RIO DE JANEIRO — It washed ashore in early September, thick globs of oil that appeared from out of nowhere and defied explanation. In the weeks since, the mysterious sludge, the largest spill in Brazil’s history, has tarred more than 1,000 miles of shoreline, polluted some of the country’s most beautiful beaches and killed all sorts of marine life.

But despite the time that has passed — and the damage done — the most important questions remain unanswered. Where is the oil coming from? And how can it be stopped?

The Brazilian government’s apparent inability to answer even these fundamental questions has drawn more scrutiny to the environmental policies of President Jair Bolsonaro, who struggled this summer to contain the fires raging in the Amazon and the international outrage they sparked.

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Now, fury is mounting again. Municipalities have resorted to imploring volunteers to help with the cleanup. Videos of the rudimentary efforts — volunteers simply rolling up oil slicks and plopping them into trash bags — are going viral. And the environmental minister, Ricardo Salles, is picking fights online with a prominent nongovernmental organization.

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“Greenpeace ‘explained’ why it can’t help clean up the beaches in the northeast,” he said. “Ahhh, okay.”

On Monday, Vice President Hamilton Mourão said the government had recovered 600 tons of oil — nearly 4,300 barrels. Mourão, a retired army general, said he would send 5,000 troops to northeastern Brazil to give “more visibility” to government efforts to control the situation.

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“This oil that is arriving now,” he said, “is the second wave of attack … This accident is unprecedented in the world.”

Analysts say the most essential piece of the response remains missing: determining the source of the oil.

“Think about in your life, if you spill a gallon of paint while painting, the first thing you do is pick up the can of paint before it empties and ends up on the carpet,” said Doug Helton, an official with the U.S. National Oceanic and Atmospheric Administration who has studied mysterious oil spills. “So if we don’t know the source, you’re picking up oil on the shore but don’t know how much more is out there.”

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In the early days of the spill, Bolsonaro said it was “dumped there criminally.” Then Salles said it was “very likely from Venezuela,” a Brazilian adversary, adding that a foreign ship may have caused the spill. A molecular analysis by IBAMA, the country’s environmental agency, showed the oil had not been produced in Brazil. Petrobras, the state-run oil conglomerate, said it wasn’t responsible.

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Bolsonaro speculated, without offering any evidence, that it might have been a “criminal action” to sabotage a massive oil auction in November for deep-sea deposits that’s expected to generate $50 billion in licensing fees for Brazil.

“I wonder, we have to be very responsible about what we say — could it have been a criminal act to harm this auction?” Bolsonaro said. “It’s a question that’s out there.”

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Mystery oil floats throughout the oceans. It may arise naturally, from seeps in the ocean floor. Or from ships that leak. Tiny bits and pieces may glom onto bigger bits and pieces, forming tar balls. Some are as small as a fingernail, others as large as a soccer ball.

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Some spills remain mysterious for a long time. In 2002, for example, the cause of a spill that had killed thousands of seabirds off the coast of San Francisco was found to be a ship that sank in 1953. Another mystery spill recently hit the Chicago River. But the Brazil spill is different.

“The magnitude of this is extremely rare,” said David Valentine, a marine science researcher at the University of California at Santa Barbara.

Christopher Reddy, a researcher at the Woods Hole Oceanographic Institution in Massachusetts, has been trying to crack the mystery. Some Brazilian colleagues recently contacted him to help determine the source of the oil, and he’s now analyzing 14 samples with the hopes of determining the molecular structure of the oil by the end of the week.

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“The reason oil is fascinating is that it’s very complex, and they all have different personalties,” he said. “It’s investigating a sample to try to figure out its source and how long it’s been around.”

The Bolsonaro administration’s response reinforced the perception among some that Brazil, long a stalwart defender of the environment, is now neglecting that role.

“The current federal government’s inaction is indeed a puzzle,” said Marcus André Melo, a political scientist at the Federal University of Pernambuco. He said it was possible the government had been preoccupied with other tasks — or hadn’t moved on the crisis for political gain.

“It was probably waiting for smoking-gun evidence about Venezuela’s involvement in the spill, make a big fuss about it, and finally intervene,” he said. “The bigger the crisis, the higher the benefits.

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“This strategy backfired.”