Japanese officials have found trace levels of plutonium in the soil at the Fukushima Dai-ichi Nuclear Power Plant. Even though officials have stressed that the levels were too small to be of worry to human or animal population, the discovery of plutonium was one more element of difficulty that safety officials at the plant would have to work through in an effort to contain a worsening situation.

The plant was badly damaged in the March earthquake and tsunami. Power was out at the plant for some time, and fires and explosions heavily damaged many of the buildings surrounding the plant's six nuclear reactors. Frantic yet efficient workers from the Tokyo Electric Power Company managed to restore power by connecting new power lines, and rescue workers dumped thousands of gallons of water directly onto the reactors in an effort to keep them cool in the wake of the power failure, which wiped out the reactors' cooling tanks.

Then, health and safety officials announced that they had found higher-than-normal levels of radiation in the food and water in the region. The plutonium might be at a low level, but the radiation certainly was not. Residents of one town were told not to drink from the tap. Several types of food were declared off-limits for selling to local supermarkets and for shipping to other countries.

Through it all, workers at the plant have struggled to keep the situation from getting much worse, their efforts hampered by explosions, fires, and leaks, including one that resulted in a report that radiation in one reactor was 100,000 times the normal level. Radioactive water has burned workers and seeped into trenches outside some reactors. Workers have continued on, knowing the risks.

In the surrounding towns and villages, a quarter of a million people remained homeless, taxing shelters and resources. Aid continues to come in from around the country and around the world. Damage estimates have stretched to $300 billion.

The death toll stood at 10,901, with 17,649 missing.

Monday brought a stark reminder of the devastation already wrought, as a strong 6.5-magnitude aftershock, the latest of dozens in the past few weeks, rattled the northeastern coast of Honshu, the main island, triggering a tsunami alert. No injuries or damage were reported.