Karina Moskalenko, Russia’s leading human rights lawyer fell ill in the French city of Strasbourg, and traces of mercury were found in her car. Moskalenko shares a home in Strasbourg with her husband and two children, and where she tries cases against the Russian government in the European Court of Human Rights.

She and members of her family were treated for nausea and headaches.

But a French prosecutor says it seems the mercury came from a broken thermometer or barometer, and was spilled by the car’s previous owner, the BBC reported.

The vehicle was bought last August by Moskalenko’s husband from an antique dealer who used it to carry his wares.

On investigation, it turned out that an old thermometer or barometer had been broken accidentally during a journey, the BBC quoted French officials as saying.

Moskalenko’s clients include the jailed former Russian oil tycoon, Mikhail Khodorkovsky, and the family of murdered journalist Anna Politkovskaya.

Fears had been aroused that she had been subject to an attack similar to the one that killed former Russian agent Alexander Litvinenko  – also a former client of Mosklenko’s – in London in 2006.