Surface water pathways

Surface Water Pathway. The surface water pathway of DPM rates the potential for contaminants from a waste site to enter surface waters via overland flow routes, or from ground water discharge to surface water. If pollutants are not directly observed in surface water, but are present in sediments or soil, there is a potential for surface water contamination so it is necessary to collect information from which their likelihood to reach a receptor can be estimated. The following variables are scored to provide an indication of this exposure potential ... 

The documented occurrence of pesticides in surface water is indicative that mnoff is an important pathway for transport of pesticide away from the site of appHcation. An estimated 160 t of atra2ine, 71 t of sima2ine, 56 t of metolachlor, and 18 t of alachlor enter the Gulf of Mexico from the Mississippi River annually as the result of mnoff (47). Field appHcation of pesticides inevitably leads to pesticide contamination of surface mnoff water unless mnoff does not occur while pesticide residues remain on the surface of the soil. The amount of pesticides transported in a field in mnoff varies from site to site. It is controUed by the timing of mnoff events, pesticide formulation, physical—chemical properties of the pesticide, and properties of the soil surface (48). Under worst-case conditions, 10% or more of the appHed pesticide can leave the edge of the field where it was appHed. 

Surface water enrichment is the result of aeolian and fluvial inputs, which are thought to be the most important sources of Th to the ocean. Thorinm-232 has been proposed as a link between the radiogenic thorium isotopes and trace metals and anthropogenic pollutants. " While the pathways are very different for the radiogenic thorium isotopes, Th is delivered to the ocean in a fashion similar to many pollutants and trace metals. For example, Guo et found Th distributions in the Gulf of Mexico and off Cape Hatteras in the North Atlantic Ocean agreed well with the general distribution pattern of aluminum. 

The indirect pathway by which air pollutants interact with plants is through the root system. Deposition of air pollutants on soils and surface waters can cause alteration of the nutrient content of the soil in the vicinity of the plant. This change in soil condition can lead to indirect or secondary effects of air pollutants on vegetation and plants. 

Figures 16-3 through 16-5 present the decision network for screening contaminant fate in air, surface water, ground water, and biota. Pathways must be further evaluated to determine the likelihood of population exposure.

Contaminant transfer to bed sediments represents another significant transfer mechanism, especially in cases where contaminants are in the form of suspended solids or are dissolved hydrophobic substances that can become adsorbed by organic matter in bed sediments. For the purposes of this chapter, sediments and water are considered part of a single system because of their complex interassociation. Surface water-bed sediment transfer is reversible bed sediments often act as temporary repositories for contaminants and gradually rerelease contaminants to surface waters. Sorbed or settled contaminants are frequently transported with bed sediment migration or flow. Transfer of sorbed contaminants to bottomdwelling, edible biota represents a fate pathway potentially resulting in human exposure. Where this transfer mechanism appears likely, the biotic fate of contaminants should be assessed. 

System considers surface water and groundwater pathways of exposure in evaluating the potential for adverse effects. Air and soil pathways will be added as will numerous built-in error checking routines. 

Recent studies provide evidence for rapid dermal absorption of inorganic lead in adults however, these studies have not quantified the fraction of applied dose that was absorbed (Stauber et al. 1994). The quantitative significance of the dermal absorption pathway as a contributor to lead body burden remains an uncertainty. In children who experience extensive dermal contact with lead in soil, sand, or surface water and suspended sediment (e.g., beach or shoreline exposure scenario), even a low percent absorption... 

FIGURE 8.10. A framework including pollutant sources, pathways and transformations in surface waters receiving CSOs. 

TiCU readily functionalizes hydrophilic polymers such as poly(vinyl alcohol), m-ciesol novolac and methacrylic acid copolymers as well as moderately hydrophobic polymers such as poly(methyl methacrylate), poly(vinyl acetate), poly(benzyl methacrylate) and fully acetylated m-cresol novolac. HCI4 did not react with poly(styrene) to form etch resistant films indicating that very hydrophobic films follow a different reaction pathway. RBS analysis revealed that Ti is present only on the surface of hydrophilic and moderately hydrophobic polymer films, whereas it was found diffused through the entire thickness of the poly(styrene) films. The reaction pathways of hydrophilic and hydrophobic polymers with HCI4 are different because TiCl is hydrolysed by the surface water at the hydrophilic polymer surfaces to form an etch resistant T1O2 layer. Lack of such surface water in hydrophobic polymers explains the absence of a surface TiC>2 layer and the poor etching selectivities. 

The Iron Cycle in the Photic Zone of Surface Waters In the photic zone the formation of iron(II) occurs as a photochemical process. The photochemical iron II) formation proceeds through different pathways 1) through the photochemical reductive dissolution of iron(III)(hydr)oxides, and 2) through photolysis of dissolved iron(lll) coordination compounds, Fig. 10.16. 

Disulfoton enters the environment primarily during its use as an insecticide/acaricide in crops and vegetables, and in homes and gardens. Other important pathways for disulfoton s entry into the environment are the disposal of liquid disulfoton wastes into soil evaporation pits, ditches, ponds (Winterlin et al. 1989), and hazardous waste sites. Thus, soil is the environmental medium most likely to be contaminated with disulfoton. The processes that may transport disulfoton from soil to other environmental media include leaching to groundwater, runoff to surface water, and absorption by plants (Holden 1986 Mostaghimi et al. 1993 Nash 1974 Plumb 1991 Sanborn et al. 1977 ... 

Surface Water. Aniline degraded in pond water containing sewage sludge to catechol, which then degrades to carbon dioxide. Intermediate compounds identified in minor degradative pathways include acetanilide, phenylhydroxylamine, as,cA-muconic acid, p ketoadipic acid, levulinic acid, and succinic acid (Lyons et al, 1984). 

The redox potential in subsurface water varies with alterations from aerobic to anaerobic conditions. In and around anaerobic environments, conditions for reduction exist and contaminants are transformed accordingly. Under aerobic conditions, is the predominant oxidation agent (mainly through biological processes), because the transformation of contaminants is mainly through oxidative pathways. Aerobic and anaerobic states may occur both in surface waters and in deeper subsurface water. 

Photolysis Abiotic oxidation occurring in surface water is often light mediated. Both direct oxidative photolysis and indirect light-induced oxidation via a photolytic mechanism may introduce reactive species able to enhance the redox process in the system. These species include singlet molecular O, hydroxyl-free radicals, super oxide radical anions, and hydrogen peroxide. In addition to the photolytic pathway, induced oxidation may include direct oxidation by ozone (Spencer et al. 1980) autooxidation enhanced by metals (Stone and Morgan 1987) and peroxides (Mill et al. 1980). 

Five pathways were assessed during the project Groundwater, Surface water. Air pathway. Direct contact, and Stream sediments. 

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