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Prion sorption to soil is thought to play an important role in the transmission of scrapie and chronic wasting disease (CWD) via the environment. Sorption of PrP to soil and soil minerals is influenced by the strain and species of PrP(Sc) and by soil characteristics. However, the ability of soil-bound prions to convert PrP(c) to PrP(Sc) under these wide-ranging conditions remains poorly understood. We developed a semiquantitative protein misfolding cyclic amplification (PMCA) protocol to evaluate replication efficiency of soil-bound prions. Binding of the hyper (HY) strain of transmissible mink encephalopathy (TME) (hamster) prions to a silty clay loam soil yielded a greater-than-1-log decrease in PMCA replication efficiency with a corresponding 1.3-log reduction in titer. The increased binding of PrP(Sc) to soil over time corresponded with a decrease in PMCA replication efficiency. The PMCA efficiency of bound prions varied with soil type, where prions bound to clay and organic surfaces exhibited significantly lower replication efficiencies while prions bound to sand exhibited no apparent difference in replication efficiency compared to unbound controls. PMCA results from hamster and CWD agent-infected elk prions yielded similar findings. Given that PrP(Sc) adsorption affinity varies with soil type, the overall balance between prion adsorption affinity and replication efficiency for the dominant soil types of an area may be a significant determinant in the environmental transmission of prion diseases.

Polar organic chemical integrative samplers (POCIS) are useful in monitoring for a wide range of chemicals in aquatic systems; however, a lack of available uptake rate data for compounds of environmental interest is one limitation in the application of these samplers to environmental studies. In this study, laboratory calibration experiments were conducted with POCIS for 65 compounds at 25°C under flowing conditions to determine chemical-specific uptake rates (R(s)). Experimental uptake rates measured in this study ranged from 0.034 to 1.33 L/d, and uptake rates were determined for 36 compounds with no previously reported values. Experimentally determined uptake rates were applied to data obtained from POCIS samplers deployed downstream of three wastewater treatment plant (WWTP) effluent discharges and in four surface waters influenced by agricultural runoff. Time-weighted average concentrations for atrazine and metolachlor determined using uptake rates generated in this study compare well with results from composited grab sampling previously conducted in agricultural watersheds in Nebraska, USA., (Copyright © 2011 SETAC.)

Chronic wasting disease (CWD) and sheep scrapie can be transmitted via indirect environmental routes, and it is known that soil can serve as a reservoir of prion infectivity. Given the strong interaction between the prion protein (PrP) and soil, we hypothesized that binding to soil enhances prion resistance to enzymatic digestion, thereby facilitating prion longevity in the environment and providing protection from host degradation. We characterized the performance of a commercially available subtilisin enzyme, Prionzyme, to degrade soil-bound and unbound CWD and HY TME PrP as a function of pH, temperature, and treatment time. The subtilisin enzyme effectively degraded PrP adsorbed to a wide range of soils and soil minerals below the limits of detection. Signal loss occurred rapidly at high pH (12.5) and within 7 days under conditions representative of the natural environment (pH 7.4, 22 degrees C). We observed no apparent difference in enzyme effectiveness between bound and unbound CWD PrP. Our results show that although adsorbed prions do retain relative resistance to enzymatic digestion compared with other brain homogenate proteins, they can be effectively degraded when bound to soil. Our results also suggest a topical application of a subtilisin enzyme solution may be an effective decontamination method to limit disease transmission via environmental "hot spots" of prion infectivity.

A critical obstacle to using PCR to quantify viral titers is the distinguishment of viable and nonviable genomic material. Pretreatments of ethidium monoazide (EMA) have been effective in preventing PCR amplification of DNA from nonviable bacteria. To test whether an EMA pretreatment could be used with RT-PCR to quantify viable RNA virions, avian influenza virus (AIV) survival was measured in water through 28d using cell culture titration and real-time RT-PCR with or without EMA pretreatment. Cell culture titration yielded significantly lower titers than both RT-PCR procedures, and there was no significant difference between RT-PCR results with or without EMA. Ineffective binding of EMA to AIV RNA may have allowed nonviable AIV RNA to amplify. Furthermore, since AIV inactivation may take place by means other than membrane disruption, any pretreatment distinguishing viable and nonviable AIV virions by membrane integrity may not be practical., (Copyright (c) 2009 Elsevier B.V. All rights reserved.)

It is likely that the soil environment serves as a stable reservoir of infectious CWD and scrapie prions as well as a potential reservoir of BSE. Prion adsorption to soil could play an important role in prion mobility, proteolysis, and infectivity. We modified previously published methods to quantify adsorbed prions via direct detection and studied prion adsorption to soil and soil minerals as a function of time through 60 days. Prion-infected brain homogenate was used as a complex, relevant prion source. We determined that maximum PrP adsorption requires days or weeks, depending on the soil or mineral, and is 2-5 orders of magnitude lower than previous studies using purified PrP(Sc) or recPrP. Because PrP adsorption to soil is slow and reduced in tissue homogenate, the possibility of prion transport in soil environments cannot be excluded and requires further investigation. Our results indicate that binding to soil may protect prions from degradation, consistent with prions' longevity in the environment. Adsorption of PrP to sterilized soil did not differ significantly from adsorption to unsterilized soil, which suggests that active biological processes do not significantly affect prion adsorption or degradation in the soil environment.

It is likely that the soil environment serves as a stable reservoir of infectious chronic wasting disease (CWD) and scrapie prions, as well as a potential reservoir of bovine spongiform encephalopathy (BSE, or "mad cow" disease). Prion adsorption to soil may play an important role in prion mobility, proteolysis, and infectivity. Differences in PrP environmental fate are possible due to the strain- and species-dependent structure of PrP(Sc). Kinetic and isothermal studies of PrP adsorption to sand and two whole soils were conducted using HY and DY TME-infected hamster, uninfected hamster, and CWD-infected elk brain homogenates as competitive PrP sources. The role of the N-terminus in PrP adsorption was also investigated. We report strain and species differences in PrP adsorption to soil over time and as a function of aqueous concentration, indicating that the fate of prions in the environment may vary with the prion strain and species infected. Our data also provide evidence that the N-terminal region of PrP enhances adsorption to clay but may hinder adsorption to sand. PrP adsorption was maximal at an intermediate aqueous concentration, most likely due to the competitive brain homogenate matrix in which it enters the soil environment.

An integral component in preventing an avian influenza pandemic is containment and disposal of infected bird (poultry) carcasses. Disposal of carcasses in Subtitle D municipal solid waste (MSW) landfills may be an advantageous option due to their large capacities and facility distribution in the U.S. In this study, the survival of H6N2 avian influenza virus (AIV) was measured in a methanogenic landfill leachate and water as a function of temperature, conductivity, and pH. Elevated temperature and nonneutral pH resulted in the quickest inactivation times for AIV in both media, whereas conductivity did not have a significant influence on AIV survival. Media effects were significant and AIV inactivation in leachate was consistently the same or faster than AIV inactivation in water. Based on an initial titer of 10(5) TCID50/mL, calculated inactivation times ranged from 30 days to greater than 600 days, indicating that AIV will remain infectious during and after waste disposal. Disposal of infected carcasses in a MSW landfill may be an appropriate option as inactivation times are within the design life of required barrier systems at Subtitle D landfills.

The occurrence and estimated concentration of twenty illicit and therapeutic pharmaceuticals and metabolites in surface waters influenced by wastewater treatment plant (WWTP) discharge and in wastewater effluents in Nebraska were determined using Polar Organic Chemical Integrative Samplers (POCIS). Samplers were installed in rivers upstream and downstream of treated WWTP discharge at four sites and in a discharge canal at a fifth location. Based on differences in estimated concentrations determined from pharmaceuticals recovered from POCIS, WWTP effluent was found to be a significant source of pharmaceutical loading to the receiving waters. Effluents from WWTPs with trickling filters or trickling filters in parallel with activated sludge resulted in the highest observed in-stream pharmaceutical concentrations. Azithromycin, caffeine, 1,7-dimethylzanthine, carbamazepine, cotinine, DEET, diphenhydramine, and sulfamethazine were detected at all locations. Methamphetamine, an illicit pharmaceutical, was detected at all but one of the sampling locations, representing only the second report of methamphetamine detected in WWTP effluent and in streams impacted by WWTP effluent.

Models describing the behavior of organic chemicals in landfills can be useful to predict their fate and transport and also to generate input data for estimates of exposure and risk. The landfill coupled-reactor (LFCR) model developed in this work simulates a landfill as a series of fully mixed reactors, each representing a daily volume of waste. The LFCR model is a numerical model allowing time-variable input parameters such as gas generation, and cover type and thickness. The model was applied to three volatile organic chemicals (acetone, toluene, benzene) as well as naphthalene and the chemical warfare agent sarin under three landfill conditions (conventional, arid, bioreactor). Sarin was rapidly hydrolyzed, whereas naphthalene was largely associated with the landfill solid phase in all scenarios. Although similar biodegradation rates were used for acetone and toluene, toluene was more persistent in the landfill due to its hydrophobicity. The cover soil moisture content had a significant impact on gaseous diffusive losses.

Scrapie and CWD are horizontally transmissible, and the environment likely serves as a stable reservoir of infectious prions, facilitating a sustained incidence of CWD in free-ranging cervid populations and complicating efforts to eliminate disease in captive herds. Prions will enter the environment through mortalities and/or shedding from live hosts. Unfortunately, a sensitive detection method to identify prion contamination in environmental samples has not yet been developed. An environmentally-relevant prion model must be used in experimental studies. Changes in PrP(Sc) structure upon environmental exposure may be as significant as changes in PrP(Sc) quantity, since the structure can directly affect infectivity and disease pathology. Prions strongly bind to soil and remain infectious. Conformational changes upon adsorption, competitive sorption and potential for desorption and transport all warrant further investigation. Mitigation of contaminated carcasses or soil might be accomplished with enzyme treatments or composting in lieu of incineration.

Scrapie and chronic wasting disease (CWD) are prion diseases of particular environmental concern as they are horizontally transmissible and can remain infectious after years in the environment. Recent evidence suggests that the N-terminus of PrPSC, the infectious conformation of the prion protein, plays an important role in the mechanism of sorption to soil particles. We hypothesize that, in a prion-infected animal carcass, a portion of the N-terminus of PrPSc could be cleaved by proteinases in the brain at ordinary temperatures. Hamster (HY transmissible mink encephalopathy-infected), transgenic mice (CWD-infected), and elk (CWD-infected) brain homogenates were incubated at 22 and 37 degrees C for up to 1 month and then analyzed by Western blot using N-terminal and middle region monoclonal anti-PrP antibodies. For all three systems, there was a very faint or undetectable N-terminal PrP signal after 35 days at both temperatures, which indicates that full-length PrPSc might be rare in the brain matter of animal carcasses. Future studies on prion-soil interactions should therefore consider N-terminal-degraded PrPSc in addition to the full-length form. Both mouse and elk CWD PrPSc demonstrated greater resistance to degradation than HY TME PrPSc. This indicates that the transgenic mouse-CWD model is a good surrogate for natural CWD prions, but that other rodent prion models might not accurately represent CWD prion fate in the environment.

Although heuristic optimization techniques are increasingly applied in environmental engineering applications, algorithm selection and configuration are often approached in an ad hoc fashion. In this study, the design of a multilayer sorptive barrier system served as a benchmark problem for evaluating several algorithm-tuning procedures, as applied to three global optimization techniques (genetic algorithms, simulated annealing, and particle swarm optimization). Each design problem was configured as a combinatorial optimization in which sorptive materials were selected for inclusion in a landfill liner to minimize the transport of three common organic contaminants. Relative to multilayer sorptive barrier design, study results indicate (i) the binary-coded genetic algorithm is highly efficient and requires minimal tuning, (ii) constraint violations must be carefully integrated to avoid poor algorithm convergence, and (iii) search algorithm performance is strongly influenced by the physical-chemical properties of the organic contaminants of concern. More generally, the results suggest that formal algorithm tuning, which has not been widely applied to environmental engineering optimization, can significantly improve algorithm performance and provide insight into the physical processes that control environmental systems.

One component of preparedness for a chemical attack is planning for the disposal of contaminated debris. To assess the feasibility of contaminated debris disposal in municipal solid waste (MSW) landfills, the fate of selected chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) in MSW landfills was predicted with a mathematical model. Five blister agents [sulfur mustard (HD), nitrogen mustard (HN-2), lewisite (L), ethyldichloroarsine (ED), and phosgene oxime (CX)], eight nerve agents [tabun (GA), sarin (GB), soman (GD), GE, GF, VX, VG, and VM], one riot-control agent [CS], and two TICs [furan and carbon disulfide] were studied. The effects of both infiltration (climate) and contaminant biodegradability on fate predictions were assessed. Model results showed that hydrolysis and gas-phase advection were the principal fate pathways for CWAs and TICs, respectively. Apart from CX and the TICs, none of the investigated compounds was predicted to persist in a landfill for more than 5 years. Climate had little impact on CWA/TIC fate, and biodegradability was only important for compounds with long hydrolysis half-lives. Monte Carlo simulations were performed to assess the influence of uncertainty in model input parameters on CWA/TIC fate predictions. Correlation analyses showed that uncertainty in hydrolysis rate constants was the primary contributor to variance of CWA fate predictions, while uncertainty in the Henry's Law constant and landfill gas-production rate accounted for most of the variance of TIC fate predictions. CWA hydrolysates were more persistent than the parent CWAs, but limited information is available on abiotic or biotic transformation rates for these chemicals.

Sorption of three nonionic organic solutes (benzene, trichloroethene, and 1,2-dichlorobenzene) to hexadecyltrimethylammonium bentonite (HDTMA bentonite) and benzyltriethylammonium bentonite (BTEA bentonite) was measured as a function of total organic-carbon content at quaternary ammonium cation loadings ranging from 30 to 100% of the clay's cation-exchange capacity. Sorption of all three solutes to HDTMA bentonite was linear and sorption of all three solutes by the HDTMA bentonite increased as the organic-carbon content of the clay increased. 1,2-Dichlorobenzene sorbed most strongly to HDTMA bentonite, followed by benzene and TCE. The stronger sorption of benzene to HDTMA bentonite compared to TCE was unexpected based on a partition mechanism of sorption and consideration of solute solubility. LogK(oc) values for all three solutes increased with organic-carbon content. This suggests that the increased organic-carbon content alone may not explain the observed increase in sorption capacity. Sorption of the three solutes to BTEA bentonite was nonlinear and solute sorption increased with decreasing organic-carbon content, with a peak in the magnitude of solute sorption occurring at an organic-carbon content corresponding to 50% of CEC. Below 50% of CEC, sorption of all three solutes to BTEA bentonite decreased with decreasing organic-carbon content. Surface area measurements indicate that the surface area of both organobentonites generally decreased with increasing organic-carbon content. Since nonionic organic solute sorption to BTEA bentonite occurs by adsorption, the reduced sorption is likely caused by the reduction in surface area corresponding to increased organic-cation loading.

We investigate the use of organobentonites as liners for underground gasoline storage tanks to reduce the risk of subsurface contamination. A series of permeability measurements were conducted on two types of organobentonites: benzyltriethylammonium-bentonite (BTEA-bentonite) and hexadecyltrimethylammonium-bentonite (HDTMA-bentonite). Both water and commercial unleaded gasoline were used as the permeant liquids. Results of these measurements indicate that the intrinsic permeability of the organobentonite decreases by one to two orders of magnitude when the permeant liquid is changed from water to gasoline. Results of batch sorption measurements reveal that benzene sorption to both organobentonites from water is greater than benzene sorption to conventional bentonite. The magnitude of benzene sorption is related to the loading of the organic quaternary ammonium cation on the clay. As the HDTMA cation loading increases from 25% of cation exchange capacity (CEC) to 120% of CEC, benzene sorption increases. However, as the BTEA cation loading increases from 40 to 120% of CEC, benzene sorption decreases. Collectively, these results suggest that organobentonites can be used effectively to reduce hydrocarbon migration rates beneath leaking underground gasoline storage tanks, and that the optimal organic cation loading with respect to pollutant sorption may be less than 50% of cation exchange capacity for some organobentonite-solute combinations.

In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.