Lethal Method

For assessment of dominant lethals, it is essential to avoid noise as much as possible. The largest fraction of the experimental noise comes from embryos that die from recessive lethals accumulated in the genome of the strains used. Since many recessive lethal mutations occur spontaneously and are accumulated in the genome, these cannot be distinguished phenotypically from dominant lethals. Hence, the use of inbred or narrowly maintained strains should be avoided. Instead, the test of dominant lethals using a hybrid will prove to be much more useful. 

Experiments on dominant lethal induction in this insect have been carried out extensively by Tazima with X or 7 rays, and the silkworm was found to be rather insensitive to ionizing radiation in the induction of dominant e-thals. Induction rates per kR are in the range of 0.62-3.75% for spermato- 

Experimental data with chemical mutagens have been scanty in the silkworm. Recently, Datta et studied the induction rate of dominant lethals with the well-known mutagen EMS. They used as material Nistari, a strain indigenous to India. The chemical was administered by injection at a dose of 0.04 ml per insect. Three different concentrations, 0.05, 0.10, and 0.15%, were prepared in 0.75% aqueous solution of NaCl, and all these concentrations were injected at three different developmental stages of the silkworm the 5th instar larvae Just after the 4th molt and 2-day-old and 7-day-old pupae. 

Their data indicated that the relative sensitivity to EMS is lower in spermatocytes than in spermatids and spermatozoa. Since the administered doses were too high for the latter highly sensitive cells, the data were inadequate for drawing dose-mutation curves. But they got a clear relationship curve for treated spermatocytes, which showed a rapid increase with increasing concentration of the chemical. 

Similar experiments were carried out by Murota and Murakami using methyl methanesulfonate (MMS), EMS, DES, mitomycin C (MMC), and X rays. By calculation, 0.05% EMS used by Datta corresponds to 1.6 X 10 M/g (assuming the average body weight of male pupa of Nistari to be 1 g). For this concentration, the induced rates of dominant lethals are 14.2% in Murota s experiment and 39.0% in that of Datta et Whether or not the dis- 

---

Baker RF, Blanchfield PJ, Paterson MJ, Flett RJ, Wesson L. 2004. Evaluation of non-lethal methods for the analysis of mercury in fish tissue. Trans Am Fish Soc 133 568-576. 

These contrasting characteristics make Bombyx worthy to work on in the study of mutagenesis even if it lacks several advantages of Drosophila. Although, in Bombyx a suitable sex-linked recessive lethal method is not yet available, instead, a specific locus method is conveniently used, and the work to be reviewed in this chapter was mostly performed using this method. 

Several methods have been used in the silkworm for the quantitative assessment of mutations induced by radiation and/or chemical agents. These are the specific locus method, the recessive lethal method,the dominant lethal method, and the method for detection of nondisjunction. A recessive lethal method assesses lethal mutations occurring on a whole genome and is used for the study of both spontaneously accumulated and radiation-induced lethals in the silkworm. Th system, however, is rather complicated and tedious and will not be dealt with in this article. 

Clearly, some bacterial vaccines work exceedingly well at controlling disease. However, basic questions remain about the dose, duration of protection and whether or not boosters are needed. There have been questions about the precise mode of action insofar as there is not always a correlation with antibody titre. Instead, it is appropriate to look towards cell-mediated and innate immunity. The current dominance of challenge methods to determine the potency of vaccines is emotive. Consideration needs to be given to the use of non-lethal methods although reliable alternatives are... 

Subsection B This subsection contains rules pertaining to the methods of fabrication of pressure vessels. Part UW is applicable to welded vessels. Service restric tions are defined. Lethal service is for lethal substances, which are defined as poisonous gases or liquids of such a nature that a very small amount of the gas or the vapor of the liquid mixed or unmixed with air is dangerous to life when inhaled. It is stated that it is the user s responsibility to advise the designer or manufacturer if the service is lethal. All vessels in lethal service shall have all butt-welded joints fully radiographed, and when practical, joints shall be butt-welded. All vessels fabricated of carbon or low-aUoy steel shall be postweld-heat-treated. 

The last arrangement of voltage feedbaek is the isolated feedback. This is used when the input voltage is eonsidered lethal to the operator of the equipment (>42.5 VDC). The two aeeepted methods of eleetrieal isolation are optical (optoisolator) or magnetic (transformer). This seetion will talk about the more eommon method of isolation, when an optoisolator is used to isolate the lethal portions of the eireuit from the operator portion. The optoisolator s Ct (eurrent transfer ratio (or drifts with temperature, ean degrade slightly with age,... 

Parenteral lethality was determined by injecting rabbits of mixed sexes intraperitoneally with 31.6, 63, 126, 252, and 500 /xg/kg of 2,3,7,8-TCDD as a 0.01% corn oil suspension control rabbits were injected with corn oil. The rabbits were housed in individual holding cages and were observed for signs of toxicity for four weeks. The LDso s were calculated by the Weil modification of the Thompson method 14, 15) or by the Litchfield and Wilcoxon method (9). The acute lethality studies were terminated when it was evident that the survivors were not showing signs of toxicity. 

We were surprised to find that no method existed that was sensitive enough to detect TCDD in animal tissues even after administration in some species of lethal doses. An example is the guinea pig, the most susceptible species of the few that have been tested, and therefore a good choice for establishing desirable limits of detection. The lethal single oral dose (LD50) in males of this species is 0.6 /xg/kg body weight... 

Acute Toxicity. The LD50 following oral administration of parathion, either in propylene glycol solutions or in aqueous suspensions of the 15% wettable powder, has been determined for rats, mice, and guinea pigs. The lethal dose was approximated for rabbits and dogs. The results of these experiments are summarized in Table I. Statistical evaluation was by the method of Wilcoxon and Litchfield (11). 

Fate. Preliminary investigations directed at adapting the method of Averell and Norris (2) to the analysis of animal tissues indicated that if precautions were taken to avoid emulsions the method could be used satisfactorily. Tissue samples of about 5 grams were most convenient, and the usual reagent and tissue blanks were run simultaneously. Following the administration of an acutely lethal intravenous dose to a dog it was found that parathion could be recovered from the urine, liver, bile, kidney, spleen, and lung. 

Polyalphaolefin Hydraulic Fluids. Aside from the acute lethality of inhalation exposure to certain polyalphaolefin hydraulic fluids, little is known regarding the toxic effects produced by these materials. Additional animal studies to identify the possible toxic effects of exposure to these materials may provide information relevant to the investigation of methods for reducing the toxic effects. 

Experiments with gaseous acetic acid have been performed for disinfection of seeds intended for the production of bean sprouts (Delaquis et al., 1999). Salmonella typhimurium and E. coli 0157 H7 were eradicated from the surface of mung bean seeds and it was reported that the seed germination loss was not too large. The seeds have often been the suspected source of contamination in sprout-associated outbreaks and sanitation methods that do not interfere with the germination of the seeds are appreciated. Other volatile chemical treatments have been tested for lethality to Salmonella spp. on alfalfa seeds and sprouts with varying results both on the efficacy of the disinfectant and its effect on sensory qualities (Weissinger et al., 2001). 

All fire smoke is toxic. In the past two decades, a sizable research effort has resulted in the development of over twenty methods to measure the toxic potency of those fire smokes (6). Some methods have been based on determinations of specific chemical species alone. Values for the effect (e.g., lethality) of these chemicals on humans are obtained from (a) extrapolation from preexisting, lower concentration human exposure data or from (b) interpretation of autopsy data from accident and suicide victims. The uncertainty in these methods is large since ... 

Because a regression analysis of lethality data for squirrel monkeys and dogs showed an approximately linear response (n = 0.97 and 0.99, respectively, see Appendix B), the lethality threshold estimate (27.3 ppm) was linearly scaled (C1 xt=k) t° the AEGL time periods using the methods often Berge et al. (1986) (Appendix A). 

The New Jersey Department of Environmental Protection uses the TXDS method of consequence analysis to estimate potentially catastrophic quantities of toxic substances, as required by the New Jersey Toxic Catastrophe Prevention Act (TCPA). An acute toxic concentration (ATC) is defined as the concentration of a gas or vapor of a toxic substance that will result in acute health effects in the affected population and 1 fatality out of 20 or less (5% or more) during a 1-hr exposure. ATC values, as proposed by the New Jersey Department of Environmental Protection, are estimated for 103 extraordinarily hazardous substances and are based on the lowest value of one of the following (1) the lowest reported lethal concentration (LCLO) value for animal test data, (2) the median lethal concentration (LC50) value from animal test data multiplied by 0.1, or (3) the IDLH value. 

---