Researchers issue warning after discovering overlooked fallout of major oil spill: 'I'd never observed anything like this'

A decade after an oil byproduct spill in Brazil's Amazon region, new research has revealed just how severe the ecological fallout was and why it continues to threaten delicate ecosystems.

What happened?

In 2013, roughly 16,000 gallons of petroleum asphalt cement — an oil byproduct used in road construction — spilled into the Negro River near Manaus. When biologist Helen Sadauskas-Henrique saw the news, she immediately abandoned her Easter holiday plans to investigate.

"I had already conducted lab tests on the effects of oil exposure on fish in the Negro River, but I'd never observed anything like this in the natural environment," Sadauskas-Henrique, now a professor at Universidade Santa Cecília and a researcher with the National Institute of Amazonian Research, told Mongabay.

Her team's findings were published in Environmental Research and reveal that the spill caused genetic damage and neurological stress in at least two fish species — the threadfin acara and the demon eartheater, both native to the Negro River. Even after contamination levels fell after 90 days, the fish continued to show DNA damage and signs of cellular stress that impaired their ability to swim, feed, and reproduce.

Why are oil spills in the Amazon concerning?

The study shows how the unique chemistry of Amazonian "blackwater" rivers, which are rich in dissolved organic carbon, can make oil toxicity a big problem. These conditions allow harmful hydrocarbons to bind with organic matter, making it easier for fish to absorb them and prolonging the contamination.

Because many Amazonian species are sedentary and bottom-feeding, they're more likely to eat oil-contaminated sediments — putting them at higher risk of long-term genetic damage and population decline. Because of that, repeated spills could devastate the food web, threatening the communities that depend on fishing for their livelihoods.

Sadly, oil contamination is not rare in the Amazon. In Peru alone, Oxfam says 474 spills were documented from 2000 to 2019, and many other occurrences have been recorded in Brazil's Amazonas state. As governments consider new oil exploration projects, scientists worry that future disasters could overwhelm ecosystems already stressed by drought, deforestation, and pollution.

What's being done to protect Amazonian waters?

Brazil has fined companies for illegal operations, but enforcement is inconsistent. The researchers behind this study pointed out the need for stricter monitoring and comprehensive spill databases to track long-term ecological effects.

Environmental advocates argue that this should lead to the halting of oil development in the world's largest rainforest. Groups such as Stand.earth and the Coordination of Indigenous Organizations of the Brazilian Amazon are doing their part to urge financial institutions to divest from oil exploration and instead support renewable energy alternatives that protect biodiversity and Indigenous lands.

For readers, supporting these movements — and just staying informed about the hidden costs of oil dependence — helps build pressure for better management and protection of precious natural spaces such as the Amazon.

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