Toxic radioactive substances were detected again in groundwater at the Fukushima nuclear plant, its Japanese operator said on Sunday. Tokyo Electric Power Co (Tepco) said tests showed that tritium, a radioactive isotope of hydrogen, was present at levels 10 times the permitted rate. “From test samples on July 5... we detected a record high 600,000 becquerels per litre” of tritium, 10 times higher than the government guideline of 60,000 becquerels per litre, it said . The new readings came after Tepco said in late June that it had detected the highly toxic strontium-90, a by-product of nuclear fission that can cause bone cancer if ingested, at levels 30 times the permitted rate. It had also detected tritium at around eight times the level, or 500,000 becquerels per litre. — AFP