Brass utensils or food containers that are not enamelled or tinned adequately can lead to copper poisoning and conditions like childhood cirrhosis of the liver. It's the acids in foods that reacts with the brass to leach out copper. A different but related problem with some brass utensils is lead because sometimes a mixture of tin + lead is used to "tin" brass utensils, causing lead toxicity, too. Both situations are quite rare in the US these days, but still cause problems in countries like India where untinned or inadequately tinned brass utensils can still be found.