Cod liver oil the foul-tasting vitamin supplement forced on generations of children, has been found to contain traces of dangerous industrial chemicals. The Food Commission, an independent watchdog, said although the levels were low, mothers should be aware there was some concern for the effects on young children and consider alternatives. A report by the Agriculture ministry, MAFF, said their investigations have found 'relatively high concentrations' of dioxins and PCBs in fish liver oils.They are picked up by fish swimming in polluted waters and stored in their liver.