These Frequently Asked Questions relate to Planetary’s general process and operations.


For questions specific to individual sites, please visit our project pages: Cornwall FAQs and Nova Scotia FAQs.  


If you have a question that isn’t addressed on our site, or if you’d like your question answered in more detail, we encourage you to reach out. We’re always grateful for engaged participation from communities around the world.

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  • Is Planetary’s process safe?


    We, along with our third party scientific and academic partners, are confident that these projects are safe for humans, animals, and the marine environment – from plankton to whales, and everything in between. 

    Marine safety is of paramount importance to every member of Planetary’s team, and we approach all research with an abundance of caution. Our precautions are too lengthy to answer in a brief FAQ, but we encourage you to visit our safety page to read in detail about how we have built safety into our process and our operations.

    To summarize:

    • Magnesium hydroxide has been ingested by humans and commonly used in wastewater treatment, without trouble, for decades.
    • Testing indicates that the compound is safe for aquatic animals, and there is no evidence that magnesium hydroxide is bio-accumulative.
    • Our studies are conducted for a short duration, and at a low concentration, below all safety and regulatory limits. 
    • We monitor our alkalinity and the receiving waters before, during, and after a study begins to ensure there are no unforeseen impacts on the ecosystem. (More information on that ocean monitoring is available here.

    Mike Kelland
    Chief Executive Officer, Co-Founder & Board Member

  • How do you respond to concerns about the potential moral hazard of Carbon Dioxide Removal (CDR)?


    This question strikes at the moral implications of carbon removal – and is a difficult question to address fully as a single question. Mike Kelland has therefore taken this moment to offer a more detailed response as a blog post.

    Mike Kelland
    Chief Executive Officer, Co-Founder & Board Member

Monitoring and Verification

  • You have stated that the carbon you sequester will be stored for 100,000 years. How do you know?


    This storage timescale is widely accepted by the scientific community and policy makers and is considered one of the main attractions for this type of carbon removal compared to other less permanent approaches that are currently proposed. 

    Our planet and atmosphere form a closed environment. Carbon continuously cycles in and out of the land and sea – into the atmosphere and back again. The ocean plays a very important role in this cycle as it stores the vast majority of the carbon on earth (approximately 34,000 metric Gigatons or 34,000 Gt) in the form of dissolved, alkaline carbon seawater. In addition, we also know that this carbon is stored out of the atmosphere for very long periods of time. We know this by measuring how much alkaline carbon the ocean intakes annually, and by verifying how much of this carbon is precipitated out annually. The net result is approximately 0.3 Gt carbon loss from the alkaline carbon pool. From this we can calculate the mean time that the carbon will be locked away, which is called residence time: 

    Residence time of carbon = (total carbon stored) (net loss of carbon/year)
    34,000 Gt / (0.3 Gt/year) = 113,333 years

    We round this down to 100,000 years to be conservative and to account for uncertainties in the calculation. 

    Our process captures CO2 and converts it to this same long-lived alkaline carbon. Doing so will allow the ocean to plan the important role of safely removing and sequestering carbon from the atmosphere. While the chemistry involved in this form of carbon storage is a bit complicated, it is also well published and well understood.

    Dr. Greg Rau
    Chief Technical Officer, Co-Founder & Board Member

  • How do you plan to monitor biological impacts before, during, and beyond your study periods?


    We believe that all our studies are safe. We won’t conduct studies that we think will cause harm. That would simply go against everything we believe in – our Code of Conduct, the scientific method, and our dedication to the restoration of the ocean. Therefore, we have developed a rigorous monitoring program that will make sure that our assumptions are correct and that nothing unexpected occurs. 

    For more information on how we monitor for biological impacts, please see our Ocean Monitoring and Safety pages.

    While exact details of monitoring will depend on individual sites and local partnerships, we have published a blog post to outline our monitoring process before, during, and beyond our study at Cornwall.

    Dr. Will Burt
    Chief Ocean Scientist


  • How do you source your alkalinity? How do you intend to source it as you scale up?


    Ultimately, Planetary’s goal is always to use the nearest and lowest-carbon source of safe alkalinity. Each project site is unique, and careful incremental trials of our process are required before we can scale up in any substantial way. That’s how we keep things safe. As a result, it doesn’t typically make sense to invest in building a new, low carbon supply of alkalinity nearby until we’re gone through an incremental scale up and have the “demand” that would make that large investment worthwhile. That means that at low scales, we need to rely on the sources that are available today. 

    There are several pathways to produce magnesium hydroxide (MH) for carbon removal: 

    • MH can be mined directly from the ground as brucite, its mineral form. Brucite is relatively scarce in a pure form, so the cost can be high, but it has a low carbon footprint as it requires little processing. Our first trials use brucite, since it’s available today without needing large infrastructure to be built. 
    • It can also be produced through the addition of slaked lime (Ca(OH)2) to brines such as seawater. If the slaked lime is produced from limestone using a kiln that captures CO2 emissions, and the brine does not contain carbon or the carbon is kept in the brine through the process, this can be a suitable MH source for carbon removal. This could ultimately be a lo-cost and globally abundant source, since limestone is so prevalent, once carbon-capture kilns are more commonly in use. 
    • MH can be produced through its extraction from magnesium silicate rock. Planetary is pioneering this process and it will be several years before it gets to scale. This process, though, has the highest potential because magnesium silicate is globally abundant and is produced at a massive scale as a waste in nickel, lithium, and other mining activities. 

    From a cost and efficiency standpoint, local sources of MH are preferred. Every mile of transport creates emissions which reduce the total net removals of our OAE process and increase costs. Transportation emissions depend on the mode of transport. For bulk product shipments, the emissions, from lowest per-tonne mile to highest are long-haul ship, short-haul ship, rail, truck, and plane. This means that the most viable sources are those which are coastally located. It also means that removals can generally be achieved at various places around the world based on these coastal sources. Assuming that our trials are successful, our goal is to source MH as near to the point of addition as possible. While none of the following sourcing arrangements are currently in place, we see the following potential sources: 

    • Development of the Planetary process to utilise magnesium silicate waste from mining operations (such as in Cornwall).
    • Provision of a carbon-capturing kiln to existing MH producers. 
    • Development of new brine processing from the use of UK limestone with a carbon-capturing kiln. 

    Until these processes are developed and deployed, we’ll use MH from other sources on a per-project basis that provides a net carbon benefit despite transportation emissions. 

    Jason Vallis
    Vice President, Operations

  • What safeguards are there at the mining/mineral processing stage to prevent toxic minerals from entering the ocean?


    We have a multi-step process and several safeguards in place to ensure that the antacid added to the ocean outfall is fully compliant with local regulatory standards like the UK Environmental Quality Standards (EQS) or the requirements of Canada’s Fisheries Act. 

    First, we work with mineral suppliers to select products that are known to be safe in multiple applications. For example, one of the reasons that we have chosen Magnesium Hydroxide (MH) for projects is that it has been safely used in water treatment for decades.

    We then have samples sent to an independent third-party mineral testing facility to conduct trace element analysis. This allows us to measure any impurities in the product and assess its variability. 

    Next, we compare the elemental analysis results with local regulation for coastal waters. This allows us to predict how much alkalinity can be added as a percentage of the flow rate, as well as how much can be added over a given period while complying with these standards. 

    We conduct elemental analysis on each batch of alkalinity prior to shipping. Any batch that does not meet regulatory standards at the base addition rate will not be accepted. 

    Throughout the addition phase, we will be taking samples of the treated water upstream and downstream of the addition point to measure any baseline impurities in the outflow, as well as any changes resulting from the addition. 

    As a final safeguard, we work with independent scientific consultants to collect water column and sediment samples at and around the outfall to determine if a difference in trace element concentrations can be detected over baseline samples. 

    Jason Vallis
    Vice President, Operations

Archived Questions

Planetary will always answer community questions to the best of its current knowledge. However, our understanding of our project sites is improving over time, and our answers may shift based on new scientific data or newly published research. When this happens, we may update our responses to FAQs on this page.

To maintain transparency, we have preserved previous versions of FAQ responses, and these can be read below.

  • Is your process safe? (August 2023)


    We, along with our third party scientific and academic partners, are confident that these projects are safe for humans, animals, and the marine environment – from plankton to whales, and everything in between. 

    The scale of our research is always carefully calculated to be well within all safety thresholds. Magnesium hydroxide is used in wastewater treatment and is regularly consumed by humans and animals in foods and medicines. 

    In seawater, magnesium hydroxide reacts with CO2 to form carbonates and bicarbonates – the same stuff that’s in a Rennie or a TUMS. Magnesium and carbonates are vital and abundant components of seawater. Carbonates are the building materials for shells and bones. Without them, most sea life as we know it would not exist. 

    The net effect of our addition to wastewater is to make it more similar to the seawater it flows into. Since wastewater is made of fresh water and contains biological CO2 after treatment, it’s slightly more acidic than seawater. Adding magnesium hydroxide has the effect of balancing it to make it the same pH as the sea. 

    As with everything, doses matter. Even water is fatal in doses that are too large. Within the wastewater pipe, where the concentration will be the highest, it will still be less than half of the concentration required to affect a water flea (here is an example of a safety data sheet with relevant information). Once it reaches the sea, it dilutes within seconds to a concentration that is undetectable by the best sensors in the world. 

    Despite how safe this material has been shown to be in centuries of human use and decades of lab and open ocean experiments, we approach all research with an abundance of caution. We do this by: 

    • Testing every batch of alkalinity that we use for trace metals and rejecting batches that don’t pass.
    • Planning sediment and biological surveys before, during, and after the research period. 
    • Deploying sensors throughout the system from the point of addition through to the surrounding ocean. 

    Given all of that, let’s dig into the details!

    Safe for Ocean Mammals and Fish

    The “gold standard” of testing for aquatic animals is a test of acute levels of any substance on fish, specifically Pimephales promelas (fathead minnows) and on aquatic invertebrates (specifically Daphnia Magna or “water flea”, a small planktonic crustacean). In both tests (here and here, click on Reference 1), magnesium hydroxide is shown to not be toxic at levels that are much higher than any level considered during research projects. 

    Some people have asked us if the addition could have a laxative effect on ocean mammals. The answer is no. For humans, a regular “laxative” dose is 3,735 mg. Based on this calculation, a female adult seal would need to drink up to 100,000 litres of water from within a very close proximity (approximately 10 metres) of the outfall in one sitting to get a similar laxative dose. 

    Safe for Ocean Plankton

    What about plankton – the very important foundation of the food chain?

    Planetary’s process is safe for ocean plankton. A recent study published in Tasmania showed very limited impacts to phytoplankton communities that were subjected to prolonged alkalinity increases at more than 100 times higher concentrations than what is being considered for our studies. These authors consider the climatic benefits to far outweigh the concerns for these communities (Ferderer et al., 2022).

    Similar studies have been conducted at Dalhousie University in Canada. Although they have not yet been published, preliminary results from these studies also conclude that no impacts were found on the phytoplankton species tested in scenarios that mimic the naturally flushed systems where field additions will occur. It has been noted in recent research that in much higher concentrations, there could be some impact on plankton if the light reaching the plankton is blocked in some way, for example if the water were to become murky because of large amounts of magnesium hydroxide particles. Luckily, there is no reasonable risk of water becoming murky as a result of Planetary’s process, and even at a concentration level that is much higher than what is planned for our research. 

    Nonetheless, because plankton are so important to the ocean ecosystem, we will carefully monitor both the turbidity of the water and the plankton communities themselves near the diffuser area to ensure that there is no unforeseen impact. 

    Risks Do Not Build Over Time

    We have been asked whether there is a chance that this substance is like a pesticide, similar to DDT or some other substance that slowly accumulates in plant and animals, becoming more dangerous as it moves up the food chain. 

    The answer is no. This question (called bioaccumulation) has been directly studied. There is no evidence that magnesium hydroxide is bio accumulative.

    Planetary Combines Basic Safety with Low Concentrations and Short Durations

    The short duration of our research is another element that creates additional safety. 

    As a safety precaution, all research starts at a very low concentration. For context, milk of magnesia is produced at a concentration of 415 mg/5ml (which is 83,000 ml/L). This is more than 700 times the concentration that we plan to add into the ocean. And what’s more, as soon as our material reaches the ocean, it disperses very quickly, about 1000 times within 50-100 metres of the diffuser, and even more as the tide and currents wash it away from the area. This means that even a short way away from the diffuser, the concentration is more than 700,000 less than the milk of magnesia you can buy in a store. 

    To Recap:

    • Magnesium hydroxide has been ingested by humans and commonly used in wastewater treatment, without trouble, for decades.
    • Testing indicates that it is safe for aquatic animals. 
    • There is no evidence that magnesium hydroxide is bio accumulative. 
    • Our studies are conducted for a short duration, and at a low concentration. 

    We are confident that our research projects are safe. Please see our blog post on monitoring to learn how we will gather data to prove that no harm occurs, and please see our answers on the bloc post on the moral imperative of carbon removal to see why we believe that this is a critical tool in healing our climate.

    Mike Kelland
    Chief Executive Officer, Co-Founder & Board Member

  • If the study in Cornwall is deemed a success, you mentioned scaling your project up […] Please can you clarify your maths and how you get to your calculations of 1GT of annual CO2 removal by 2035?


    Question archived as this goal no longer reflects our current timeline.

    As our company has evolved, we’ve learned a lot. At the outset we set ourselves the goal of 1 Gt (one billion tonnes) by 2035. This was based on looking at high level markers, including the availability of alkalinity sources, the capacity of the ocean to take up additional CO2, and the urgency of the climate crisis. There are a number of reasons that we now see that timeline as unrealistic. One very important factor is the time required to do the science to ensure that a scale up of the process is safe. And then there’s the economic and coincident moral implication – decarbonisation needs to be the priority in the near term and the markets will reflect that – we doubt now that there will be a market that would support a billion tonnes of removal in place by 2035. We’ve therefore set ourselves a new goal of 1 Gt by 2045. This is in alignment with IPCC climate models and the scale up of carbon removal those models tell us that we’ll need.

    But why a 1 Gt goal at all?

    Simply put – we believe that setting a high goal helps to shape our thinking. Because we think at climate-relevant scales, we design systems that can sustainably operate at that level. It helps us to make harder decisions today in order to build a better solution for the future. In short – we aren’t spending time on a process that won’t be able to work on a global level.

    Having a high goal as a guiding principle means that we:

    • Invest heavily today in environmental safety and community engagement. It sets us on a path to be here for the long term, and not to just create a short-term and small-scale approach. It forces us to be transparent and incorporate social and environmental justice in our business models rather than punting those questions to the future.
    • Design systems with strong controls on side effects. For example, it’s pushed us to reject simpler solutions that produce toxic waste streams – the burden of those wastes would be impossible at scale.
    • Contribute to the general growth of the field, understanding that we work in an ecosystem, rather than trying to capture short term value – as evidenced by the public release of our MRV protocol last month, and as evidenced by our cooperation with research efforts at university and research institutions around the world who are leading the efforts to validate the safety and effectiveness of this process.

    Will we reach 1 Gt/y by 2045? We hope so. But if we don’t, we still believe that building towards that goal is the right thing to do.

    The Hayle discharge rate is many times smaller than other wastewater facilities (about 30 times smaller than Boston MA for example), and several hundred times smaller than other potential discharges such as cooling water loops from power plants. We see this single ocean outfall as a small part of a large network of additional sites, where the total amount of carbon removal can be at the gigatonne level.

    All of these logistical items, however, must be held to the standard of safety. The true limit to scale will be the pace at which science tells us that this process is safe. This is one of the key reasons for this small study – to continue the solid science that has been done in the lab and the ocean around the world.

    Mike Kelland
    Chief Executive Officer, Co-Founder & Board Member