Fraction nonextractable

A sediment-water system was used to study the partition and the degradation of C-labeled 4-nitrophenol and 3,4-dichloroaniline (Heim et al. 1994). The results clearly illustrated the importance of water-to-sediment partitioning, and that a substantial fraction of the substrates existed in the form of nonextractable residues. 

A series of soil microcosms were used to study the biodegradation and bioavailability of pyrene during long-term incubation. The nonextractable fraction of -labeled pyrene that had been introduced into pristine soil and incubated with or without the addition of azide was substantially greater in the latter (Guthrie and Pfaender 1998). It was also shown that microbial activity produced a number of unidentified polar metabolites that might plausibly be involved in the association. 

This nonextractable radioactivity was probably the result of covalent binding of the furazolidone intermediates to endogenous macromolecules. The bioavailability of these bound tissue residues from the above pig residue depletion study was determined by feeding rats lyophilized samples of liver and muscle tissues from animals sacrificed at 0 and 45 days after the last treatment (132). Results showed that the fraction of the bound residues bioavailable to rats was in the range 16-41%. The toxicological impact of these bioavailable bound residues has not been yet determined. 

A residual CP concentration is often observed after soil bioremediation. The leveling-off of degradation is not due to decreased microbial activity, since freshly added CPs are rapidly degraded (Harmsen, 1993 Salkinoja-Salonen et al., 1989). The residual concentrations are explained by the gradual diffusion of pollutants deep into micropores, as well as by their adsorption onto soil organic matter (Harmsen, 1993). Lagas (1988) observed that the nonextractable fraction of CPs in sterile soil increased according to the square root of time as a consequence of diffusion into humic material. 

The metribuzin metabolite DK is deaminated, conjugated, and rapidly bound to insoluble fractions in soybean, as shown in Figure 7.17. Frear et al. (1985) hydroponically treated excised soybean leaves with 14C-DK for 48h. Only 16% of the total radioactive residues were organosoluble with a 3 1 ratio of DK and DADK. The water-soluble fraction was mainly A-malonyl DK, amounting to 17% of the residue. The remainder of the residues was nonextractable. iV-malonated DK was detected as a minor metabolite in this study. 

Barriuso, E. and W.C. Koskinen (1996). Incorporating nonextractable atrazine residues into soil size fractions as a function of time. Soil Sci. Soc. Am. J., 60 15-157. 

Barriuso, E., M. Schiavon, F. Andreux, and J.M. Portal (1991). Localization of atrazine nonextractable (bound) residues in soil size fractions. Chemosphere, 22 1131-1140. 

An important issue emerged from the results of experiments with 14C-labeled pyrene added to a pristine forest soil (Guthrie and Pfaender 1998) (1) extensive mineralization took place only in samples amended with a pyrene-degrading microbial community, (2) there was a substantially greater nonextractable fraction of label in soils containing either the natural or introduced microflora compared with an azide-treated control, (3) metabolites that could be released by acid and base extraction remained in the soil after 270 days of incubation. 

Whereas transformation has generally been demonstrated — often to quinones — only relatively low levels of mineralization to C02 have frequently been observed, for example in Pleurotus ostreatus (Bezalel et al. 1996a Hofrichter et al. 1998), and it has been shown that a substantial fraction of phenanthrene was nonextractable and presumably bound to fungal mycelia (Bezalel et al. 1996b). 

Using common extraction procedures and chemical degradation techniques as described above the extractable and nonextractable fraction of four sediment samples of the Teltow Canal were investigated. The extracts as well as the degradation products were analysed by means of gas chromatographic - mass spectrometric analyses. 

With respect to the nonextractable fraction also numerous obviously anthropogenic compounds were identified, but they were superimposed by huge amounts of degradation products derived from natural... 

In addition to the local contamination numerous substances were detected within the nonextractable fraction, that are common riverine contaminants including e.g. phosphates, nitro compounds, UV-protectors, pesticides, fragrances, organotin compounds and halogenated aromatics (see Table 2). 

Tab. 4 Specific contaminants quantified in the nonextractable fraction of Teltow Canal sediment samples after a separate application of different chemical degradation procedures (contents are given in pg/kg dry matter, nd = not determined).

Brominated phenols, nitrobenzoic acid, butylated nitrophenols, tributylphosphate and bisphenol A formed a third group of contaminants that occurred only in the nonextractable fraction. 

Based on their distribution and concentration data two groups of bound contaminants can be differentiated. A major portion of the contaminants determined appeared in the extractable as well as in the nonextractable fraction with concentrations generally higher in the latter. A second group occurred only in the nonextractable fraction with substantial concentrations but not in the extractable fraction. 

In contrast the occurrence of only a few substances was spatially restricted. Also only few compounds were determined exclusively after application of one degradation method. For these contaminants a more specific interaction with the macromolecular organic matter of the nonextractable fraction has to be assumed. 

Additionally, the bound fraction of numerous further anthropogenic contaminants were investigated by quantitation of the extractable and nonextractable matter. The selection of the contaminants (including chlorinated and brominated naphthalenes, 2,4,6-tribromoaniline, mono-and dibrominated phenols, phthalates, tri-n-butylphosphate, 2,4,4-trimethylpentane-l,3-dioldi-Ao-butyrate, bisphenol A, butylated nitrophenols, 4-nitrobenzoic acid, galaxolide and tonalide) was based on the results of extended GC-MS-screening analyses applied to the extracts of the sediment samples as well to the extracts derived from selective chemical degradation procedures. 

---