Fate of Pollutants in Soils and Sediments

Regarding soils, a central issue is the persistence and movement of pesticides that are widely used in agriculture. Many different insecticides, fungicides, herbicides, and molluscicides are applied to agricultural soils, and there is concern not only about effects that they may have on nontarget species residing in soil, but also on the possibility of the chemicals finding their way into adjacent water courses. 

Organic Pollutants An Ecotoxicological Perspective, Second Edition 

Concentration that would have been found if all applied material were retained by soil 

FIGURE 4.3 Loss of pesticides from soil, (a) Breakdown of herbicides in soil, (b) Disappearance of persistent organochlorine insecticides from soils (from Walker et al. 2000). 

Although the major concern about the fate of organic pollntants in soil has been about pesticides in agricultural soils, other scenarios are also important. The disposal of wastes on land (e.g., at landfill sites) has raised questions about movement of pollutants contained in them into the air or neighboring rivers or water conrses. The presence of polychlorinated biphenyls (PCBs) or PAHs in snch wastes can be a significant source of pollution. Likewise, the disposal of some industrial wastes in landfill sites (e.g., by the chemical industry) raises questions about movement into air or water and needs to be carefully controlled and monitored. 

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The adsorption behavior of colloidal material onto river particles can play a vital role in the transport and fate of pollutants. FFF methods provide a means to evaluate the relative importance of different fractions in adsorption of contaminants in soils and sediments. 

Environmental processes include fate and transport of pollutants in the environment, which are components of the field of environmental chemistry. The fate of pollutants in the environment depends upon the compartment in which they occur air, surface water, ground water, soil, sediment (the mud at the bottom of water bodies), or living organisms. The water compartment may include ground water, surface water (water bodies such as rivers, streams, lakes, ponds, oceans, etc.), or pore water (water in between soil or sediment particles). Within each compartment, the chemical may remain unaltered, but more often is altered by biotic (living) or abiotic (nonliving) components of the environment. 

The remaining chapters in the first section of the book cover the measurement and investigation of the fate and transport of specific chemicals in the soil, water and atmosphere and exchange among these media. Chapter 3 by West and Wilson reviews subsurface natural attenuation of contaminants. Chapters 4, 5, and 6 by Stone et ai, Soderstrom et ai, and Butler and Hayes, respectively, all relate to the movement and fate of organic chemicals in soils and sediments, while Chaper 9 by Pedersen and Suffet and Chapter 10 by Salmun and Farhan focus on runoff from the terrestrial environment to nearby waters. These last two chapters illustrate the need to understand the complexities of non-point source pollutant inputs. Recent books have also focused on similar topics for persistent and bioaccumulative toxics (PBTs) (41,42). 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

There are also several methods to determine patterns of fate and transport of pollutants in the environment. In some cases, microcosms and me-socosms are used to study fate, biodegradability, bioavailability, and transport within compartments. Field surveys may also be used to study fate and transport of pollutants in contaminated environments. Such studies involve collection and analysis of biota, water, air, soil, or sediment. In some cases, radioactively labeled contaminants ( tracers ) may be introduced in mesocosms or noncontaminated environments in order to determine their fate and patterns of transport. Finally, mathematical models are often used to produce computer simulations to... 

Toxaphene has been described as a ubiquitous contaminant in various environmental compartments and has a widespread distribution around the world [52-54], even in very remote areas, such as the polar regions, due to aerial transport [55]. Extensive reviews on the chemistry, biochemistry, toxicity, analysis, and environmental fate of toxaphene have been published [32,38,52]. Toxaphene, similar to other pollutants such as DDT, PCBs, and other organochlorine compounds, was found in air [54 56], freshwater [57,58], food [59], soil and sediment [60,61], human milk [53], and even marine biota [41,62-66]. 

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