Turkmenistan has added its signature to a landmark environmental accord signed in Tehran on November 5 by the four other Caspian Sea states, officials said. After requesting more time before inking the Convention for the Protection of the Marine Environment of the Caspian Sea during what was supposed to be its formal signing last week, officials said Turkmen Environment Minister Matkarim Radzhapov returned to Tehran Saturday to sign up. The convention now becomes the first legally-binding treaty on any subject signed by the five Caspian Sea states -- Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan. The aim of the United Nations Environment Programme (UNEP)-sponsored convention is to halt mounting damage to the world\'s largest freshwater lake from industrial pollution, sewage inflows and leaks from oil extraction and refining. Once ratified by each country in a process that could take several years, it will commit signatory governments to preventing and reducing pollution, restoring the environment, using the Caspian\'s resources in a sustainable and reasonable manner, and cooperating with one another and with international organisations to protect the environment. In the past decade, the Caspian has come under increasing stress from waste dumping and an upsurge in oil and gas exploration. Other problems include the overfishing of caviar-producing sturgeon, despite strict controls on the trade. (AFP)