Bound residues, sediment

The humic/organic matter coatings of different solid phases (i. e., SPm /SP0M), such as soils, sediments, suspended solids, colloids, and biocolloids/biosolids, interact with organic pollutants in aqueous systems in various ways. Adsorption is an important interaction mode. The reversibility and/or irreversibility of the adsorption processes is of major importance. The question whether the bound residues of pollutants are to be considered definitely inactivated has been the focus of extensive research. This question was posed as follows. Have the adsorbed pollutants become common components incorporated into the humic polymer coating of solid phases (i. e., being absorbed), or are they only momentarily inactivated in reversibly bound forms thus representing a possible source of pollution by a time-delayed release of toxic units ... 

We conclude this section by noting that sorption of charged species to NOM is generally fast and reversible, provided that no real chemical reactions take place that lead to the formation of covalent bonds (i.e., to bound residues see chapter 14). This conclusion is based on experimental data and on the assumption that in aqueous solution the more polar NOM sites are more easily accessible as compared to the more hydrophobic domains. For charged species, we may, therefore, assume that equilibrium is established within relatively short time periods. Hence, for example, in the case of TBT and TPT, contaminated sediments may represent an important source for these highly toxic compounds in the overlying water column (Berg et al., 2001). 

From a practical point of view, reduction of NACs is of great interest for two reasons. First, the amino compounds formed may exhibit a considerable (eco)toxi-city, and therefore may be of even greater concern as compared to the parent compounds. Additionally, the reduced products may react further with natural matrices, in particular with natural organic matter, thus leading to bound residues (see sections on oxidations below). One prominent example involves the reduction products of the explosive, 2,4,6-trinitrotoluene (TNT see Fig. 14.6), particularly the two isomeric diaminonitrotoluenes (2,4-DA-6-NT and 2,6-DA-4-NT) and the completely reduced triaminotoluene (TAT). These have been found to bind irreversibly to organic matter constituents present in soils (Achtnich et al., 2000) and sediments (Elovitz and Weber, 1999). This process offers interesting perspectives for the treatment of NAC contaminated sites. In fact, a dual step anaerobic/aerobic soil slurry treatment process has been developed for remediation of TNT contaminated soils (Lenke et al., 2000). 

The greater proportion of unextractable residues in the unshaded system may reflect formation of degradation products in the water column which are subsequently irreversibly bound to sediments or sedimented detritus. Phosphate diesters, in particular, are difficult to extract from sediments as well as water (13) and may account much of this unextractable residue. 

Bound residues in sediments of the Teltow Canal, Berlin - 245... 

All sediment samples were pre-extracted with methanol, butanol and solutions of hexane/acetone. The principal analytical flow scheme applied to the samples for the detection and determination of bound residues is given in Fig. 2. 

Quantitation of bound residues in Teltow Canal sediments - 285... 

Northcott GL, Jones KC (2000) Experimental approaches and analytical techniques for determining organic compounds bound residues in soil and sediment. Environ Poll 108, 19-43. 

Regarding triazines, methanol modified CO2 enabled the extraction of atrazine, deethyla-trazine, and deisopropylatrazine from spiked sediment samples, while methanol containing 2% (v/v) water was efficient for atrazine and 2-hydroxyatrazine in a spiked soil (4% organic matter). However, more stringent conditions were required for bound residues. For example, 30% methanol was needed to efficiently extract bound atrazine from a mineral soil, along with high pressure (350 bar) and temperature (125°C). ... 

Limited bio availability may lead to unexpected persistence of transformation products in soil and sediment, and longer persistence could lead to accumulation of residues. Whether bound pesticide residues in soils are occluded or may remain bioavailable in the long term in the environment is still an ongoing debate [33]. Generally, soil-bound chemicals are not considered bioavailable prior to desorption [41]. However, some evidence suggests that bound residues can be bioavailable or at least that desorption is not a requisite for biodegradation. Bioavailability is considerably lower from bound residues than from freshly treated soil. It has been suggested that the uptake ratio of chemicals and their transformation products from bound residues compared to those from freshly treated soils was about 1 5 [42]. 

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