Lethality, sources

Lethal Arrhythmias. Arrhythmias are a second significant source of cardiovascular problems. An arrhythmia is an abnormal or irregular heart rhythm. Bradyarrhythmias result in heart rates that are too slow tachyarrhythmias cause abnormally fast rates. A bradyarrhythmia can be debiUtating, causing a person to be short of breath, unable to climb stairs, black out, or even to go into cardiac arrest. Tachyarrhythmias can be un settling and painful at best, life-threatening at worst. 

In a flash fire, a gas cloud or plume fonns and moves in a downwind direction. Subject to contact witli an ignition source, a wall of flame will flash back to the vapor source, sometimes witli explosive force. The beliavior of flash fire flames is not well documented. It is generally assumed tliat a flash fire will spread tliroughout tlie vapor cloud emitted and tliat it can be calculated by gas outflow dispersion. It is generally assumed tliat tlie fire is lethal to anyone within the contours of tlie cloud who is not wearing special protective gear. ... 

The first of the antibiotics that found practical use as a therapeutic was penicillin. The success of penicillin initiated a vast screening process all over the world, which resulted in the isolation of a large number of antibiotic substances from various natural sources. Many of these compounds were produced by micro-organisms and prove to be lethal for other micro-organisms. Many of these compounds were also very toxic to humans and could not be used therapeutically. Nevertheless a large number of classes of useful compounds were produced. The chemical structures of members of some of the most important classes are shown in Figure 6.1. 

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). 

LCt inhy. 3000-5000 mg-min/m3 (230-380 ppm for a 2-min exposure). This toxicity estimate is from an older source (ca. 1952) and has not been updated. Current sources do not provide an estimate on a lethal concentration. 

In marine ecosystems, the high copper levels measured in heavily contaminated coastal areas sometimes approach the incipient lethal concentrations for some organisms (Neff and Anderson 1977). Elevated copper concentrations in marine and estuarine environments may result from atmospheric deposition, industrial and municipal wastes, urban runoff, rivers, and shoreline erosion. Chesapeake Bay, for example, receives more than 1800 kg of copper daily from these sources (Hall et al. 1988). Copper concentrations in abiotic marine materials are generally higher near shore than... 

Experiments by Peter Elsbach and colleagues in the 1970s showed that although E. coli lost viability very quickly after incubation with neutrophils, these non-viable organisms still retained several important biochemical functions, such as membrane transport and macromolecular biosynthesis. As these functions are associated with the inner plasma membrane of the bacteria, these observations suggested that the lethal hit on E. coli by neutrophils occurred on the outer membrane. Because disrupted neutrophils also affected the bacteria in this way, it was concluded that the process was independent of the respiratory burst hence these workers investigated the granule proteins for the source of this activity (reviewed in Elsbach Weiss, 1983). 

Most of our knowledge of the biological effects of petrolemn pollution is based on studying the acute effects of major spills or heavily contaminated sediments. These effects tend to be directly lethal. Acute toxicity has been foimd to be largely related to water solubility, with cmnulative toxicity reflecting the smn of the effects of each individual hydrocarbon. Relatively little is known about the effects of chronic exposures at lower concentrations, especially in the presence of other stressors, such as heavy metals. Effects of chronic inputs from land-based sources on populations, communities, and ecosystem structure and function are also not sufficiently known. 

---