210Pb content in natural gas pipeline residues (“black-powder”) and its correlation with the chemical composition

Typical “black-powder” generated in the natural gas pipeline from Campos Basin oilfield contains mainly iron oxide (∼81%) and residual organic matter (∼9%). The 210Pb content ranges from 4.9 to 0.04 kBq kg−1 and seems to be inversely correlated with the distance to the platforms. On the other hand, 226Ra concentration is higher on the pipeline branch between the platform and the onshore installations. 228Ra was only observed in few samples, in particular, in the samples with the highest 226Ra content.