As groundwater flows through it, the barrier extracts
contaminants, significantly reducing their concentration.
Both materials are capable of extracting metals and organic pollutants
from groundwater ii) Extraction of iodine from urine 131I
may be given to patients with thyroid problems for diagnosis
or treatment. About 30% of the activity (2-3 GBq) is excreted
in urine during the first day after administration. In some
parts of Europe, the radioactive urine is collected in tanks at
the hospital.