Leaked video footage of ocean pollution shines light on deep-sea mining

Video footage from a deep-sea mining test, showing sediment discharging into the ocean, has raised fresh questions about the largely untested nature of the industry, and the possible harms it could do to ecosystems as companies push to begin full-scale exploration of the ocean floor as early as this year.

The Metals Company (TMC), a Canadian mining firm that is one of the leading industry players, spent September to November of last year testing its underwater extraction vehicle in the Clarion Clipperton Fracture Zone, a section of the Pacific Ocean between Mexico and Hawaii.

But a group of scientists hired by the company to monitor its operations, concerned by what they saw, posted a video of what they said was a flawed process that accidentally released sediment into the ocean. The scientists also said the company fell short in its environmental monitoring strategy, according to documents viewed by the Guardian.

As the push for deep-sea mining intensifies, experts are increasingly concerned that companies will kick up clouds of sediment, which could be laden with toxic heavy metals that may harm marine life. At least 700 scientists – along with France, Germany and Chile – are calling for a moratorium on deep-sea mining.

In a post to its website, TMC acknowledged the incident, but framed the discharge from its cyclone separator as a “minor event” in which “a small amount” of sediment and nodule fragments spilled into the ocean. The company said it fixed the issue in its equipment to prevent further overflows and concluded that the incident “did not have the potential to cause serious harm”.

In a statement to the Guardian, the International Seabed Authority (ISA), a UN-affiliated agency set up to control and regulate deep-sea mining, said its preliminary assessment “identified no threat of harm to the environment” but it was waiting for a more detailed report of the incident from the company.

While many of the technologies used in deep-sea mining were developed decades ago, the inadvertent discharge during testing highlights the challenges of fine-tuning equipment for use in the field.

Experts and critics caution that the incident highlights the relative uncertainties surrounding deep-sea mining. Companies are scrambling to scavenge the ocean floor for valuable metals, used in electric vehicle batteries and a host of other technologies such as green energy production, amid a global fight for stable supply.

“What we’ve seen is an unauthorised release and, in terrestrial mining, this would have consequences of some sort. And the company says they told the regulator as a courtesy? This is bizarre,” said Catherine Coumans of MiningWatch Canada, adding that the incident runs counter to the assurances from companies that sediment won’t be released near the surface of the ocean.

TMC, which is based in Vancouver but whose senior staff are scattered across the US and Europe, says it has been exploring vast tracts of seabed to mine “polymetallic nodules”, formed of nickel, copper, cobalt and manganese, that have precipitated out of ocean water over millions of years.

It has long been known that the nodules contain critical elements for constructing batteries and other electronics, but their depth meant that extracting them had, until recently, been considered too costly and arduous.

Heavyweight investors now looking hungrily at deep-sea mining include the Danish logistics giant Maersk and the commodity multinational Glencore, underscoring the hopes that industry has for unearthing new sources of critical metals, such as copper, cobalt and nickel.

Investor materials from TMC suggest the company believes its mine sites in the Pacific could produce more than $30bn (£24bn) in profits over the next 20 years with minimal harm to the environment. But the push is increasingly controversial: two years ago, major battery users including Google, Samsung, Volvo and BMW joined a World Wildlife Fund (WWF) call for a moratorium on seabed mining over fears of lasting environmental damage.

Scientists hired by TMC and its subcontractors say the sediment monitoring plan, critical for the company’s approval to begin mining, was developed without full consideration of how sediment plumes (debris kicked up from mining the sea floor) actually work, and that those tasked with overseeing the efforts had little experience working with the plumes.

In one instance, scientists observing the testing allege that a subcontractor on the project, the DHI company, used a robot to generate a disturbance after mining operations weren’t going as planned. As a result, the scientists called any of the data obtained “uncontrolled and unscientific”, and largely useless.

They also said DHI attempted to “influence independent scientific sampling activities” by directing scientists to take samples when no plume was present, warning that the deficiencies created a “failed and flawed monitoring operation”. In their notes, the scientists concluded the data “cannot be considered for any future study and cannot support any modelling validation or future modelling effort”.

Related: Race to the bottom: the disastrous, blindfolded rush to mine the deep sea

DHI told the Guardian that testing parts of the water without sediment, known as “out-of-plume” measurements, is a critical part of the monitoring process in order to establish the boundary of the plume. Tom Foster, president of DHI Water and Environment, said it was “highly misleading” to characterise the testing procedure as an attempt to “influence” scientific sampling. The company followed “industry standard precautions” for assessing possible contamination of samples, he said, and procedures were in place to reject any samples “negatively impacted by contamination”.

In a statement to the Guardian, TMC said that, as part of its monitoring efforts, samples were taken of various plume concentration levels to better understand the “behaviour and impact of the collector system and plume”. The company said it hired “world-leading experts in the field” to oversee the monitoring, and dismissed “baseless” claims of any attempt to manipulate the data.

Critics have long feared the plumes of sediment created from extraction could seriously harm marine ecosystems by limiting light penetration and releasing harmful toxins. “We don’t know what the consequences of those problems were under the surface of the sea,” said Coumans. “We’re only seeing the tip of the iceberg. We’re not getting transparency.”