Abstract: The invention relates to a statistical polysaccharide with a weight-average molecular weight of between 100 kDa and 1000 kDa of the following formula (I): in which: each Rc independently represents a group containing a chelating agent, each Z independently represents a binder which may be a single bond or a hydrocarbon chain containing between 1 and 12 carbon atoms, said chain able to be either linear or branched and being able to contain one or more unsaturations and being able to contain one or more heteroatoms, preferably chosen from nitrogen, oxygen, sulfur and atoms of the halogen family, x is between 0.005 and 0.7, preferably between 0.05 and 0.7, and preferentially between 0.2 and 0.6, y is between 0.01 and 0.7, preferably between 0.05 and 0.2, the ratio of y/x being greater than or equal to 0.05, preferably greater than or equal to 0.15, and the sum of x+y being greater than or equal to 0.30, preferably greater than or equal to 0.35.