Clay E. Easterly

Cytotoxic activity of spark‐decomposed sulfur hexafluoride and analysis of cytotoxic contributions of individual spark decomposition products†

Sulfur hexafluoride decomposed by electrical sparks has been found to by cytotoxic to hamster cells when tested in an in vitro cell survival assay, while SF6 shows no cytotoxic activity. Chemical analysis of spark‐decomposed SF6 has identified and quantified the following compounds: SOF2, SO2F2, SF4, SOF4, SiF4, SO2 and HF. Each of these gases, at concentration ranges expected in spark‐decomposed SF6, were tested for cytotoxic activity toward hamster cells. Of the gases showing cytotoxic activity, SO2F2 and SOF4 were similar in activity, as were SOF2 and SF4, while the behavior of SiF4 was different from the rest. None of these individual gases, at concentrations expected in spark‐decomposed SF6, has sufficient cytotoxic activity to account for the cytotoxic effect of spark‐decomposed SF6 observed in our assay system. A four‐component mixture of some of the gases enumerated above (at concentrations overestimating their abundance in spark‐decomposed SF6) was much less cytotoxic than the spark‐decomposed SF...

Formaldehyde in drinking water: comparative hazard evaluation and an approach to regulation.

Formaldehyde, a widely used industrial chemical to which humans are ubiquitously exposed, presented cause for concern when it was demonstrated to be carcinogenic in laboratory animals. Risk assessment protocols subsequently applied to formaldehyde are of questionable validity in light of the results of recent mechanistic investigations of biological responses to formaldehyde. Further, the hazard of ingested formaldehyde is not addressed in current assessment protocols. This paper addresses the potential human health risks accompanying low-level exposure to formaldehyde as a contaminant in drinking water. In this exposure scenario, noncarcinogenic risk from inhalation of formaldehyde from drinking water is evaluated through knowledge of the metabolism and biological effects of formaldehyde exposure. Noncarcinogenic risk from ingestion of formaldehyde in drinking water is evaluated from the perspective gained by comparison with dietary sources of formaldehyde. Carcinogenic risk to humans is evaluated in light of recent investigations into the mechanisms underlying biological responses to formaldehyde exposure. Finally, based on a comparison of ingestion of formaldehyde in drinking water with ingestion of naturally occurring formaldehyde in foods, a comparative hazard approach to formaldehyde regulation is offered as a supplement to the rigid evaluation protocols currently used.

Environmental Effects of Fusion Power Plants. Part II: Tritium Effluents

Tritium releases from fusion reactors were estimated for normal (nonaccident) operating conditions. The STARFIRE reactor design was used as a reference case, but the effects of alternate design choices and conditions were also addressed. Potential environmental losses were examined for each of the major tritium handling systems. Estimates of --20 Ci/day were made for the 1000-MW (electric) reactor, with approximately equal portions coming from the gas handling systems (plasma, vacuum, and fuel systems) and from the coolant system.

A Meta-Analysis of the Epidemiological Evidence Regarding Human Health Risk Associated with Exposure to Electromagnetic Fields

There is evidence to suspect that a human health risk could exist from exposure to electromagnetic fields (EMF). Such a risk is likely to be very small and thus elusive to measure. This paper aims to evaluate the magnitude and manner of the potential human cancer risk associated with EMF exposure using the published literature. To accomplish this objective, a metaanalysis was performed with the published literature through 1991. Two conventional, summary techniques were used: geometric means and sample size weighing (Mantel-Haenszel). The summary risk estimates using these methods for cancer risk from EMF exposure are 1.6 and 2.0, respectively.Epidemiological studies are currently underway to address the EMF question and to measure EMF exposure more specifically. Until these studies are published and their results can be integrated into appropriate safety procedures, minimizing public health exposures is a prudent course.

Ranking of carcinogenic potency using a relative potency approach

Protocols for long-term carcinogen bioassays have become highly refined. The ability to interpret these bioassay results beyond the experimental setting, however, has not improved commensurately. As a consequence, society is still faced with the fact that data derived in these bioassays reflect highly specific experimental conditions which are vastly different from environmental exposures of the freely roaming, outbred human. The scientific community has responded with a “collective wisdom” approach by using expert committees to interpret bioassay evidence. This committee approach is believed to be successful in protecting human health, but the list of suspected carcinogens is growing faster than the expert committees can respond.We have developed a relative potency framework for ranking the hazards represented by potential human carcinogens. The results demonstrate a rank ordering of a variety of compounds which is independent of the reference compound used to standardize the information. The philosophic basis of the approach may facilitate expert risk assessment systems development because it: (1) complements and supports “expert committee” data selection; (2) has a simple set of rules and does not require mathematical modeling; (3) requires no special situation judgments; and (4) is suitable for use with electronic data bases.

Cell Membrane Potentials Induced During Exposure to EMP Fields

Internal current densities and electric fields induced in the human body during exposure to electromagnetic pulsed (EMP) fields are reviewed and used to predict resulting cell membrane potentials. Using several different approaches with a spherical cell model, membrane potentials of about 100 mV are predicted. These values are comparable to the static membrane potentials maintained by cells as a part of normal physiological function, but the EMP-induced potentials persist for only about 10 ns. Possible biological implications of EMP-induced membrane potentials include conformational changes and electroporation.

Spark decomposition of SF/sub 6/: chemical and biological studies

Because electric arcs, sparks or corona can decompose SF/sub 6/ insulators into byproducts having chemical properties different from SF/sub 6/, environmental concerns arise regarding inadvertent human exposures to electrically decomposed SF/sub 6/. Biological assays using mammalian cell culture systems have revealed that SF/sub 6/, spark-decomposed under specific experimental conditions, can produce cell death. Chemical analysis of spark-decomposed SF/sub 6/ has identified the major decomposition pathways and byproducts. Biological testing of individual byproduct mixtures has indicated that these major decomposition products may not account for the majority of the cell-killing effects seen in the assays. Further experiments have suggested that S/sub 2/F/sub 10/ may be produced and accumulate under the specific decomposition conditions and that this compound may be a major contributor to the observed cell lethality. It is concluded that testing of samples from commercial facilities and assays of decomposed gas after ameliorative treatments would both be appropriate investigations. >

Cardiovascular risk from exposure to static magnetic fields

The increasing potential for exposure to magnetic fields in science, industry and public sectors requires an assessment of the attendant potential biological consequences. At present, no model exists for such an assessment. Based on the physical principle of pressure loss when a conductive fluid moves through a magnetic field, a model of the cardiovascular system is used to estimate the potential increase in blood pressure in the presence of a magnetic field. This increased pressure, confined to the major arteries, along with epidemiological data, is used to provide the basis of a model which could be applied to make upper limit estimates of risk for blood pressure related health effects resulting from exposure to magnetic fields.

The effect of chronic environmental noise on the rate of hypertension : a meta-analysis

Abstract Critical reviews of noise on human human health, performed during the past 15 y have raised questions regarding the potential for noise to result in adverse health impacts. Previous syntheses have been based on critiques of methods used in individual works but have not attempted to provide quantitative evaluations of the collected works. Work described in this paper presents a synthesis of carefully selected investigations from the available literature, including a meta-analysis on selected data, in order to provide some insight into the possibility that chronic ambient noise is related to hypertension as a function of increasing noise levels. Given the large number of persons exposed to environmental noise sources, the strength of association between hypertension and cardiovascular disease, and the derived odds ratios for noise induced hypertension in this paper, noise may be one of the most important environmental factors presently being neglected within the regulatory arena.

Spark Decomposition of SF6: Chemical and Biological Studies

This paper presents a methodology which can be used to calculate underground cable ampacities and other cable parameters. Capabilities of the methodology include the ability to model both thermally and electrically the presence of conductors, shields, and neutrals in an underground cable system. Unbalanced phase currents associated with conductors connected in parallel and shied and neutral currents along with the effects of ground connections are calculated from the electrical circuit model and are used in the thermal analysis of the cable system. Temperature dependent parameters are determined based on calculated system temperatures. Solutions of both the thermal and electrical circuit models are performed in an iterative procedure until convergence based on conductor temperature occurs. Results from this procedure include not only the calculation of thermal parameters, such as cable ampacities and system temperatures, but also electrical parameters, such as cable voltage drops and open-circuited shield voltages. The temperature rise of a conductor due to conductor losses is based on the current in the conductor, its electrical resistance, and the thermal circuit through which the heat from the conductor losses flows. The current in the conductor is a result of the applied system voltage, the impedance of the electrical circuit, and the inductive coupling between other system conductors. Certain parameters with a cable system are temperature dependent, such as conductor electrical resistances (losses) and duct air space thermal resistances. System temperatures are usually not known precisely and initial estimates of certain temperature dependent parameters can lead to errors in the calculated results. To overcome this problem, a procedure can be implemented which utilizes calculated system temperatures in an iterative process, which stops when conductor temperatures have converged to a specified value. One such procedure which has been successfully implemented is illustrated as follows: