title: Naphthalene and phenanthrene sorption to very low organic content diatomaceous earth: modeling implications for microbial bioavailability.
abstract: Naphthalene and phenanthrene sorption was investigated on microporous/high surface area and low-microporous/low surface area particles with very low organic (f(oc)) content. Partitioning coefficients (K(p)) for naphthalene were similar to those predicted from the Karickhoff equation in both competitive and non-competitive sorption isotherms, even given the very low f(oc). In contrast, phenanthrene K(p) values in competitive isotherms were 10-fold higher than predicted by Karickhoff, suggesting phenanthrene out-competes naphthalene for sorption sites. Naphthalene exhibited greater non-competitive K(p) at higher concentrations on the microporous particles, as evidenced by a Freundlich n=0.74. Both compounds had 100-fold lower adsorption and desorption mass flux on the microporous particles. Adsorption followed first order kinetics, with phenanthrene adsorbing at 1.5 and 3 times the rate of naphthalene on the low surface area and high surface area particles, respectively. Naphthalene and phenanthrene desorption kinetics were well-described by a Fickian diffusion model with observed diffusivities (D(obs)) of 1.7-1.9 x 10(-8) and 0.93-1.9 x 10(-8) cm(2) s(-1) for naphthalene and phenanthrene, respectively. Phenanthrene D(obs) were 3-5 orders of magnitude faster than those reported in organic-rich sediments. Naphthalene D(obs) were 100-fold lower than fast-domain diffusivities, indicating access to micropores. Naphthalene sorption non-linearity was investigated via simulations with two coupled desorption-biodegradation models. Results indicate that non-linearity would not significantly affect bioavailability in low f(oc) geosorbents. In contrast, sorption non-linearity would result in greatly decreased bioavailability in organic-rich geosorbents, indicating that desorption non-linearity should be considered for surface soils and sediments but may not be critical for low f(oc) aquifer material.
authors.affiliation: Department of Civil and Materials Engineering, 842, W. Taylor Street (m/c 246), University of Illinois at Chicago, Chicago, IL 60607, USA.
authors.forename: Menka
authors.initials: M
authors.lastname: Mittal
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Rockne
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry; D001419:Bacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D001682:Biological Availability; D000077215:Clay; D045424:Complex Mixtures / Q000737:chemistry; D007692:Diatomaceous Earth / Q000737:chemistry*; D004058:Diffusion; D004785:Environmental Pollutants / Q000737:chemistry / Q000378:metabolism; D019015:Geologic Sediments / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D009281:Naphthalenes / Q000737:chemistry* / Q000378:metabolism*; D010316:Particle Size; D010616:Phenanthrenes / Q000737:chemistry* / Q000378:metabolism*; D016062:Porosity; D012987:Soil / Q000032:analysis; D012995:Solubility
chemical_list: D000538:Aluminum Silicates; D045424:Complex Mixtures; D004785:Environmental Pollutants; D009281:Naphthalenes; D010616:Phenanthrenes; D012987:Soil; C031721:naphthalene; C031181:phenanthrene; D007692:Diatomaceous Earth; D000077215:Clay