Electrons defeat anthrax

Perhaps, bioterrorists will not be able to spread lethal bacteria of anthrax in envelopes all over the world. Siberian biologists and physics have thought up how to adapt electron accelerator that is usually used for sterilizing medical equipment for decontamination of letters. To optimize the power of the accelerator they calculated how many bacteria could get into a human body when touching the letter infected and how many bacteria should be destroyed to avoid the tragedy.

For their experiment the scientists chose two bacteria species that form almost ineradicable spores. Both species were genetically close to anthrax. One of them is a harmless inhabitant of soils whereas the other causes a disease in insects. Its spores in the mixture with the powdered mineral kaolin can be used as insecticide.

When imitating the probable actions of mail terrorists the scientists made 60 paper packets with the sides of 50 and 25 millimeters and poured a quarter of a gram of sterile kaolin. Then several drops of suspension, which contained 10 million spores per one milliliter, were added into each packet and intensively mixed with kaolin. Then the packets were dried at 70 C and put into envelopes.

The samples were treated with an electron beam from the industrial electron accelerator. The doses applied were varied from 1 to 400 kGy. To find out the effect from a particular dose the powder with the bacteria was dissolved in distilled water and placed in culture medium. It turned out that the dose of 10 kGy killed a lot of spores. The scientists could not find any live microbes after treating the samples with the dose of 20 kGy and the dose of 400 kGy even made the paper destroy. It became fragile.

When you touch the powder about 50 mg of kaolin may remain on your fingers. However, the skin is better protected against penetrating the infection inside in comparison with the lungs. How much kaolin with the spores can a person breathe in? To find it out the researchers tore the envelopes open, placed the powder on a platter and collected the air polluted with a pump with a filter at a height of 30 cm above the platter for a minute. The operation was repeated three times and then the quantity of kaolin on the filter was determined chemically. According to the data obtained a person can breathe in 1 – 2 thousandth of a milligram of the powder. Based on the results and the calculations, the scientists recommend irradiating the correspondence with a dose of about 50 kGy. However, to reduce the probability of infection from one letter to one case per a million the dose of 22 kGy proved to be quite sufficient. The electron accelerator, which is produced at the Budker Institute of Nuclear Physics (Novosibirsk), can be used for this purpose. The accelerator weighs about ten tons and can be placed on the area of about 50 square meters. To protect the staff from radiation the accelerator is isolated with concrete layer of one and a half meter.

Electron accelerator can sterilize relatively thin objects. That is why the letters should be placed in one layer. According to the calculations the rate of sorting will remain within the norm if the number of staff doubles or the process of sorting is automated. The sterilization of parcels seems to be more complicated task. Only dangerous sources of gamma radiation are able to solve it. However, the biologists doubt that terrorists will start using parcels for their subversive activity and believe that electron accelerator can eliminate the problem of mail terrorism sufficiently.