Volunteers wearing protective gear walk across a street covered by toxic red sludge Monday in Devecser, Hungary. Devecser, with a population of 5,300, is in the likely path of a possible new sludge deluge.

Bucharest, Romania ? Abandoned mines in Romania leach waters contaminated by heavy metals into rivers. A Hungarian chemical plant produces more than 100,000 tons of toxic substances a year. Soil in eastern Slovakia is contaminated with cancer-producing PCBs.

The flood of toxic sludge in Hungary is but one of the ecological horrors that lurk in Eastern Europe 20 years after the collapse of the Iron Curtain, serving as a reminder that the region is dotted with disasters waiting to happen.

Much of Eastern Europe is free of many of its worst environmental sins with the help of Western funds and conditions imposed on Hungary, Romania, Bulgaria, Slovakia and the Czech Republic in exchange for membership in the European Union.

Still, the sludge has focused attention on less-visible dangers that survived various cleanups in the region.

The caustic spill — Hungary’s worst ecological disaster — also has raised questions about whether investors who took over Soviet-era factories from the state 20 years ago are at fault for not spending enough on safety.

Eight people died in the Oct. 4 deluge of red sludge from a 24-acre storage pool where a byproduct of aluminum production is kept.

Calls for greater cleanup efforts apply not only to Hungary, which considered itself ahead of most of the former Soviet bloc in fixing ecological harm, but also to neighbors like Serbia that hope to join the 27-nation bloc.

“The scary thing is we didn’t know this existed and there could be other ones,” says Andreas Beckmann, director of the World Wildlife Fund Danube-Carpathian program, alluding to the Hungarian spill. “How many other facilities and sites are there that could be a ticking time bomb?”

Environmentalists warn of other potential disasters from seven storage ponds about 60 miles northwest of Budapest that hold 12 million tons of sludge accumulated since 1945 — more than 10 times the amount that spilled this week.

“If the gates break there, much of Hungary’s drinking water would be endangered,” says WWF official Martin Geiger.

Other sites — like the Borsodchem plant in northeastern Hungary — pose similar risks to groundwater. That factory churns out 100,000 tons of the toxin PVC that contains dioxin, the same poison released into the air by a factory explosion in Seveso, Italy, 34 years ago that killed hundreds of animals and turned much of the town into a no man’s land.

Slovakia, Hungary’s northern neighbor, has its own toxic problems, including a huge area in the east of the country that is still contaminated with PCBs from communist times.

Government officials in Bulgaria, alarmed by the Hungarian spill, have ordered safety checks of a dozen waste dams — huge reservoir walls that hold back often heavy metal-laden waste that are prone to leaks or collapse.