Public health concerns about caliciviruses as waterborne contaminants.

Caliciviruses are disseminated by the fecal-oral route and are found in contaminated surface and ground waters. The US Environmental Protection Agency (EPA) is interested in preventing calicivirus contamination in treated waters used for consumption, and these viruses are on the EPA's "contaminant candidate list" for regulatory consideration in drinking waters. These viruses also present a health threat for recreation and shellfish-growing waters. However, before EPA can make regulatory decisions regarding caliciviruses, significant information and technology needs must be established, including analytical methods for sampling, identifying, and quantifying the viruses; applicability of surrogates to determine their presence; efficacy of water and wastewater treatment or disinfection; waterborne occurrence levels and distribution; dose response; and the viruses' effect(s) on health. Future drinking-water regulations may need to ensure that treatments are adequate to remove caliciviruses from source waters. For recreation and shellfish-growing waters, surrogate indicators and health criteria may need to be based upon establishing risks of exposure to caliciviruses.

Design of a phase/doppler light-scattering system for measurement of small-diameter glass fibers during fiberglass manufacturing.

We present fundamental studies examining the design of a phase/Doppler laser light-scattering system applicable to on-line measurements of small-diameter (<15 mum) fibers during fiberglass manufacturing. We first discuss off-line diameter measurement techniques currently used in the fiberglass industry and outline the limitations and problems associated with these methods. For the phase/Doppler design study we have developed a theoretical computer model for the response of the measurement system to cylindrical fibers, which is based on electromagnetic scattering theory. The model, valid for arbitrary fiber diameters and hardware configurations, generates simulated detector output as a function of time for a finite absorbing, cylindrical fiber oriented perpendicular to the two incident laser beams. Results of experimental measurements are presented, confirming predictions of the theoretical model. Parametric studies have also been conducted using the computer model to identify experimental arrangements that provide linear phase-diameter relationships for small-diameter fibers, within the measurement constraints imposed by the fiberglass production environment. The effect of variations in optical properties of the glass as well as fiber orientation effects are discussed. Through this research we have identified phase/Doppler arrangements that we expect to have future applications in the fiberglass industry for on-line diameter monitoring and process control.

Development of a generalized theoretical model for the response of a phase/doppler measurement system to arbitrarily oriented fibers illuminated by gaussian beams.

We present a generalized theoretical model for the response of the phase/Doppler (P/D) measurement system to light scattered by cylindrical fibers. This theoretical model is valid for arbitrary fiber diameters and refractive indices, for Gaussian incident beams, and it accounts for arbitrary fiber orientations, fiber positions, and effects that are due to the two-dimensional receivers. The generalized P/D computer model (GPDCM) is the extension of an earlier study by the authors, combining past P/D simulation methodology with recent developments in modeling light scattering by tilted cylindrical fibers. A fortran computer program that implements the GPDCM theoretical development was written and tested against known P/D results and physical expectations. To illustrate the capabilities of the GPDCM, we present computation results, comparing the effect of fiber tilt, fiber position, and receiver aperture on the performance of P/D systems configured in backscatter and sidescatter arrangements. Calculations show that the effects of fiber tilt and position are most pronounced in the backscatter P/D arrangement, resulting in broadening of the measured phase distribution. The calculated mean phase shifts, however, were found to be essentially independent of the above factors. Computational results also showed that the effect of fiber tilt and position on phase-distribution measurements can be reduced through proper choice of aperture shape and by imposition of threshold criteria on measurable signal characteristics such as the amplitude ratio and visibilities. The GPDCM provides a computational tool that will be valuable in the design, optimization, and evaluation of P/D fiber measurement systems.

Theoretical analysis of the effects of particle trajectory and structural resonances on the performance of a phase-Doppler particle analyzer.

A generalized theoretical model for the response of a phase-Doppler particle analyzer (PDPA) to homogeneous, spherical particles passing at arbitrary locations through a crossed beam measurement volume is presented. The model is based on the arbitrary beam theory [J. Appl. Phys. 64, 1632 (19$8)] and is valid for arbitrary particle size and complex refractive index. In contrast to classical Lorenz-Mie theory, the arbitrary beam approach has the added capability of accounting for effects that are due to the presence of the finite-size crossed incident beams that are used in the PDPA measurement technique.

The theoretical model is used to compute phase shift as a function of both the particle position within the measurement volume and particle diameter (1.0 µm < diameter water droplets < 10.0 µm for both resonant and nonresonant sizes) for 30° off-axis receiver configuration. Results indicate that trajectory effects are most pronounced for particle trajectories through the edge of the crossed beam measurement volume on the side opposite the detector. Trajectories through the center of the probe volume gave phase shifts that are nearly identical to those obtained with Lorenz-Mie plane-wave theory. Phase shifts calculated for particle diameters corresponding to electric-wave resonances showed the largest deviation from the corresponding nonresonance diameter phase shifts. Phase shifts for droplets at magnetic wave resonance conditions showed smaller effects, closely following. the behavior of nonresonant particle sizes. The major influence of aerosol trajectory on actual particle size determination (for both resonant and nonresonant particle sizes) is that the measured aerosol size distributions will appear broader than the actual size distribution that exists within a spray.

Multilaboratory evaluation of methods for detecting enteric viruses in soils.

Two candidate methods for the recovery and detection of viruses in soil were subjected to round robin comparative testing by members of the American Society for Testing and Materials D19:24:04:04 Subcommittee Task Group. Selection of the methods, designated "Berg" and "Goyal," was based on results of an initial screening which indicated that both met basic criteria considered essential by the task group. Both methods utilized beef extract solutions to achieve desorption and recovery of viruses from representative soils: a fine sand soil, an organic muck soil, a sandy loam soil, and a clay loam soil. One of the two methods, Goyal, also used a secondary concentration of resulting soil eluants via low-pH organic flocculation to achieve a smaller final assay volume. Evaluation of the two methods was simultaneously performed in replicate by nine different laboratories. Each of the produced samples was divided into portions, and these were respectively subjected to quantitative viral plaque assay by both the individual, termed independent, laboratory which had done the soil processing and a single common reference laboratory, using a single cell line and passage level. The Berg method seemed to produce slightly higher virus recovery values; however, the differences in virus assay titers for samples produced by the two methods were not statistically significant (P less than or equal to 0.05) for any one of the four soils. Despite this lack of a method effect, there was a statistically significant laboratory effect exhibited by assay titers from the independent versus reference laboratories for two of the soils, sandy loam and clay loam.

Nonlinear interaction of KrF laser radiation with small water droplets.

Results have been obtained for the interaction of KrF excimer laser radiation (lambda = 248 nm, t(pulse) = 17 ns) with 60-microm diam distilled water droplets for irradiance values ranging from 3 to 230 GW/cm(2). Laser images of the droplet breakup during the time intervals from 0 to 100 ns indicate that the dynamic breakup processes are highly nonlinear. At low irradiance (3 GW/cm(2)) material is ejected from both the illuminated and shadow hemispheres of the droplet in qualitative agreement with the location of the electric field peaks predicted by plane wave Lorenz-Mie theory calculations. As the irradiance is increased, the interaction on the shadow hemisphere becomes stronger while the interaction on the illuminated hemisphere decreases. This nonlinear behavior is attributed to rapid electrical breakdown of the droplet near the shadow surface. The breakdown region destroys the ability of the droplet to redirect energy toward the front hemisphere of the droplet. Without this mechanism, the localized electric field maxima near the illuminated surface of the droplet cannot arise. Measurements were also taken of the average material velocities during the time intervals from 0 to 50 ns after arrival of the high energy pulse. Velocities ranged from 1000 m/s at 3 GW/cm(2) to 6000 m/s at 230 GW/cm(2).

Electromagnetic field for a beam incident on two adjacent spherical particles.

Through an application of our previously derived single spherical particle-arbitrary beam interaction theory, an iterative procedure has been developed for the determination of the electromagnetic field for a beam incident on two adjacent spherical particles. The two particles can differ in size and composition and can have any positioning relative to each other and relative to the focal point and propagation direction of the incident beam. Example calculations of internal and near-field normalized source function ( approximately |E|(2)) distributions are presented. Also presented are calculations demonstrating the effect of the relative positioning of the second adjacent particle on far-field scattering patterns.

Theoretical model of the laser imaging of small aerosols: applications to aerosol sizing.

A theoretical model is presented for the formation of small-particle shadow images in a single-lens laser-imaging system. The model uses a modification of classical Lorenz-Mie theory, presented by the authors in an earlier paper, to calculate the external electromagnetic fields resulting from the interaction of a Gaussian laser beam with a finite absorbing spherical particle. Propagation of the electric field through the imaging system components is developed from a scalar viewpoint using the thin-lens transformation and the Fresnel approximation to the Huygens-Fresnel propagation equation. The theoretical model is valid for either transparent or absorbing spheres and has no restrictions on the allowable degree or direction of aerosol defocus. Direct comparisons between theoretical calculations and experimental observations are reported for 53-microm-diameter transparent water droplets and 66-microm-diameter absorbing nickel spheres for defocus ranging from -2 mm (toward the lens) to +2 mm (away from the lens). Theory and experiment showed good agreement in the boundary edge gradient and the location of the external peaks, while observable differences existed in the magnitude of the central spots. Theoretical results, comparing water and nickel aerosols, showed observable differences in the calculated average internal intensity (AII). In contrast, the boundary edge gradient showed less dependence on changes in the optical properties of the particle. These results indicate that criteria, such as the AII, used in focus determination must be reevaluated when applying in-focus sizing algorithms to aerosols with significantly different optical properties.

Scattering of incident KrF laser radiation resulting from the laser-induced breakdown of H(2)O droplets.

The time history of elastically scattered incident radiation (ESIR) is presented for 60-microm-diameter water droplets irradiated by KrF (lambda = 248 nm) laser pulses with power densities in the range of 1-200 GW/cm(2). The ESIR shows a distinct two-peak structure that is dependent on the incident irradiance. The time delay between the arrival of the incident pulse and the first local minimum in the ESIR varied from 7 nsec at 200 GW/cm(2) to 21 nsec at 5 GW/cm(2). The time between incident pulse arrival and the first peak in the ESIR showed a similar irradiance dependence, with delays ranging from 4 to 12 nsec. Images of droplet breakup and the average velocities of ejected material are presented for times between 0 and 1000 nsec after the arrival of 3-GW/cm(2) laser pulses.

Focused laser beam interactions with methanol droplets: effects of relative beam diameter.

The effect of the local diameter of a focused CO(2) laser beam on calculated internal source function distributions and experimentally observed explosive characteristics is examined for 165-microm spherical methanol droplets. Experimental results show that the location and the characteristics of the explosive process change as the droplet is moved out of the laser focal point along the axis of propagation. Theoretical calculations indicate that, when the beam diameter is of the same order of magnitude as the droplet diameter, a modification of Mie theory, accounting for the finite beam size of the laser, is necessary to provide results which are consistent with experimental observations.

Round robin investigation of methods for recovering human enteric viruses from sludge.

To select a tentative standard method for detection of viruses in sludge the American Society for Testing and Materials D19:24:04:04 Subcommittee Task Group initiated round robin comparative testing of two procedures that, after initial screening of several methodologies, were found to meet the basic criteria considered essential by the task group. Eight task group member laboratories agreed to perform round robin testing of the two candidate methods, namely, The Environmental Protection Agency or low pH-AlCl3 method and the Glass or sonication-extraction method. Five different types of sludge were tested. For each particular type of sludge, a single laboratory was designated to collect the sludge in a single sampling, make samples, and ship it to the participating laboratories. In most cases, participating laboratories completed all the tests within 48 h of sample arrival. To establish the reproducibility of the methods, each laboratory tested each sludge sample in triplicate for the two candidate virus methods. Each processed sludge sample was quantitatively assayed for viruses by the procedures of each individual round robin laboratory. To attain a more uniform standard of comparison, a sample of each processed sample from all laboratories was reassayed with one cell line and passage number by a single laboratory (Environmental Protection Agency Environmental Monitoring and Support Laboratory, Cincinnati, Ohio). When the data were statistically analyzed, the Environmental Protection Agency method was found to yield slightly higher virus recoveries for all sludge types, except the dewatered sludge. The precisions of both methods were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Fate of virus in wastewater applied to slow-infiltration land treatment systems.

The removal of seeded coliphage f2 and indigenous enteroviruses from primary and secondary wastewaters applied by spray irrigation to sandy loam and silt loam soils in field test cells was examined. The amount of f2 recovered from 170-cm-deep soil percolate samples taken over a 53-day period never exceeded 0.1% of applied virus levels and was usually below detection limits. Indigenous enterovirus levels in percolate waters also constituted only a small portion of those found in the wastewaters. At 10 days after seeding, f2 virus was present throughout the soil column but tended to accumulate around the soil core middepths. Coliphage f2 disappeared from the soil surface regions at a high rate, and by 53 days very little virus could be detected within the length of the soil columns. Sterilized soil core segments from different depths were studied to determine their virus adsorption capabilities when suspended in either wastewater, test cell percolate water, or distilled water containing divalent cations. The adsorptive capacity of Windsor and Charlton soils for poliovirus 1 and coliphage f2 increased greatly with the soil sample depth until leveling off at the midcore depths. Soil suspended in wastewater had the least virus adsorption capability for all depths studied.

Comparison of coliphage and bacterial aerosols at a wastewater spray irrigation site.

Microbiological aerosols were measured on a spray irrigation site at Fort Huachuca, Ariz. Indigenous bacteria and tracer bacteriophage were sampled from sprays of chlorinated and unchlorinated secondary-treatment wastewaters during day and night periods. Aerosol dispersal and downwind migration were determined. Bacterial and coliphage f2 aerosols were sampled by using Andersen viable type stacked-sieve and high-volume electrostatic precipitator samplers. Bacterial standard plate counts averaged 2.4 x 10(5) colony-forming units per ml in unchlorinated effluents. Bacterial aerosols reached 500 bacteria per m3 at 152 m downwind and 10,500 bacteria per m3 at 46m. Seeded coliphage f2 averaged 4.0 x 10(5) plaque-forming units per ml in the effluent and were detected 563 m downwind. Downwind microbial aerosol levels were somewhat enhanced by nighttime conditions. The median aerodynamic particle size of the microbial aerosols was approximately 5.0 micrometer. Chlorination reduced wastewater bacterial levels 99.97% and reduced aerosol concentrations to near background levels; coliphage f2 was reduced only 95.4% in the chlorinated effluent and was readily measured 137 m downwind. Microbiological source strength an meteorological data were used in conjunction with a dispersion model to generate mathematical predictions of aerosol strength at various sampler locations. The mean calculated survival of aerosolized bacteria (standard plate count) in the range 46 to 76 m downwind was 5.2%, and that of coliphage f2 was 4.3 %.

Evaluation of the overland runoff mode of land wastewater treatment for virus removal.

The removal of enteric and tracer viruses by the overland runoff mode of domestic wastewater treatment was evaluated. Raw and primary and secondary treated wastewaters were sprayed onto grass-covered, 36-m soil plots of fine, sandy loam overlying an impermeable clay subsoil. Tracer bacteriophage f2 was seeded into the applied wastewaters, which were subsequently sampled at several points along the length of the plots. Assay of effluent samples revealed modest tracer virus removals of 30 to 60%. Data from timed experiments indicated that advancement of tracer virus to the bottom of the slopes proceeded at the same rate as wastewater, reaching the plot effluents within 50 to 90 min after application. Indigenous enteric virus levels were reduced by approximately 68 to 85% during migration down the treatment slopes. Soil sampling revealed that, although some f2 virus was found associated with the wastewater-saturated topsoil, little penetration of virus into the soil profile occurred. Laboratory soil adsorption studies revealed that poliovirus I was adsorbed much more readily than f2 virus. Comparison of virus removal characteristics during overland runoff with chemical removal characteristics of wastewater did not reveal any obvious correlations that could be used to predict virus removal.

Virus and bacteria removal from wastewater by rapid infiltration through soil.

A rapid infiltration land wastewater application site, composed of unconsolidated silty sand and gravel, which has been in continuous operation for over 30 years was examined for the accumulation and/or migration of a tracer virus (coliphage f2), indigenous enteroviruses, and enteric indicator bacteria in the soils and underlying groundwater. Tracer f2 penetrated into groundwater together with the front of percolating primary effluent and was not observed to concentrate on the upper soil layers. The tracer virus concentration in a 60-foot (about 18.3-m)-deep observation well directly beneath the wastewater application area began to increase within 48 h after application to the soil. The tracer level in this well stabilized after 72 h at a level of approximately 47% of the average applied concentration. Indigenous enteroviruses and tracer f2 were sporadically detected in the groundwater at horizontal distances of 600 feet (about 183 m) from the application zone. Laboratory soil adsorption studies confirmed the poor virus adsorption observed at the site. This was especially true on surface soils when contained in wastewater. Enteric indicator bacteria were readily concentrated on the soil surface by filtration on the soil surface mat. However, during tracer f2 virus tests, comparison studies with fecal Streptococcus revealed that bacteria capable of penetrating the surface were able to migrate into the groundwater. They were detected at the same locations as tracer and enteric viruses.

Association of enteroviruses with natural and artificially introduced colloidal solids in water and infectivity of solids-associated virions.

Encephalomyocarditis viruses adsorb to introducted organic and inorganic solids in water over a wide range of pH and with various concentrations and species of metal cations. Visible flocculation of solids was not a prerequisite for significant virus association. Virus adsorption to natural solids in various types of natural waters was significant but variable. Clay-adsorbed virus retained its infectivity in tissue culture monolayers. These solids-associated viruses also retained infectivity in mice.