Surfactant enhanced recovery of tetrachloroethylene from a porous medium containing low permeability lenses. 1. Experimental studies

A matrix of batch, column and two-dimensional (2-D) box experiments was conducted to investigate the coupled effects of rate-limited solubilization and layering on the entrapment and subsequent recovery of a representative dense NAPL, tetrachloroethylene (PCE), during surfactant flushing. Batch experiments were performed to determine the equilibrium solubilization capacity of the surfactant, polyoxyethylene (20) sorbitan monooleate (Tween 80), and to measure fluid viscosity, density and interfacial tension. Results of one-dimensional column studies indicated that micellar solubilization of residual PCE was rate-limited at Darcy velocities ranging from 0.8 to 8.2 cm/h and during periods of flow interruption. Effluent concentration data were used to develop effective mass transfer coefficient (Ke) expressions that were dependent upon the Darcy velocity and duration of flow interruption. To simulate subsurface heterogeneity, 2-D boxes were packed with layers of F-70 Ottawa sand and Wurtsmith aquifer material within 20-30 mesh Ottawa sand. A 4% Tween 80 solution was then flushed through PCE-contaminated boxes at several flow velocities, with periods of flow interruption. Effluent concentration data and visual observations indicated that both rate-limited solubilization and pooling of PCE above the fine layers reduced PCE recovery to levels below those anticipated from batch and column measurements. These experimental results demonstrate the potential impact of both mass transfer limitations and subsurface layering on the recovery of PCE during surfactant enhanced aquifer remediation.     

The effects of crude oil and the effectiveness of cleaner application following oiling on US Gulf of Mexico coastal marsh plants

Field studies were conducted in two different marsh habitats in Louisiana coastal wetlands to evaluate the effects of oiling (using South Louisiana Crude oil, SLC) and the effectiveness of a shoreline cleaner (COREXIT 9580) in removing oil from plant canopies. The study sites represented two major marsh habitats; the brackish marsh site was covered by Spartina patens and the freshwater marsh was covered by Sagittaria lancifolia. Field studies were conducted in each habitat using replicated 5.8 m2 plots that were subjected to three treatments; oiled only, oiled + cleaner (cleaner was used 2 days after oiling), and a control. Plant gas exchange responses, survival, growth, and biomass accumulation were measured. Results indicated that oiling led to rapid reductions in leaf gas exchange rates in both species. However, both species in 'oiled + cleaned' plots displayed improved leaf conductance and CO2 fixation rates. Twelve weeks after treatment initiation, photosynthetic carbon fixation in both species had recovered to normal levels. Over the short-term, S. patens showed more sensitivity to oiling with SLC than S. lancifolia as was evident from the data of the number of live shoots and above-ground biomass. Above-ground biomass remained significantly lower than control in S. patens under 'oiled' and 'oiled + cleaned' treatments while it was comparable to controls in S. lancifolia. These studies indicated that the cleaner removed oil from marsh grasses and alleviated the short-term impact of oil on gas exchange function of the study plants. However, use of cleaner had no detectable effects on above-ground biomass production or regeneration at the end of the first growing season in S. patens. Similarly, no beneficial effects of cleaner on carbon fixation and number of live shoots were apparent beyond 12 weeks in S. lancifolia.     

Biosurfactant-enhanced solubilization of NAPL mixtures

Remediation of nonaqueous phase liquids (NAPLs) by conventional pump-and-treat methods (i.e., water flushing) is generally considered to be ineffective due to low water solubilities of NAPLs and to mass-transfer constraints. Chemical flushing techniques, such as surfactant flushing, can greatly improve NAPL remediation primarily by increasing the apparent solubility of NAPL contaminants. NAPLs at hazardous waste sites are often complex mixtures. However, the equilibrium and nonequilibrium mass-transfer characteristics between NAPL mixtures and aqueous surfactant solutions are not well understood. This research investigates the equilibrium solubilization behavior of two- and three-component NAPL mixtures (containing akylbenzenes) in biosurfactant solutions. NAPL solubilization is found to be ideal in water (i.e., obeys Raoult's Law), while solubilization in biosurfactant solutions was observed to be nonideal. Specifically, the relatively hydrophobic compounds in the mixture experienced solubility enhancements that were greater than those predicted by ideal enhanced solubilization theory, while the solubility enhancements for the relatively hydrophilic compounds were less than predicted. The degree of nonideality is shown to be a nonlinear function of the NAPL-phase mole fraction. Empirical relationships based on the NAPL-phase mole fraction and/or micelle-aqueous partition coefficients measured in single-component NAPL systems are developed to estimate values for the multicomponent partition coefficients. Empirical relationships that incorporate both the NAPL-phase mole fraction and single-component partition coefficients yield much improved estimates for the multicomponent partition coefficient.     

Determination of source contributions to ambient PM2.5 in Kaohsiung, Taiwan, using a receptor model

Ambient particulates of PM2.5 were sampled at three sites in Kaohsiung, Taiwan, during February and March 1999. In addition, resuspended PM2.5 collected from traffic tunnels, paved roads, fly ash of a municipal solid waste (MSW) incinerator, and seawater was obtained. All the samples were analyzed for twenty constituents, including water-soluble ions, organic carbon (OC), elemental carbon (EC), and metallic elements. In conjunction with local source profiles and the source profiles in the model library SPECIATE EPA, the receptor model based on chemical mass balance (CMB) was then applied to determine the source contributions to ambient PM2.5. The mean concentration of ambient PM2.5 was 42.69-53.68 micrograms/m3 for the sampling period. The abundant species in ambient PM2.5 in the mass fraction for three sites were OC (12.7-14.2%), SO4(2-) (12.8-15.1%), NO3- (8.1-10.3%), NH4+ (6.7-7.5%), and EC (5.3-8.5%). Results of CMB modeling show that major pollution sources for ambient PM2.5 are traffic exhaust (18-54%), secondary aerosols (30-41% from SO4(2-) and NO3-), and outdoor burning of agriculture wastes (13-17%).     

Changes in concentration of five PCDD/F congeners after cooking beef from treated cattle

A large piece of meat taken from a single animal, which had been dosed with five selected PCDD/Fs, was prepared and cooked by a selection of different methods; burgers (fried, grilled, barbecued), roasts (cooked using conventional and microwave ovens) and stews (open pan and pressure cooked). For some of the cooking methods, concentration changes, on a whole product basis, were observed between raw and cooked product. However, in all cases these could be explained simply through changes arising from loss of water and elimination of PCDD/Fs with released fat. The total amounts of PCDD/Fs present in the system (including in released fat) remained unchanged. Dietary intake of PCDD/Fs could therefore be reduced by the removal of visible fat from meat before cooking and by discarding any fat released from foods during the cooking process.     

Seveso Women's Health Study: does zone of residence predict individual TCDD exposure?

The compound, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is produced as an unwanted by-product of various chemical reactions and combustion processes, including the manufacture of chlorinated phenols and derivatives. In animals, TCDD exposure is associated with toxic, carcinogenic, developmental, and reproductive effects. In 1976, a chemical plant explosion in Seveso, Italy, exposed the residents in the surrounding community to the highest exposure to TCDD known in humans. Materials from an aerosol cloud of sodium hydroxide, sodium trichlorophenate and TCDD were deposited over an 18.1 km2 area. As evidence of the significant level of TCDD exposure, numerous animals died and 193 cases of chloracne were reported among residents of the area. Initially, the contaminated area was divided into three major exposure Zones (A, B, R) based on the concentration of TCDD in surface soils. To date, the majority of epidemiologic studies conducted in Seveso have used Zone of residence as a proxy measure of exposure. The purpose of the present study is to validate the use of Zone of residence in Seveso as a proxy measure of exposure against individual serum TCDD measurement, and to determine whether questionnaire information can improve the accuracy of the exposure classification. Using data collected from the Seveso Women's Health Study (SWHS), the first comprehensive epidemiologic study of the reproductive health of women in Seveso, we determined that Zone of residence is a good predictor of individual serum TCDD level, explaining 24% of the variance. Using questionnaire information could have improved prediction of individual exposure levels in Seveso, increasing the percent of the variation in serum TCDD levels explained to 42%.     

PCDD and PCDF exposures in workers and controls living near an industrial waste incinerator

This study measured the levels of 17 congeners of PCDDs/PCDFs in serum to compare the levels between potentially exposed workers at an industrial waste incinerator and any residents with no known exposures. The 1,2,3,6,7,8- and 1,2,3,7,8,9-HxCDD were detected in serum of workers but in controls. Likewise, 1,2,3,7,8-PeCDF, 1,2,3,6,7,8- and 1,2,3,7,8,9-HxCDF were detected only in serum of workers. The international toxic equivalent (TEQ) levels of PCDDs/PCDFs in sera of workers are much higher than in controls. Among PCDDs, the proportion of total concentration and TEQ level is dominated predominantly by 1,2,3,6,7,8- and 1,2,3,7,8,9-HxCDD. We need extensive studies to estimate human exposure and are continuing this investigation.     

Adsorption of imidazolinone herbicides on ferrihydrite-humic acid associations.

Adsorption of the imidazolinone herbicides imazapyr, imazethapyr and imazaquin was studied on two binary systems (ferrihydrite-humic acid) prepared by treating ferrihydrite (Fh) immediately after its precipitation with a soil humic acid (HA) at different loadings (4% and 8% HA content), and on a blank ferrihydrite sample prepared in the same way, but without HA addition. Imidazolinone adsorption on pure Fh and on the 4% Fh-HA decreased with increasing of the herbicide hydrophobicity (imazaquin相似文献   

Sorption of ametryn and imazethapyr in twenty-five soils from Pakistan and Australia.

Sorption of ametryn and imazethapyr in 25 soils from Pakistan and Australia was investigated using the batch method. The soils varied widely in their intrinsic capacities to sorb these herbicides as shown by the sorption coefficients, Kd, which ranged from 0.59 to 47.6 for ametryn and 0.02 to 6.94 for imazethapyr. Generally the alkaline soils of Pakistan had much lower Kd values of both herbicides than the soils of Australia. Both soil pH and soil organic carbon (SOC) were correlated significantly with the sorption of ametryn, whereas only soil pH was strongly correlated with imazethapyr sorption. No correlation was found between Kd values of the herbicides and the clay contents of the soils. Multiple regression analysis showed that Kd values were better correlated (r2=0.94 and 0.89 for ametryn and imazethapyr, respectively) if SOC and pH were simultaneously taken into account. The study indicated that sorption of these herbicides in the alkaline soils of Pakistan was low and consequently there is considerable risk of groundwater contamination.