Distribution, fate and formation of non-extractable residues of a nonylphenol isomer in soil with special emphasis on soil derived organo-clay complexes

Abstract

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.

First evidence for a stereoselective incorporation of nonylphenol diastereomers in soil-derived organo-clay complexes

“…Radioanalysis applied on the extractable as well as the different bound fractions from the 14 C-experiments indicated a specific distribution of the spiked 353-NP as discussed recently (Riefer et al 2011). Briefly, major proportions of 353-NP accumulated in the extractable as well as the hydrolysable fractions of humic acids and humins with absolute quota between 4 and 35% of the total applied radioactivity (see Table 1).…”

“…Details are described elsewhere (Riefer et al 2011). Thus, three subfractions were obtained: alkaline soluble humic acids, alkaline and acidic soluble fulvic acids, as well as insoluble humin.…”

“…Details on this procedure are reported by Schwarzbauer et al (2003). After hydrolysis, the released contaminants have been extracted with diethylether and subsequently fractionated on a silica gel column by liquid chromatography according to Riefer et al (2011).…”

“…This soil is characterized by a clay content around 5%, a maximum water holding capacity of approximately 42 g H 2 O/100 g soil, and total organic carbon (TOC) values in the clay fraction around 15%. More details are reported elsewhere (Riefer et al 2011). For the first two experiments, soil samples have been used either without further treatment or after sterilization by c-radiation.…”

Biochar, activated carbon and carbon nanotubes have different effects on fate of 14C-catechol and microbial community in soil

“…Humin fractions are more lipophilic and contain organoclay complexes with high surface area 43 , which may provide more adsorption and incorporation sites for 14 C residues and facilitate the incorporation of 14 C residues into the humin fractions. The incorporation of 14 C residues into the humin indicates the stabilization of 14 C residues because humin is recalcitrant and represents the stable stage of SOM 42 44 . The stabilization of 14 C residues in soil in this study, which occurred through the binding of 14 C residues to soil organic and inorganic components, aligned with the results of previous studies, in which more than 70% of 14 C-catechol derived residues were incorporated into the humin fractions 22 45 .…”