Browsing by Subject "Exposure"

Purpose: (1) To verify the accuracy and linearity of the ThermoScientific Radeye G Personal Rate Meter with respect to exposure rate across the full dynamic range of the instrument. (2) Use a combination of empirical data and Monte Carlo methods to estimate dose distribution in a GE Discovery 690 PET/CT scanner room and adjacent hallway. (3) Quantify components of occupational dose to PET technologists.

Materials & Methods: (Project 1) The Radeye unit and a calibrated ion chamber were placed in the beam of a Cesium 137 calibrator. They were exposed from 46 μR/hr to 1 R/hr with the pulse of each beam lasting for 90 seconds. The Radeye made 15 exposure rate measurements during each pulse. The ion chamber was read in the mid-point of each pulse's duration. (Project 2) Six Radeye units were placed at key points within the Discovery 690 scan room and two were placed in the adjacent hallway. 1600 exposure rate measurements were made over eleven hours during each day of operation. Data was collected for seven days. The total integrated data from the detectors inside the room was used to develop a Monte Carlo model of the room using FLUKA software. This model was then able to estimate the contribution from radiation escaping the scan room to the detectors in the hallway. (Project 3) Three PET technologists wore Radeye units while performing their daily tasks. The detectors recorded a mean exposure rate over each 25 second sampling period. The technologists were also asked to maintain a written log of all their interaction with radioactive material as well as their interactions with injected patients. Each day the Radeye unit produced a plot of radiation exposure with respect to time. Each interaction with radioactivity from the logs was highlighted on the plot and integrated to obtain the exposure received while performing that task.

Results: (Project 1) The Radeye deviated from the known value of exposure by up to 9.3% and deviated from the ion chamber measurement by up to 8.6% for exposure rates of 1 mR/hr and greater. The Radeye measured up to 29.6% higher than the known rate and up to 33.6% higher than the ion chamber measurement for exposure rates less than 1 mR/hr. The variance in the Radeye measurements decreased as exposure rate increased. The standard deviation of the Radeye measurements were less than 4% of their respective mean values for exposure rates less than 1 mR/hr. This value increased for lower exposure rates, up to 14% at 0.046 mR/hr. (Project 2) Mean daily exposures to five points in the PET/CT scan room were measured for CT and PET emissions separately. A Monte Carlo model of the scan room was created to model the distribution, including an initial approximation for the scanner gantry. The simulations showed that the virtual scanner should be thinner (i.e. less attenuating), especially for the 511KeV PET photons. (Project 3) The mean exposure received per dose draw and accompanying injection was 0.70±0.23mR for the 113 injections recorded over the course of the study. No correlation was observed between the dosage injected and the exposure received. The percent contributed to the total exposure by each category and participant was as follows. Technologist #1: 68% from Dose Draw, 6% from Patient Positioning, 4% from Patient Transport, 1% from General Patient Care, 21% from nonspecific sources. Technologist #2: 34%, 32%, 14%, 6%, and 14%. Technologist #3: 32%, 32%, 16%, <1%, and 20%. The dose draws and accompanying injections account for between one and two thirds of daily exposure. This indicates it is likely a 30% daily dose reduction could be achieved with use of automated injection equipment.

Arsenic (As) exposure via groundwater consumption is a global health problem affecting millions. Monitoring exposure is a key step in understanding and predicating future health outcomes. This thesis explores the relationships between arsenic concentrations in toenails and arsenic in water. Three case studies were investigated, with residents from: North Carolina, USA (n=103); the Rift Valley, Ethiopia (n=60); and the Mekong Delta, Vietnam (n=65). Arsenic concentrations above the WHO's recommended 10ppb limit were found in groundwater from the three research sites.

Arsenic in toenails was analyzed by inductively coupled plasma mass spectrometry (ICP-MS).

In the Rift Valley of Ethiopia, 53% of the tested drinking wells (n=34) had As above the WHO's limit. Arsenic concentrations in toenails (n=60) were significantly correlated to As concentrations in groundwater (r=0.72; p<0.001), reflecting the direct exposure of rural communities to As in well water, which is their principle water source. Male minors (<18 years old) were found to have greater nail-As concentrations compared with adults consuming equal amounts of As (p<0.05). Estimated As dose specifically from drinking water sources was also associated with nail concentrations (p<0.01).

In the Mekong Delta of Vietnam (Dong Thap Province), 36 out of the 68 tested wells had As content above the WHO's recommended limit of 10ppb, with levels as high as 981 ppb. Arsenic contents in nails collected from local residents (n=62) were significantly correlated to As in drinking water (r=0.49, p<0.001). Demographic and survey data show that the ratio of As in nail to As in water varies among residents that reflects differential As accumulation in the exposed population. The data show that water filtration and diet, particularly increased consumption of animal protein and dairy and reduced consumption of seafood, were associated with lower ratios of As in nail to As in water and thus could play important roles in mitigating As exposure.

Sixty-one wells were tested from Union County, North Carolina, with 15 out of 61 wells exceeded the WHO's 10 ppb limit. Arsenic values ranged from below the limit of detection (0.07) to 130ppb, with a mean of 11ppb (median=1.5ppb). Nails were collected from county residents (n=103) and were statistically correlated with As-water concentrations (r=0.48, p<0.001).

Integration of the data from the three cases studies across different populations and ethnicities show high correlation between As concentrations in groundwater and As in nails in all the three locations (r(Union County)= 0.48, p<0.001; r(Ethiopia)=0.72 p<0.001; r(Vietnam)=0.49, p<0.001). For As-nail to As-water pairs in which As in water was above 1ppb, these three locations are statistically indistinguishable from one another (r=0.62, p<0.001, n=176). These results support the hypothesis that nails can be used as a biomarker of exposure regardless of geographic or ethnic differences in populations considered. Nutrition (meat, seafood, and milk consumption) rather than gender, ethnicity, or dose is suggested to be the major confounding issue affecting the magnitude of As exposure in the human body.

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals used in a wide array of products and applications (e.g., nonstick cookware, waterproof and water-repellent textiles, firefighting foam). Following their decades of use, PFAS have garnered concern as “forever chemicals” due to their extreme persistence in the environment and in humans. PFAS have further elicited concern because they have been linked to adverse health effects in humans, and their huge number (over 12,000 different chemicals) and complex chemistry make them very challenging to analyze and study for exposure and toxicology. Two particular PFAS chemicals, perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS), are drinking water contaminants that can be found in the blood of the vast majority of people. PFOA and PFOS are also linked to toxic effects like kidney and testicular cancer, increased blood cholesterol, and reproductive outcomes. These two chemicals are being phased out of use and federal drinking water standards are likely upcoming. However, the replacements for these two chemicals are much less well-characterized, and many of these newer, replacement PFAS chemicals can be found in the environment of North Carolina due (at least in part) to industrial pollution.

The overarching goal of this dissertation was to characterize the potential exposure and health effects of PFAS in North Carolina communities. The surface water and drinking water in some areas of North Carolina have been found to be contaminated with PFAS; however, there are additional routes of PFAS exposure beyond drinking water, such as ingestion of house dust or placental transfer during pregnancy. This dissertation explores various routes of PFAS exposure and better characterizes the specific PFAS analytes that can be found in North Carolina and the concentrations in which they are present. Additionally, this dissertation evaluates this exposure and potential associations with some adverse health outcomes in a few North Carolina communities.

In Chapter 2, the relationships between PFAS exposure during pregnancy and birth outcomes are explored. This chapter includes data on PFAS concentrations in placenta samples from 120 participants in Durham, North Carolina and evaluates the subsequent associations between placental PFAS exposure and birth outcomes (e.g., infant birth weight, gestational age). A total of 11 PFAS were measured in placental tissues collected in 2010-2011, and the compounds PFOS, PFOA, PFNA, and PFDA were detected in all placenta samples. A few placental PFAS were associated with birth outcomes. The most striking result was that placental PFOS was associated with changes in birth weight, but the direction of change depended on the sex of the infant. For male infants, placental PFOS was associated with lower birthweight, and in female infants, placental PFOS was associated with higher birthweight.

In Chapter 3, the exposure to PFAS through drinking water is evaluated in a community with known PFAS water contamination. This chapter includes data on PFAS concentrations in blood serum and drinking water samples from 49 participants in Pittsboro, North Carolina. The community receives its drinking water from the Haw River, a part of the Cape Fear River watershed. Blood and water samples were collected at two different timepoints to explore temporal variability in contamination. This community was found to have blood levels of PFAS about two to four times higher than the U.S. average. This chapter also includes results on the associations between PFAS blood level and clinical chemistry measurements, such as serum lipids, as indicators of health. Negative associations were found between serum PFOS and PFHxA with decreased electrolytes and decreased liver enzymes. Positive associations were found between serum PFOA and PFHxS with increased total cholesterol and increased non-HDL cholesterol.

In Chapter 4, the effects and toxicokinetics of PFAS in a pregnant rabbit model are evaluated. This chapter includes data from an animal study of 21 pregnant rabbits provided with drinking water that is representative of the PFAS exposure observed in Pittsboro, North Carolina. Rabbits were exposed to this environmentally-relevant mixture of ten different PFAS during and before pregnancy. After exposure, the wastes and tissues were evaluated to measure the PFAS concentration that accumulated. This provided information on where PFAS are distributed in the body after exposure. The liver of the pregnant rabbit was also evaluated to determine if there was an increase in lipids in the liver, or any changes in liver lipid metabolism. For this study, few differences were noted between treated animals and control animals, indicating that the environmentally-relevant dose had little effect on pregnant rabbits. However, due to the lack of PFAS accumulation in blood, tissue, or in wastes, it is likely that the dose of PFAS given through drinking water was too low.

In Chapter 5, the levels of PFAS in indoor house dust were evaluated. This chapter includes data on PFAS concentrations in indoor dust from 184 homes in Durham, North Carolina, as well as 49 fire stations across the U.S. and Canada. House dust and fire station dust PFAS concentrations were then evaluated for associations with characteristics of the building (e.g., square footage, amount of carpeting, age of building construction). Levels of precursor PFAS, such as fluorotelomer alcohols, were typically higher in dust than the perfluoroalkyl acids. This study, along with previous literature, shows that the legacy PFAS in dust has been decreasing, but the precursor PFAS has been increasing in U.S. house dust. Few associations were found between building characteristics and dust PFAS. However, one notable result was that higher 8:2 FTOH was found in dust from buildings with more carpeting, indicating that carpets may be an important source of exposure to fluorotelomer alcohols (possibly from stain-proofing treatment).

Collectively, this dissertation provides important information on the potential exposure and health effects of PFAS in North Carolina communities.

In highly polluted cities, many residents seek to reduce their personal exposure to air pollutants. However, over the course of a day, people spend time in a variety of micro-environments (e.g., different rooms in their home, at school or work, in vehicles, outdoors), making it challenging to prioritize actions to reduce exposure. In China, air purifiers are a common mitigation strategy. The impacts of air purifiers on indoor air quality and personal exposure can differ greatly in real-world settings depending on the participants’ behavior, the home environment, and the selected purifier. This work uses low-cost monitors to compare the impacts of air filtration on indoor air and personal exposure. Before deploying low-cost monitors, steps needed to be taken to ensure data quality: low-cost air monitors were evaluated against reference measurements in multiple field locations (i.e. Atlanta, Hyderabad, Beijing, and Shanghai), and various calibration methods were developed to reduce monitor error and bias. Results highlight the need to calibrate low-cost monitors under the same conditions in which they will be deployed, and illustrate methods to reduce error that will allow low-cost monitors to make powerful insights into addressing additional air quality issues in the future. After evaluation and calibration, low-cost air monitors were installed indoors (in study participants’ bedrooms) and outdoors. Additionally, monitors were worn by study participants to measure personal exposure. To evaluate the impacts of bedroom air filtration, participants in Beijing (N=7 adult participants) and Shanghai (N=43 child participants) had filtration devices set up in their bedrooms. During the study, all participants experienced both true and sham (i.e., placebo, with the filters removed) filtration. Personal exposure to O3 was significantly lower than ambient levels due to low indoor concentrations. However, few conclusions can be drawn about the impacts of filtration on O3 and the micro-environmental exposure to O3 since indoor concentrations were so often below the detection limit of our monitors (6 ppb). Measurements suggested that indoor PM2.5 was primarily of outdoor origin (≥75%). Purifiers significantly reduced bedroom PM2.5 concentrations by 70% and 78% during true filtration in Shanghai and Beijing, respectively. The reduction to personal exposure was less prominent, but still significant (Shanghai=24% and Beijing=36%). The largest time-weighted exposure to PM2.5 occurred in the bedroom during sham filtration since children spent the most time there. This suggests that the bedroom is the most important environment to tackle to reduce personal exposure. True filtration reduced the contribution of the bedroom micro-environment below that of the classroom and other rooms at home, highlighting that the classroom and other home environments should be the next-microenvironments to be address to reduce these children’s exposure. These results highlight the importance of reducing outdoor PM2.5 levels, but show that Chinese residents can reduce their PM2.5 exposure by installing an effective air purifier in the indoor environment where they spend the most time. Reductions in multiple micro-environments are likely required to further reduce exposure to PM2.5.

The study and application of materials possessing size dimensions in the nano scale range and, as a result, unique properties have led to the birth of a new field; nanotechnology. Scientists and engineers have discovered and are exploiting the novel physicochemical characteristics of nanoparticles (NPs) to enhance consumer products and technologies in ways superior to their bulk counterparts. Escalating production and use of NPs will unavoidably lead to release and exposure to environmental systems. This introduction of emerging potential contaminant NPs will provide new and interesting challenges for exposure and risk forecasting as well as environmental endurance.

The ultimate goal of this research is to develop a framework that incorporates experimental and computational efforts to assess and better understand the exposure of metal and metal-oxide NPs released to wastewater treatment plants (WWTPs) and further implications on land application units (LAUs) where biosolids can be applied. The foundation of the computational effort is comprised of Monte Carlo mass balance models that account for the unique processes affecting NP fate and transport through the different technical compartments of a WWTP and LAU. Functional assay and bioreactor experiments in environmental media were used to determine parameters capable of describing the critical processes that impact the fate of NPs in wastewater.

The results of this research indicate that a simplified, but still environmentally relevant nano-specific exposure assessment is possible through experimentation to parameterize adapted models. Black box modeling efforts, which have been shown in previous studies, show no disadvantage relative to discretization of technical compartments as long as all key transport and fate mechanisms are considered. The distribution coefficient (_), an experimentally determined, time-dependent parameter, can be used to predict the distribution of NPs between the liquid and solid phase in WWTPs. In addition, this parameter can be utilized a step further for the estimation of the more fundamental, time independent attachment efficiency between the NPs and the solids in wastewater. The NP core, size, and surface coating will influence the value of these parameters in addition to the background particle characteristics as the parameters are specific to the environmental system of study. For the metal and metal-oxide NPs studied, preferential overall association of approximately 90% or greater with the solid phase of wastewater was observed and predicted.

Furthermore, NP transformations including dissolution, redox reactions, and adsorption can potentially impact exposure. For example, experimental results showed that nano-CeO2 is reduced from Ce(IV) to Ce(III) when in contact with wastewater bacteria where Ce2S3 will likely govern the Ce(III) phase in biosolids. From the literature, similar transformations have been observed with Ag and ZnO NPs to Ag2S and ZnS. With respect to TiO2 NPs, studies indicated that due to high insolubility, these NPs would not undergo transformation in WWTPs. The distribution and transformation rate coefficients can then be used in fate models to predict the NP species exposed to aquatic and terrestrial systems and environmentally relevant concentrations released from WWTPs.

Upon completion of the WWTP model, the predicted concentrations of NPs and NP transformation byproducts released in effluent and biosolids were attainable. A simple mass balance model for NP fate in LAUs was then developed to use this output. Results indicate that NP loading on LAUs would be very low but that build up over time to steady state could result in mass concentrations on the order of the typical level for the background metal in soil. Transport processes of plant uptake and leaching were expected to greatly impact the solid phase concentration of the NPs remaining in the LAU, while rainfall did not impart a significant influence upon variation between low and high annual amounts. The significance of this research is the introduction of a method for NP exposure assessment in WWTPs and subsequently in LAUs. This work describes and quantifies the key processes that will impact Ag, TiO2, CeO2 and ZnO NP fate and transport, which can inform future studies, the modeling community and regulatory agencies.

Nanomaterials are being increasingly produced and used across a myriad of applications while their novel properties are still in the midst of being designed and explored. Thus the full implications of introducing these materials into the environment cannot be understood, yet the need to assess potential risks is already upon us. This work discusses a comprehensive view of environmental impact with respect to material flows from across the value chain into all compartments of the environment, whereby interactions and potential hazardous effects become possible. A subset of this broad system is then chosen for evaluation; a model is derived to describe the fate of nanomaterials released to wastewater.

This analysis considers the wastewater treatment plant (WWTP) as a complete mixed reactor aerobic secondary clarifier, and predicts whether nanomaterials will associate with effluent or sludge to project potential concentrations in each. The concentration of nanomaterials reaching a WWTP is estimated based on a linear weighting of total production, and the fate of nanomaterials within the WWTP is based on a characteristic inherent to the material, partition coefficient, and on design parameters of the WWTP, such as retention times and suspended solids concentration.

Due to the uncertainty inherent to this problem, a probabilistic approach is employed. Monte Carlo simulation is used, sampling from probability distributions assigned to each of the input parameters to calculate a distribution for the predicted concentrations in sludge and effluent. Input parameter distributions are estimated from values reported in the literature where possible. Where data do not yet exist, studies are carried out to enable parameter estimation. In particular, nanomaterial production is investigated to provide a basis to estimate the magnitude of potential exposure. Nanomaterial partitioning behavior is also studied in this work, through laboratory experiments for several types of nano-silver.

The results presented here illustrate the use of nanomaterial inventory data in predicting environmentally relevant concentrations. Estimates of effluent and sludge concentrations for nano-silver with four different types coatings suggest that these surface treatments affect the removal efficiency; the same nanomaterial with different coatings may have different environmental fates. Effluent concentration estimates for C60 and nano-TiO2 suggest that these nanomaterials could already be present at problematic concentrations at current levels of annual production.

Estimates of environmentally relevant concentrations may aid in interpretation of nanotoxicology studies. These relative estimates are also useful in that they may help inform future decisions regarding where to dedicate resources for future research. Beyond attempting to estimate environmental concentrations of nanomaterials, this type of streamlined model allows the consideration of scenarios, focusing on what happens as various input parameters change. Production quantity and the fraction of this quantity that is released to wastewater are found to greatly influence the model estimates for wastewater effluent concentrations; in the case of wastewater sludge concentrations, the model is sensitive to those parameters in addition to solids retention time.

Background: Brick kiln workers in Nepal are a neglected population who are exposed to high concentrations of respirable silica. We aimed to characterize the prevalence of respiratory personal protective equipment (PPE) use, understand knowledge and attitudes towards kiln dust and respiratory PPE, and identify factors associated with current respiratory PPE use among brick kiln workers in Nepal. Methods: We conducted a cross-sectional study in Bhaktapur, Nepal. We used simple random selection to identify 10 out of 64 total kilns and stratified random sampling to enroll workers aged ≥14 years and household members aged ≥9 years within selected kilns. Field workers surveyed participants using structured questionnaires. Our primary outcome was to characterize prevalence of current respiratory PPE use, and secondary outcomes were summaries of knowledge, attitudes, and practice of PPE use. Results: We surveyed 83 workers (mean age 30.8 years, 77.1% male). Of these, 28.9% reported current respiratory PPE use at work. 3.6% of workers heard of silicosis prior to the survey and 24.1% correctly identified the best respiratory PPE for reducing dust exposure. Respiratory PPE users had higher income (non-brick kiln season mean monthly household income USD 206 vs. 145) and education levels (25% vs. 5.1% completed more than primary school) compared to non-users. Conclusions: Prevalence of respiratory PPE use was low. Workers had poor knowledge of kiln dust health effects and proper respiratory PPE. We highlight important barriers to PPE use, particularly knowledge gaps, which can guide future investigations to reduce silicosis burden among brick kiln workers.