Biomedical subjects

R D Waters

Publications and source records attributed to R D Waters.

3 recordsLinked to original sources

PubMed1999

Reliability analysis for hazardous waste treatment processes.

The reliability of a treatment process is addressed in terms of achieving a regulatory effluent concentration standard and the design safety factors associated with the treatment process. This methodology was then applied to two aqueous hazardous waste treatment processes: packed tower aeration and activated sludge (aerobic) biological treatment. The designs achieving 95 percent reliability were compared with those designs based on conventional practice to determine their patterns of conservatism. Scoping-level treatment costs were also related to reliability levels for these treatment processes. The results indicate that the reliability levels for the physical/chemical treatment process (packed tower aeration) based on the deterministic safety factors range from 80 percent to over 99 percent, whereas those for the biological treatment process range from near 0 percent to over 99 percent, depending on the compound evaluated. Increases in reliability per unit increase in treatment costs are most pronounced at lower reliability levels (less than about 80 percent) than at the higher reliability levels (greater than 90 percent, indicating a point of diminishing returns. Additional research focused on process parameters that presently contain large uncertainties may reduce those uncertainties, with attending increases in the reliability levels of the treatment processes.

Aerobiosis↗

PubMed1996

Risks from radionuclide migration to groundwater in the Chernobyl 30-km zone.

Remediation of contaminated groundwater in the Chernobyl 30-km evacuation zone is frequently identified as a priority by technical experts and Chernobyl site officials in Ukraine. In order to evaluate the health risk basis for this groundwater remediation, we have estimated both on-site and off-site health risks caused by radionuclide migration to the groundwater and compared these risks with those from exposure to radioactive contamination on the ground surface. A simple and conservative analytical model was developed to assess radionuclide transport to the groundwater from the soil surface contaminated by radioactive fallout. 90Sr, the primary radioactive contaminant of concern for the groundwater-migration exposure pathway, was evaluated in the analysis. The estimated health risk to hypothetical, self-sufficient residents in the 30-km zone is dominated by external and internal irradiation (due primarily to ingestion of agricultural products) from 137Cs, which is present in soils of the 30-km zone in roughly equal proportion with 90Sr. The estimated risk from contaminated groundwater is approximately an order of magnitude lower. Analysis of 90Sr migration via groundwater to surface water and down-river population centers shows that, despite generally unfavorable environmental conditions in the 30-km exclusion zone, radionuclide transport via the groundwater pathway has potential to contribute only marginally to the off-site radiological risk, which is governed by wash-out of radionuclides from the contaminated river flood plain and catchment areas by surface water during spring snowmelt and rains. Health risks due to off-site radionuclide migration via groundwater are below the level requiring application of counter-measures. This analysis implies that, relative to other exposure pathways, there is little current or future health risk basis for the proposed complex and costly groundwater remediation measures in the 30-km zone. Therefore, these activities should be abandoned in favor of more pressing health issues caused by the Chernobyl accident.

Humans↗

PubMed1989

On the natural enrichment of cadmium and molybdenum in the sediments of Ucluelet Inlet, British Columbia.

Cadmium concentrations in Ucluelet Inlet sediments are usually high compared with most marine environments, ranging up to 8 micrograms g-1. The distribution of the element is closely correlated with Mo, organic carbon and total nitrogen in depth profiles at three stations. Paradoxically, organic carbon concentrations are high in inlet sediments, reaching up to 9 wt.%, although the sedimentation rate determined from 210Pb measurements is low at all three sites (less than 0.03 to 0.28 cm year-1). C:N ratio data indicate a mixed marine-terrigenous provenance for the organic material and a relatively recent increase in the terrigenous proportion which probably represents wood debris associated with logging and log booming activity in the area. The complete absence of Mn enrichments in surface sediments, coupled with qualitative observations that H2S is present at very shallow depths, strongly suggest that the deposits are anoxic very near the sediment-water interface. The Cd and Mo enrichments are not due to anthropogenic inputs but are instead ascribed to diffusion of the dissolved metals from overlying seawater into the slowly-accumulating, organic-rich, anoxic sediments and their fixation in the solid phase as CdS and as a coprecipitate with FeS, respectively.

British Columbia↗