene, and its short half-life it would not be expected to persist long in plants after a spray with a solvent containing fluorene. McLeese et al. (27) examined the uptake and depuration of "585 oil by mussels and found a similar result. The steady state bioconcentration factor was 160 but the half-life was only 0.3 days. 

Gooch, J.A., Hamdy, M.K. (1982) Depuration and biological half-life of 14C-PCB in aquatic organisms. Bull. Environ. Contam. Toxicol. 28, 305. 

An estimated bioconcentration factor value suggests that bioconcentration in aquatic organisms is very high however, depuration half-lives ranging from 4 to 6 days for TOCP isomers indicate that bioconcentration may not be an important process. TOCP is not expected to volatilize from water surfaces. Biodegradation of TOCP in river water and bottom sediment followed first-order kinetics the half-life in river water and bottom sediment at 25 °C was 10 days. Vapor-phase TOCP is degraded in the atmosphere by reaction with photochemically produced hydroxyl radicals the half-life in air is... 

TCP s low water solubility and high adsorption to particulates causes adsorption onto river or lake sediment and soil. Biodegradation in river water is rapid, almost complete within 5 days. Abiotic degradation is slower with a half-life of 96 days. BCFs of 165-2768 were measured for several fish species in the laboratory using radiolabelled TCP. Radioactivity was lost rapidly on cessation of exposure, depuration half-lives ranged between 25.8 and 90 hours. 

TOXICITY uptake and depuration by Oysters Crassostrea virginica) from oil treated enclosure half-life for depuration 5 days Neanthes arenaceodentata 96 hr TLm in seawater 22°C 0.5 ppm (initial concentration in static assay)... 

Fig. 3. Relationship between the length of exposure period and the half-life of subsequent depuration of a range of hydrocarbons (paraffins, PAH, alkylated PAH, mixtures, dibenzothiophenes) by a variety of molluscan bivalve species. Data are from Table 9 (indicated in table by ). Correlation coefficient of the logio-logio regression = 0.863 (n = 20) 95% confidence limits for the regression line shown on graph. The data for field exposures (i.e. undefined exposure periods) are shown but are not included in the regression...

Fish that bioaccumulate poorly degradable, lipid-soluble organic compounds from water will lose them back to water if they are placed in an unpolluted environment. The process by which this occurs is called depuration. The time required to lose half of the bioaccumulated xenobiotic material is called the half-life of the substance. 

Two topics are addressed here. The first involves the calculation of the time required to attain 95% of the ultimate steady state during toxin uptake. This conveys a sense of the speed with which this process occurs. In the second calculation, we seek to quantify the depuration process by calculating its half-life, i.e., the time required for the toxin concentration to drop to one half its original steady-state concentration. This again serves as an indicator of the speed with which depuration proceeds. 

Fish absorb hydrocarbons primarily from the water, although ingestion of tainted food also leads to tissue contamination. Rate of uptake depends directly upon exposure concentration and lipid content of the fish. Apparently, the various components of petroleum hydrocarbons are sorbed at different rates and are also selectively deposited in specific tissues. For example. Whittle etaL (1977) treated juvenile herring with " C-hexadecane and C-benzo[a]pyrene to determine the sites of deposition of these compounds. It was then shown that 59% of the hexadecane was found in the muscle, whereas 8% and 3% occurred in the mesenteric fat and stomach fat, respectively. By contrast, the corresponding values for benzo[a]pyrene were 0.1, 0.02, and 87.1%, respectively. In most cases, the rate of depuration is rapid but once again depends on the chemical composition of the oil, lipid content of the fish, and environmental factors such as temperature. Although the maximum half-life of /2-alkanes in kerosene-tainted mullet was 18 days, the concentration of naphthalenes in gulf killifish exposed to No. 2 fuel oil declined to nondetectable levels within 15 days (Connell and Miller, 1981). 

Rate of depuration from fish tissues is extremely variable. Phenol has a particularly short half-life (<1 hour), as does 3-nitrophenol (- 1 hour). Several other compounds, such as 3,5-diethylphenol and 4-aminophenol, also have a short half-life (5-7 hours), but a number of the alkylphenols persist in tissues for extended periods of time. For example, McLeese etal. 

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