Aerosol toxins

From the human perspective, HABs are problematic because they cause (1) risks to human health, (2) loss of natural or cultured seafood resources, (3) impairment of tourism and recreational activities, and (4) damage to noncommercial marine resources and wildlife. Exposure pathways include (1) consumption of toxic shellfish that have accumulated phytoplankton toxins filtered from the water, (2) consumption of tropical fish that have accumulated phytoplankton toxins (ciguatera), (3) inhalation of aerosolized toxins ejected from the sea surface, and (4) skin contact resulting in irritations due to allergy-like reactions. Harmful health effects from acute exposures have been relatively well studied. Less well known are the health effects resulting from chronic exposures to low toxin levels. This is of particular concern with regards to marine mammals and seabirds. 

Nerve gases Probably the most widely stocked chemical agents liquid, gas or aerosol toxins belonging to the group of organophosphorus compounds, which are absorbed by the skin or lungs, usually within 20 to 30 minutes. 

BoNTs present a very real threat to the public health and are the most toxic substances known to humankind. In a military or bioterrorist incident, intoxication by BoNT is likely to occur by inhalation of aerosolized toxin or by ingestion of contaminated food or beverages (Franz, 1997 Sobel et al,... 

Chemical Abstracts Service Registry Number CAS 93384-43-1. Botulinum toxins comprise a series of seven related protein neurotoxins that prevent fusion of synaptic vesicles with the presynaptic membrane and thus prevent release of acetylcholine. Exposure in a battlefield or terrorist setting would most likely be to inhaled aerosolized toxin. The clinical presentation is that of classical botulism, with descending skeletal muscle weakness (with an intact sensorium) progressing to respiratory paralysis. A toxoid vaccine is available for prophylaxis, and a pentavalent toxoid can be used following exposure its effectiveness wanes rapidly, however, after the end of the clinically asymptomatic latent period. Because treatment is supportive and intensive (involving long-term ventilatory support), the use of botulinum toxin has the potential to overwhelm medical resources especially at forward echelons of care. 

Most species contributing to algal blooms are harmless however, some of the toxins produced by certain species are highly toxic. Often, the algae and the shellfish that consume them are unaffected. However, further up the food chain, these toxins can be fatal. Man, dolphins, manatees, and reptiles are potentially exposed to aerosolized toxins. Brevetoxins are potent ichthyotoxins and have been responsible for the death of billions of fish over the years. Brevetoxin is absorbed directly across the gill membranes of fish or through ingestion of K. brevis cells. Some of these toxicity differences will depend on the differential susceptibility of fish species to exposure to K. brevis strains involved, toxic components and concentration, stability of extracellular toxins, and exposure routes. Mortality typically occurs at cell concentrations of 2.5 x 10 K. brevis cells per liter, which is often considered to be a lethal concentration. 

Atmospheric conditions and particle size determine the persistence of aerosolized toxin in the environment. Temperature and humidity extremes facilitate toxin degradation, and smaller particles dissipate more quickly into the atmosphere. Studies estimate that aerosolized toxin would decay between less than 1 and 4% per minute. At a 1% decay rate, insubstantial amounts of toxin would remain after 2 days (36). Although botulinum toxin can penetrate mucosal surfaces, it cannot penetrate intact skin. If a release were recognized or announced, and authorities anticipated potential airborne exposure, people could protect themselves by covering their mouths and noses with clothing, such as underwear, shirts, scarfs, or handkerchiefs. In addition, after exposure, washing with soap and water would decontaminate clothing, and a 0.1% hypochlorite bleach solution would be effective on contaminated objects and surfaces (36). 

The above documents the consequences of toxin ingestion. A few reports suggest that inhalation of aerosolized toxin may cause conjunctival irritation, rhinorrhea, respiratory irritation, and possibly exacerbate or cause symptoms similar to reactive airways disease [168, 169]. Several recent studies have provided additional evidence of adverse respiratory effects, including upper airway irritation and discomfort, decreases in pulmonary function parameters, and worsening asthma symptoms, due to occupational and environmental exposures to aerosolized brevetoxins. 

The protective mask, worn properly, is effective against toxin aerosols. Its efficacy, however, depends on two factors (1) mask-to-face or hood-to-head fit and (2) use during an attack. Proper fit is vital. Because of the extreme toxicity of some of the bacterial toxins, a relatively small leak could result in a significant exposure. Eyes should be protected when possible. Definitive studies have not been done to assess the effects of aerosolized toxins on the eyes. In general, however, ocular exposure to a toxin aerosol, unless the exposed individual is near the release point, would be expected to cause few systemic effects because of the low doses absorbed. A few toxins have direct effects on the eyes, but these are generally not toxins we would expect to be used as aerosols. Donning the protective mask prior to exposure would, of course, protect the eyes. 

The anthrax bioterrorist attacks that followed the events of September 11th 2001 resulted in a renewed interest BadUus anthracis, the causative agent of this disease. Research has focused on the development of better vaccines than the one currently available. It has been estimated that the aerosolized release of 100 kg of anthrax spores upwind of Washington DC would cause mortalities of 130,000-3,000,000 [63]. Nonetheless, wild-type Bacillus anthracis is susceptible to conventional antibiotics, including penicillin, oxyfloxacin and ciprofloxacin. The problem lies not with the bacterial infection itself, but with three proteins released by the bacteria - protective antigen (PA, 83 kDa), lethal factor (LF, 90 kDa) and edema factor (EF, 89 kDa) -known as anthrax toxins [63]. 

All toxins are nonvolatile. Once the initial aerosol has settled, there is minimal inhalation hazard unless the toxin is released as an aerosolized powder that has been modified to increase the potential of reaerosolization. Solubility in water depends on the specific toxin, presence of solvents, and isolation as salts. 

Immediately dangerous to life or health (IDLH) levels are the ceiling limit for respirators other than SCBAs. However, IDLH levels have not been established for toxins. Therefore, any potential exposure to aerosols of these agents should be regarded with extreme caution and the use of SCBAs for respiratory protection should be considered. 

In the event that dermally hazardous toxins have been released, responders should wear a Level A protective ensemble. Also, because of the extreme hazard posed by toxin aerosols to any area of cut or lacerated skin, responders should wear a Level A protective ensemble whenever there is any potential for exposure to airborne agent. 

Casualties I personnel Do not attempt to brush the agent off the individual or their clothing as this can aerosolize the agent. Remove all clothing immediately. To avoid further exposure of the head, neck, and face to the agent, cut off potentially contaminated clothing that must be pulled over the head. Wash the skin surface and hair at least three times with copious amounts of soap and water. Do not delay decontamination to find warm or hot water if it is not readily available. Rinse with copious amounts of water. If there is a potential that the eyes have been exposed to toxins, irrigate with water or 0.9% saline solution for a minimum of 15 minutes. 

Decontamination Soap and water, or diluted sodium hypochlorite solution (0.5 percent). If contamination of foodstuffs is suspected, boil for ten minutes to kill toxin. Botulism is not dermally active and secondary aerosols do not endanger medical personnel. 

Signs and Symptoms From three to six hours after aerosol exposure, sudden onset of chills, fever, headache, pain in one of more muscles, and nonproductive cough. Some patients may develop shortness of breath and retrostenal (situated or occurring behind the sternum) chest pain. Fever may last two to five days, and cough may persist for up to four weeks. Patients may also experience nausea, vomiting, and diarrhea if they swallow toxin. Higher exposure levels can lead to septic shock and death. 

Diagnosis Be suspicious if an aerosol attack occurs in the form of yellow rain with droplets of yellow fluid contaminating clothing and the environment. Confirmation requires testing of blood, tissue and environmental samples. As for treatment, there is no specific antidote however, super-activated charcoal should be given orally if the toxin is swallowed. The only defense is to wear a protective mask and clothing during an attack. No specific immunotherapy or chemotherapy is available for use in the field. 

Caution The T-2 mycotoxins are the only potential biological warfare agents that can harm and be absorbed through intact skin. Aerosol doses of T-2 toxins may be ten times more potent than parenteral doses. 

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