Collected from Hackney Brick WorksThe extractable/leachable metal content refers to metals soluble in Aqua Regia using methods based onISO11466 (1995).TotalCertified valuesAs. 70 mg/kgFe .47500 mg/kgNi . 291 mg/kgBa . 305 mg/kgK .16300 mg/kgPb . 411 mg/kg