Under the collaborative project among University of the Witwatersrand, nuclear energy officials and conservationists, five rhinos were injected Thursday in what the university hopes will be the mass injection of the declining rhino population.

Last year, about 20 rhinos at a sanctuary were injected with isotopes as part of initial trials that paved the way for Thursday's launch. The radioactive isotopes even at low levels can be recognized by radiation detectors at airports and borders, which can lead to the arrest of poachers and traffickers.

Researchers at Witwatersrand's Radiation and Health Physics Unit say that tests conducted throughout the pilot study confirmed that the radioactive material was not harmful to the animals.

"We have demonstrated, beyond scientific doubt, that the process is completely safe for the animal and effective in making the horn detectable through international customs nuclear security systems," said James Larkin, chief scientific officer of the Rhisotope Project.

"Even a single horn with significantly lower levels of radioactivity than what will be used in practice successfully triggered alarms in radiation detectors," said Larkin.