Publications by authors named "Jeffrey J Whicker"

23 Publications

  • Page 1 of 1

Radionuclide resuspension across ecosystems and environmental disturbances.

J Environ Radioact 2021 Jul 25;233:106586. Epub 2021 Mar 25.

Los Alamos National Laboratory, Mail Stop J978, Los Alamos, NM, 87545, USA.

Exposure assessment from radionuclides and other soil-bound contaminants often requires quantifying the amount of contaminant resuspended in the air. Rates and controlling factors of radionuclide resuspension and wind erosion of soil are clearly related but have largely been studied separately. Here, we review both and then integrate wind erosion measurements with the radiological resuspension paradigm to provide better estimates of resuspension factors across a broad range of ecosystems and environmental conditions. Radionuclide resuspension by wind was initially investigated during the era of aboveground nuclear weapons testing. Predictive dose models were developed from empirically-derived ratios of air and soil concentrations, otherwise called the resuspension factor. Resuspension factors were shown to generally predict radionuclide concentrations in air, but they were site-specific and largely derived from the arid and semi-arid environments surrounding nuclear weapons testing locations. In contrast, wind erosion studies from the agricultural and environmental sciences have produced more mechanistic models and a relatively robust data set of wind erosion rates and model parameters across a range of ecosystems. We sequentially show the mathematics linking measured sediment flux from wind erosion rate measurements to resuspension factors using the concept of transport capacity and its relationship to the deposition velocity. We also describe the conceptual framework describing how resuspension factors change through time and the mathematical models describing this decrease. We then show how vertical mass flux measurements across ecosystems were categorized and used to calculate ecosystem-based resuspension factors. These calculations allow generalized estimation of radionuclide resuspension factors across ecosystem types as a function of disturbance and as input for dose calculations.
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http://dx.doi.org/10.1016/j.jenvrad.2021.106586DOI Listing
July 2021

Response to Evans.

Health Phys 2020 06;118(6):689

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http://dx.doi.org/10.1097/HP.0000000000001256DOI Listing
June 2020

Validation Tests of Resuspension Models for a Finite and Infinite Site.

Health Phys 2019 10;117(4):408-415

Los Alamos National Laboratory, Los Alamos, NM.

Dose assessment for deposited radionuclides often requires estimates of air concentrations that are derived from measured soil concentrations. For this, dose assessors typically use literature resuspension values that, while empirically based, can vary by orders of magnitude making it difficult to provide accurate dose estimates. Despite the complexities of the physical processes involved in resuspension, the models generally used for dose assessment are relatively simplistic and rarely are the models validated for a specific site, thus making prediction of air concentrations or airborne emissions highly uncertain. Additionally, the size of the contaminated area can have an impact on downwind concentrations, yet literature values do not account for smaller-sized contaminated sites adding additional uncertainty. To test resuspension models for soil-bound radionuclides at finite and infinite spatial scales, measurements of soil and air concentrations are made at (1) a location downwind of a former outfall where Pu was released into the environment (a finite site), and (2) uncontaminated locations where regional air sampling provides background measurements of naturally occurring U in sampled dust (an infinite site). Measured air concentrations were compared to those predicted using the resuspension factor model and the mass loading model. An area factor was applied to the smaller contaminated site to account for dilution of dust from the contaminated site with dust originating from offsite locations. Results show that when properly parameterized to site conditions, resuspension models can predict air concentrations to within a factor of 10.
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http://dx.doi.org/10.1097/HP.0000000000001078DOI Listing
October 2019

Gamma-Ray Dose From an Overhead Plume.

Health Phys 2017 05;112(5):445-450

*MS J978, Los Alamos National Laboratory, MS J978, Los Alamos, NM 87544.

Standard plume models can underestimate the gamma-ray dose when most of the radioactive material is above the heads of the receptors. Typically, a model is used to calculate the air concentration at the height of the receptor, and the dose is calculated by multiplying the air concentration by a concentration-to-dose conversion factor. Models indicate that if the plume is emitted from a stack during stable atmospheric conditions, the lower edges of the plume may not reach the ground, in which case both the ground-level concentration and the dose are usually reported as zero. However, in such cases, the dose from overhead gamma-emitting radionuclides may be substantial. Such underestimates could impact decision making in emergency situations. The Monte Carlo N-Particle code, MCNP, was used to calculate the overhead shine dose and to compare with standard plume models. At long distances and during unstable atmospheric conditions, the MCNP results agree with the standard models. At short distances, where many models calculate zero, the true dose (as modeled by MCNP) can be estimated with simple equations.
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http://dx.doi.org/10.1097/HP.0000000000000643DOI Listing
May 2017

Accuracy of Cloudshine Gamma Dose Calculations in the CAP-88 Dispersion Model.

Health Phys 2017 04;112(4):414-419

*MS J978, Los Alamos National Laboratory, Los Alamos, NM 87545.

The U.S. Environmental Protection Agency dispersion model, CAP-88, calculates ground-level dose using the ground-level concentration and the semi-infinite cloud approximation. Doses can be underestimated for elevated plumes during stable atmospheric conditions at receptor locations within a kilometer downwind of a stack. The purpose of this paper is to identify when CAP-88 calculations of gamma dose from cloudshine are inaccurate and provide estimates of the inaccuracy. The method used compares CAP-88 estimates with Monte Carlo N-Particle (MCNP) estimates. Comparisons were made at distances of 800 m and 3,000 m downwind of the stack and for plume heights from 0 to 50 m. For these conditions, the annual dose calculated by CAP-88 is greater than or equal to that calculated by MCNP.
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http://dx.doi.org/10.1097/HP.0000000000000653DOI Listing
April 2017

Modeling aeolian transport of soil-bound plutonium: considering infrequent but normal environmental disturbances is critical in estimating future dose.

J Environ Radioact 2013 Jun 1;120:73-80. Epub 2013 Mar 1.

Los Alamos National Laboratory, Environmental Stewardship Group, Mail Stop J978, Los Alamos, NM 87544, USA.

Dose assessments typically consider environmental systems as static through time, but environmental disturbances such as drought and fire are normal, albeit infrequent, events that can impact dose-influential attributes of many environmental systems. These phenomena occur over time frames of decades or longer, and are likely to be exacerbated under projected warmer, drier climate. As with other types of dose assessment, the impacts of environmental disturbances are often overlooked when evaluating dose from aeolian transport of radionuclides and other contaminants. Especially lacking are predictions that account for potential changing vegetation cover effects on radionuclide transport over the long time frames required by regulations. A recently developed dynamic wind-transport model that included vegetation succession and environmental disturbance provides more realistic long-term predictability. This study utilized the model to estimate emission rates for aeolian transport, and compare atmospheric dispersion and deposition rates of airborne plutonium-contaminated soil into neighboring areas with and without environmental disturbances. Specifically, the objective of this study was to utilize the model results as input for a widely used dose assessment model (CAP-88). Our case study focused on low levels of residual plutonium found in soils from past operations at Los Alamos National Laboratory (LANL), in Los Alamos, NM, located in the semiarid southwestern USA. Calculations were conducted for different disturbance scenarios based on conditions associated with current climate, and a potential future drier and warmer climate. Known soil and sediment concentrations of plutonium were used to model dispersal and deposition of windblown residual plutonium, as a function of distance and direction. Environmental disturbances that affected vegetation cover included ground fire, crown fire, and drought, with reoccurrence rates for current climate based on site historical patterns. Using site-specific meteorology, accumulation rates of plutonium in soil were modeled in a variety of directions and distances from LANL sources. Model results suggest that without disturbances, areas downwind to the contaminated watershed would accumulate LANL-derived plutonium at a relatively slow rate (<0.01 Bq m(-2) yr(-1)). However, model results under more realistic assumptions that include environmental disturbances show accumulation rates more than an order-of-magnitude faster. More generally, this assessment highlights the broader need in radioecology and environmental health physics to consider infrequent but normal environmental disturbances in longer-term dose assessments.
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http://dx.doi.org/10.1016/j.jenvrad.2013.01.011DOI Listing
June 2013

Operational experience of continuous air monitoring of smoke for ²³⁹Pu during a wildfire.

Health Phys 2012 Aug;103(2 Suppl 2):S161-8

Los Alamos National Laboratory, Mail Stop M996, Los Alamos, NM 87545, USA.

Smoke from a wildfire in northern New Mexico that moved along the border of the Los Alamos National Laboratory (LANL) was monitored for ²³⁹Pu in the event that the fire might cross into LANL property containing locations with low, but greater than background, levels of ²³⁹Pu and other alpha-emitting radionuclides. Three Environmental Continuous Air Monitors (ECAMs) in operation at LANL at the time of the fire provided near real-time measurements of the ²³⁹Pu in the smoke. Sampling data from routine measurements of PM-10 and PM-2.5 concentrations in the city of Los Alamos showed that smoke in the air rose during the fire to several hundred μg m⁻³, which produced limited visibility (several hundred meters) and resulted in poor air quality alerts for about a week-long period. Previous studies have shown that airborne dust can significantly impair continuous air monitors, so the purpose of this study was to assess the performance of the ECAMs under smoky conditions, which is important for many emergency response scenarios. Additionally, ECAMs are not required to be tested in smoke by ANSI standards, so there is little to no published data on performance of any ECAM while sampling smoke. Results show that the deployed ECAMs had reduced flow as the filter clogged with fine particles, but the goodness-of-fit parameter of the peak shape fitting algorithms and the minimum detectable concentration and dose were not impacted until the flow was reduced by more than about 20%, and even then they were within tolerable limits. Overall, ECAM performance was not impacted during the fire even under heavy smoke conditions and fluctuating radon levels, though changing the filters to limit any reductions in flow to less than 20% would maintain optimal ECAM performance.
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http://dx.doi.org/10.1097/HP.0b013e318259f286DOI Listing
August 2012

Interactive effects of grazing and burning on wind- and water-driven sediment fluxes: rangeland management implications.

Ecol Appl 2011 Jan;21(1):22-32

School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona 85721, USA.

Rangelands are globally extensive, provide fundamental ecosystem services, and are tightly coupled human-ecological systems. Rangeland sustainability depends largely on the implementation and utilization of various grazing and burning practices optimized to protect against soil erosion and transport. In many cases, however, land management practices lead to increased soil erosion and sediment fluxes for reasons that are poorly understood. Because few studies have directly measured both wind and water erosion and transport, an assessment of how they may differentially respond to grazing and burning practices is lacking. Here, we report simultaneous, co-located estimates of wind- and water-driven sediment transport in a semiarid grassland in Arizona, USA, over three years for four land management treatments: control, grazed, burned, and burned + grazed. For all treatments and most years, annual rates of wind-driven sediment transport exceeded that of water due to a combination of ongoing small but nontrivial wind events and larger, less frequent, wind events that generally preceded the monsoon season. Sediment fluxes by both wind and water differed consistently by treatment: burned + grazed > burned > grazed > or = control, with effects immediately apparent after burning but delayed after grazing until the following growing season. Notably, the wind:water sediment transport ratio decreased following burning but increased following grazing. Our results show how rangeland practices disproportionally alter sediment fluxes driven by wind and water, differences that could potentially help explain divergence between rangeland sustainability and degradation.
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http://dx.doi.org/10.1890/09-2369.1DOI Listing
January 2011

Corrections for measurements of tritium in subterranean vapor using silica gel.

Environ Monit Assess 2011 Jan 6;172(1-4):135-43. Epub 2010 Feb 6.

Environmental Programs, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.

Hazardous contaminants buried within vadose zones can accumulate in soil gas. The concentrations and spatial extent of these contaminants are measured to evaluate potential transport to groundwater for public risk evaluation. Tritium is an important contaminant found and monitored for in vadose zones across numerous sites within the US nuclear weapons complex, including Los Alamos National Laboratory. The extraction, collection, and laboratory analysis of tritium from subterranean soil gas presents numerous technical challenges that have not been fully studied. Particularly, the lack of moisture in the soil gas in the vadose zone makes it difficult to obtain enough sample (e.g., > 5 g) to provide for the required measurement sensitivity, and often, only small amounts of moisture can be collected. Further, although silica gel has high affinity for water vapor and is prebaked prior to sampling, there is still sufficient residual moisture in the prebaked gel to dilute the relatively small amount of sampled moisture; thereby, significantly lowering the "true" tritium concentration in the soil gas. This paper provides an evaluation of the magnitude of the bias from dilution, provides methods to correct past measurements by applying a correction factor (CF), and evaluates the uncertainty of the CF values. For this, 10,000 Monte Carlo calculations were performed, and distribution parameters of CF values were determined and evaluated. The mean and standard deviation of the distribution of CF values were 1.53 ± 0.36, and the minimum, median, and maximum values were 1.14, 1.43, and 5.27, respectively.
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http://dx.doi.org/10.1007/s10661-010-1322-xDOI Listing
January 2011

Work to save dose: contrasting effective dose rates from radon exposure in workplaces and residences against the backdrop of public and occupational regulatory limits.

Health Phys 2009 Sep;97(3):248-56

Los Alamos National Laboratory, Environmental Programs, Mail Stop M992, Los Alamos, NM 87545, USA.

Office workers are exposed to radon while at work and at home. Though there are a multitude of studies reporting radon concentrations and potential lung and effective doses associated with radon progeny exposure in homes, similar studies in non-mine workplaces are lacking. Additionally, there are few, if any, comparative analyses of radon exposures at more "typical" workplace with residential exposures within the same county. The purposes of this study were to measure radon concentrations in office and residential spaces in the same county and explore the radiation dose implications. Sixty-five track-etch detectors were deployed for 3-mo sampling periods in office spaces and 47 were deployed in residences, all within Los Alamos County, New Mexico. The measured concentrations were used to calculate and compare effective dose rates resulting from exposure while at work and at home. Results showed that full-time office workers receive on average about 8 times greater exposure at home than while in the office (2.3 mSv y-1 vs. 0.3 mSv y-1). The estimated effective dose rate for a more homebound person was about 3 mSv y-1. Estimating effective doses from background radon exposure in the same county as Los Alamos National Laboratory, with thousands of "radiological workers," highlights interesting contrasts in radiation protection standards that span public and occupational settings. For example, the effective dose rate from background radon exposure in unregulated office spaces ranged up to 1.1 mSv y-1, which is similar to the 1 mSv y-1 threshold for regulation of a "radiological worker," as defined in the Department of Energy regulations for occupational exposure. Additionally, the estimated average effective dose total of >3 mSv y-1 from radon background exposure in homes stands in contrast to the 0.1 mSv y-1 air pathway effective public dose limit regulated by the Environmental Protection Agency for radioactive air emissions, and both these are substantially lower than effective doses associated with priority radon levels in homes of "tens of pCi L-1 and greater" (>370 Bq m-3), as suggested by the Health Physics Society.
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http://dx.doi.org/10.1097/HP.0b013e3181aba9e4DOI Listing
September 2009

Probabilistic model evaluation of continuous air monitor response for meeting radiation protection goals.

Health Phys 2009 Sep;97(3):228-41

Los Alamos National Laboratory, Environmental Programs, Mail Stop M992, Los Alamos, NM 87545, USA.

Effective continuous air monitor (CAM) programs can eliminate or significantly reduce the amount of inhaled radioactive material following an accidental release. Numerous factors impact the levels of protection CAM programs provide to the workers during these releases. These factors range from those related to the capability of the CAM instrument (e.g., CAM alarm set point and length of counting intervals) to those related to CAM placement in the room relative to dispersion rates and patterns of the released material in a room. While the impact of many of these factors on alarm sensitivity has been investigated in isolation, there are no methods for holistic evaluations of CAM programs relative to radiation protection goals (RPGs) or the contribution of the factors, either individually or combined, toward limiting worker dose. In this study, worker exposure was predicted using CAM response models developed to evaluate protection levels for continuous and acute releases. Monte Carlo simulations of 10,000 releases were performed using various combinations of model parameter values, with associated uncertainty distributions, to assess the expected ability of a CAM program to meet RPGs, and, further, to assess the relative influence of each factor toward lowering worker exposure. Results showed that improvements to CAM instrument capability combined with better ventilation and CAM placement improve worker protection nonlinearly and that these improvements are critical to meet RPGs. The sensitivity analysis showed that ventilation-driven dilution had the greatest impact on exposure reduction with the selected counting interval for alarm decisions and the alarm set point as secondarily important.
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http://dx.doi.org/10.1097/HP.0b013e3181abaaa7DOI Listing
September 2009

Calculating Capstone depleted uranium aerosol concentrations from beta activity measurements.

Health Phys 2009 Mar;96(3):238-50

U.S. Army Center for Health Promotion and Preventive Medicine, 5158 Blackhawk Road, Aberdeen Proving Ground, MD 21010-5403, USA.

Beta activity measurements were used as surrogate measurements of uranium mass in aerosol samples collected during the field testing phase of the Capstone Depleted Uranium (DU) Aerosol Study. These aerosol samples generated by the perforation of armored combat vehicles were used to characterize the DU source term for the subsequent Human Health Risk Assessment (HHRA) of Capstone aerosols. Establishing a calibration curve between beta activity measurements and uranium mass measurements is straightforward if the uranium isotopes are in equilibrium with their immediate short-lived, beta-emitting progeny. For DU samples collected during the Capstone study, it was determined that the equilibrium between the uranium isotopes and their immediate short-lived, beta-emitting progeny had been disrupted when penetrators had perforated target vehicles. Adjustments were made to account for the disrupted equilibrium and for wall losses in the aerosol samplers. Values for the equilibrium fraction ranged from 0.16 to 1, and the wall loss correction factors ranged from 1 to 1.92. This paper describes the process used and adjustments necessary to calculate uranium mass from proportional counting measurements.
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http://dx.doi.org/10.1097/01.HP.0000290612.27848.cdDOI Listing
March 2009

Adaptive management: a paradigm for remediation of public facilities following a terrorist attack.

Risk Anal 2008 Oct 29;28(5):1445-56. Epub 2008 Aug 29.

Los Alamos National Laboratory, NM, USA.

Terrorist actions are aimed at maximizing harm (health, psychological, economical, and political) through the combined physical impacts of the act and fear. Immediate and effective response to a terrorist act is critical to limit human and environmental harm, effectively restore facility function, and maintain public confidence. Though there have been terrorist attacks in public facilities that we have learned from, overall our experiences in restoration of public facilities following a terrorist attack are limited. Restoration of public facilities following a release of a hazardous material is inherently far more complex than in industrial settings and has many unique technical, economic, social, and political challenges. For example, there may be a great need to quickly restore the facility to full operation and allow public access even though it was not designed for easy or rapid restoration, and critical information is needed for quantitative risk assessment and effective restoration must be anticipated to be incomplete and uncertain. Whereas present planning documents have substantial linearity in their organization, the "adaptive management" paradigm provides a constructive parallel paradigm for restoration of public facilities that anticipates and plans for uncertainty, inefficiencies, and stakeholder participation. Adaptive management grew out of the need to manage and restore natural resources in highly complex and changing environments with limited knowledge about causal relationships and responses to restoration actions. Similarities between natural resource management and restoration of a public facility after a terrorist attack suggest that integration of adaptive management principles explicitly into restoration processes will result in substantially enhanced and flexible responses necessary to meet the uncertainties of potential terrorist attacks.
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http://dx.doi.org/10.1111/j.1539-6924.2008.01102.xDOI Listing
October 2008

Considerations for data processing by continuous air monitors based on accumulation sampling techniques.

Health Phys 2008 Feb;94(2 Suppl):S4-15

China Institute for Radiation Protection, Taiyuan, PR China.

Continuous air monitors (CAMs) sample air and alarm when concentration levels of radioactivity in air exceed preset alarm levels. The air concentrations through time are calculated based on accumulation sampling techniques. Accumulation air sampling is the process in which radioactive aerosol is continually deposited onto a collection medium and a radiation detector provides continuous measurements of the radioactivity on the filter. To assess the air concentration, time intervals are established for the counting and sampling times, and the measurement of concentration represents an average over the measurement interval. There are multiple methods that can be used to determine the concentration for the most recent measurement interval, and based on the method used, each can result in significantly different values for concentrations, associated uncertainties, and response times. We evaluate and compare several methods for determining air concentrations based on accumulation counting techniques. Further, we provide a real-life example of accumulation counting and the effects of compensating for background radiation in the context of monitoring for plutonium concentrations against a fluctuating radon progeny background. Results show the importance of selecting a method that provides for a balance of response time, measurement interval, background compensation technique, and uncertainty for optimal protection of workers.
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http://dx.doi.org/10.1097/01.HP.0000286517.19932.c7DOI Listing
February 2008

Uranium partition coefficients (Kd) in forest surface soil reveal long equilibrium times and vary by site and soil size fraction.

Health Phys 2007 Jul;93(1):36-46

Los Alamos National Laboratory, Radiation Protection Division, Mail Stop G761, Los Alamos, NM 87544, USA.

The environmental mobility of newly deposited radionuclides in surface soil is driven by complex biogeochemical relationships, which have significant impacts on transport pathways. The partition coefficient (Kd) is useful for characterizing the soil-solution exchange kinetics and is an important factor for predicting relative amounts of a radionuclide transported to groundwater compared to that remaining on soil surfaces and thus available for transport through erosion processes. Measurements of Kd for 238U are particularly useful because of the extensive use of 238U in military applications and associated testing, such as done at Los Alamos National Laboratory (LANL). Site-specific measurements of Kd for 238U are needed because Kd is highly dependent on local soil conditions and also on the fine soil fraction because 238U concentrates onto smaller soil particles, such as clays and soil organic material, which are most susceptible to wind erosion and contribute to inhalation exposure in off-site populations. We measured Kd for uranium in soils from two neighboring semiarid forest sites at LANL using a U.S. Environmental Protection Agency (EPA)-based protocol for both whole soil and the fine soil fraction (diameters<45 microm). The 7-d Kd values, which are those specified in the EPA protocol, ranged from 276-508 mL g-1 for whole soil and from 615-2249 mL g-1 for the fine soil fraction. Unexpectedly, the 30-d Kd values, measured to test for soil-solution exchange equilibrium, were more than two times the 7-d values. Rates of adsorption of 238U to soil from solution were derived using a 2-component (FAST and SLOW) exponential model. We found significant differences in Kd values among LANL sampling sites, between whole and fine soils, and between 7-d and 30-d Kd measurements. The significant variation in soil-solution exchange kinetics among the soils and soil sizes promotes the use of site-specific data for estimates of environmental transport rates and suggests possible differences in desorption rates from soil to solution (e.g., into groundwater or lung fluid). We also explore potential relationships between wind erosion, soil characteristics, and Kd values. Combined, our results highlight the need for a better mechanistic understanding of soil-solution partitioning kinetics for accurate risk assessment.
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http://dx.doi.org/10.1097/01.HP.0000258924.55225.cdDOI Listing
July 2007

From dust to dose: Effects of forest disturbance on increased inhalation exposure.

Sci Total Environ 2006 Sep 17;368(2-3):519-30. Epub 2006 Apr 17.

Los Alamos National Laboratory, Health Physics Measurements Group, Mail Stop J573, Los Alamos NM 87545, USA.

Ecosystem disturbances that remove vegetation and disturb surface soils are major causes of excessive soil erosion and can result in accelerated transport of soils contaminated with hazardous materials. Accelerated wind erosion in disturbed lands that are contaminated is of particular concern because of potential increased inhalation exposure, yet measurements regarding these relationships are lacking. The importance of this was highlighted when, in May of 2000, the Cerro Grande fire burned over roughly 30% of Los Alamos National Laboratory (LANL), mostly in ponderosa pine (Pinus ponderosa) forest, and through areas with soils containing contaminants, particularly excess depleted and natural uranium. Additionally, post-fire thinning was performed in burned and unburned forests on about 25% of LANL land. The first goal of this study was to assess the potential for increased inhalation dose from uranium contaminated soils via wind-driven resuspension of soil following the Cerro Grande Fire and subsequent forest thinning. This was done through analysis of post-disturbance measurements of uranium air concentrations and their relationships with wind velocity and seasonal vegetation cover. We found a 14% average increase in uranium air concentrations at LANL perimeter locations after the fire, and the greatest air concentrations occurred during the months of April-June when wind velocities are highest, no snow cover, and low vegetation cover. The second goal was to develop a methodology to assess the relative contribution of each disturbance type towards increasing public and worker exposure to these resuspended soils. Measurements of wind-driven dust flux in severely burned, moderately burned, thinned, and unburned/unthinned forest areas were used to assess horizontal dust flux (HDF) in these areas. Using empirically derived relationships between measurements of HDF and respirible dust, coupled with onsite uranium soil concentrations, we estimate relative increases in inhalation doses for workers ranging from 15% to 38%. Despite the potential for increased doses resulting from these forest disturbances, the estimated annual dose rate for the public was <1 microSv yr(-1), which is far below the dose limits for public exposures, and the upper-bound dose rate for a LANL worker was estimated to be 140 microSv yr(-1), far below the 5 x 10(4) microSv yr(-1) occupational dose limit. These results show the importance of ecosystem disturbance in increasing mobility of soil-bound contaminants, which can ultimately increase exposure. However, it is important to investigate the magnitude of the increases when deciding appropriate strategies for management and long-term stewardship of contaminated lands.
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http://dx.doi.org/10.1016/j.scitotenv.2006.03.003DOI Listing
September 2006

Increased wind erosion from forest wildfire: implications for contaminant-related risks.

J Environ Qual 2006 Mar-Apr;35(2):468-78. Epub 2006 Feb 2.

Los Alamos National Laboratory, Health Physics Measurements Group, Mail Stop J573, Los Alamos, NM 87545, USA.

Assessments of contaminant-related human and ecological risk require estimation of transport rates, but few data exist on wind-driven transport rates in nonagricultural systems, particularly in response to ecosystem disturbances such as forest wildfire and also relative to water-driven transport. The Cerro Grande wildfire in May of 2000 burned across ponderosa pine (Pinus ponderosa Douglas ex P.&C. Lawson var. scopulorum Englem.) forest within Los Alamos National Laboratory in northern New Mexico, where contaminant transport and associated post-fire inhalation risks are of concern. In response, the objectives of this study were to measure and compare wind-driven horizontal and vertical dust fluxes, metrics of transport related to wind erosion, for 3 yr for sites differentially affected by the Cerro Grande wildfire: unburned, moderately burned (fire mostly confined to ground vegetation), and severely burned (crown fire). Wind-driven dust flux was significantly greater in both types of burned areas relative to unburned areas, by more than one order of magnitude initially and by two to three times 1 yr after the fire. Unexpectedly, the elevated dust fluxes did not decrease during the second and third years in burned areas, apparently because ongoing drought delayed post-fire recovery. Our estimates enable assessment of amplification in contaminant-related risks following a major type of disturbance-wildfire, which is expected to increase in intensity and frequency due to climate change. More generally, our results highlight the importance of considering wind- as well as water-driven transport and erosion, particularly following disturbance, for ecosystem biogeochemistry in general and human and ecological risk assessment in particular.
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http://dx.doi.org/10.2134/jeq2005.0112DOI Listing
September 2006

Characterization of plutonium aerosol collected during an accident.

Health Phys 2004 Dec;87(6):596-605

Lovelace Respiratory Research Institute, 2425 Ridgecrest Drive SE, Albuquerque, NM 87115, USA.

This study determined the plutonium particle size distribution and dissolution rate of PuO2 aerosol collected during the 16 March 2000 release of an undetermined amount of PuO2 in a room within a plutonium facility at Los Alamos National Laboratory. The facility has been in operation since 1978 to support the development, fabrication, and testing of Pu heat sources for the U.S. Department of Energy. Several workers were in the room at the time of the release and in vivo study of five of the workers began the day after the exposure event. Four of the subjects subsequently received chelation therapy. Over 30 fixed air filter samplers (FASs) and four continuous air monitors (CAMs) were operating in the room during the radiological release. One 47-mm-diameter glass fiber FAS filter and one 25-cm-diameter mixed cellulose ester CAM filter containing Pu aerosol from the incident were examined in the study described here. Total alpha radioactivity on the filters was determined by gross alpha counting. Isotopic identification of the Pu was made by alpha spectrometry. Film autoradiography was used to characterize the spatial distribution of alpha-emitting particles on the filters. Track-etch autoradiography was used to estimate the distribution of alpha radioactivity in individual plutonium particles on the filters for particle size measurement. The glass fiber filter was then cut into six sections. Particles from two sections were resuspended in alcohol, dispersed as an aerosol using a Lovelace nebulizer, and characterized by aerodynamic diameter using a Lovelace Multi-jet cascade impactor. The measured activity median aerodynamic diameter from the cascade impactor was 4.8 mum with a geometric standard deviation of 1.5. That agreed with the size distribution obtained from the alpha track detection technique. The remaining four filter sections were used in an in vitro dissolution study with synthetic serum ultrafiltrate. The retention of undissolved Pu was consistent with a biphasic exponential function. The majority of the Pu dissolved with a half-time of 900 d. The information on particle size distribution and solubility from this study was useful in assigning a radiation dose to the exposed workers, supporting the decision to administer chelation therapy, and providing a model for characterizing accident-associated aerosols in the future.
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http://dx.doi.org/10.1097/01.hp.0000138577.21388.a7DOI Listing
December 2004

A quantitative method for optimized placement of continuous air monitors.

Health Phys 2003 Nov;85(5):599-609

L Los Alamos National Laboratory, Health Physics Measurements Group, Mail Stop G761, Los Alamos, NM 87545, USA.

Alarming continuous air monitors (CAMs) are a critical component for worker protection in facilities that handle large amounts of hazardous materials. In nuclear facilities, continuous air monitors alarm when levels of airborne radioactive materials exceed alarm thresholds, thus prompting workers to exit the room to reduce inhalation exposures. To maintain a high level of worker protection, continuous air monitors are required to detect radioactive aerosol clouds quickly and with good sensitivity. This requires that there are sufficient numbers of continuous air monitors in a room and that they are well positioned. Yet there are no published methodologies to quantitatively determine the optimal number and placement of continuous air monitors in a room. The goal of this study was to develop and test an approach to quantitatively determine optimal number and placement of continuous air monitors in a room. The method we have developed uses tracer aerosol releases (to simulate accidental releases) and the measurement of the temporal and spatial aspects of the dispersion of the tracer aerosol through the room. The aerosol dispersion data is then analyzed to optimize continuous air monitor utilization based on simulated worker exposure. This method was tested in a room within a Department of Energy operated plutonium facility at the Savannah River Site in South Carolina, U.S. Results from this study show that the value of quantitative airflow and aerosol dispersion studies is significant and that worker protection can be significantly improved while balancing the costs associated with CAM programs.
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http://dx.doi.org/10.1097/00004032-200311000-00008DOI Listing
November 2003

Temporal and spatial variation of episodic wind erosion in unburned and burned semiarid shrubland.

J Environ Qual 2002 Mar-Apr;31(2):599-612

Health Physics Measurements, Los Alamos National Laboratory, NM 87545, USA.

Redistribution of soil, nutrients, and contaminants is often driven by wind erosion in semiarid shrublands. Wind erosion depends on wind velocity (particularly during episodic, high-velocity winds) and on vegetation, which is generally sparse and spatially heterogeneous in semiarid ecosystems. Further, the vegetation cover can be rapidly and greatly altered due to disturbances, particularly fire. Few studies, however, have evaluated key temporal and spatial components of wind erosion with respect to (i) erosion rates on the scale of weeks as a function of episodic high-velocity winds, (ii) rates at unburned and burned sites, and (iii) within-site spatial heterogeneity in erosion. Measuring wind erosion in unburned and recently burned Chihuahuan desert shrubland, we found (i) weekly wind erosion was related more to daily peak wind velocities than to daily average velocities as consistent with our findings of a threshold wind velocity at approximately 7 m s(-1); (ii) greater erodibility in burned vs. unburned shrubland as indicated by erosion thresholds, aerodynamic roughness, and nearground soil movement; and (iii) burned shrubland lost soil from intercanopy and especially canopy patches in contrast to unburned shrubland, where soil accumulated in canopy patches. Our results are among the first to quantify post-fire wind erosion and highlight the importance of accounting for finer temporal and spatial variation in shrubland wind erosion. This finer-scale variation relates to semiarid land degradation, and is particularly relevant for predictions of contaminant resuspension and redistribution, both of which historically ignore finer-scale temporal and spatial variation in wind erosion.
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September 2002

Influence of room geometry and ventilation rate on airflow and aerosol dispersion: implications for worker protection.

Health Phys 2002 Jan;82(1):52-63

Los Alamos National Laboratory, Health Physics Measurements Group, NM 87545, USA.

Knowledge of dispersion rates and patterns of radioactive aerosols and gases through workrooms is critical for understanding human exposure and for developing strategies for worker protection. The dispersion within rooms can be influenced by complex interactions between numerous variables, but especially ventilation design and room furnishings. For this study, dependence of airflow and aerosol dispersion on workroom geometry (furnishings) and ventilation rate were studied in an experimental room that was designed to approximate a plutonium laboratory. Three different configurations of simulated gloveboxes and two ventilation rates (approximately 6 and 12 air exchanges per hour) were studied. A sonic anemometer was used to measure airflow parameters including all three components of air velocity vectors and turbulence intensity distributions at multiple locations and heights. Aerosol dispersion rates and patterns were measured by releasing aerosols multiple times from six different locations. Aerosol particle concentrations resolved in time and space were measured using 16 multiplexed laser particle counters. Comparisons were made of air velocities, turbulence, and aerosol transport across different ventilation rates and room configurations. A strong influence of ventilation rate on aerosol dispersion rates and air velocity was found, and changes in room geometry had significant effects on aerosol dispersion rates and patterns. These results are important with regards to constant evaluation of placement of air sampling equipment, benchmarking numerical models of room airflow, and design of ventilation and room layouts with consideration of worker safety.
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http://dx.doi.org/10.1097/00004032-200201000-00007DOI Listing
January 2002