Heavy rains from the typhoon worsened the spread of radioactive materials in groundwater around the Fukushima I and Fukushima II nuclear power plants, which suffered nuclear meltdowns in 2011 following a MW9.0 earthquake and subsequent tsunami. Levels of the radioactive hydrogen isotope tritium soared ten-fold from the previous month to 150,000 becquerels per liter. Strontium-90, a substance known to cause bone cancer, rose to a record 1.2 million becquerels per liter. A separate sampling site showed a doubling in the levels of a beta particle-emitting substance from prior to the typhoon.