Remediation of PAH-Contaminated Soils and Sediments: A ...

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Darcy’s Law: q = -k (∆H / ∆L) Where: q = volume of water flowing per unit time per area k = hydraulic conductivity of the soil/sediment ∆H / ∆L = hydraulic gradient or the change in head per unit distance of water movement. Hydraulic conductivity (k) is the most important component of Darcy’s Law and affects the relative leaching of PAHs through soils because it is dependent up on soil moisture content and pore size distribution. The rate of water movement in unsaturated soils is very slow (< 1 cm/day) due to suction forces (negative potentials). However, once the soil becomes saturated, water flow rates can increase dramatically (Letey and Oddson, 1972) and are controlled principally by soil texture and structural development, particularly by the extent and interconnectivity of macropores. For example, coarse textured or well aggregated soils have large pores and higher saturated conductivity (Ksat) values. The hydraulic gradient (∆H / ∆L) is basically the change in water head (or relative elevation) across or down the measured flow path. As dredge soils dewater, water flow (i.e. leaching) and PAH transfer rates will obviously change based on changes in Ksat, particularly as deep cracking and aggregation lead to the development of continuous vertical macropore. Minimal leaching (33 μg total PAH) of freely dissolved PAHs was observed from a soil containing 2077 μg total PAH after two years of landfarming (Saison et al., 2004). Leaching of PAH compounds dissolved in water is likely a negligible transfer process (Stroo et al., 2000), but leaching of PAHs attached to colloidal organic matter is of concern (Jones et al., 1989b; McCarthy and Jimenez, 1985; Maxin and Kogel-Knabner, 1995). Therefore, leaching needs to be monitored in a field and greenhouse situation, especially when studying dredge sediments. Erosion: Soil erosion is primarily affected by climate, topography, soil and land use cover (Toy et al., 2002). Transfer of PAH compounds specifically through erosion (both wind and water transport) is influenced by the following: � Rainfall (amount and intensity) � Wind speed � Size of clay and organic matter particles with adsorbed PAH compounds � Soil aggregation As dredge sediments dewater, erosional processes increasingly influence the transfer of PAHs from the sediments. Erosion is the detachment, entrainment and transfer of soil particles (which may or may not have PAHs adsorbed). With 22
increasing rainfall intensity or wind speed, soil particles are more likely to be detached and transported (Toy et al., 2002). PAH Degradation Degradation rates of PAHs vary depending on molecular weight and solubility of the PAH compound (Alexander, 1999). Polycyclic aromatic hydrocarbon compounds can be grouped into different degradation and sequestration fractions in both soil and sediments depending on their bioavailability. Brion and Pelletier (2005) suggested dividing them based on decreasing availability into the following phases: � water-extractable phase (or easily degraded) � slow molecular diffusion of PAHs into microsites (transition) � sequestered residual phase which requires extraction with organic solvents The ultimate goal of degradation is the complete mineralization of PAHs to CO2, water, microbial carbon, and other inorganic compounds (Lundstedt, 2003). Unfortunately, degradation of PAHs may result in the accumulation of metabolites (mainly ketones, quinones, dicarboxylic acid anhydrides and coumarins) that can be more toxic and/or more soluble than the parent compound (Lundstedt, 2003). For example, fluoranthene degradation has been found to produce more soluble and potentially leachable metabolites (Vessigaud et al. 2007). Haeseler et al. (2001) showed enhanced, but incomplete, degradation of PAH compounds in a field study and noted a brief spike in leachate toxicity due to the accumulation of more soluble metabolites. However, after remediation was complete, final toxicity was negligible because the metabolites tended to be less stable and more soluble than the parent compounds, making them more available to degraders (Haeseler et al., 2001). Intermediates of PAH degradation are not always bioavailable and can also be incorporated into the humic fraction of soil, making them less available and less toxic (Kastner et al., 1999). Biological: Microbial communities (including bacteria and fungi) can biologically degrade PAH compounds during direct microbial metabolism of carbon and energy sources or by cometabolism while consuming another substrate (Lundstedt et al., 2007). Biological degradation is highly dependent upon several abiotic soil factors, including (Eweis et al., 1998; Huesemann, 2004): � nutrients � pH � metals � temperature 23
Page 1 and 2: Remediation of PAH-Contaminated Soi
Page 3 and 4: Abstract Polycyclic aromatic hydroc
Page 5 and 6: soil is the primary environmental r
Page 7 and 8: Solubility Solubility of PAH compou
Page 9 and 10: Figure 1. Structures of US EPA’s
Page 11 and 12: � If you were to add 2 benzene ri
Page 13 and 14: and their mutagenic and carcinogeni
Page 15 and 16: PAH in humans The carcinogenicity o
Page 17 and 18: persist in the soil (Alexander, 199
Page 19 and 20: Figure 3. Relative PAH concentratio
Page 21: the gas phase was attributed to tem
Page 25 and 26: in contaminated soils than uncontam
Page 27 and 28: Ideal biodegradation of PAHs, where
Page 29 and 30: Figure 5. Aerobic degradation of PA
Page 31 and 32: Cometabolism is explained by three
Page 33 and 34: donate electrons. The redox potenti
Page 35 and 36: 1. Fenton’s reagent - formation o
Page 37 and 38: Figure 7. Schematic of integrated e
Page 39 and 40: Figure 8. Possible mechanism for di
Page 41 and 42: Freundlich adsorption equation: x/m
Page 43 and 44: Diffusion: Weber et al. (1992), Web
Page 45 and 46: Biological Techniques for Enhancing
Page 47 and 48: oot extract resulted in continuous
Page 49 and 50: Composting Composting is a form of
Page 51 and 52: The addition of inorganic nutrients
Page 53 and 54: � Yu et al. (2006) found no effec
Page 55 and 56: Carrot Daucus carota Wild and Jones
Page 57 and 58: Surfactants Mass transfer of PAH co
Page 59 and 60: � Straube et al. (2003) showed th
Page 61 and 62: encountered with biodegradation, an
Page 63 and 64: volatilization of some compounds, s
Page 65 and 66: Regulatory Framework Dredged materi
Page 67 and 68: transition phase between slurried s
Page 69 and 70: In addition to equation manipulatio
Page 71 and 72: Coastal Zone Management Act (CZMA)
Page 73 and 74:
EPA Region V NA http://www.epa.gov/
Page 75 and 76:
Indiana Department of Environmental
Page 77 and 78:
New York State Department of Enviro
Page 79 and 80:
Analytical Methods The following is
Page 81 and 82:
Sample Cleanup After extraction, cl
Page 83 and 84:
Table 13. Detection limits for cert
Page 85 and 86:
Citations Accardi-Dey, A., and P.M.
Page 87 and 88:
Cerniglia, C.E., and D.T. Gibson. 1
Page 89 and 90:
EPA. 2008. Integrated Risk Informat
Page 91 and 92:
Harmsen, J. 2007. Measuring bioavai
Page 93 and 94:
Kelsey, J.W., B.D. Kottler, and M.
Page 95 and 96:
Mackay, D., and D. Callcott. 1998.
Page 97 and 98:
O’Mahony, M., A. Dobson, J. Barne
Page 99 and 100:
Saison, C., C. Perrin-Ganier, M. Sc
Page 101 and 102:
Vessigaud, S., C Perrin-Ganier, L.
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Remediation of PAH-Contaminated Soils and Sediments: A ...

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