Changes In Activity Concentration Research Articles

Radon-222: environmental behavior and impact to (human and non-human) biota.

As an inert radioactive gas, 222Rn could be easily transported to the atmosphere via emanation, migration, or exhalation. Research measurements pointed out that 222Rn activity concentration changes during the winter and summer months, as well as during wet and dry season periods. Changes in radon concentration can affect the atmospheric electric field. At the boundary layer near the ground, short-lived daughters of 222Rn can be used as natural tracers in the atmosphere. In this work, factors controlling 222Rn pathways in the environment and its levels in soil gas and outdoor air are summarized. 222Rn has a short half-life of 3.82days, but the dose rate due to radon and its radioactive progeny could be significant to the living beings. Epidemiological studies on humans pointed out that up to 14% of lung cancers are induced by exposure to low and moderate concentrations of radon. Animals that breed in ground holes have been exposed to the higher doses due to radiation present in soil air. During the years, different dose-effect models are developed for risk assessment on human and non-human biota. In this work are reviewed research results of 222Rn exposure of human and non-human biota.

A COMPREHENSIVE CHARACTERISTIC OF 222Rn ACTIVITY CONCENTRATION CHANGES AND IONISING RADIATION EXPOSURE IN NEWLY DISCOVERED PARTS OF BEAR CAVE IN KLETNO, POLAND.

The article presents the results of research into 222Rn activity concentration changes and ionising radiation exposure in newly discovered parts of Bear Cave in Kletno, unknown until 2012. 222Rn activity concentration was registered at three measurement points located inside over 500-m-long newly discovered cave passages. The air in these parts of the cave is characterised by a stable temperature of about 5°C and a relative humidity of 100%. The measurements started in September 2013 and were completed by mid-July 2016. The measured data were recorded continuously, including hourly registration of 222Rn activity concentration with the use of three Polish semiconductor detectors SRDN-3a. Three data sets were obtained. Two of them, containing the same numbers of data, were recorded between 4 September 2013 and 10 July 2016 by SRDN-3a detectors no 7 and 9 located at sites no 1 and no 3, respectively. The third set comprises data registered between 27 October 2014 and 10 July 2016 by SRDN-3a probe no 8 at site no 2. Distinct daily changes in 222Rn activity concentration in the new parts of Bear Cave occur in early spring (from March to May) and in autumn (October). This observation confirms the notion that radon concentration changes depend on natural convective air exchange between the cave and the atmosphere. It has been shown that daily radon concentration changes in other seasons are irregular and rather small. The highest values of 222Rn activity concentration inside the cave are more frequent in daytime, i.e. from the morning to midday. The recorded annual mean values of 222Rn activity concentration in successive measurement years are comparable for all the three sites and range from 2690 to 3179Bqm-3 in 2013, from 2676 to 2973Bqm-3 in 2014, from 2587 to 2917Bqm-3 in 2015 and from 2581 to 3719Bqm-3 in 2016. These values exceed those recommended as maximum allowable radon concentrations in such spaces (0.5-1.5kBqm-3) and are many times as high as the values recommended for workplaces (0.3kBqm-3). The recorded values of 222Rn activity concentration in the air of the new parts of Bear Cave in Kletno result in a risk of exposure to a radiation dose higher than the national standard of 1mSv per year adopted for the general public. In the most unfavourable conditions, it appears as early as after 25hours spent inside the cave. The minimum effective dose to which a person staying inside the cave is exposed within 1hour is 0.002mSv, and the maximum dose is 0.04mSv. The results of the conducted measurements demonstrate the necessity of introducing appropriate solutions, crucial in terms of radiological protection and legislation, that would minimise the risk of exposure to ionising radiation in the new parts of Bear Cave.

Radiocesium in North Pacific coastal and offshore areas of Japan within several months after the Fukushima accident

We measured activity concentrations of radiocesium (134Cs and 137Cs) in seawater samples collected in North Pacific coastal and offshore areas of Japan within several months after the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident in March 2011, including archived seawater samples whose radiocesium concentrations were previously reported to be below detection limits. By merging 329 new data with published results, we succeeded in reconstructing the temporal changes in activity concentrations and inventories of FNPP1-derived radiocesium in the coastal and offshore areas within several months after the accident for the first time. 137Cs directly-discharged from the FNPP1 was transported eastward within the coastal area about 250 km from the FNPP1 during two months after the accident due to complex movements of coastal surface currents. The eastward speed was calculated to be about 5 cm s−1. Eastward transport of 137Cs to the offshore area more than 600 km away from the FNPP1 along the north flank of the Kuroshio Extension Current was faster (about 9 cm s−1) and probably more dominant in the eastward transport. The total inventory of directly-discharged 137Cs in early April 2011 was estimated to be 3–6 PBq approximately, which agrees with the smaller estimates in previous studies (2–6 PBq).

Effect of PET-MR Inconsistency in the Kernel Image Reconstruction Method.

Anatomically-driven image reconstruction algorithms have become very popular in positron emission tomography (PET) where they have demonstrated improved image resolution and quantification. This work, consider the effect of spatial inconsistency between MR and PET images in hot and cold regions of the PET image. We investigate these effects on the kernel method from machine learning, in particular, the hybrid kernelized expectation maximization (HKEM). These were applied to Jaszczak phantom and patient data acquired with the Biograph Siemens mMR. The results show that even a small shift can cause a significant change in activity concentration. In general, the PET-MR inconsistencies can induce the partial volume effect, more specifically the 'spill-in' of the affected cold regions and the 'spill-out' from the hot regions. The maximum change was about 100% for the cold region and 10% for the hot lesion using KEM, against the 37% and 8% obtained with HKEM. The findings of this work suggest that including PET information in the kernel enhances the flexibility of the reconstruction in case of spatial inconsistency. Nevertheless, accurate registration and choice of the appropriate MR image for the creation of the kernel is essential to avoid artifacts, blurring, and bias.

Surrogate potency assays: Comparison of binding profiles complements dose response curves for unambiguous assessment of relative potencies

Surface plasmon resonance (SPR) systems are widely used for detailed characterization of antibody activities including antigen and Fc-receptor binding. During the later stages of development, where the focus is to ensure that established critical quality attributes (CQAs) are maintained during cell culture, purification and formulation processes, analysis is simplified, and relative potencies are often determined. Here, simulation of binding data revealed that relative potency values, determined via parallel line analysis (PLA) and half maximal effective concentration (EC50) analysis accurately reflect changes in active concentration only if binding kinetics remain unchanged. Changes in the association rate constant shifted dose response curves, and therefore relative potencies, in the same way as changes in analyte concentration do. However, for interactions characterized by stable binding, changes in the dissociation rate constant did not result in any shift, suggesting that this type of change may go unnoticed in the dose response curve. Thus, EC50 and PLA analyses of dose response curves obtained with an anti-TNF-α antibody were complemented with the Biacore functionality for sensorgram comparison analysis, whereby changes in antigen and Fc-receptor binding profiles could be detected. Next, analysis of temperature stressed TNF-α antibody revealed that calibration free concentration analysis (CFCA) data correlated perfectly with relative potency values. Together, these results demonstrate that combinations of SPR based dose response curves, sensorgram comparison and CFCA can be used to strengthen the confidence in relative potency assessments, and suggest that SPR can potentially be used as a surrogate potency assay in the quality control of biotherapeutic medicines.

Study of Atmospheric Instabilities through Radioactivity

Radon and its progeny concentration are measured at 1m height from surface of Earth in the premises of National Atmospheric Research Laboratory, Gadanki to observe the changes in activity concentration of radon particularly during instabilities that are occurring in the atmosphere. The measurements were carried out using AlphaGUARD and Alpha Progeny Meter for the measurement of radon and its progenies, respectively. It has been observed that, the changes in daily and weekly atmospheric radon levels are related to the stability or turbulence of the lower troposphere. The analysis reveals that from sunny windless days indicates growth and dissolution of the inversion layer. The study of radon concentrations during several atmospheric instabilities including period during Nilam cyclone, has shown interesting features, which are correlated with the conditions of stability or turbulence in the atmosphere.

Atmospheric Instabilities through Radioactivity Study

The radon in the atmosphere is widely used as tracer. A campaign was conducted at National Atmospheric Research Laboratory, Gadanki, Andhra Pradesh to observe the changes in activity concentrations of radon particularly during instabilities that are occurring in the atmosphere. The observations were made at a height of 1m above from the surface of Earth using AlphaGUARD radon monitoring system that has an accuracy of 85%, which measures radon and Alpha Progeny Meter for the measurement of radon progenies. From the studies, it has been observed that the changes in daily and weekly atmospheric radon levels are accounted for some extent to the stability or turbulence of the lower troposphere. The analysis shows that during calm sunny days, the growth and dissolution of the inversion layer is based on the turbulence and is a measure of radon concentration near to the surface. The study of radon concentrations during several atmospheric instabilities are correlated with the conditions of stability or turbulence in the atmosphere.

Application of spectral decomposition of 222Rn activity concentration signal series measured in Niedźwiedzia Cave to identification of mechanisms responsible for different time-period variations

The authors present an application of spectral decomposition of 222Rn activity concentration signal series as a mathematical tool used for distinguishing processes determining temporal changes of radon concentration in cave air. The authors demonstrate that decomposition of monitored signal such as 222Rn activity concentration in cave air facilitates characterizing the processes affecting changes in the measured concentration of this gas. Thanks to this, one can better correlate and characterize the influence of various processes on radon behaviour in cave air. Distinguishing and characterising these processes enables the understanding of radon behaviour in cave environment and it may also enable and facilitate using radon as a precursor of geodynamic phenomena in the lithosphere. Thanks to the conducted analyses, the authors confirmed the unquestionable influence of convective air exchange between the cave and the atmosphere on seasonal and short-term (diurnal) changes in 222Rn activity concentration in cave air. Thanks to the applied methodology of signal analysis and decomposition, the authors also identified a third process affecting 222Rn activity concentration changes in cave air. This is a deterministic process causing changes in radon concentration, with a distribution different from the Gaussian one. The authors consider these changes to be the effect of turbulent air movements caused by the movement of visitors in caves. This movement is heterogeneous in terms of the number of visitors per group and the number of groups visiting a cave per day and per year. Such a process perfectly elucidates the observed character of the registered changes in 222Rn activity concentration in one of the decomposed components of the analysed signal. The obtained results encourage further research into precise relationships between the registered 222Rn activity concentration changes and factors causing them, as well as into using radon as a precursor of geodynamic phenomena in the lithosphere.

The activity concentration of post-Chernobyl ¹³⁷Cs in the area of the Opole Anomaly (southern Poland).

During the years 2007 and 2010, the activity concentration of (137)Cs accumulated in soil, mosses Pleurozium schreberi and lichens Hypogymnia physodes was measured. The studies covered the areas of the so-called Opole Anomaly. In consequence of the Chernobyl nuclear power plant breakdown in 1986, relatively large amounts of this radionuclide were deposited in this area. In some areas of the Anomaly, over 100 times higher surface activity of (137)Cs was detected, compared to the lowest values registered in Poland. Currently, (137)Cs is still present in woodlands and wastelands. As at 2 April 2013, the surface activity concentration of (137)Cs in soil on the tested area was from 0.34 to 67.5kBqm(-2). In comparison, the surface activity concentration of (137)Cs as at 1 June 1986, soon after deposition, was from 2.08 to over 125kBqm(-2). The maximum specific activity concentrations of (137)Cs in mosses and lichens sampled for testing in 2010 were respectively 1234 and 959Bqkg(-1). It was also proven that the changes in activity concentration of (137)Cs in the area of the Anomaly are mainly the consequence of the radioactive decay of this radionuclide.

Short-term radon activity concentration changes along the Underground Educational Tourist Route in the Old Uranium Mine in Kletno (Sudety Mts., SW Poland)

Short-term 222Rn activity concentration changes along the Underground Educational Tourist Route in the Old Uranium Mine in Kletno were studied, based on continuous measurements conducted between 16 May 2008 and 15 May 2010. The results were analysed in the context of numbers of visitors arriving at the facility in particular seasons and the time per day spent inside by staff and visitors. This choice was based on partially published earlier findings (Fijałkowska-Lichwa and Przylibski, 2011). Results for the year 2009 were analysed in depth, because it is the only period of observation covering a full calendar year. The year 2009 was also chosen for detailed analysis of short-term radon concentration changes, because in each period of this year (hour, month, season) fluctuations of noted values were the most visible. Attention has been paid to three crucial issues linked to the occurrence and behaviour of radon and to the radiological protection of workers and visitors at the tourist route in Kletno.The object of study is a complex of workings in a former uranium mine situated within a metamorphic rock complex in the most radon-prone area in Poland. The facility has been equipped with a mechanical ventilation system, which is turned on after the closing time and at the end of the working day for the visitor service staff, i.e. after 6 p.m.Short-term radon activity concentration changes along the Underground Educational Tourist Route in the Old Uranium Mine in Kletno are related to the activity of the facility's mechanical ventilation. Its inactivity in the daytime results in the fact that the highest values of 222Rn activity concentration are observed at the time when the facility is open to visitors, i.e. between 10 a.m. and 6 p.m.The improper usage of the mechanical ventilation system is responsible for the extremely unfavourable working conditions, which persist in the facility for practically all year. The absence of appropriate radiological protection (i.e. preventive measures like shortening working day, dosimetric measurements in the workplace) is a serious problem in the Kletno adit.

Short-term <sup>222</sup>Rn activity concentration changes in underground spaces with limited air exchange with the atmosphere

Abstract. The authors investigated short-time changes in 222Rn activity concentration occurring yearly in two underground tourist facilities with limited air exchange with the atmosphere. One of them is Niedźwiedzia (Bear) Cave in Kletno, Poland – a natural space equipped with locks ensuring isolation from the atmosphere. The other site is Fluorite Adit in Kletno, a section of a disused uranium mine. This adit is equipped with a mechanical ventilation system, operated periodically outside the opening times (at night). Both sites are situated within the same metamorphic rock complex, at similar altitudes, about 2 km apart. The measurements conducted revealed spring and autumn occurrence of convective air movements. In Bear Cave, this process causes a reduction in 222Rn activity concentration in the daytime, i.e. when tourists, guides and other staff are present in the cave. From the point of view of radiation protection, this is the best situation. For the rest of the year, daily concentrations of 222Rn activity in the cave are very stable. In Fluorite Adit, on the other hand, significant variations in daily 222Rn activity concentrations are recorded almost all year round. These changes are determined by the periods of activity and inactivity of mechanical ventilation. Unfortunately this is inactive in the daytime, which results in the highest values of 222Rn activity concentration at the times when tourists and staff are present in the adit. Slightly lower concentrations of radon in Fluorite Adit are recorded in the winter season, when convective air movements carry a substantial amount of radon out into the atmosphere. The incorrect usage of mechanical ventilation in Fluorite Adit results in the most unfavourable conditions in terms of radiation protection. The staff working in that facility are exposed practically throughout the year to the highest 222Rn activity concentrations, both at work (in the adit) and at home (outside their working hours). Therefore, not very well considered solution for the ventilation system not only does not prevent radioactive exposure of the staff, but can even increase it. The authors have also observed comparable characteristics of the annual patterns of 222Rn activity concentration changes in underground spaces and residential buildings situated in the same or similar climatic zones.

NORM risk assessment for the Søve mining complex, Norway

The Sove site is a disused mining complex in Telemark County, Norway, exhibiting enhanced levels of naturally occurring radionuclides from the 238 U and 232 Th decay series. The nascent General Assessment Methodology Process (‘GAMP’), developed under IAEA’s EMRAS II programme, has been applied at the site. The a priori fixed screening criteria were exceeded in the scenario, precipitating the requirement to undertake a more detailed assessment. The USDOE’s RESRAD-OFFSITE code was employed to investigate potential changes in activity concentrations in various environmental compartments over time and the contribution of various exposure pathways to effective doses. Owing to problems associated with model parameterisation and results interpretation a simple leaching and groundwater migration compartmental model was also applied. This allowed activity concentrations in three waste compartments to be calculated with time. Furthermore, an existing external dose-rate model that correlates information on activity concentrations with depth in soil to dose rates in air above ground has been used to estimate prospective external dose-rates to humans and evaluate the efficacy of applying various remediation options.

Numerical Study on Tritium Behavior by Using Isotope Exchange Reactions in Thermochemical Water-Splitting Iodine—Sulfur Process

One potential problem in the hydrogen production system coupled with the high-temperature gascooled reactor (HTGR) is transmission of tritium from the primary coolant to the product hydrogen by permeation through the heat transfer tubes. Tritium accumulation in the process chemicals in the components of a hydrogen plant, a thermochemical water-splitting iodine-sulfur (IS) process, will also be a critical issue in seeking to license the hydrogen plant as a non-nuclear plant in the future. A numerical analysis model for tritium behavior in the IS process was developed by considering the isotope exchange reactions between tritium and the hydrogen-containing process chemicals, i.e., H2O, H2SO4 and HI. The tritium activity concentration in the IS process coupled with the high-temperature engineering test reactor (HTTR), the HTTR-IS system, was preliminarily evaluated in regard to the effects of some indeterminate parameters, i.e., equilibrium constants of the isotope exchange reactions, permeability of tritium through heat transfer tubes, tritium and hydrogen concentrations in the secondary helium coolant, and the leak rate from the secondary coolant loop. The results describing how the tritium activity concentration changes with variations in these parameters and which component has the maximum tritium activity concentration in the IS process are described in this paper.

The transfer of different forms of 35S to goat milk

Sulphur-35 is released during the routine operation of UK gas-cooled reactors. An experiment to determine the rates of transfer of different forms of 35S to goat milk is described. Lactating goats received 35S orally as single administrations of sulphate, l-methionine, or grass contaminated either through root uptake of 35S as sulphate or through aerial deposition of 35S as carbonyl sulphide onto the grass. Transfer was higher for 35S administered as methionine compared with 35S administered as sulphate. Changes in activity concentrations in milk for all sources of 35S demonstrated two components of loss. The first component had a half-life of circa 1 d for all sources, the second was longer in goats administered carbonyl sulphide (44 d) than in all of the other treatments ( circa 10 d). The rate of transfer of 35S to milk of a further group of goats receiving 35S-sulphate daily appeared to reach equilibrium within 30 d. Extrapolation of transfer parameters derived to other dairy ruminants is discussed.

Numerical Study on Tritium Behavior by Using Isotope Exchange Reactions in Thermochemical Water-Splitting Iodine–Sulfur Process

One potential problem in the hydrogen production system coupled with the high-temperature gascooled reactor (HTGR) is transmission of tritium from the primary coolant to the product hydrogen by permeation through the heat transfer tubes. Tritium accumulation in the process chemicals in the components of a hydrogen plant, a thermochemical water-splitting iodine-sulfur (IS) process, will also be a critical issue in seeking to license the hydrogen plant as a non-nuclear plant in the future. A numerical analysis model for tritium behavior in the IS process was developed by considering the isotope exchange reactions between tritium and the hydrogen-containing process chemicals, i.e., H2O, H2SO4 and HI. The tritium activity concentration in the IS process coupled with the high-temperature engineering test reactor (HTTR), the HTTR-IS system, was preliminarily evaluated in regard to the effects of some indeterminate parameters, i.e., equilibrium constants of the isotope exchange reactions, permeability of tritium through heat transfer tubes, tritium and hydrogen concentrations in the secondary helium coolant, and the leak rate from the secondary coolant loop. The results describing how the tritium activity concentration changes with variations in these parameters and which component has the maximum tritium activity concentration in the IS process are described in this paper.

Study on poly depletion in sub-0.1 μm metal–oxide–semiconductor field effect transistors by scanning capacitance microscopy

We study the relative changes in active concentrations in the n- and p-type poly gates of 90 nm node metal–oxide–semiconductor field effect transistors (MOSFETs) by scanning capacitance microscopy on beveled and backside etched samples. We polished and etched from the backside of MOSFETs to expose the bottom of poly gates. Measurements at different Lg show that the boron and phosphorus concentrations in short-channel devices are lower than in long-channel ones. By using staircase calibration standards and NIST FACTC2D, we estimate that boron concentration is reduced by about 5× while phosphorus concentration is reduced by about 2× when Lg shrinks from 10 μm to 50 nm. The effects of high-frequency voltage on quantitatively determining the dopant concentration are discussed. By beveling the poly, we are able to get the lateral dc/dv profiles in Lg=50 nm MOSFETs. The active boron concentration is lower at the p-poly edge while the phosphorus profile is flatter in n-poly.

Predicting transfers of137Cs in terrestrial and aquatic environments: A whole-ecosystem approach

lt is well known that during the years after a nuclear accident the bioavailability and environmental mobility of radionuclides may change significantly, resulting in significant changes in contamination of foodstuffs and surface waters. Studies on l 3 7Cs and, to a lesser extent, Sr, have quantified these changes in some ecosystems. However, variability in temporal changes of these radionuclides in aquatic and terrestrial systems is not yet well quantified. Estimation of such variability is a key component of any predictive model for long-term transfers of radionuclides in the environment. We have analysed measurements (from both weapons testing and Chernobyl deposits) of 1 3 ,Cs in runoff waters and in aquatic and terrestrial foodstuffs in order to determine temporal changes in their bioavailability and mobility. Using these empirical data, and the results of parallel modelling studies of vertical migration of radiocaesium in soils, we have quantified the relative importance of transport processes of l 3 7Cs, as compared to slow changes in its chemical availability in the soil. On the basis of these results, we have developed simple models for predicting time changes in activity concentrations of l 3 7Cs in surface water, foodstuffs and the human body during the years to decades after radioactive fallout. Importantly, we also determine uncertainties in model parameter estimates, and highlight the potential causes of this uncertainty.

High resolution SPECT in small animal research.

Single Photon Emission Computed Tomography (SPECT) is a technique used to assess physiological and biochemical processes under in vivo conditions. SPECT generates tomographic images from blood flow, glucose metabolism and receptor characteristics using radioactively labelled substances. This paper reviews the state of the art of in vivo imaging of laboratory animals in modified human and dedicated animal SPECT scanners. SPECT cameras with special collimators currently reach spatial resolutions up to 1 mm and sensitivities of about 1000 cps/MBq, allowing observation of receptor activity concentration changes in the pico-mole range. The time resolution of such cameras strongly depends on the pharmacological behaviour of the tracer and can range from several minutes to hours. Within these limits the functional characterization of many processes is possible. SPECT also offers the possibility to set up dynamic study protocols and repeated measurements of the same animal. This technique reduces the need for sacrificing animals, as was commonly practiced before the development of animal cameras. Animal SPECT gives the opportunity to monitor physiological and biochemical processes in animals in vivo, without interfering with the system under observation, and may become a valuable adjunct to the instrumentation (autoradiography, in vitro methods) of animal research.

Optimization of PET activation studies based on the SNR measured in the 3-D Hoffman brain phantom.

This work investigates the noise properties of O-15 water PET images in an attempt to increase the sensitivity of activation studies. A method for computing the amount of noise within a region of interest (ROI) from the uncertainty in the raw data was implemented for three-dimensional (3-D) positron emission tomography (PET). The method was used to study the signal-to-noise ratio (SNR) of regions-of-interest (ROI's) inside a 3-D Hoffman brain phantom. Saturation occurs at an activity concentration of 2.2 mCi/l which corresponds to a 75-mCi O-15 water injection into a normal person of average weight. This establishes the upper limit for injections for human brain studies using 3-D PET on the Siemens ECAT 921 EXACT scanner. Data from human brain activation studies on four normal volunteers using two-dimensional (2-D) PET were analyzed. The biological variation was found to be 5% in 1-ml ROI's. The variance for a complete activation study was calculated, for a variety of protocols, by combining the Poisson noise propagated from the raw data in the phantom experiments with the biological variation. A protocol that is predicted to maximize the SNR in dual-condition activation experiments while remaining below the radiation safety limit is: ten scans with 45 mCi per injection. The data should not be corrected for random or scatter events since they do not help in the identification of activation sites while they do add noise to the image. Due to the lower noise level of 3-D PET, the threshold for detecting a true change in activity concentration is 10%-20% lower than 2-D PET. Because of this, a 3-D activation experiment using the Siemens 921 scanner requires fewer subjects for equal statistical power.

Cytotoxic and cytolytic activity of nonadecafluoro-n-decanoic acid on Acholeplasma laidlawii.

We studied the interactions between the perfluorinated fatty acid nonadecafluoro-n-decanoic acid (NDFDA) and the cell wall-less procaryote Acholeplasma laidlawii, which were cultured in an identical medium base but with different serum supplements. When grown in mycoplasma media supplemented with PPLO serum fraction (Difco Laboratories, Detroit, Mich.), A. laidlawii was rapidly killed by low concentrations of toxicant (less than 1.0 mM). At higher concentrations (greater than 10 mM), NDFDA treatment appeared to lyse cells. A. laidlawii cells grown in horse serum-supplemented mycoplasma media were both killed and lysed at the same NDFDA concentration (greater than 10 mM). These data suggest that this perfluorinated fatty acid can be cytotoxic and cytolytic to mycoplasmas. Changes in active concentrations occurred in parallel with changes in growth medium serum supplementation, which is known to alter mycoplasma membrane composition. We propose that NDFDA interacts with the membranes of A. laidlawii cells, resulting in cell death or cell lysis or both.