Russian environment protection agency (EPPA) suspended two researchers over alleged cover up of contamination.
EPPA director Mikhail Semenov said that one of the scientists who investigated the case is being held in an unknown location in Russia, and another was not being allowed to continue his work.
He said the scientists are still working on their report, but were not ready to share it.
The two scientists who were arrested in February 2015, Oleg Shkarinin and Dmitry Gubarev, have not been formally charged, but are still under investigation, according to the official.
EPPA had previously suspended three scientists in Russia who were found to have been involved in the investigation.
According to the EPPA website, the Russian Agency for Environmental Protection is tasked with protecting the environment and ensuring its safety from external and internal disturbances.
In 2016, the EPPGA was criticized for its role in the poisoning of the Yamal river, which poisoned more than 1,200 people and killed dozens of fish.