Thirty years ago, on the night of December 2, 1984, an accident at the Union Carbide pesticide plant in Bhopal, India, released at least 30 tons of a highly toxic gas called methyl isocyanate, as well as a number of other poisonous gases. The pesticide plant was surrounded by shanty towns, leading to more than 600,000 people being exposed to the deadly gas cloud that night. The gases stayed low to the ground, causing victims throats and eyes to burn, inducing nausea, and many deaths. Estimates of the death toll vary from as few as 3,800 to as many as 16,000, but government figures now refer to an estimate of 15,000 killed over the years. Toxic material remains, and 30 years later, many of those who were exposed to the gas have given birth to physically and mentally disabled children. For decades, survivors have been fighting to have the site cleaned up, but they say the efforts were slowed when Michigan-based Dow Chemical took over Union Carbide in 2001. Human rights groups say that thousands of tons of hazardous waste remain buried underground, and the government has conceded the area is contaminated. There has, however, been no long-term epidemiological research which conclusively proves that birth defects are directly related to the drinking of the contaminated water.