Cytogenetic changes in the Bhopal population exposed to methyl isocyanate (MIC) in 1984: Then and 30 years later

MIC accident: lesson may guide for evaluation of genotoxic potential of the industrial chemicals for prevention of industrial accidents

Most of the individual and/or amalgamated compounds present in the atmospheric air are not known for their toxicologic potential and impact on human health. The toxicologic strength of methyl isocyanate (MIC) gas was unknown till its accidental leakage that instantly claimed thousands of lives. Cytogenetic study showed increased chromosome aberrations (CA) and sister chromatid exchanges (SCEs) and delayed cell replication index (RI) in a multicentre genetic screening program on gas victims immediate post-disaster. A surveillance study after 30 years displayed reduction in CA compared to the initial status in survivors of the severely and moderately exposed strata. Altogether, cytogenetic damage was significantly predominant in the severely exposed population. Stable and replicable aberrations and chromatid exchanges were detected in both studies, which collectively indicate genetic instability. The variation in individual cytogenetic spectrum from similar exposure status could be the result of inter-individual response to the external factors over 30 years post-disaster. The spectrum of CA detected after 30 years might be the cumulative effect of occupational, environmental and life-style factors at a background of one episode of acute MIC exposure. Had MIC's toxicologic potential was known before, fatality and health effects could have been averted. In vitro assessment of toxicity of tin showed a positive correlation with dose and age of exposure, which was aggravated by smoking. Age has shown a significant effect on CA in the general population. The present report recommends evaluation of toxicity prior to use, and reduction of pollution at source for a maintaining a sustainable environmental context.

Spectrum of stable and unstable rearrangements in lymphocytic chromosomes investigated in Bhopal population 30 years post MIC disaster amid co-exposure to lifestyle, living, and occupational hazards

Immediate assessment of genetic damage in methyl isocyanate (MIC) gas-exposed population in small and heterogeneous samples using diversified study designs and solid-stained metaphases could not depict the actual genetic impact of MIC on accidentally exposed individuals. The outcome of the then large multi-center genetic screening program was not available to the public and scientific community. Also, the routine and regular epidemiological health survey does not capture the genetic and long-term effect of MIC. Therefore, genetic screening was carried out 30 years post disaster during 2015-2017 with a view to screen the present status of chromosomal consequences in lymphocytic cells. Participants were recruited from moderate (34) and severely (78) exposed and unexposed (35) cohorts with their informed consent. Analysis of ~100 mitotic cells and karyotyping of at least 10-15 and all abnormal metaphases detected structural and numerical alterations, including stable and replicable ones. Clonal abnormalities were detected with monosomal and complex karyotypes, trisomy 8, del5q/20q, loss of Y, etc. Among all, X-chromosome was frequently involved in numerical alterations. Structural aberrations appeared higher in the then exposed populations, though abnormalities cannot be linked directly to MIC exposure 30 years post disaster. Collectively, all rearrangements were markedly higher in the severely exposed population. Altogether, the detected abnormalities appeared random and indicated genomic instability, suggesting follow-up at shorter intervals for the individuals detected with clonal aberrations. G-banding has facilitated recognition of chromosomal involvement and their breakpoints and classification of structural rearrangements. The present data has been derived from the 30-year post-disaster genetic screening.

Exposure index of methyl isocyanate (MIC) gas disaster and a comprehensive spectrum of cytogenetic analysis after 30 years

Severity of clinical expression and high mortality could not facilitate establishing exposure index/association following MIC disaster in Bhopal. Mortality-based exposure stratification was critiqued by the International Medical Commission on Bhopal (IMCB). IMCB stratified exposure considering distance as surrogate at 2 km intervals after 10 years. The first follow-up cytogenetic screening of the pre-screened survivors after 30 years has demonstrated chromosome abnormalities (CA). Exposure stratification was attempted considering cytogenetic screening conducted during 1986-1988. Elevation of CA appeared proportional to exposure status and authenticated the initial mortality-based stratification. The one-on-one comparison of the previous and present cytogenetics has described the individual response to MIC exposure over 30 years. Chi-square test has been carried out for checking the cytogenetic changes at the individual level statistically, which revealed that differences of chromosomal aberrations collected immediately post-disaster and 30 years later are nonsignificant. The prominence of interindividual variation was noticed in general. The impact of overall exposure was higher in males. Constitutional abnormalities in 8.5% of the study population, including translocation, inversion, deletion, fragile sites, etc., necessitate screening of blood-linked members. The incidence of acrocentric association was prominent in the study population. Normal karyotype in children born to severely exposed parents with congenital anomalies indicates necessity of molecular karyotyping and/or screening of mutations. The study highlights follow-up of the health of the index cases at shorter (3-6 months) intervals. This comprehensive spectrum of cytogenetic report highlights immediate post-disaster chromosomal aberrations, the changes that occurred over 30 years in conjunction with other environmental factors at the individual level, constitutive genomic aberrations, polymorphic variations, and chromosomal patterns in congenitally malformed children of the survivors, which collectively indicate the possibility of acquisition/persistence of stable aberrations in MIC-exposed lymphocytes through interaction with environmental/biological confounders.

Effect of age at exposure on chromosome abnormalities in MIC-exposed Bhopal population detected 30 years post-disaster

Follow-up cytogenetic study was carried out on 145 individuals from areas stratified by Indian Council of Medical Research, for evaluation of the effect of age-at-exposure and its interaction with exposure status on chromosomal aberrations (CA) in blood-lymphocytes. CA was presented as abnormal cell (Abc), aberrations (Abn) and number of aberration/abnormal cell (Abn/Abc), and correlated with age-at-exposure (childhood: <1-10 years; young: 11-26 years; adult: >27 years). Age related increase in abnormalities (Abc, Abn, Abn/Abc) was observed in all exposure strata, except moderately exposed adult-group, which has exhibited lower Abn/Abc than similarly exposed childhood and young age-groups. Elevation of CA was also related to exposure status. Abn/Abc frequency was significantly higher in the severely exposed young and adult groups compared to the controls of the same age. Two-way ANOVA revealed significant abnormalities between the exposed groups; however, interaction of age and exposure was not statistically significant. Significant difference in group-means of Abc and Abn was also observed between adult and childhood in Tukey HSD test. Altogether, a significant interaction of age and MIC-exposure on CA could not be established due to inter-individual variation and lack of baseline information on CA. Significantly higher Abn was observed in people consuming tobacco; however, interaction of lifestyle with additional environmental/occupational exposures during last 30 years against a background exposure to MIC remained un-elucidated. Nevertheless, the study was important for demonstration of the correlation of the current status of CA in circulating lymphocytes with age and exposure status of the MIC-exposed survivors.

Spectrum of health condition in methyl isocyanate (MIC)-exposed survivors measured after 30 years of disaster

Health effects of methyl isocyanate (MIC) exposure were mostly reported on the one-time acute exposure in Bhopal population. Epidemiological survey conducted by the Indian apex body of health research has been reported as Technical Reports, which were lacking in peer review by the expert epidemiologic scientists. The present pilot survey was aimed to measure the health effects 30 years post disaster in MIC-exposed survivors. Questionnaire-based survey has captured every health complaint in 168 individuals and grouped as systemic functions for interpreting the long-term effects of MIC. Key health parameters, including reproductive outcome and respiratory/orthopedic/general morbidity, were prevalent among the severely exposed population compared to control and moderately exposed groups. The collective incidence of diabetes, hypertension, and cancer also was prevalent in the severely exposed group. Ophthalmic morbidity was almost similar in the three groups, rather with higher incidence in the control group, though not statistically significant. Among all health parameters, reproductive, ophthalmic, and respiratory effects were prevalent over others. Although the incidence of health problems has been declined among the survivors, long-term effect is apparent as scars of one-time acute exposure might trigger sequel of long-term effects. Additionally, acquisition of genetic rearrangements, survival of T cell sub-populations, variable latency of chemical effect on DNA nucleosides, nutritional status, occupational exposure, living environment, lifestyle, and overall gene-environment interaction might perturb individual immunity and favor onset of long-term illness in a scenario of background exposure to MIC. However, the exercise should be continued on a larger sample size for drawing a conclusive result on long-term MIC effect on survivors' health.