I discussed with a friend who worked in a hospital and who used this radionuclide with a longer half-life than iodine-131 and therefore wondered whether someone had already measured it in the environment.
With a half life of roughly 10 days, there will be no accumulation effects. And as a electron-capture nuclide, the detection will be difficult. I guess, even the detection in the hospitals collected waste water will be ambitious.
The I-131 has very short half life (8.02 d) and there rules for release. In Brazil the release can be made only when the concentration is low. And there is dilution. these factors minimize the risk of releases. Each country has its laws and it must be fulfilled. Browse the laws of your country and a look at the legislation, before measuring the river.