Question: What was dropped from helicopters after Chernobyl?
About the article "Chernobyl disaster", section "Debris removal".

Candidate passages:
The Chernobyl disaster in 1986 was a pivotal event for Germany's anti-nuclear movement.
After the radioactive fallout cloud covered large parts of the country, Germans went to great lengths to deal with the contamination.
Contaminated crops were destroyed, firemen dressed in protective gear cleaned cars as they crossed the border from other countries, and sand in playground sandboxes was replaced.
Following Chernobyl, the Green Party strived "for the immediate shut-down of all nuclear facilities".
The SPD pushed for a nuclear phase-out within ten years.
Länder governments, municipalities, parties and trade unions explored the question of "whether the use of nuclear power technology was reasonable and sensible for the future".
In May 1986 clashes between anti-nuclear protesters and West German police became common.
More than 400 people were injured in mid-May at the site of a nuclear-waste reprocessing plant being built near Wackersdorf.
Police "used water cannons and dropped tear-gas grenades from helicopters to subdue protesters armed with slingshots, crowbars and Molotov cocktails". 
 city after the disaster.
Chernobyl was evacuated soon after the disaster.
The base of operations for the administration and monitoring of the Chernobyl Exclusion Zone was moved from Pripyat to Chernobyl.
Chernobyl currently contains offices for the State Agency of Ukraine on the Exclusion Zone Management and accommodation for visitors.
Apartment blocks have been re-purposed as accommodation for employees of the State Agency.
Because of regulations implemented to limit exposure, workers in the Chernobyl Exclusion Zone are limited in the number of days per week or weeks per month they stay in Chernobyl. 
The company employed or contracted Mykola Melnyk, a Chernobyl hero helicopter pilot from Ukraine, using his expertise in piloting the Soviet-made Kamov helicopters. 
The worst of the radioactive debris was collected inside what was left of the reactor, much of it shoveled in by liquidators wearing heavy protective gear (dubbed "bio-robots" by the military); these workers could only spend a maximum of 40 seconds at a time working on the rooftops of the surrounding buildings because of the extremely high doses of radiation given off by the blocks of graphite and other debris.
The reactor itself was covered with bags of sand, lead and boric acid dropped from helicopters: some 5,000 metric tons of material were dropped during the week that followed the accident.
At the time there was still fear that the reactor could re-enter a self-sustaining nuclear chain-reaction and explode again, and a new containment structure was planned to prevent rain entering and triggering such an explosion, and to prevent further release of radioactive material.
This was the largest civil engineering task in history, involving a quarter of a million construction workers who all reached their official lifetime limits of radiation.
By December 1986, a large concrete sarcophagus had been erected to seal off the reactor and its contents.
A unique "clean up" medal was given to the workers.
Many of the vehicles used by the "liquidators" remain parked in a field in the Chernobyl area.
During the construction of the sarcophagus, a scientific team re-entered the reactor as part of an investigation dubbed "Complex Expedition", to locate and contain nuclear fuel in a way that could not lead to another explosion.
These scientists manually collected cold fuel rods, but great heat was still emanating from the core.
Rates of radiation in different parts of the building were monitored by drilling holes into the reactor and inserting long metal detector tubes.
The scientists were exposed to high levels of radiation and radioactive dust.
After six months of investigation, in December 1986, they discovered with the help of a remote camera an intensely radioactive mass in the basement of Unit Four, more than two metres wide and weighing hundreds of tons, which they called "the elephant's foot" for its wrinkled appearance.
The mass was composed of sand, glass and a large amount of nuclear fuel that had escaped from the reactor.
The concrete beneath the reactor was steaming hot, and was breached by solidified lava and spectacular unknown crystalline forms termed chernobylite.
It was concluded that there was no further risk of explosion.
The industrial, transport, and residential infrastructure has been largely crumbling since the 1986 evacuation.
There are at least 800 known "burial grounds" (Ukrainian singular: "mohyl'nyk") for the contaminated vehicles with hundreds of abandoned military vehicles and helicopters.
River ships and barges lie in the abandoned port of Chernobyl.
The largest "vehicle graveyard" was dismantled recently and no longer exists, but the port of Chernobyl can easily be seen in satellite images of the area.
However, the infrastructure immediately used by the existing nuclear-related installations is maintained and developed, such as the railway link to the outside world from the Semykhody station used by the power plant.