Croda tightens up testing for dioxin-like PCBs in omega-3 Croda tightens up testing for dioxin-like PCBs in omega-3 03-Nov-2006 By staff reporter Croda is taking steps to assure customers of the purity of its omega-3 concentrates, certifying that dioxin-like PCB levels in Incromega are more than 60 per cent below the new EC limits due to come into force this month.