Biomedical subjects

Margaret M MacDonell

Publications and source records attributed to Margaret M MacDonell.

3 recordsLinked to original sources

PubMed2004

Engineered containment and control systems: nurturing nature.

The development of engineered containment and control systems for contaminated sites must consider the environmental setting of each site. The behaviors of both contaminated materials and engineered systems are affected by environmental conditions that will continue to evolve over time as a result of such natural processes as climate change, ecological succession, pedogenesis, and landform changes. Understanding these processes is crucial to designing, implementing, and maintaining effective systems for sustained health and environmental protection. Traditional engineered systems such as landfill liners and caps are designed to resist natural processes rather than working with them. These systems cannot be expected to provide long-term isolation without continued maintenance. In some cases, full-scale replacement and remediation may be required within 50 years, at an effort and cost much higher than for the original cleanup. Approaches are being developed to define smarter containment and control systems for stewardship sites, considering lessons learned from implementing prescriptive waste disposal regulations enacted since the 1970s. These approaches more effectively involve integrating natural and engineered systems; enhancing sensors and predictive tools for evaluating performance; and incorporating information on failure events, including precursors and consequences, into system design and maintenance. An important feature is using natural analogs to predict environmental conditions and system responses over the long term, to accommodate environmental change in the design process, and, as possible, to engineer containment systems that mimic favorable natural systems. The key emphasis is harmony with the environment, so systems will work with and rely on natural processes rather than resisting them. Implementing these new integrated systems will reduce current requirements for active management, which are resource-intensive and expensive.

Journal Article↗

PubMed2002

Synergy and other ineffective mixture risk definitions.

A substantial effort has been spent over the past few decades to label toxicologic interaction outcomes as synergistic, antagonistic, or additive. Although useful in influencing the emotions of the public and the press, these labels have contributed fairly little to our understanding of joint toxic action. Part of the difficulty is that their underlying toxicological concepts are only defined for two chemical mixtures, while most environmental and occupational exposures are to mixtures of many more chemicals. Furthermore, the mathematical characterizations of synergism and antagonism are inextricably linked to the prevailing definition of 'no interaction,' instead of some intrinsic toxicological property. For example, the US EPA has selected dose addition as the no-interaction definition for mixture risk assessment, so that synergism would represent toxic effects that exceed those predicted from dose addition. For now, labels such as synergism are useful to regulatory agencies, both for qualitative indications of public health risk as well as numerical decision tools for mixture risk characterization. Efforts to quantify interaction designations for use in risk assessment formulas, however, are highly simplified and carry large uncertainties. Several research directions, such as pharmacokinetic measurements and models, and toxicogenomics, should promote significant improvements by providing multi-component data that will allow biologically based mathematical models of joint toxicity to replace these pairwise interaction labels in mixture risk assessment procedures.

Animals↗

PubMed2002

Volume and activity of buried transuranic-contaminated wastes at U.S. Department of Energy facilities.

From the 1940's through the 1970's, radioactive wastes meeting the current definition of transuranic wastes were disposed of by shallow land burial and other techniques at a number of sites owned and operated by the federal government in support of the nuclear weapons program. After transuranic wastes were identified as a separate category of radioactive wastes (distinct from low-level wastes) in 1970 by the U.S. Atomic Energy Commission, they were generally segregated and placed in retrievable storage pending the availability of a geologic repository. Updated information on buried transuranic wastes was recently developed to support future decisions on how to manage these materials. This paper summarizes the approach used to develop this information for U.S. Department of Energy facilities and presents the volumes and transuranic activities of these wastes. The total volume of buried transuranic wastes at DOE sites is approximately 126,000 m3 with a much smaller volume (about 11,000 m3) disposed of at intermediate depths. The reported transuranic activity in these previously disposed of wastes is about 28,000 TBq.

Radioactive Waste↗