Can assessing for potential contribution of soil organic and inorganic components for butachlor sorption be improved?

Sorption of Polycyclic Musks on Soil Components of Different Aggregate Sizes: The Effect of Organic Matter-Mineral Interactions

Polycyclic musks (PCMs) in soils have been of increasing concern because of their potential characteristics of persistence, bioaccumulation, and ecological risk. However, little is known about their fate process in soil environment. Here, two PCMs namely galaxolide (HHCB) and tonalide (AHTN) were selected as sorbates to explore their sorption process in soils. Sorption batch experiments with six soils and their different aggregate fractions were carried out to elucidate the effect of organic matter-mineral interactions in different aggregate fractions on sorption of these two PCMs. The possible causes of variation in the organic carbon-normalized partition coefficient (K_oc) for HHCB and AHTN have been investigated. The strong influence of organic matter-mineral interactions on K_oc was evidenced by the large variation in K_oc on HF-treatment for both bulk soils and their different aggregate fractions. This study verified the dual effect of organic matter-mineral interactions among selected soils, and in promoting or inhibiting sorption may be related to the types of organic matter-mineral interactions. There were also interactions between soil components with different aggregate sizes, which affected the variation of K_oc in the bulk soil. This study represents a valuable contribution to the understanding of the fate processes and behaviors of HHCB and AHTN in soils and its implication on the risk assessment.

Quantification of the sorption of organic pollutants to minerals via an improved mathematical model accounting for associations between minerals and soil organic matter

The retention of organic pollutant (OP) in soils is commonly attributed to interactions with soil organic matter (SOM), perhaps overlooking substantial involvement of soil minerals. In this study, 36 soil samples with far-ranging ratios of clay to organic carbon were used to examine contribution of minerals on soil sorption of pentachlorophenol (PCP) and phenanthrene (PHE). Sorption isotherms (n = 216) were fit individually using three typical sorption models, with the most fitted K_d values screened out for quantification of the net mineral contribution to total sorption via development of mathematical model accounting for associations between minerals and SOM. Two mineral-relevant parameters [adsorption distribution coefficient (K_min) and mineral contribution index (MCI)] were simultaneously defined. Previously reported soil sorption data of PCP, PHE and butachlor (13, 12 and 46, respectively) were also extracted and included to improve the credibility of mathematic model. The average MCI values were calculated as 0.421, 0.405 and 0.512 in PCP, PHE and butachlor treated soils, respectively, very close to or even over than the minerals dominant critical value (0.5). This suggested the significant, or even predominant, contribution of minerals - as compared to SOM. Significant dependence of MCI with four conventional parameters of soil property further offered the possibility to roughly evaluate mineral contributions based on estimated threshold values of soil property parameters (especially TOC). This study provides an accessible approach for predicting the contribution of minerals in soil OP retention, especially highlighting their predominant roles vs. SOM in regulating OP removal in most of subsurface soil or contaminated brownfields where organic carbon content of soil was very low, that was not like what previously believed.

Distribution and interactions of pentachlorophenol in soils: The roles of soil iron oxides and organic matter

Soil iron oxides (IOs) and organic matter (OM) play varying roles in pentachlorophenol (PCP) retention and mobility, but the extent and mechanism are still unknown. Therefore, in order to have a better understanding of the adsorption of PCP on soils, batch sorption studies were carried out on whole soils and soils selectively treated to remove IOs (IOR) and OM (OMR). The effects of pH, time, and temperature were investigated. Results showed that PCP sorption was temperature and pH dependent; sorption decreased as both temperature and pH increased. Sorption was partly surface adsorption and partly partitioning within voids of IOs components as revealed by the kinetics models. The surface adsorption was multi-layer in nature. Equilibria were faster in the IOR soils than the untreated and OMR soils. IOs played greater roles in PCP sorption than OM. Removal of soil components, especially the IOs, as experienced in soils plagued by soil erosion, may lead to increased risks of PCP pollution of environmental media especially the aquifer.

Impact of soil primary size fractions on sorption and desorption of atrazine on organo-mineral fractions

In the current study, a mechanical dispersion method was employed to separate clay (<2 μm), silt (2-20 μm), and sand (20-50 μm) fraction in six bulk soils. Batch equilibrium method was used to conduct atrazine sorption and desorption experiments on soil organo-mineral fractions with bulk soils and their contrasting size fractions separately. The potential contribution of total organic carbon (TOC) for atrazine retention in different fractions was further investigated. It was found that clay fraction had the highest adsorption but the least desorption capacities for atrazine, while sand fraction had the lowest adsorption but the highest desorption capacities for atrazine. The adsorption percentage of atrazine, as compared with adsorption by the corresponding bulk soils, ranged from 53.6 to 80.5%, 35.7 to 56.4%, and 0.2 to 4.5% on the clay, silt, and sand fractions, respectively. TOC was one of the key factors affecting atrazine retention in soils, with the exact contribution dependent on varying degree of coating with mineral component in different soil size fractions. The current study may be useful to predict the bioavailability of atrazine in different soil size fractions.

Sorption of hydrophobic organic compounds on natural sorbents and organoclays from aqueous and non-aqueous solutions: a mini-review

Renewed focus on the sorption of hydrophobic organic chemicals (HOCs) onto mineral surfaces and soil components is required due to the increased and wider range of organic pollutants being released into the environment. This mini-review examines the possibility of the contribution and mechanism of HOC sorption onto clay mineral sorbents such as kaolinite, and soil organic matter and the possible role of both in the prevention of environmental contamination by HOCs. Literature data indicates that certain siloxane surfaces can be hydrophobic. Therefore soils can retain HOCs even at low soil organic levels and the extent will depend on the structure of the pollutant and the type and concentration of clay minerals in the sorbent. Clay minerals are wettable by nonpolar solvents and so sorption of HOCs onto them from aqueous and non-aqueous solutions is possible. This is important for two reasons: firstly, the movement and remediation of soil environments will be a function of the concentration and type of clay minerals in the soil. Secondly, low-cost sorbents such as kaolinite and expandable clays can be added to soils or contaminated environments as temporary retention barriers for HOCs. Inorganic cations sorbed onto the kaolinite have a strong influence on the rate and extent of sorption of hydrophobic organic pollutants onto kaolinite. Structural sorbate classes that can be retained by the kaolinite matrix are limited by hydrogen bonding between hydroxyl groups of the octahedral alumosilicate sheet and the tetrahedral sheet with silicon. Soil organic carbon plays a key role in the sorption of HOCs onto soils, but the extent will be strongly affected by the structure of the organic soil matter and the presence of soot. Structural characterisation of soil organic matter in a particular soil should be conducted during a particular contamination event. Contamination by mining extractants and antibiotics will require renewed focus on the use of the QSAR approaches in the context of the sorption of HOCs onto clay minerals from aqueous and non-aqueous solutions.

Nonpoint source pollution, environmental quality, and ecosystem health in China: introduction to the special section

The rapid economic and industrial growth of China, exemplified by a 10-fold increase in its gross domestic product in the past 15 years, has lifted millions of its citizens out of poverty but has simultaneously led to severe environmental problems. The World Health Organization estimates that approximately 2.4 million deaths in China per year could be attributed to degraded environmental quality. Much of China's soil, air, and water are polluted by xenobiotic contaminants, such as heavy metals and organic compounds. In addition, soil quality is degraded by erosion, desertification, and nutrient runoff. Air quality is further compromised by particulates, especially in heavily populated areas. Research shows that 80% of urban rivers in China are significantly polluted, and poor water quality is a key contributor to poverty in rural China. Economic and industrial growth has also greatly expanded the demand for water sources of appropriate quality; however, pollution has markedly diminished usable water resource quantity. Desertification and diminishing water resources threaten future food security. In recent years, China's government has increased efforts to reverse these trends and to improve ecosystem health. The Web of Science database showed that the percentage of articles on China devoting to environmental sciences increased dramatically in recent years. In addition, the top 25 institutes publishing the papers in environmental sciences were all in China. This special issue includes seven articles focusing on nonpoint source pollution, environmental quality, and ecosystem health in China. The major issues, and results of these studies, are discussed in this introduction.