Anthropogenic contaminants like nonylphenols (NP) are added to soil, for instance if sewage-sludge is used as fertilizer in agriculture. A commercial mixture of NP consists of more than 20 isomers. For our study, we used one of the predominate isomers of NP mixtures, 4-(3,5-dimethylhept-3-yl)phenol, as a representative compound. The aim was to investigate the fate and distribution of the isomer within soil and soil derived organo-clay complexes. Therefore, (14)C- and (13)C-labeled NP was added to soil samples and incubated up to 180 days. Mineralization was measured and soil samples were fractionated into sand, silt and clay; the clay fraction was further separated in humic acids, fulvic acids and humin. The organo-clay complexes pre-incubated for 90 or 180 days were re-incubated with fresh soil for 180 days, to study the potential of re-mobilization of incorporated residues. The predominate incorporation sites of the nonylphenol isomer in soil were the organo-clay complexes. After 180 days of incubation, 22 % of the applied (14)C was mineralized. The bioavailable, water extractable portion was low (9 % of applied (14)C) and remained constant during the entire incubation period, which could be explained by an incorporation/release equilibrium. Separation of organo-clay complexes, after extraction with solvents to release weakly incorporated, bioaccessible portions, showed that non-extractable residues (NER) were preferentially located in the humic acid fraction, which was regarded as an effect of the chemical composition of this fraction. Generally, 27 % of applied (14)C was incorporated into organo-clay complexes as NER, whereas 9 % of applied (14)C was bioaccessible after 180 days of incubation. The re-mobilization experiments showed on the one hand, a decrease of the bioavailability of the nonylphenol residues due to stronger incorporation, when the pre-incubation period was increased from 90 to 180 days. On the other hand, a shift of these residues from the clay fraction to other soil fractions was observed, implying a dynamic behavior of incorporated residues, which may result in bioaccessibility of the NER of nonylphenol.

The incorporation process of a defined (13)C- and (14)C-labeled nonylphenol isomer (4-(3,5-dimethylhept-3-yl)phenol) into soil-derived organo-clay complexes was investigated. Isolated organo-clay complexes were separated into humic subfractions. Noninvasive ((13)C-CP/MAS NMR) and invasive methods (sequential chemical degradation, pyrolysis) were applied to obtain detailed information about the mode of incorporation, chemical structure, and change of the incorporation character of nonextractable residues in course of incubation. (13)C-CP/MAS NMR measurements of humic acids revealed an increasing incorporation of phenolic compounds during the experimental time which was referred to residues of the introduced (13)C-labeled NP isomer. Detailed investigations by means of sequential chemical degradation indicated a predominant incorporation of nonextractable NP isomer residues via reversible ester (amide) bonds. In course of time, the amount of releasable compounds decreased, pointing to altering processes which affected the mode of incorporation. BBr3-treatment, RuO4 oxidation, and thermochemolysis released only low portions of nonextractable radioactivity giving evidence of strongly incorporated residues. With the comprehensive application of complementary methods (e.g., humic matter fractionation, (13)C-CP/MAS NMR, sequential chemical degradation) it was possible to provide a comparatively detailed insight into the incorporation behavior of the applied NP isomer.

The original publication shows the authors' given names as family names and vice versa. The names are correct in this erratum.The online version of the original article can be found under

Organo-clay complexes in soil are a major sink for xenobiotics and, thus, often enhance their persistence dramatically. However, the knowledge on environmental processes of non-extractable residue formation on a short time scale is very restricted. Therefore, this study examined the distribution of 4-(3,5-dimethylhept-3-yl)phenol (NP) and 4-chloro-2-methylphenoxyacetic acid (MCPA) in soil over a short time period of 48 h and in different soil subfractions. The overall proportion of organo-clay-associated bound residues was not only abundant but also in the same range for both substances (MCPA: 8%; NP: 11% of applied 14 C-radioactivity). However, a more detailed view revealed two different distribution patterns: a higher proportion of clay-associated NP was accompanied by a lower content of bound residues, whereas a smaller fraction of clay-associated MCPA was characterized by a higher proportion of non-extractable residues. Further on, a selective accumulation of bound residues among clay-associated humic fractions was observed. NP residues were linked predominantly to humic acids, whereas MCPA residues tended to be incorporated more into fulvic acids. It was evident that the overall distribution was influenced primarily by the physico-chemical properties of the contaminants. This study demonstrates in detail a rapid initial incorporation accompanied by a specific distribution into soil sub-fractions for selected xenobiotics in soil and points to a complex interaction of clay-associated organic matter with low molecular weight compounds.

Environmental processes can affect the stereochemical properties of organic pollutants. In particular, biotic processes like microbial transformations or membrane penetration alter the ratios of enantiomers as well as diastereomers. These effects have been intensively used not only in environmental studies but also in medicine, toxicology, pharmacy, and agricultural sciences. However, in order to identify unambiguously biotic-initiated alteration of organic compounds, the knowledge on the stereoselective effect of all relevant processes is mandatory. Therefore, here we report the first evidence for a stereospecific formation of non-extractable residues of a xeniobiotic in a highly relevant soil subfraction, the organo-clay complexes. In this study, soils were spiked with labeled and unlabeled nonylphenol isomer, and incubation experiments were performed to study its long-term incorporation behavior into soil-derived organo-clay complexes under abiotic and biotic conditions. Besides the extractable particle-associated proportion especially the humic fractions comprising the bound residues have been analyzed by GC/ MS. Our results from biotic experiments revealed alterations of the diastereomeric composition of the contaminant in the different soil humic subfractions. A depletion of the first eluting diastereomer as expressed by diastereomeric ratios around 0.6 has been observed for the extractable fraction, whereas the non-extractable proportion was enriched in the first diastereomer (diasteremoric ratio around 1.0). On the contrary, the diastereomeric ratios remained unaffected during the abiotic experiments (diasteremoric ratio around 0.8). These systematic observations give clear evidence that the process of microbial-assisted incorporation of nonylphenol into soil organo-clay complexes is a stereoselective process. To our knowledge, this is the first report on a stereoselective incorporation process of organic substances forming non-extractable residues. Consequently, the formation of non-extractable residues has to be considered in environmental studies dealing with stereoselective analysis of organic pollutants in soils to study their microbial transformation.