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Sorption of non-ionic organic compounds to soil is usually expressed as the carbon-normalized partition coefficient (KOC), because it is assumed that the main factor that influences the amount sorbed is the organic carbon content of the soil. However, KOC can vary by a factor of at least ten across a range of soils. We investigated two potential causes of variation in diuron KOC - organic matter-mineral interactions and organic matter chemistry - for a diverse set of 34 soils from Sri Lanka, representing a wide range of soil types. Treatment with hydrofluoric acid (HF-treatment) was used to concentrate soil organic matter. HF-treatment increased KOC for the majority of soils (average factor 2.4). We attribute this increase to the blocking of organic matter sorption sites in the whole soils by minerals. There was no significant correlation between KOC for the whole soils and KOC for the HF-treated soils, indicating that the importance of organic matter-mineral interactions varied greatly amongst these soils. There was as much variation in KOC across the HF-treated soils as there was across the whole soils, indicating that the nature of soil organic matter is also an important contributor to KOC variability. Organic matter chemistry, determined by solid-state (13)C nuclear magnetic resonance (NMR) spectroscopy, was correlated with KOC for the HF-treated soils. In particular, KOC increased with the aromatic C content (R=0.64, p=1×10(-6)), and decreased with O-alkyl C (R=-0.32, p=0.03) and alkyl C (R=-0.41, p=0.004) content., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The persistence of contaminants entering the environment through land application of biosolids needs to be understood to assess the potential risks associated. This study used two biosolids treatments to examine the dissipation of four organic compounds: 4-nonylphenol, 4-t-octylphenol, bisphenol A and triclosan, under field conditions in South Australia. The pattern of dissipation was assessed to determine if a first-order or a biphasic model better described the data. The field dissipation data was compared to previously obtained laboratory degradation data. The concentrations of 4-nonylphenol, 4-t-octylphenol and bisphenol A decreased during the field study, whereas the concentration of triclosan showed no marked decrease. The time taken for 50% of the initial concentration of the compounds in the two biosolids to dissipate (DT50), based on a first-order model, was 257 and 248 d for 4-nonylphenol, 231 and 75 d for 4-t-octylphenol and 289 and 43 d for bisphenol A. These field DT50 values were 10- to 20-times longer for 4-nonylphenol and 4-t-octylphenol and 2.5-times longer for bisphenol A than DT50 values determined in the laboratory. A DT50 value could not be determined for triclosan as this compound showed no marked decrease in concentration. The biphasic model provided a significantly improved fit to the 4-t-octylphenol data in both biosolids treatments, however, for 4-nonylphenol and bisphenol A it only improved the fit for one treatment. This study shows that the use of laboratory experiments to predict field persistence of compounds in biosolids amended soils may greatly overestimate degradation rates and inaccurately predict patterns of dissipation., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Land application of biosolids is common practice in many countries, however, there are some potential risks associated with the presence of contaminants within the biosolids. This laboratory study examined the degradation of four commonly found organic compounds, 4-nonylphenol, 4-t-octylphenol, bisphenol A, and triclosan, in soil following the addition of two biosolids over 32 weeks. The pattern of degradation was assessed to determine if it followed a standard first-order decay model or if a biphasic model with a degrading and a recalcitrant fraction better described the data. The time taken for the initial concentrations to decrease by 50% (DT50), based on a first-order model, was 12-25 d for 4-nonylphenol, 10-14 d for 4-t-octylphenol, 18-102 d for bisphenol A, and 73-301 d for triclosan. For 4-nonylphenol, bisphenol A and triclosan, the biphasic model fitted the degradation data better than the first-order model, indicating the presence of a degrading fraction and a non-degrading recalcitrant fraction. The recalcitrant fraction for these three compounds at the completion of the 32 week experiment was 17-21%, 24-42%, and 30-51% of the initial concentrations, respectively. For 4-t-octylphenol, the first-order model was sufficient in explaining the degradation data, indicating that no recalcitrant fraction was present. This study showed that biphasic degradation occurred for some organic compounds in biosolids amended soil and that the use of standard first-order degradation models may underestimate the persistence of some organic compounds following land application of biosolids., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

The effect of solvent-conditioning on the sorption of diuron and phenanthrene was investigated. The organic carbon-normalized sorption coefficients (K(OC)) for diuron and phenanthrene (determined from single initial concentrations of 0.8mgL(-1) and 1.5mgL(-1), respectively) were consistently higher following solvent-conditioning of a whole soil with five organic solvents (acetonitrile, acetone, methanol, chloroform and dichloromethane). The relative increase in K(OC) was inversely related to the polarity of the conditioning solvent (i.e. greater increases in K(OC) were observed for the least polar solvents: chloroform and dichloromethane). The effect of solvent-conditioning on the sorption properties of the same soil that had been lipid-extracted using accelerated solvent extraction (ASE) was also investigated. Since lipid extraction involves treatment with a non-polar solvent (95:5 dichloromethane:methanol) one may have expected no further increase in K(OC) on solvent-conditioning. On the contrary, the lipid-extracted soil exhibited very similar increases in K(OC) as the whole soil. This demonstrated that lipid removal and solvent-conditioning, which both increased K(OC) for this soil, are quite separate phenomena.

The influence of lipids on the sorption of diuron and phenanthrene to soils was investigated. Accelerated solvent extraction (ASE) was used to extract lipids from twelve soil horizons. Extractable lipids accounted for 3-13% of organic C. The organic carbon-normalized sorption coefficients (K(OC)) for diuron and phenanthrene were consistently higher for the lipid-extracted soils than for the whole soils (average of 31% for diuron and 29% for phenanthrene), indicating that lipids compete for or block sorption sites on the organic matter. Sorption experiments on one pair of HF-treated soils indicated that the blocking effects of minerals and lipids are independent, since lipid extraction and HF-treatment combined increased K(OC) by more than either treatment alone. Lipids extracted from whole and HF-treated soils were very similar in composition, consisting predominantly of long-chain polymethylene structures. K(OC) of the lipid itself was lower than for any of the whole soils and soil fractions (lipid extracted and HF-treated) for diuron, but higher for phenanthrene. Solid-state (13)C NMR spectra of the HF-treated soils before and after lipid extraction indicated that 15-20% of alkyl C was removed by ASE and that no other structures were affected.

The behaviour and fate of macronutrients and pollutants in sewage sludge applied to the land are affected by the chemical composition of the sludge organic matter, which in turn is influenced by both sewage source and by sewage treatment processes. In this study, (13)C nuclear magnetic resonance (NMR) spectroscopy was used to characterise the organic matter of sludges collected at three different points along the treatment stream of a municipal sewage works with a domestic catchment. Sludge at the first point, an undigested liquid (UL) sludge, had a substantially different composition to the anaerobically digested (AD) and dewatered sludge cake (DC) materials, which were similar to each other. In particular, the UL sludge contained more alkyl C than the AD or DC sludges. All three sludges were found to contain mobile alkyl C that is poorly observed using the cross polarisation (CP) technique, necessitating the use of the less sensitive, but more quantitatively reliable direct polarisation (DP) technique to obtain accurate distributions of C types.

Even though it is well established that soil C content is the primary determinant of the sorption affinity of soils for non-ionic compounds, it is also clear that organic carbon-normalized sorption coefficients (K(OC)) vary considerably between soils. Two factors that may contribute to K(OC) variability are variations in organic matter chemistry between soils and interactions between organic matter and soil minerals. Here, we quantify these effects for two non-ionic sorbates-diuron and phenanthrene. The effect of organic matter-mineral interactions were evaluated by comparing K(OC) for demineralized (HF-treated) soils, with K(OC) for the corresponding whole soils. For diuron and phenanthrene, average ratios of K(OC) of the HF-treated soils to K(OC) of the whole soils were 2.5 and 2.3, respectively, indicating a substantial depression of K(OC) due to the presence of minerals in the whole soils. The effect of organic matter chemistry was determined by correlating K(OC) against distributions of C types determined using solid-state (13)C NMR spectroscopy. For diuron, K(OC) was positively correlated with aryl C and negatively correlated with O-alkyl C, for both whole and HF-treated soils, whereas for phenanthrene, these correlations were only present for the HF-treated soils. We suggest that the lack of a clear effect of organic matter chemistry on whole soil K(OC) for phenanthrene is due to an over-riding influence of organic matter-mineral interactions in this case. This hypothesis is supported by a correlation between the increase in K(OC) on HF-treatment and the soil clay content for phenanthrene, but not for diuron.

Organic matter has long been recognized as the main sorbent phase in soils for hydrophobic organic compounds (HOCs). In recent times, there has been an increasing realization that not only the amount, but also the chemical composition, of organic matter can influence the sorption properties of a soil. Here, we show that the organic carbon-normalized sorption coefficient (K(OC)) for diuron is 27-81% higher in 10 A11 horizons than in 10 matching A12 horizons for soils collected from a small (2ha) field. K(OC) was generally greater for the deeper (B) horizons, although these values may be inflated by sorption of diuron to clays. Organic matter chemistry of the A11 and A12 horizons was determined using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. K(OC) was positively correlated with aryl C (r2=0.59, significance level 0.001) and negatively correlated with O-alkyl C (r2=0.84, significance level <0.001). This is only the second report of correlations between whole soil K(OC) and NMR-derived measures of organic matter chemistry. We suggest that this success may be a consequence of limiting this study to a very small area (a single field). There is growing evidence that interactions between organic matter and clay minerals strongly affect K(OC). However, because the soil mineralogy varies little across the field, the influence of these interactions is greatly diminished, allowing the effect of organic matter chemistry on K(OC) to be seen clearly. This study in some way reconciles studies that show strong correlations between K(OC) and the chemistry of purified organic materials and the general lack of such correlations for whole soils.