The potential for nonaqueous phase liquid (NAPL) mobilization is one of the most important considerations in the development and implementation of surfactantbased remediation technologies. Column experiments were performed to investigate the onset and extent of tetrachloroethylene (PCE) mobilization during surfactant flushing. To induce mobilization, the interfacial tension between residual PCE and the aqueous phase was reduced from 47.8 to 0.09 dyn/ cm by flushing with different surfactant solutions. The resulting PCE desaturation curves are expressed in terms of a total trapping number (N T ), which relates viscous and buoyancy forces to the capillary forces acting to retain organic liquids within a porous medium. The critical value of N T required to initiate PCE mobilization fell within the range of 2 × 10 -5 to 5 × 10 -5 , while complete displacement of PCE was observed as N T approached 1 × 10 -3 . The interplay of viscous and buoyancy forces during PCE mobilization is illustrated in horizontal column experiments, in which angled banks of PCE were displaced through the columns. These results demonstrate the potential contribution of buoyancy forces to PCE mobilization and provide a novel approach for predicting NAPL displacement during surfactant flushing.

A coupled experimental and mathematical modeling investigation was undertaken to explore nanoscale fullerene aggregate (nC60) transport and deposition in water-saturated porous media. Column experiments were conducted with four different size fractions of Ottawa sand at two pore-water velocities. A mathematical model that incorporates nonequilibrium attachment kinetics and a maximum retention capacity was used to simulate experimental nC60 effluent breakthrough curves and deposition profiles. Fitted maximum retention capacities (S(max)), which ranged from 0.44 to 13.99 microg/g, are found to be correlated to normalized mass flux. The developed correlation provides a means to estimate S(max) as a function of flow velocity, nanoparticle size, and mean grain size of the porous medium. Collision efficiency factors, estimated from fitted attachment rate coefficients, are relatively constant (approximately 0.14) over the range of conditions considered. These fitted values, however, are more than 1 order of magnitude larger than the theoretical collision efficiency factor computed from Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (0.009). Data analyses suggest that neither physical straining nor attraction to the secondary minimum is responsible for this discrepancy. Patch-wise surface charge heterogeneity on the sand grains is shown to be the likely contributor to the observed deviations from classical DLVO theory. These findings indicate that modifications to clean-bed filtration theory and consideration of surface heterogeneity are necessary to accurately predict nC60 transport behavior in saturated porous media.

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The exposome is the cumulative measure of environmental influences and associated biological responses throughout the lifespan, including exposures from the environment, diet, behavior, and endogenous processes. A major challenge for exposome research lies in the development of robust and affordable analytic procedures to measure the broad range of exposures and associated biologic impacts occurring over a lifetime. Biomonitoring is an established approach to evaluate internal body burden of environmental exposures, but use of biomonitoring for exposome research is often limited by the high costs associated with quantification of individual chemicals. High-resolution metabolomics (HRM) uses ultra-high resolution mass spectrometry with minimal sample preparation to support high-throughput relative quantification of thousands of environmental, dietary, and microbial chemicals. HRM also measures metabolites in most endogenous metabolic pathways, thereby providing simultaneous measurement of biologic responses to environmental exposures. The present research examined quantification strategies to enhance the usefulness of HRM data for cumulative exposome research. The results provide a simple reference standardization protocol in which individual chemical concentrations in unknown samples are estimated by comparison to a concurrently analyzed, pooled reference sample with known chemical concentrations. The approach was tested using blinded analyses of amino acids in human samples and was found to be comparable to independent laboratory results based on surrogate standardization or internal standardization. Quantification was reproducible over a 13-month period and extrapolated to thousands of chemicals. The results show that reference standardization protocol provides an effective strategy that will enhance data collection for cumulative exposome research. In principle, the approach can be extended to other types of mass spectrometry and other analytical methods.

Exposure to pesticides has been suggested to increase the risk of Parkinson's disease (PD), but the mechanisms responsible for this association are not clear. Here, we report that perinatal exposure of mice during gestation and lactation to low levels of dieldrin (0.3, 1, or 3 mg/kg every 3 days) alters dopaminergic neurochemistry in their offspring and exacerbates MPTP toxicity. At 12 wk of age, protein and mRNA levels of the dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT2) were increased by perinatal dieldrin exposure in a dose-related manner. We then administered MPTP (2 x 10 mg/kg s.c) at 12 wk of age and observed a greater reduction of striatal dopamine in dieldrin-exposed offspring, which was associated with a greater DAT:VMAT2 ratio. Additionally, dieldrin exposure during development potentiated the increase in GFAP and alpha-synuclein levels induced by MPTP, indicating increased neurotoxicity. In all cases there were greater effects observed in the male offspring than the female, similar to that observed in human cases of PD. These data suggest that developmental exposure to dieldrin leads to persistent alterations of the developing dopaminergic system and that these alterations induce a "silent" state of dopamine dysfunction, thereby rendering dopamine neurons more vulnerable later in life.

Experimental and mathematical modeling studies were performed to investigate the transport and retention of nanoscale fullerene aggregates (nC60) in water-saturated porous media. Aqueous suspensions of nC60 aggregates (95 nm diameter, 1 to 3 mg/L) were introduced into columns packed with either glass beads or Ottawa sand at a Darcy velocity of 2.8 m/d. In the presence of 1.0 mM CaCl2, nC60 effluent breakthrough curves (BTCs) gradually increased to a maximum value and then declined sharply upon reintroduction of nC60-free solution. Retention of nC60 in glass bead columns ranged from 8 to 49% of the introduced mass, while up to 77% of the mass was retained in Ottawa sand columns. When nC60 suspensions were prepared in deionized water alone, effluent nC60 BTCs coincided with those of a nonreactive tracer (Br-), with minimal nC60 retention. Observed differences in nC60 transport and retention behavior in glass beads and Ottawa sand were consistent with independent batch retention data and theoretical calculations of electrostatic interactions between nC60 and the solid surfaces. Effluent concentration and retention profile data were accurately simulated using a numerical model that accounted for nC60 attachment kinetics and a limiting retention capacity.

Environmental factors have been shown to contribute to the incidence of Parkinson's disease (PD). Pesticides, which represent one of the primary classes of environmental agents associated with PD, share the common feature of being intentionally released into the environment to control or eliminate pests. Pesticides consist of multiple classes and subclasses of insecticides, herbicides, rodenticides, fungicides, fumigants and others and exhibit a vast array of chemically diverse structures. In this review we examine the evidence regarding the ability of each of the major pesticide subclasses to increase the incidence of PD. We propose that, from a toxicological perspective, it would be beneficial to identify specific subclasses, common structural features and the propensity for widespread human exposure when considering the potential role in PD, rather than using the overly broad term of 'pesticides' to describe this diverse group of chemicals. Furthermore, these chemicals and their environmentally relevant combinations should be evaluated for their ability to promote or accelerate PD and not merely for being singular causative agents.

Knowledge of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) accumulation at the air−water interface is critical to understanding the fate and transport of these substances in subsurface environments. The surface tension of aqueous solutions containing PFOA and PFOS at concentrations ranging from 0.1 to >1000 mg/L and with dissolved solids (i.e., cations and anions) commonly found in groundwater was measured using the Wilhelmy plate method. The surface tensions of solutions containing dissolved solids were lower than those for ultrapure water, indicating an increase in the surface excess of PFOA and PFOS in the presence of dissolved solids. An equation for the surface excess of PFOA and PFOS with total dissolved solids was developed by fitting the measured surface tension values, which ranged from 72.0 to 16.7 mN/m, to the Szyszkowski equation. On the basis of mass distribution calculations for a representative unsaturated, fine-grained soil, up to 78% of the PFOA and PFOS mass will accumulate at the air−water interface, with the remaining mass dissolved in water and adsorbed on the solids.