Black pools, long trenches and charred earth have become common sights in the fields of north-west Syria, signs of an informal oil economy that has developed during the war.

Despite damaging both the environment and health, up to 5,000 backyard oil refineries, crucial to the livelihoods of besieged Syrians, have cropped up in recent years, identified through satellite imagery in a report by open source investigators Bellingcat.

In and around the last remaining rebel-held areas, these refineries have provided fuel to a region where almost half the population has been displaced internally or from elsewhere in Syria. Yet they also bring a range of risks, according to the report’s author Wim Zwijnenburg, a researcher with Dutch peace advocacy group Pax.

“There was a need for oil and you could see on satellite imagery that artisanal refinery was growing but there are also concerns about health because of the dangerous working conditions like barrels that could explode,” said Zwijnenburg. “People were exposed to toxic fumes from burning that’s going on, and also a lot of children were involved.”

You see issues around respiratory problems, skin diseases and you see long-term concerns about cancer Wim Zwijnenburg, Pax

The clusters of refineries around the region receive oil transported from fields in eastern Syria and process it into fuel used for cooking, heating and transport by using rudimentary set-ups to burn it.

The open source material and satellite imagery used by Zwijnenburg shows that many refineries have emerged in fields that were still green until 2016.

There had previously been tens of thousands of refineries operating in north-east Syria, closer to the oil fields, before territory was seized from Isis and formal production returned.

Locals say the toxic smoke produced by the refineries has caused air pollution, contaminated water supplies and caused explosions that have forced a response from the White Helmets, the rescue group that runs operations in anti-government areas.

“Some of these locations are operational for a year, so you see issues around respiratory problems, skin diseases and you see long-term concerns about cancer. Burning this fuel day in, day out raises a lot of concerns among locals,” said Zwijnenburg.

He said oil waste produced by these operations was increasingly turned into cooking coals, which heightens health risks because it involves scraping the waste from barrels used in the burning process.

“It’s a very dirty job,” said Syrian activist Wissam Zarqa. “[A worker’s] skin would become darkened all the time, not from lack of cleanness. However he tries to clean himself, it would not work.”

A displaced former resident from the Aleppo countryside, who did not want to be named, said the refineries have increased the suffering of Syrians but also been necessary, especially in areas resisting the return of government control.

Men work at a primitive oil refinery in countryside outside al-Qahtaniyah, a town in Syria’s north-eastern Hasakeh province. Photograph: Delil Souleiman/AFP via Getty Images

“It is a problem, especially for the children. Personally I had problems sometimes because my village is small and some of the villagers were burning oil very close to the homes, only 150 metres away.

“In the area of the burners there is a lot of pollution because of the smell from the smoke, which reached into my house. My son was very small and he developed breathing problems.”

The resident said, however, that the refineries had also become important for Syrians living in rebel-held areas. This was partly because oil, which costs more than $100 (£81) a barrel, has become so expensive, and partly down to refineries becoming a major source of work, both within processing plants and for those who transport oil from the oil fields.

Much of the oil is transported by tanker through Kurdish-held areas in northern Syria, activity that has been captured on satellite imagery included in the Bellingcat report.

The Syrian Observatory for Human Rights has claimed that much of the oil is pumped from fields in Kurdish-held areas and owned by politicians with links to President Bashar al-Assad.

A bombing campaign by Assad’s forces and Russia displaced hundreds of thousands in Idlib and intensified food and fuel shortages through the winter, especially as many of the refineries were targeted.

“This is a fundamental problem for the residents here, fuel is needed for cars and to fuel the ovens we need to bake bread,” the former resident said.

“People don’t have a choice, they are forced by this matter,” he added, suggesting that the refineries would not be needed if fuel were provided to them or prices were cheaper.

“If only there was some help to providing an alternative, people would take another route.”

• This article was amended on 25 April 2020 to correct the main picture caption, which described the oil refinery at al-Qahtaniyah as being in the north-west of Syria when it is in the north-east.