Compart- ment Primary digestion functions Main added “reagents” pH Residence time Contaminant dissolution function Mouth grinding cleavage of starch moisture amylase 6,5 seconds to minutes grinding enhances subsequent dissolution Gullet transport none 6,5 seconds none Stomach cleavage of proteins and fats hydrochloric acid proteases lipases 1-5 8 minutes to 3 hours acid dissolves labile mineral oxides, sulfides and carbonates to release metals and adsorbed organic com- pounds Small intestine cleavage of oligosac- charides, proteins, fats and other constituents solubilisation of fats bicarbonate bile proteases lipases oligosac- charases phospha- tases 4-7,5 3-10 timer organic matter is dissolved and bound contami- nants released apolar organic contaminants are solubilised by bile cationic metals are solubilised by complexation with bile acids some metals are precipitated by the high pH or by phosphate