Shell is facing a federal lawsuit over pollution at its refining and chemical plant along the Houston Ship Channel. The suit, brought by the Sierra Club, seeks a fine of up to $32,500 for each of around 1,000 separate incidents.

Shell has said that it hopes to "continue discussions" with the Sierra Club on the circumstances behind the lawsuit. Last year, a study by the   University of Texas suggested that there could be a link between childhood leukemia and proximity to the refinery.