Protestors rallied in more than six Bulgarian cities on Saturday (14 January) calling for a moratorium on ‘fracking’ - shale gas tests using hydraulic fracturing - and demanding a new law to ban unconventional drilling for gas in the country.
“I am opposed because we do not know what chemicals they will put in the ground. Once they poison the water, what shall we drink?” said Olga Petrova, 24, a student who attended a protest in Sofia.
In June, the centre-right government granted a licence to the US energy company Chevron to test for shale gas in northeastern Bulgaria, hoping that it could reduce the country's almost complete dependence on gas imports from Russia’s Gazprom.
Shale gas is natural gas locked in rock formations that in the past decade has been found in abundance around the world, offering a major potential future energy source.
However, some studies suggest that it could have a worse global warming effect than coal, because of the amount of methane that shale gas extraction can release into the atmosphere.
There are also concerns about the environmental impact of the drilling method involved.
Fracking involves injecting water mixed with sand and chemicals into shale formations at high pressures to extract fuel. Critics worry that fracking fluids might get into groundwater-holding aquifers and contaminate them.
The possibility for shale gas wells in the Dobrudzha region, Bulgaria's main grain producer, is stirring growing opposition by environmentalists who want to safeguard drinking water and land.
They worry that fracking may also trigger earthquakes and cause cancer and other diseases to those who live near the shale wells.
The government has tried to ease concerns by saying the tests for shale gas are not the same as actual drilling.
Under pressure by green groups, however, it decided to seek an environment impact study prior to tests after consulting with the European Commission.
Neighbouring Romania and Serbia are also planning shale gas tests, and Poland expects its first shale gas production to start in 2014-15.
The impact from shale gas exploration, which has revolutionised the US natural gas industry, has been put under scrutiny globally.
Public health professionals and advocates in the United States called recently for rigorous studies on public health effects.
France banned fracking in July, while Britain suspended the deep-excavation practice near Blackpool after minor tremors in the spring.