Tritium dispersion in the English Channel
Tritium dispersion in the English Channel is monitored and measured, as illustrated by this map taken from an IRSN report. Owing to the effect of sea currents, the Normandy coast is most affected, with a peak of 5 Bq per litre near Dieppe. As a comparative yardstick, a litre of milk produces 100 Bq. Note that the radiotoxicity of tritium is very low, due to the low energy of the emitted rays.
IRSN