DACHANG, China — Day and night, overfilled trucks rumble down Nanjiu Road in the saw-toothed hills that stretch to the Vietnam border. It's a procession at the heart of one of China's most hazardous industries.

The trucks load up on metal ore in the valley below, where 13 miners died in October in underground shafts laden with tin, copper and zinc. Then the trucks motor up the mountain toward belching smelters — the culprit, researchers say, behind arsenic levels in Dachang’s dust reaching more than 100 times the government limit.

Across southern China — far from the affluent coasts and Beijing’s gaze — a vast metals industry has fed the country’s manufacturing boom and sated global demand for components used in products from smartphone batteries to electric motors to jet airframes.

China’s production of material such as aluminum, copper, lead and zinc, known as base or nonferrous metals, has soared as the country has become the world’s factory floor. Combined output was 57 million tons last year, up from 6 million in 1998, according to the China Nonferrous Metals Industry Association.

But some of the country’s most isolated, impoverished communities are paying the price.

In Guangxi, a balmy southern region that has some of China’s most concentrated mineral deposits, large tracts of farmland lay wasted by runoff carrying cadmium and lead. Metal miners toil in shafts deadlier than China’s notorious coal pits.

Villagers roll up their sleeves to show deformities caused by ingesting food contaminated by heavy metals. Residents wait daily for shipments of fresh water.

In the past decade, China’s top leaders have steadily tightened regulations on the metals industry, including introducing the country’s first soil pollution law last year.

After an eight-year study that began as a state secret, the Chinese government said in 2014 that 20 percent of the country’s farmland was contaminated and a third of its surface water unfit for human contact. Top officials said last month that they had set aside $4 billion to clean up contaminated soil — similar to the U.S. Superfund — yet it’s a fraction of the $1 trillion that some Chinese experts predict is needed.

A review of soil and water data, interviews with environmental researchers, and a 500-mile journey through Guangxi illustrated how the sheer financial cost is only the tip of the challenge facing China.

“Central leaders may have a great vision,” said Song Guojun, a former environmental-protection official who studies policy at Renmin University. “But at the local level, there is no transparency, no upward accountability, no money.”

As a result, metal producers appear to operate with a degree of impunity — and leave a toxic trail — as they transform crude mountain ore into the essential nuggets of modern life. There are zinc slabs for coating steel, copper cathodes for wires and transformers, and grains of nickel matte, a step in making purified nickel used in batteries and other products.

From his soot-smeared home on Nanjiu Road, Wei Shujian has watched the trucks multiply since the 1970s.

“They are unstoppable,” the farmer growled, wheezing from an incurable lung disease caused by dirty air.

Wei nodded toward the hillside, where a huge elevator reached deep into the source of fortune and grief: the mines.

'No other choice'

Meng was sitting deep underground at the end of a 1,000-yard mineshaft, waiting to start his shift around 7 p.m. on Oct. 28, when the damp air was blasted by a shock wave.

Meng fled in a trolley to the surface, where he listened to the groaning earth: A branch of the Qingda No. 2 tin mine had collapsed. State media later said two miners were confirmed dead and 11 “had no chance of survival” inside the mine, about 10 miles north of Dachang.

Twenty years ago, Chinese coal miners had, statistically speaking, the deadliest job on Earth. Today, more metal miners are dying — 484 in 2017 — than their coal worker counterparts, according to the most up-to-date government data.

That’s partly because China’s coal mine safety has improved significantly under pressure from Beijing. But less attention has been paid to the metal industry, where about 83 percent of outfits are small and loosely run.

“The fundamental situation hasn’t changed,” a government cabinet spokesman said. “Production accidents are extremely likely.”

The Qingda No. 2 mine, run by a local mining boss, Chen Xiangsheng, is a case study.

Filings with the Industry and Commerce Bureau show that a government inspection in August found that Chen’s mine didn’t obtain approval for an expansion and that its construction blueprints “lacked authenticity.” Chen was fined twice in June for “substandard equipment and facilities” and “illegal production.”

Yet his mine kept humming around the clock, employing about 800 locals like Meng, a 32-year-old father of two young children.

Chen’s small operation paid $1,140 a month, Meng said. The state giant Gaofeng, which owns a maze of shafts directly under Dachang’s streets, is considered more professional but pays $300 a month.

“You can’t raise a family on that,” said Meng, who spoke on the condition that his full name be withheld. “The difference is, private bosses go wherever there is ore. State companies might leave it if it’s dangerous.”

After the Oct. 28 collapse, local authorities briefly froze mining in the county. One month later, Dachang’s miners were heading back to their shifts. The township of 30,000 lives in the shadow of a single industry with a chilling legacy.

In 2000, a toxic tailings pond broke and washed away an entire village, killing 28.

Dachang’s worst accident came a year later. Local officials tried to cover up a flood that killed 81 miners; the news got out after a week. Prosecutors later said that the mine contributed a third of local tax revenue and that its owner, the richest man in Guangxi, had transferred 15 percent of company shares to local officials.

The mines north of town continue to regularly experience explosions and collapses, killing one or two workers, residents said. Fatal accidents are not always reported.

“These tuhuangdi” — local tyrants — “get away with everything,” said Pan, a fruit seller who quit mining last year at age 34.

Many Dachang residents, like Pan, declined to give their full names for fear of reprisal. One taxi driver trembled when he was asked to drive by a three-story home owned by the mining baron Chen. After Chen’s mine collapsed in October, local authorities said, they arrested eight executives.

Meng shrugged off his recent brush with disaster, which he called “unavoidable.” He’s considered working as a security guard, he said, but would prefer going back to a small mine.

“If you want higher pay around here,” he said, “there is no other choice.”

Lead-poisoned children

Outside the mines, the risks don’t end.

Water used to separate the valuable minerals must be carefully stored and treated. The minerals are then purified at temperatures up to 1,800 degrees at smelters — a process that, without proper controls, releases harmful levels of heavy-metal byproducts including lead, cadmium and arsenic into the atmosphere.

Researchers from the Guangxi Institute of Occupational Technology and Nanning University sampled dust on road surfaces around Dachang. A study published in June said they found heavy-metal concentrations far above national safety limits: arsenic at 111 times, cadmium at 55 times and lead at 2.45 times.

Heavy-metal levels inside homes were only slightly lower, according to the researchers.

Off National Road 210, Wei Chun, a farmer, said more than 20 out of 25 children in his village, Tanghan, tested positive as early as a decade ago for excessive lead levels in their blood. For years, he said, county officials gave households with poisoned kids 30 eggs and liters of milk every month as compensation.

In another village, Tanghuang, people pointed to chestnut trees that no longer bore fruit and loquat trees and squash vines that turned yellow during summer rainstorms. Evaporating puddles left reddish circles on the ground, they said.

Between the villages was a swollen lake covered in a shimmering film. A sample of the water contained eight times the lead content deemed safe to drink by the U.S. Environmental Protection Agency, according to an independent lab test commissioned by The Washington Post.

Unlike in the United States or Australia, many polluted areas in China overlap with its southern agricultural heartland, which poses unique challenges. National panics have broken out in the past decade after consumers discovered high heavy-metal content in rice grown near smelters.

China has “a phenomenon of mining-agriculture mixed areas,” said Chen Nengchang of the Guangdong Institute of Eco-Environmental and Soil Sciences.

Yet talk of rehabilitating spoiled farmland often collides with reality.

In Daxin County, a four-hour drive south of Dachang, Huang Guiqing passed the field office of a soil cleanup operation and sighed.

“They’re still doing preparatory work,” he said.

In a bare living room, Huang struggled with a paper folder, his fingers distended like misshapen balloons. Growths the size of golf balls bulged out of his forearm and elephantine ankles. His documents told the full story: Huang spent years eating crops and drinking water laced with cadmium.

More than 46 other residents of Huang’s village were poisoned as early as the 1970s as a lead-zinc mine funneled wastewater for years into a ditch that locals used to irrigate their fields of cassava and sugar cane. The stream turned turbid, Huang said, “the color of soy sauce.”

Officials came in 2000 and found soil cadmium levels 30 times the national limit. But the local government didn’t take action except to pay each resident 15 kilograms of rice, according to a letter the villagers wrote pleading for help.

The mine went bankrupt in 2002. It wasn’t until 2015 that local officials responded.

In a directive to various departments and residents, a copy of which Huang provided, the local government acknowledged that it had neglected the disaster but said its hands were tied. “The polluted area is vast and the cleanup cost is tremendous,” officials wrote, estimating a $33 million bill. “The financial resources of Daxin County are utterly limited.”

The directive set a deadline for soil cleanup in late 2017. Then there was a new date that came and went: late 2018.

“Maybe they’ll start in 2020,” said a villager, Wei Tianlai, 68.

Local government agencies did not respond to faxed questions and requests for comment.

It’s the same story for communities across China, where local authorities are grappling with a sharply slowing economy and soaring debt levels.

“There are pressures on national expenditures,” said Chen You­jian, chief scientist at BCEG, an environmental remediation firm in Beijing. “As for the historical debts incurred, we do what we can.”

Red mud, undrinkable water

In 1986, Chinese officials informed leader Deng Xiaoping of Guangxi’s wealth of aluminum deposits. “It must be done!” Deng famously snapped back.

Two decades later, Xinfa Group, an aluminum conglomerate from northern China, has brought $2.4 billion in investments to sleepy Jingxi, the next county over from Daxin.

“You can see this from space,” Huang Qi said as he strode across a dam holding back a small valley filled with goopy red mud.

It was a reservoir of spent bauxite — aluminum ore — left by Xinfa, which has been locked in repeated disputes with locals going back 10 years. Three times in the past 18 months, waste has seeped out of such reservoirs, jamming underground rivers, flooding village streets and rendering the local reservoir water undrinkable.

In June, dozens of locals blockaded a Xinfa facility for three days to demand water before police dispersed them.

Chen Wenxi, a Beijing-based environmentalist, helped sue Xinfa on local villagers’ behalf in August 2018, seeking $2.8 million in damages. A preliminary hearing in local court in June lasted 15 minutes, he said. Chen has sought Xinfa’s environmental records, but the government denied him on the grounds that they were state secrets.

“There are biases, certain political factors, when one side has so much money and the other side is so poor,” Chen said.

Xinfa, whose chairman sits in China’s National People’s Congress, has been named a “core enterprise” in Jingxi’s five-year development plan.

Huang Lituo, a Jingxi deputy propaganda chief, acknowledged several “unavoidable” industrial accidents involving Xinfa. The local government would hold it accountable for the cleanup, he told The Post.

In recent months, the local government has fined Xinfa $15,000 for illegal prospecting. Officials have also ordered the company to truck in potable water to communities stranded without it.

But the influence of Xinfa’s presence is undeniable. Last year, Xinfa contributed more than $100 million in tax revenue, more than any other source.

“If not for Xinfa, we couldn’t carry out poverty alleviation, build schools, build kindergartens, build medical clinics,” said Huang Lituo.

Huang Hua, a villager in his 30s, saw bitter irony in depending on the firm for survival.

“We were fighting a water war with Xinfa,” he said. “Now if Xinfa moved away, we might actually die of thirst.”

Huang Hua looked out a car window at the Caterpillar excavators chipping away in the distance, turning verdant mountain faces into rust-colored terraces.

He wondered what Beijing was like and what he could possibly do to get help from the Chinese president himself.

“I wish Xi Jinping would see this,” he said, referring to China’s leader.

Then he quoted a proverb suggesting central authorities can have little sway over local affairs: “But the mountains are high, and the emperor is far.”

Wang Yuan and Lyric Li in Beijing contributed to this report.