Angus J. Beck

The form and bioavailability of non-ionic organic chemicals in sewage sludge-amended agricultural soils

The application of sewage sludges to agricultural land may increase the concentrations of many toxic organic chemicals in soils which could have adverse effects on wildlife and human health if these compounds enter foodchains. Chlorobenzenes (CBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) are amongst those compounds currently receiving most attention. The form in which these, and other organic chemicals, are present in soils and their potential to be lost by various processes including leaching, volatilisation and (bio)degradation is shown to be dependent on the physicochemical characteristics of the soil and sewage sludge, environmental conditions and the properties of the chemicals themselves. The distinction is made between those compounds that are labile, reversibly sorbed and irreversibly sorbed by sewage sludge-amended soils. The implications of the form in which the chemicals are present in soil for their availability to transfer from the soil to bacteria, fungi, earthworms, grazing livestock and food crops followed by the potential for further transfers, metabolism or bioaccumulation are discussed. The importance of the timing and method of sewage sludge application to soil on form and availability are also considered.

Movement of nonionic organic chemicals in agricultural soils

Abstract During the last decade, it has been reported that groundwater, surface water, food crops, livestock, and human tissue have all been contaminated with organic chemicals. Although much of the early work focused on pesticides, more recent studies have shown that a wider range of anthropogenic organic chemicals, many of which are designated as priority pollutants, also have been detected. Clearly, the movement of these chemicals through soil governs their potential to be transferred into water courses and foodchains. This review presents an overview of recent advances in sorption/desorption and transport phenomena. Theories currently being invoked to explain the mechanisms of sorption/desorption are discussed and their classification and numerical characterization are described. Water movement and its implications for solute transport are discussed, with emphasis being placed on the importance of soil structure. Finally, the impact of intrinsic factors, such as spatial and temporal variability of wea...

Kinetic constraints on the loss of organic chemicals from contaminated soils: Implications for soil-quality limits.

Generic or site-specific soil-quality limits for organic contaminants have been adopted or proposed in various countries in an effort to control or assess contamination. The most comprehensive generic limits, established in the Netherlands, distinguish between background concentrations for naturally occurring substances and analytical detection limits for man-made organic compounds (target values) and threshold concentrations above which remediation may be necessary (intervention values). These are being employed to highlight contaminated sites that require treatment/remediation, ideally resulting in the reduction of the compounds of concern. These limits have been derived in a number of ways but are largely based on professional judgment, usually on information concerning pathways of human exposure, phytotoxicity, and ecotoxicological effects. Effective remediation of contaminated soils is frequently limited by the slow kinetics of contaminant loss from soils under prevailing environmental conditions. This is frequently underestimated, even though it may be of fundamental importance in determining the success of treatment/remediation with respect to the assigned quality limits. This is because loss of contaminants from soils is often biphasic, whereby a short period of rapid dissipation is followed by a longer period of contaminant release. Dissipation processes, including leaching and volatilization, exhibit similar behavior. The primary rate-limiting factors governing this behavior are postulated to be fundamental sorption/ desorption mechanisms, including intraparticle diffusion, intrasorbent diffusion and chemisorption, which control the distribution of contaminant between the solid and aqueous or gaseous phases of soils and, hence, the supply of contaminant available to the various dissipation processes. In this article, we consider the relevance of biphasic desorption kinetics to existing soil-quality limits. We contend that the concentration of a given contaminant in a given soil when the “residual” phase of dissipation is reached represents an intrinsic kinetic constraint to the remediation of contaminated soil. Because of the effects of the primary rate-limiting mechanisms discussed above, it is unlikely that (in the absence of any engineering solution to the problem) any appreciable change in the contaminant concentration will occur over practical time scales under prevailing environmental conditions for a given soil. We define this contaminant concentration as a kinetically constrained soil quality limit (KCSQL) and apply it to selected examples of contaminant dissipation from the literature, including polychlorinated biphenyls, polynuclear aromatic hydrocarbons, industrial solvents, and pesticides in a range of soils. Finally, we examine the relationship between the derived KCSQLs and the Dutch “cleanup” values and soil-quality criteria adopted in other countries.

The effects of particle size, organic matter content, crop residues and dissolved organic matter on the sorption kinetics of atrazine and isoproturon by clay soil.

Reliable predictions of the fate and behaviour of pesticides in soils is dependent on the use of accurate ‘equilibrium’ sorption constants and/or rate coefficients. However, the sensitivity of these parameters to changes in the physicochemical characteristics of soil solids and interstitial solutions remains poorly understood. Here, we investigate the effects of soil organic matter content, particle size distribution, dissolved organic matter and the presence of crop residues (wheat straw and ash) on the sorption of the herbicides atrazine and isoproturon by a clay soil. Sorption Kds derived from batch ‘equilibrium’ studies for both atrazine and isoproturon by <2 mm clay soil were approximately 3.5 L/kg. The similarity of Kocs for isoproturon sorption by the <2 mm clay soil and <2 mm clay soil oxidised with hydrogen peroxide suggested that the sorption of this herbicide was strongly influenced by soil organic matter. By contrast, Kocs for atrazine sorption by oxidised soil were three times greater than those for <2 mm soil, indicating that the soil mineral components might have affected sorption of this herbicide. No significant differences between the sorption of either herbicide by <2 mm clay soil and (i) <250 μm clay soil, (ii) clay soil mixed with wheat straw or ash at ratios similar to those observed under field conditions, (iii) <2 mm clay soil in the presence of dissolved organic matter as opposed to organic free water, were observed.

Long-Term Persistence of Organic Chemicals in Sewage Sludge-Amended Agricultural Land: A Soil Quality Perspective

Publisher Summary Papers have been published reporting on the persistence and movement of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (FCBs), and chlorobenzenes (CBs) in a range of soils subjected to single and multiple applications of sewage sludge and soils that have never received sewage sludge. This chapter presents a comprehensive overview of these studies and provides a review of the mechanisms that have been postulated to be responsible for the long-term persistence and dissipation of organic chemicals in sewage sludge-amended soils. The chapter discusses long-term experiments and the compounds investigated. It is apparent that the behavior of organic chemicals in sewage sludge-amended soils is complicated by the number of loss processes involved and the complexity of their dependence on site-specific environmental and anthropogenic factors. One possible alternative is to use simple behavior assessment or screening models based on organic compound physicochemical properties to predict their likely environmental fate and behavior. Soil quality criteria have been established in some countries to assess the effectiveness of remediation strategies employed in the cleanup of contaminated soil and as a means of limiting future contamination. These quality criteria must be both practicable and scientifically defensible so that they may be widely recognized as cost effective and protective of environmental quality and human health. The chapter also discusses the Kinetically Constrained Soil Quality Limit (KCSQL) concept.

Spatial and temporal variation of isoproturon residues and associated sorption/desorption parameters at the field scale

Spatial and temporal variation of isoproturon (IPU) residues (IPUr), and their sorption (Kd) and desorption (Kapp) coefficients were monitored at the field scale in the cultivated horizon of a clay soil following pre- and postemergent IPU applications to a winter barley crop. The half life in 25 subplots ranged from 31 to 483 days with a median value of 90 days. Kapp increased as IPUr declined, ranging from a median value of 9.9 L/kg, 27 days after the pre-emergent application (autumn 1991) to 77.8 L/kg four days prior to the post-emergent application (spring of 1992). Kds were more consistent, with median values ranging from 3.7 to 6.4 L/kg over the same period. However, median Kds of 7.1 and 8.7 L/kg in May and June 1992 respectively would suggest that increases may occur during the summer months when temperatures increase and the soil dries. Sorption nonideality (Kd/Kapp) was observed on each sampling occasion, ranging from approximately 0.5, 27 days after the pre-emergent herbicide application, to approximately 0.2 four days prior to the post-emergent application. All parameters were positively skewed. Variation of all parameters at the local scale (i.e. within 1 m2) was less than that at the field scale, but greater than that associated with the experimental methods employed indicating that both intrinsic and extrinsic factors influenced the distribution of IPUr, Kd and Kapp. Variability of IPUr and Kd on individual sampling dates was consistent with coefficients of variation generally ranging from 26 to 44% and from 18 to 44% respectively. Variability of Kapp was more erratic, increasing to over 200% and 100% following two major rainstorm events in November 1991 and February 1992 repectively. Normalization of Kds on a soil organic matter basis failed to reduce the variability observed. The implications of these results for contaminant transport and fate modelling are discussed

Movement of water and the herbicides atrazine and isoproturon through a large structured clay soil core

A large (1.1 m × 0.8 m in diameter) core of strongly cracked clay soil was instrumented with eight suction samplers, ten zero-suction samplers and sixteen pressure transducer tensiometers. Results of three rainfall events labelled with potassium bromide, pentafluorobenzoic acid and 2,6-difluorobenzoic acid indicate rapid bypass flow, matrix advection and mixing of water between the soil macropores and the matrix all occurred. Generally, no sharp distinction was observed between crack flow and matrix advection; water flow was best described by a continuum of flow phenomena. Before rainfall application, the herbicides atrazine and isoproturon were applied to the soil surface at rates typically used in the field (2.475 kg active ingredient/ha). Rapid bypass flow in large cracks, by which some of the solutes were transported with limited contact with the soil, was mainly responsible for redistribution of the herbicides and their movement to depth in short time periods. Over the course of the experiments 0.23 pore volumes of rainfall were applied to the core but only 0.02 pore volumes were recovered by gravity drainage. Less than 1% of the herbicides applied was lost in water draining from the soil core.

Kinetic constraints on theIn-situ remediation of soils contaminated with organic chemicals.

Cleanup of contaminated soils to comply with soil quality limits currently receives much interest.In-situ remediation of contaminated soils relies on the ability of the techniques employed to enhance the rate of release of contaminants from the soil-sorbed and nonaqueous phase liquid (NAPL) phases into the aqueous or gaseous phases from which they can be more readily removed and treated. Contaminant concentrations in these “environmentally mobile” forms usually decline over time so that the economic efficiency and the overall success of remediation technologies are subject to the “law of diminishing returns”. In this paper we consider the “state of the art” in our understanding of NAPL dissolution and transport, desorption of soilsorbed contaminants and fluid flow in porous media. The extent to which these processes may constrain the success of bioremediation, pump-and-treat remediation and soil venting in relation to established soil quality limits is addressed. Finally, we suggest directions for future research and comment on legislative considerations.

Leaching of recently applied and aged residues of the herbicides atrazine and isoproturon through a large, structured clay soil core

Leaching of recently applied atrazine and isoproturon (2.475 kg/ha) through a large (1.1 m × 0.8 m in diameter), heavily cracked core of clay soil is compared with leaching of their aged residues twenty-one months later. Following application, herbicide losses were mainly from gravity drainage samplers at 0.55 m whilst 21 months later losses were mainly from samplers at 0.175 m. This change was due to differences in water flow regimes resulting from changes in the structure of the cultivated horizon between rainfall events. Nonequilibrium conditions were observed. After herbicide application, solution concentrations ranged from 1–26% and 1–34% of those predicted for atrazine and isoproturon respectively at equilibrium in the core top soil whilst twenty-one months later they ranged from 1–3% for both herbicides. Nonequilibrium became more pronounced with depth on both occasions. Over the course of four rainfall events comprising 353 mm, only 3% of the atrazine and 1% of the isoproturon applied to the core was recovered in drainage water.

Limitations to the In-Situ Remediation of Soils Contaminated with Organic Chemicals in Relation to the Potential to Achieve Clean-Up Criteria

In-situ remediation relies on enhancing the rate of release of contaminants from the soil-sorbed and nonaqueous phase liquid (NAPL) phases into the aqueous or gaseous phases. Contaminant concentrations in these ‘mobile’ forms usually decline over time so that the success of remediation technologies is subject to the ‘law of diminishing returns’. Here we discuss NAPL dissolution and transport, desorption of soil-sorbed contaminants and fluid flow in porous media. We then consider whether these processes constrain the success of bioremediation, pump-and-treat and soil vapor extraction (SVE) in relation to soil clean-up criteria. Finally, we introduce the kinetically constrained soil quality limit (KCSQL) concept for characterising persistent residual phases of contamination.