The potential of phytomining in Sulawesi
By: Dyna Rochmyaningsih
Tags: Science, Indonesia, Sulawesi, Biodiversity

Sixteen years ago, Aiyen Tjoa, an Indonesian soil-biologist, explored a small mining town located on the heart of Sulawesi. Sorowako, as it is called, once had been home to the immense diversity of plants, most of them were found nowhere else. But then (and now), it has been one of the largest nickel mining areas in the world. When Tjoa got there, most of the areas in the town were already deserted for mining, but some were still bushes or even newly-grown forests. At that time, Tjoa felt she still had a chance to find something that was disappearing so fast in there; super plants that could take up a nickel from the soil.

Nickel-eating plants, also known as nickel hyper-accumulator, is a very rare group of plants that is able to accumulate at least 1000 microgram of nickel in one gram of their dried leaf.

In the naked eye, they may look like ordinary ones. But their adaptation on heavy metal exposure makes them superior. All plants take up large amounts of common minerals like nitrogen (N), phosphor (P), and magnesium (Mg) to grow, reproduce, and finally survive. But they also need to suck up a tiny amount of heavy metals to activate some important enzymes inside their body. As for nickel, “it is needed to activate the enzyme which is crucial in plant’s flowering process,” says Tjoa. But a little more of nickel could retard ordinary plants or even kill them. Nickel-eating plants have evolved superior ability to detoxify this excess by “binding the metals in their cell walls or even store it in vacuole [food storage organelle inside the cell],” she says.

The metallic-green sap of Pyllanthus balgooyi.Image credit: Anthony van der Ent

Some nickel-eating species like Alyssum murale could take up nickel up to 30,000 microgram and some like Phyllantus balgoyii bleed blue-green sap when the bark is tapped. So far, around 450 species of nickel-eating plants have been documented world-wide. Most of them grow in countries with less plant diversity and lower nickel deposits such as Cuba (130), Southern Europe (45), New Caledonia (65), and Malaysia (24). Curiously, only very few of them are from Indonesia, one of the most biodiverse regions and the largest nickel deposit in the world, and “none of these are as super as Alyssum murale,” says Tjoa.

After securing a permit from PT. Inco (now PT Vale Indonesia), a mining company that holds the concessions in Sorowako, Tjoa quickly packed up her gears to scan the town. It took her four years of self-funded explorations (2004–2008) before she finally spotted two species of nickel-eating plants; Sarcotheca celebica and Knema matanensis. By analyzing its nickel concentration in the lab, Tjoa found that both native plants could store 1000–5000 microgram nickel in one gram of its dried leaf. But those were not the ones she was looking for. Compared with other nickel-eating plants documented worldwide, this power is considered weak. “We’re looking for plants that could accumulate at least 10000 micrograms,” says Tjoa, who is also a lecturer at Tadulako University in Central Sulawesi.

Rainforests in Halmahera. Image credit: Anthony van der Ent

At the beginning of the millennium, scientists like Tjoa are looking into the potential use of nickel-eating plants to mine the metal (phytomining) and to recover soil condition of ex-mining site (phytoremediation). A number of research have shown these strategies could be a win-win solution for both the mining industry and the environment. Planting nickel hyper-accumulator in a mined soil could improve soil fertility, promote the return of natural vegetation, while at the same time making cash by harvesting the nickel in the plants. In the future, this technology could empower rural communities in nickel-rich areas who could cultivate the plants by themselves. Indonesia, as a country with the richest plant diversity and largest nickel deposits in the world, is said to be the most potential to adopt the technology. But scientists are struggling to get support for research and exploration.

Nickel-eating plants store the metal either in leaves, roots, or even the sap in their stems. But the highest nickel concentration hides in their shoots. Scientists say pruning, or trimming the shoots, is the most effective way to extract nickel from the plants. This biomass will then be burned and by further process separating the nickel from the ash. Anthony Van der Ent, a plant ecophysiologist from the University of Queensland, calculated that a Phyllantus species can produce an estimated 120 kilogram of nickel per hectare every year. This process is also environmentally-friendly. Even though the burning of plants' biomass releases biomass, the continuous cultivation of nickel-eating plants can be considered carbon neutral. “All carbons released from the burning will be “captured” again by the newly living crop in a few months,” he says.

This potential is even bigger because nickel-eating plants could also recover the strip-mined areas. Tjoa says most mining companies in Indonesia are ignoring revegetation requirements but some mining companies have tried to rehabilitate the mined soil by planting normal plants. A study supported by PT. Vale Indonesia reported that the company has successfully improved the soil health in their ex-mining areas by planting “pioneer plants” . “The twelve-year revegetation process has brought positive impacts on both physical and chemical parameters of soil, which are increased significantly,” the study says. “But most of these plants are a common weed that is highly undesirable for rehabilitation,” says Van der Ent.

Nickel-eating plants could do better, he says. It would improve soil health because it cleans up the toxic nickel and finally bring back the nutrient status and organic matter. “Eventually, normal crop plants can be cultivated on these soils after phytomining has finished,” he says. It could also give an economical benefit for the mining company because the nickel residue that have been accumulated in their shoots could be harvested. Currently, only soil which consists at least 1% of nickel could be mined by traditional mining technology. “But a hyper-accumulator can achieve high levels of nickel accumulation in a soil that consists of just 0.1%,” he says.

Other potential benefit is the socio-economic impact. In Sabah, Malaysia, Van der Ent has been conducting phytomining field trials since 2014. “We found out that phytomining really works,” he says. This could also be applied in outside mining areas like their “metal farm” in Mount Kinabalu. But Van der Ent underlines that the technology is not aimed to replace the current mining technology but instead it should be done in parallel in mining strategy. Most importantly, unlike traditional mining which often clashes with indigenous, “we envisage that it will be implemented by smallholders in rural communities living on nickel-rich areas as an alternative form of agriculture,” says Van der Ent.

Indonesia is known as the largest nickel producer in the world with around 80 million tons of nickel exported last year. But the country’s mining industry is also rife with social and environmental problems. A tip of the iceberg is a clash between a mining company and indigenous people in Wawonii, a small island in Southeast Sulawesi. Mining Advocacy Network (JATAM) reported that the conflict, which started in July 2019, stemmed from land grabbing done by the company which finally halted its operation in the island. A WWF-report in 2016 also shows the increasing mining activities had caused a high level of sedimentation in Sulawesi waters which threatened the coral reef in Sulawesi waters.

Tjoa says a phytomining strategy could alleviate these problems and put environmental value in the industry. “But no one seems to put attention on this potential,” says Tjoa. She says she tried to communicate with PT. Aneka Tambang (ANTAM) in 2009, Indonesia’s state-owned mining company, but the response was very slow and uncertain. PT. Inco once supported her research on phytomining when she did a field trial on the adaptation of Alyssum murale in Sorowako. But the collaboration was terminated partly because the company was transforming to PT. Vale Indonesia. “Unfortunately, no collaboration since then,” she says.

Van der Ent, says this situation is such an irony. No other country has a greater potential for phytomining than Indonesia,” he says. Given the extraordinary plant diversity and geological history, he is convinced that the country has a huge potential for the discovery of nickel hyperaccumulator. Sulawesi and Halmahera, the neighboring island, is the place where the largest ultramafic bedrocks in the world (23,400 hectares) can be found. Soils that originate from this bedrock have a very high concentration of nickel and at the same time supporting a high level of plant endemism. “That brings the minerals industry capitalizing on nickel resources in direct conflict with biodiversity,” says Van der Ent.

No other country has a greater potential for phytomining than Indonesia. Image credit: Anthony van der Ent.

Lack of research funding from the Indonesian government is also one of the problems. Since Tjoa’s exploration in Sorowako, her research proposals to explore indigenous nickel hyper-accumulator in Indonesia has always been rejected. “One reviewer even said that my work is not important,” she says. This situation is especially dire because, as the businessmen are busy clear land for mining and governments are busy ignoring phytomining research, some potential plants vanished before they are found. A study shows that Sulawesi has lost nearly 20% of its forest cover in 1990–2014 period. “We have lost such a big chance to find these plants,” says Tjoa.

This fact bothered Satria Bijaksana, a professor of rock magnetism from Bandung Institute of Technology (ITB), who met Tjoa at a conference in Sabah back in 2013. Before meeting Tjoa at a conference, Bijaksana says he was looking for relevant research in Sulawesi’s geo-ecology and fascinated by phytomining studies conducted by Tjoa and Van der Ent. Given the dire situation to find nickel-eating plants in Indonesia, he wondered if his expertise in magnetism could help to make a faster screening process. Mujahid Hamdan, his Ph.D. student who was born and raised in the island, quickly joined the research which was funded by ITB, Japan’s Asahi Glass Foundation, and Indonesia’s Ministry of Research and Technology.

“Basically no plant is magnetic,” says Bijaksana. But its magnetism can be tested once the dried leaves have been burned and become ashes, he says. A number of research have shown that nickel-uptake in hyper-accumulator plants happens at the same time with the uptake of iron (Fe), — a highly magnetic metal. Together with Tjoa and Hamdan, he designed an experiment to see if the magnetic susceptibility increases when the plants accumulate more nickel. By testing the ashes from two species of well-known hyper-accumulators (Alyssum murale and Alyssum corsicum) and ten indigenous plants in Sulawesi and Halmahera, they found a positive result. “Magnetic susceptibility analysis can be used to differentiating nickel hyper-accumulator with normal plants,” says Hamdan.

So far, scientists like Van der Ent and Aiyen use a special paper to test nickel presence in a tree. “The paper instantly turns pink when leaves are pressed against it. It’s foolproof, easy to do and fast,” says Van der Ent. To analyze its nickel concentration, scientists bring the plants to the lab and put them under X-ray Fluorescence, a device frequently used by mining companies to detect metals. “But we think using magnetism could fasten the process because it only detects a high concentration of nickel,” says Bijaksana. Their study, which was published by The Journal of Geochemical Exploration” in May 2020, even identified two new species of nickel loving plants from Sulawesi: Casearia halmaherensis and Piper. sp. Both could accumulate 2600–2900 micrograms in one gram of its dried leaf. Bijaksana admits that his research is still preliminary but he hopes it could convince research funders of the potential of phytomining technology in Indonesia.

Tjoa says there is still a chance to find nickel-eating plants in Indonesia. In Central Sulawesi, a pristine rainforest sits on nickel-rich soils that make up the mountainous region in Morowali natural reserve. This greyish soil, called serpentinite, is thought to be the perfect place for nickel-eating plants to grow. Unlike Sorowako, which has been mined a lot and therefore has a lack of available nickel ions to be taken by plants, the serpentine soil in Morowali is rife with free nickels for plants. “Our survey in Halmahera has shown that nickel hyper-accumulators are common in this category of soil, but people haven’t looked for it in Sulawesi yet,” says van der Ent.“It all comes down on concerted efforts to find them,” says Van der Ent.

In the meantime, “an overseas mining company has expressed interests to apply this novel method,” says Tjoa. In 2017, she was contacted by a US-based investor who would like to fund her 5,000 hectares of phytomining trial in Sulawesi. For this project, she says, she would like to use Alyssum murale, the power nickel-eating plant from Italy in the trial. It might be weird to use foreign species in our place, “But maybe we have to use it first to convince the Indonesian government that phytomining works,” she says. As to deal with additional funding and administrative requirements, Tjoa says he has found a local company to support her project.

Even so, she still hopes the Indonesian government to fully support the whole green technology; funding the research, developing trials, investing in the business, and making a regulation to require every mining company to reserve a portion of rainforests in their concession area. When it is done, phytomining will give a huge contribution to carbon sequestration, create less mining waste, and lead to a better social-economic impact on the mining industry. “That is extraordinary,” says Tjoa.

*The edited version was published in BBC Future Planet