Mr Bojo Leju worked for eight years for the oil consortium Greater Pioneer Operating Company (GPOC), a joint venture between Malaysian, Indian and Chinese oil companies - with South Sudan’s government owning 5%.
After a major pipeline rupture five years ago, he started photographing and filming pools of oily water and heaps of blackened soil in locations in Unity State, including sites near Roriak, where the herders live.
He says spills from oil wells and pipelines were "a recurring situation", and that he was involved in transporting contaminated soil away from roads, so it would not be seen.
He tried to raise his concerns with company managers, but he says little was done and "there was no treatment plan for soil".
Mr Bojo Leju also says "produced water" - water released from the ground when oil is extracted and often containing hydrocarbons and other pollutants - was not properly treated.