"Almost all of the heavy metals absorbed by vetiver plant stay in the roots, therefore the leaves are largely uncontaminated and to get rid of the pollutants you have to remove the roots and dispose them the usual way such as deep burying or incineration, with the bonus of a much smaller volume to deal with rather the whole volume. It is true that if you leave the leaves to rot then the metals will go back to the water/soil. But in all phytoremediation processes you have to remove the contaminiated materials offsite and in the case of vetiver to maximise the benifit you have to cut the top so it can continue to grow both root and shoot to remove the metals for you. Since the vetiver top is largely uncontaminated it can be used for other purposes such as thatching,handcraft or fodder. In short vetiver planting stop the spreading of heavy metals but it does not change the composition of the metals. However we have evidence that vetiver can degrade organic pollutants such as agro-chemicals in the soil or water.
Refering to another concern that vetiver planting will cause additional problems to be solved:
No, definitely not. Unlike other chemical, physical phytoremediation techniques, Vetiver has no toxic by-products as pointed out above. THE STRENGTH OF VETIVER PHYTOREMEDIATION IS IN NON SOURCE POLLUTION CONTROL, RETAINING, CONCENTRATING AND STOPPING THE POLLUTANTS FROM SPREADING BY BOTH WATER AND AIR, WITH THE ADDED BONUS OF ITS LOW COST, NATURAL (GREEN) SOLUTION, AND NO TOXIC BYPRODUCTS. TO REMOVE THE POLLUTANTS COMPLETELY YOU HAVE TO PHYSICALLY TAKE THEM OUT AND DEAL WITH THEM SEPARATELY."