Showing papers by "Thomas C. Voice published in 2007"

Role of exposure analysis in solving the mystery of Balkan endemic nephropathy.

Abstract: We evaluated the role of exposure analysis in assessing whether ochratoxin A or aristolochic acid are the agents responsible for causing Balkan endemic nephropathy. We constructed a framework for exposure analysis using the lessons learned from the study of endemic goiter within the context of an accepted general model. We used this framework to develop an exposure analysis model for Balkan endemic nephropathy, evaluated previous findings from the literature on ochratoxin A and aristolochic acid in the context of this model, discussed the strength of evidence for each, and proposed approaches to address critical outstanding questions. The pathway for exposure to ochratoxin A is well defined and there is evidence that humans have ingested ochratoxin A. Factors causing differential exposure to ochratoxin A and how ochratoxin A is implicated in Balkan endemic nephropathy are not defined. Although there is evidence of human exposure to aristolochic acid and that its effects are consistent with Balkan endemic nephropathy, a pathway for exposure to aristolochic acid has been suggested but not demonstrated. Factors causing differential exposure to aristolochic acid are not known. Exposure analysis results suggest that neither ochratoxin A nor aristolochic acid can be firmly linked to Balkan endemic nephropathy. However, this approach suggests future research directions that could provide critical evidence on exposure, which when linked with findings from the health sciences, may be able to demonstrate the cause of this disease and provide a basis for effective public health intervention strategies. One of the key unknowns for both agents is how differential exposure can occur.

Separating surface storage from hyporheic retention in natural streams using wavelet decomposition of acoustic Doppler current profiles

Abstract: [1] The ability to separate surface storage (eg, due to in-channel features such as eddies and pools) from retention due to hyporheic exchange is important in many solute transport considerations; however, current stream tracer approaches do not allow such separation We examined transient storage processes in a fourth-order Michigan stream using tracer studies, numerical flow and transport models, and hydrodynamic data obtained from acoustic Doppler current profiler (ADCP) surveys Since the high-resolution, three-dimensional velocity fields obtained from an ADCP relate to in-channel processes, we used wavelet decomposition to separate the flow into regions of slow and fast moving zones and to estimate the relative sizes of the main channel (A) and the storage zones (AS) Transport modeling based on the tracer data provided estimates of storage zone sizes that included contributions from both surface storage and hyporheic exchange By coupling the estimates from tracer data with those obtained from an ADCP we were able to assess the relative importance of surface storage in different stream reaches Estimated (AS/A) values in three test reaches ranged from 012 to 022, and transient storage residence times varied from approximately 4 min in a run reach dominated by surface storage (reach A) to about 13 min in a reach with some potential for hyporheic exchange (reach C) In reach A the (AS/A) values estimated from tracer and ADCP data were in good agreement, indicating that in-channel processes were the main mechanism responsible for storage in this reach Reach C estimates, however, showed that surface storage (AS/A = 005) accounted for only a fraction of the transient storage estimated using tracer data (AS/A = 012), which indicated that hyporheic exchange contributed to transient storage in the reach The wavelet decomposition approach based on the ADCP data provides a framework to better constrain transient storage models and to eliminate unrealistic parameters

Settlement monitoring for bioreactor landfill airspace management

Abstract: Landfill operators depend on the available volume for waste placement, airspace, as their primary source of revenue. The ability to measure waste settlement and the corresponding increase in airspace is key to maximizing revenue and projecting cash flow. Waste settlement predictions in landfills are uncertain due to the inherent complexity of these systems and the relative scarcity of data. Bioreactor landfills, where moisture, nutrients, and temperature are optimized to accelerate waste degradation, are even less understood. In this paper, two experimental bioreactor landfills are considered: a filled 0.4-hectare cell in Harrison, Michigan, and a new 3-hectare cell in Smiths Creek, Michigan. Several pipes were installed and settlement profilers were used to measure the settlement within several discrete lifts. This data is valuable to understanding waste degradation and settlement as well as providing a valuable management tool to optimize bioreactor landfill operation and airspace utilization. This paper examines this application of settlement profilers and its value to bioreactor landfill engineers and owners. Preliminary results show promise for calibrating settlement estimates using these measurements