11.        Chernobyl’s Radioactive Impact on Microbial Biota

Alexey V. Yablokov

Of the few microorganisms that have been studied, all underwent rapid changes in the areas heavily contaminated by Chernobyl. Organisms such as tuberculosis bacilli; hepatitis, herpes, and tobacco mosaic viruses; cytomegalovirus; and soil bacteria were activated in various ways. The ultimate long-term consequences for the Chernobyl microbiologic biota may be worse than what we know today. Compared to humans and other mammals, the profound changes that take place among these small live organisms with rapid reproductive turnover do not bode well for the health and survival of other species.

One gram of soil contains some 2,500,000,000 microorganisms (bacteria, microfungi, and protozoa). Up to 3 kg of the mass of an adult human body is made up of bacteria, viruses, and microfungi. In spite of the fact that these represent such important and fundamentally live ecosystems there are only scarce data on the various microbiological consequences of the Chernobyl catastrophe.

Several incidences of increased morbidity owing to certain infectious diseases may be due to increased virulence of microbial populations as a result of Chernobyl irradiation.

1.        Soon after the catastrophe studies observed activation of retroviruses (Kavsan et al., 1992).

2.        There is evidence of increased susceptibility to Pneumocystis carinii and cytomegalovirus in children whose immune systems were suppressed in the contaminated territories of Novozybkov District, Bryansk Province (Lysenko et al., 1996).

3.        Tuberculosis became more virulent in the more contaminated areas of Belarus (Chernetsky and Osynovsky, 1993; Belookaya, 1993; Borschevsky et al., 1996).

4.        In some heavily contaminated areas of Belarus and Russia there was a markedly higher level of cryptosporidium infestation (Lavdovskaya et al., 1996).

5.        From 1993 to 1997 the hepatitis viruses B, C, D, and G became noticeably activated in the heavily contaminated areas of Belarus (Zhavoronok et al., 1998a,b).

6.        Herpes viruses were activated in the heavily contaminated territories of Belarus 6 to 7 years after the catastrophe (Matveev, 1993; Matveev et al., 1995; Voropaev et al., 1996).

7.        Activation of cytomegalovirus was found in the heavily contaminated districts of Gomel and Mogilev provinces, Belarus (Matveev, 1993).

8.        Incidence of Pneumocystis was noticeably higher in the heavily contaminated territories of Bryansk Province (Lavdovskaya et al., 1996).

9.        The prevalence and severity of Gruby’s disease (ringworm), caused by the fungus microsporia Microspor um sp., was significantly higher in the heavily contaminated areas of Bryansk Province (Rudnitsky et al., 2003).

10.        The number of saprophytic bacteria in Belarussian sod-podzolic soils is significantly greater in areas with the level of radioactive Pollution of 15 Ci/km2 or less, compared with the territories with Pollution of 40 Ci/km2 and above (Zymenko et al., 1995).

11.        There is a wide range of radionuclide bioaccumulations in soil micromycetes. The accumulation factor of Cs-137 in Stemphylium (family Dematiaceae) is 348 and in Verticillium (family Muctdinaceae) 28 (Zymenko et al., 1995).

12.        Since the catastrophe, the prevalence of black microfungi has dramatically increased in contaminated soil surrounding Chernobyl (Zhdanova et al., 1991, 1994).

13.        Among soil bacteria that most actively accumulate Cs-137 are Agrobacterium sp. (accumulation factor 587), Enterobacter sp. (60–288), and Klebsiella sp. (256; Zymenko et al., 1995).

14.        In all soil samples from the 10-km Chernobyl zone the abundance of soil bacteria (nitrifying, sulfate-reducing, nitrogen-fixing, and cellulose-fermenting bacteria, and heterotrophic iron-oxidizing bacteria) was reduced by up to two orders of magnitude as compared to control areas (Romanovskaya et al., 1998).

15.        In contaminated areas several new variants of tobacco mosaic virus appeared that affect plants other than Solanaceous species, and their virulence is most likely correlated with the level of radioactive contamination in the areas. Infection of tobacco plants with tobacco mosaic virus and oilseed rape mosaic virus was shown to induce a threefold increase in homologous DNA recombination in noninfected tissues (Boyko et al., 2007; Kovalchuk et al., 2003).

16.        All the strains of microfungi species that were studied (Alternaria alternata, Mucor hiemalis, and Paecilomyces lilacinus) from the heavily contaminated Chernobyl areas have aggregated growth of threadlike hyphae, whereas the same species from soil with low radionuclide contamination show normal growth. Only slowly growing Cladosporium cladosporioides has aggregated growth both in contaminated and lightly contaminated soils (Ivanova et al., 2006).

17.        Sharp reduction in the abundance of bifidus bacteria and the prevalence of microbes of the genus Escherichia; in particular, a sharp increase in E. coli has been noted in the intestines of evacuee children living in Ukraine (Luk’yanova et al., 1995).

18.        In a long-term study (1954 to 1994— before and after the catastrophe) in Belarus, Ukraine, and Russia it was revealed that in areas with a high level of radioactive contamination (740–1,480 kBq/m2 and higher) in Bryansk, Mogilev, Gomel, Chernygov, Sumy, Kaluga, Oryol, Smolensk, and Kursk provinces, practically no cases of rabies in wild animals have been reported since the catastrophe (Adamovich, 1998). This suggests that the rabies virus has either disappeared or become inactivate.

19.        Rodents in the heavily contaminated territories of Belarus have been extensively invaded by coccids (obligate intracellular protozoan parasites from the phylum Api-complexa; Sutchenya et al., 1995).

20.        There are fewer than normal, more anomalous, and no sporulated oocysts of coccidia Eimeria cer na in voles (Clethrionomys glareolus) in Bryansk Province (Table 11.1).

TABLE 11.1. Characteristics of Oocysts of Coccidia (Eimeria cerna) in Voles (Clethrionomys glareolus) from Two Differently Contaminated Sites, Bryansk Province (%) (Pel’gunov, 1996)

Level of contamination

20 μR/h                 180–220 μR/h

Normal                         94.5                 76.6

Anomalous                 0                 6.3

Nonsporulated                 5.2                 12.2

21.        Six years after the catastrophe a population of Eimeria cernae from Clethrionomys glareolus living in heavily contaminated soil (up to 7.3 kBq/kg of Cs-134, Cs-137, Sr-90, and Pu) in Kiev Province had anomalous oocysts (Soshkin and Pel’gunov, 1994).

22.        There was a significant decline in the Shannon diversity index of infusoria species and a concomitant increase in their abundance in the Pripyat River mouth from 1986 to 1988 (Nebrat, 1992).

        All microorganisms (viruses, bacteria, fungi, and protozoa) and microbiological communities as a whole undergo rapid changes after any additional irradiation. The mechanism of such changes is well known: inclusion and increase in the frequency of mutations by natural selection and preservation of beneficial novel genes that for whatever reason appear more viable under the new conditions. This microevolutionary mechanism has been activated in all radioactively contaminated areas and leads to activation of old and the occurrence of new forms of viruses and bacteria. All but a few microorganisms that have been studied in Chernobyl-affected territories underwent rapid changes in heavily contaminated areas.

        Our contemporary knowledge is too limited to understand even the main consequences of the inevitable radioactive-induced genetic changes among the myriad of viruses, bacteria, protozoa, and fungi that inhabit the intestines, lungs, blood, organs, and cells of human beings. The strong association between carcinogenesis and viruses (papilloma virus, hepatitis virus, Epstein–Barr virus, Kaposi’s sarcoma-associated herpes virus, and herpes virus) provides another reason why the cancer rate increased in areas contaminated by Chernobyl irradiation (for a review, see Sreelekha et al., 2003).

        Not only cancer, but also many other illnesses are connected with viruses and bacteria. Radiologically induced pathologic changes in the microflora in humans can increase susceptibility to infections, inflammatory diseases of bacterial and viral origin (influenza, chronic intestinal diseases, pyelonephritis, cystitis, vaginitis, endocolitis, asthma, dermatitis, and ischemia), and various pathologies of pregnancy.

        The long-term consequences for microbial biota may be worse than what we understand today.