Aquatic systems methylation

Enrichment factors have been used in stndies with methyl tert-butyl ether (MTBE) that is a fuel additive and is a widespread contaminant in snbsnrface aquatic systems. 

Kelly CA, Rudd JWM, St. Louis VL, Heyes A. 1995. Is total mercury concentration a good predictor of methyl mercury concentration in aquatic systems. Water, Air Soil Pollut 80 715-724. 

Akagi, H.. Mortimer, D.C., and Miller. D.R. Mercury methylation and partition in aquatic systems. Bull Environ. Contam. Toxicol., 23(2) 372-376, 1979. 

Retene is a methyl isopropyl phenanthrene (Fig. 2). As mentioned above, Wakeham [43] was the first to address the natural non-combustion production of retene in relation to lake sediments. The starting material for retene is abietic acid, a diterpenoid found primarily in the resin of coniferous trees. When burned, the abietic acid forms retene. It can also degrade via one of two pathways to retene without combustion (Fig. 5). One pathway is through dehydro abietin and another intermediate to retene. The other proceeds through dehydroabietane, another intermediate to simonellite and finally to retene. These mechanisms can occur in both the atmosphere [44] and in aquatic systems. Therefore, where there is abietic acid, retene can follow. This becomes especially important in areas where there are high densities of conifers, and thus abietic acid. 

Equation (6) gives the overall reaction of methyl bromide with water to form the corresponding alcohol. In freshwater aquatic systems, water is the most important nucleophile, and methyl bromide is hydrolyzed to methanol. On the other hand, in sea water where... 

Several general approaches have been used to measure the activities of extracellular enzymes in aquatic systems. These methods typically measure a potential activity, inasmuch as a substrate added to a sample to measure enzyme activity is in competition with naturally occurring substrates (whose concentration is usually unknown) for enzyme active sites. The most commonly applied method involves a small substrate proxy, typically consisting of a monosaccharide or an amino acid covalently linked to a small fluorophore substrates frequently used include methyumbellifery- (MUF-) monosaccharides and 4-methyl-coumainylamide (MCA)- amino acids. Upon hydrolysis of the bond between the monomer and the fluorophore, the fluorophore becomes fluorescent, and hydrolysis is measured as an increase in fluorescence signal with time (Hoppe, 1983 Somville and Billen, 1983). 

Keil, R. G., and D. L. Kirchman. 1992. Bacterial hydrolysis of protein and methylated protein and its implications for studies of protein degradation in aquatic systems. Applied Environmental Microbiology 58 1374-1375. 

Another approach (Patterson et al., 1993), that has not been attempted in aquatic systems, uses the same basic derivatization scheme for both amino acids and for urea that was employed by Preston et al. (1996a) for amino acids in seawater. Using N-methyl-N-(teri-butyldimethysilyl)tri luoroacetamide (MTBSTFA), they quantified the isotopic composition of doubly and singly labeled N-urea in blood plasma, which suggests the method should be transferable to marine systems. 

Demethylation in the water column and sediments is receiving increasing attention. Both abiotic (e.g.. Sellers et al., 1996, 2001) and biotic (e.g., Pak and Bartha, 1998 Marvin-Dipasquale and Oremland, 1998 Marvin-Dipasquale et al., 2000 Hintehnann et al., 2000) processes are imphcated. The result is that MMHg accumulation in aquatic systems represents a balance between methylation, bioaccumulation, and the demethylation processes. In sediments, MMHg decomposition is particularly important, and it is possible that some sediments represent net sinks, rather than net sources, for MMHg in the water column. 

Gilmour C. C. and Henry E. A. (1991) Mercury methylation in aquatic systems affected by acid deposition. Environ. Pollut. 71(2-4), 131-169. 

Rainbow trout survived 48 hours of treatment with 100 ppm and 300 ppm canola methyl and ethyl esters, but were in poor condition (25). Biodiesel exhibits acute toxicity in aquatic systems but its rapid degradation and low overall toxicity make it greatly preferred to diesel fuel in environmentally sensitive areas. 

Charleson et al. 1987). It should be added that sulfide itself can be biologically methylated to methyl sulfide, and this is noted in Chapter 6, Section 6.11.4. The long-term effect of the biosynthesis of methyl sulfides on climate alteration may be considerable — and yet at first glance, this seems far removed from the production of an osmolyte by higher plants, its metabolism in aquatic systems, or microbial methylation. 

In addition organo-mercuiy compounds are of environmental interest in aquatic systems not only since the Minamata disaster (Takizawa 2000). Especially methylated mercuiy species were detected and monitored in riverine systems as the result of biotic transformation of inorganic mercury... 

Of particular concern is mono-methyl-mercury (MeHg) due to the high capacity of this species to bioaccumulate in aquatic systems and the need to be considered in risk assessment. The presence of MeHg in the atmosphere and its contribution to water bodies has been demonstrated, for example, by Bloom and Watras (1988), Hult-berg et al. (1995) and Brosset and Lord (1995). Since the concentration of MeHg in... 

PROBABLE FATE photolysis volatilized methyl bromide should photodissociate above the ocean layer, probably not significant in aquatic systems, reaction with photochemi-cally produced hydroxyl radicals has a half-life from 0.29-1.6 yrs, direct photolysis is the dominant fate in the stratosphere, but is not expected to be important in the troposphere oxidation atmospheric photooxidation by hydroxyl radicals releases inorganic bromide which is carried... 

Methylation of inorganic and methyltin compounds has been reported with the formation of mono-, di-, tri-, and tetramethyltin compounds. In addition, tributylmethyltin and dibutylmethyltin species have been found in harbor sediments, which suggests that some butyltin compounds may be methylated in aquatic systems. Methyltin formation in the environment is due mainly to methyl donation from methylcobalamin and methyl iodide. Photochemical reaction and transalkylation of inorganic tins produce methyltins methylation of tin increases the toxicity of their original metal form due, in part, to their higher volatility and lipophilicity. Methyltins are ubiquitous in the environment and have been measured in seawater, freshwater, rain, wastewaters, sediments, fish, invertebrates, birds, and humans. 

Demuth N and Heuman KG (2001) Validation of methyl-mercury determinations in aquatic systems by alkyl derivatization methods for GC analysis using ICP-MS. Analytical Chemistry 73 4020-4027. 

Aquatic systems Tetraalkyl Pb compounds, notably the methylated Pb unstable in aquatic systems, degrading to the trialkyl Pb ion overall in situ formation of alkyl Pb species is minor Simulated alkylating systems and alkyl measurements Beijer and Jernelov (1984) Jarvie et al. (1981)... 

Ealy et al have discussed the determination of methyl, ethyl and methoxyethyl mercury II halides in environmental samples such as aquatic systems, seeds and fish. 

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