Contaminated sites

Soil. The first reported field trial of the use of hyperaccumulating plants to remove metals from a soil contaminated by sludge appHcations has been reported (103). The results were positive, but the rates of metal uptake suggest a time scale of decades for complete cleanup. Trials with higher biomass plants, such as B.juncea, are underway at several chromium and lead contaminated sites (88), but data are not yet available. 

Transport processes describe movement of the pesticide from one location to another or from one phase to another. Transport processes include both downward leaching, surface mnoff, volatilization from the soil to the atmosphere, as weU as upward movement by capillary water to the soil surface. Transport processes do not affect the total amount of pesticide in the environment however, they can move the pesticide to sites that have different potentials for degradation. Transport processes also redistribute the pesticide in the environment, possibly contaminating sites away from the site of apphcation such as surface and groundwater and the atmosphere. Transport of pesticides is a function of both retention and transport processes. 

Plume Containment. WeUs can be placed at a contaminated site to prevent the contamination from spreading further or migrating offsite. In the past, containment efforts often reHed on physical methods such as bentonite slurry trenches, grout curtains, sheet pilings, weU points, and fixative injections. Containment by judiciously placed weUs generally costs less, takes less time to install, and is more flexible because pumping rates and locations can be varied. 

D. L. RusseU, Kemediation Manualfor Petroleum-Contaminated Sites Technomic Publishing Co., Inc., Lancaster, Pa., 1992. 

Another possible example of endocrine disruption in situ relates to the hndings of Moore and Stevenson" of altered sex ratios and intersex harpacticoid copepods in the vicinity of Edinburgh s long sea sewage outfall. Intersexiiality is common in some crustaceans but is extremely rare in harpacticoid copepods. There was no relationship between the frequency of intersex and distance from the most contaminated sites and nor was there evidence that other benthic species had been adversely affected. Additional work is required to prove conclusively that endocrine disruption is involved in this case. 

Subsurface drains are essentially permeable barriers designed to intercept the groundwater flow. The water must be collected at a low point and pumped or drained by gravity to the treatment system (Figure 8). Subsurface drains can also be used to isolate a waste disposal area by intercepting the flow of uncontaminated groundwater before it enters into a contaminated site. 

Table 9. Properties of Organic Chemicals Found at Contaminated Sites.

Surface finish is increasingly referred to as surface cleanliness . This can be misleading because the standards refer to the appearance of the blasted steel and do not deal with chemical contamination. Site tests for assessing the level of soluble salts on freshly blast-cleaned surfaces, and which allow the semi-quantitative determination of the chlorides, soluble sulphates and soluble iron salts, are urgently needed. 

The refractory nature of some pollutants, notably, persistent polyhalogenated compounds, has raised problems of bioremediation of contaminated sites (e.g., sediments and dumping sites). There has been interest in the identification, or the production by genetic manipulation, of strains of microorganisms that can metabolically degrade recalcitrant molecules. For example, there are bacterial strains that can reductively dechlorinate PCBs under anaerobic conditions. 

There has been considerable interest in the abiotic dechlorination of chlorinated ethenes at contaminated sites. Reductive dehalogenation has therefore been examined using a range of reductants, many of them involving reduced complexes of porphyrins or corrins. 

The use of subcritical water at 275°C was successful in removing PAHs with two to six rings (including the carcinogenic benzo[a]pyrene) from soil at a contaminated site, and the wastewater that was produced appeared to be suitable for further exploitation (Lagadec et al. 2000). 

Sediment samples from a contaminated site were spiked with Arochlor 1242 and incubated at 4°C for several months (Williams and May 1997). Degradation by aerobic organisms in the upper layers of the sediment—but not in those at >15 mm from the surface—occurred with the selective production of di- and trichlorobiphenyls. Some congeners, including... 

Stuart-Keil KG, AM Hohnstock, KP Drees, JB Herrick, EL Madsen (1998) Plasmids responsible for horizontal transfer of naphthalene catabolism genes between bacteria at a coal tar-contaminated site are homologous to pDTGl from Pseudomonas putida NCIB 9816-4. Appl Environ Microbiol 64 3633-3640. 

The bacterial aerobic degradation of pyrene is initiated by the formation of cfi-pyrene-4,5-dihydrodiol. Analysis for this metabolite was used to demonstrate the biodegradability of pyrene in an environment in which there was continuous input of the substrate, when it was not possible to use any diminution in its concentration as evidence for biodegradation (Li et al. 1996). The corresponding metabolite from naphthalene—cfi-naphthalene-1,2-dihydrodiol—has been used to demonstrate biodegradation of naphthalene both in site-derived enrichment cultures and in leachate from the contaminated site (Wilson and Madsen 1996). 

Bogardt AH, BB Hemmingsen (1992) Enumeration of phenanthrene-degrading bacteria by an overlay technique and its use in evaluation of petroleum-contaminated sites. Appl Environ Microbiol 58 2579-2582. 

In the application of the Raleigh equation to contaminated sites, complications due to the heterogeneity of the system have been addressed (Abe and Hunkeler 2006). Detailed analysis has revealed systematic problems that could result in underestimation of first-order rates, and procedures for evaluating these were provided. 

Mixed cultures of organisms that were isolated from sediments contaminated with PCBs and polybrominated biphenyls (PBBs) were shown to debrominate PBBs under anaerobic conditions (Morris et al. 1992), and the dominant congener—2,2, 4,4, 5,5 (245-245)-hexabromobiphenyl—could be successively debrominated to 2,2 -dibromobiphenyl. However, in sediments from the most heavily contaminated site containing contaminants in addition to PBBs, very little debromination occurred and the recalcitrance was attributed to the toxicity of the other contaminants (Morris et al. 1993). 

There is an additional problem that has important implications for the bioremediation of contaminated sites when two substrates such as a chlorinated and an alkylated aromatic compound are present. The extradiol fission pathway is generally preferred for the degradation of alkylbenzenes (Figure 9.17), although this may be incompatible with the degradation of chlorinated aromatic compounds since the 3-chlorocatechol produced inhibits the activity of the catechol-2,3-oxygenase (Klecka and Gibson 1981 Bartels et al. 1984). 

A number of contaminated sites have been used for illustration, though the extent to which bioremediation has received practical application is variable. For a number of reasons, emphasis is placed on basic microbiological issues that have emerged from controlled laboratory experiments ... 

The presence of metabolites determined from laboratory experiments of degradation pathways. Examples inclnde (a) di-dihydrodiols of PAHs in a marine sediment (Li et al. 1996) and naphthalene in leachate from a contaminated site (Wilson and Madsen 1996),... 

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