By Damien McGuinness
BBC News, Riga
The Baltic Sea is especially vulnerable to pollution
The Russian military allegedly dumped nuclear waste into the Baltic Sea in the early 1990s, according to a report on Swedish television.
Radioactive material from a military base in Latvia is thought to have been thrown into Swedish waters.
For many the biggest shock is that the Swedish government may have known at the time and done nothing about it.
The partly enclosed Baltic Sea is known as one of the most polluted seas in the world.
But now it seems it was also used as a dumping ground for Russian nuclear waste and chemical weapons.
According to a report on Swedish television, Russian boats sailed out at night to dump barrels of radioactive material, from a military base in Latvia, into Swedish waters.
And even though the Swedish government at the time reportedly knew this, no action was taken to find the waste.
The current government in Stockholm now wants the politicians who were then in charge to explain why they did nothing to find the barrels.
The Baltic Sea is semi-enclosed, so it takes a long time to flush out toxins. This makes it particularly vulnerable to pollution.
And after years of untreated waste from Russia's cities and heavy industries, scientists say that the Baltic is in danger of becoming a dead sea.
Next week high-ranking politicians from those countries bordering the Baltic, including Russia, are due to attend a summit in Helsinki to discuss how to save it.
But if reports about Soviet nuclear waste being dumped prove true, then Russia will have even more accusations of pollution to answer.