Planetary Ocean Alkalinity Enhancement Trial Information Page

Closes 12 Feb 2025

Opened 12 Feb 2024


  • Planetary Technologies (Planetary) and South West Water (SWW) want to carry out a carbon sequestration trial in St Ives Bay.  This aims to lock up carbon dioxide in the ocean, removing it from the atmosphere.

  • As we are the environmental regulator, they sent us their proposal and requested a Local Enforcement Position (LEP) in spring 2023.  We explain what an LEP is below.

  • We asked the Water Research Centre (WRc) to carry out a detailed and independent review of the proposal.

  • We have now received their report, which considers the proposed trial is very low risk and contains some recommendations for Planetary.

  • As a result, Planetary will make some changes to their proposal and resubmit it to us.

  • We will need to assess the changes before we can make a decision.

This webpage explains what an LEP is and describes our next steps.  You can also download and read the WRc report on this page.


What do Planetary Technologies want to do?

Planetary Technologies (Planetary) are collaborating with South West Water (SWW) on a carbon sequestration trial to help combat climate change.  Carbon sequestration is the process of removing carbon dioxide from the atmosphere and locking it up, in this case in the ocean.  They propose to trial adding magnesium hydroxide (Mg(OH)2) into the treated wastewater outlet pipe at Hayle Waste Water Treatment Works.  The wastewater pipe will transport the magnesium hydroxide 2.4km out into the sea just outside St Ives Bay.  Magnesium hydroxide is used in some wastewater treatment plants and the data used in the WRc report suggests that it is of low toxicity to aquatic organisms at the levels proposed in the trial.  This is covered in more detail in the 'What did the WRc's independent report say?' section below.

It is recognised that to address climate change we need to remove greenhouse gases from the atmosphere as well as reducing our emissions.  Ocean alkalinity enhancement (OAE) is an example of a greenhouse gas removal technique.  Planetary have told us, and multiple independent peer-reviewed papers support, that the following chemical reaction should occur in the bay and will result in carbon dioxide being removed from the atmosphere.  This is supported by the WRc's findings that the technology has the potential for significant carbon removal.  You can also find this information on their website.

  • Adding magnesium hydroxide to the sea makes it more alkaline.  Since climate change has caused the ocean to become more acidic, this is considered a benefit.
  • The magnesium hydroxide converts carbon dioxide, which is already stored in sea water, into a salt (carbonates and bicarbonates).  This can remain dissolved in the ocean for up to 100 000 years.
  • As the amount of carbon dioxide in the sea water reduces, more is drawn down from the atmosphere to balance the carbon dioxide levels between the sea and the air.
  • This should reduce the concentration of carbon dioxide in the atmosphere and therefore contribute to reducing the impacts of climate change.

Source: Planetary's website - CDR (carbon dioxide removal) and OAE Basics


If you have any questions about this process, please send them to Planetary; their contact details are at the bottom of this briefing note.


What is the next step?

Planetary have completed Phase 1 of this trial and want to increase the amount of magnesium hydroxide they use in a second trial.

South West Water is the legal holder of the permit for operation of the treated wastewater outlet pipe into St Ives Bay.  The addition of magnesium hydroxide to the treated wastewater is not an activity that is currently permitted on South West Water’s discharge permit.  They are seeking reassurance from us that we will not normally take enforcement action against them should they carry out this activity without first modifying the permit.  This reassurance, should we choose to give it, would take the form of a Local Enforcement Position (LEP).

South West Water is currently unable to apply for a full permit variation until additional information is gathered to inform the application.  The proposed trial will allow the two organisations to collect this information and allow the EA to assess the impacts of such a change in the longer term.  A variation to the current environmental permit is also not suitable for such a short-term activity.

If Planetary and South West Water decide they would like to carry out this activity permanently they will need to apply to us to vary their current environmental permit, and a standard permit change process would be followed.


What is a Local Enforcement Position?

Operators can request a local enforcement position from us if they want to carry out an activity that is not authorised by their existing environmental permit.  If we choose to issue an LEP, it reassures operators that we will not normally take enforcement action against them, provided they meet certain conditions.

LEPs are normally only issued when the activity is considered short term and of low risk to the environment.  They include several conditions which aim to protect the environment and set out various monitoring and reporting requirements while the activity is carried out.

If we decided to issue an LEP but consider that the activity is causing pollution at any point, or the requirements aren’t met, we will withdraw the LEP immediately and if the trial did not cease, we would consider enforcement action.


What is the role of the Environment Agency?

As the environmental regulator, it is our responsibility to decide:

  • If we will issue a Local Enforcement Position (LEP).
  • What conditions Planetary and SWW need to comply with if we do issue an LEP.
  • If this activity presents a risk to the environment, wildlife or human health.
  • If Planetary's monitoring programme is suitable, and ensure they share the results with us.
  • If Planetary and SWW have suitable mitigation in place to prevent any harm and minimise these risks.

We are required under the Regulators Code to provide clarity to those we regulate.  This includes providing clarity as to whether we are likely to take enforcement action if the trial went ahead.


We understand you have a lot of questions for us and concerns about this trial, especially considering it is a relatively new technology.  We want to reassure you that we are considering this proposal in a lot of detail and seeking the evidence and information we need to make an informed decision.  We will not issue a Local Enforcement Position if we think the activity is likely to harm the environment, wildlife or human health.


Alongside the proposal from South West Water and Planetary, we also now have the following information from them:

  • An Environmental Impact Assessment.
  • Details of a monitoring programme and a commitment to share the results with us at regular intervals.
  • An explanation of the appropriate measures they plan to use to minimise risk of pollution and harm to human health and the environment.
  • A detailed assessment on the overall life-cycle carbon footprint of the project.
  • Details of how they will increase public engagement with local interest groups, environmental charities, the local authority, and others.


We instructed the Water Research Centre (WRc) to carry out an independent audit and appraisal of the proposed operation by Planetary and South West Water.  This audit addresses many of the questions and issues we have already received from stakeholders.  Planetary is revising its proposal and providing a response which we hope will provide further answers to the questions raised.

We are also seeking the views of other organisations with a marine environment regulatory role.  These will include Natural England and the Marine Management Organisation, amongst others.


What did the WRc's independent audit say?

We asked the Water Research Centre (WRc) to carry out an independent desk-based pre-trial audit.  With technical verification from two external third parties, WRc investigated aspects of the proposed trial, including:

  • Investigating the source of magnesium hydroxide.  This included its content and quality as well as supply chain impacts, such as social responsibility and the carbon footprint.
  • Any potential impacts on St Ives Bay and how they might be monitored.
  • Checking the calculations behind the modelling of the rate that carbon dioxide is dissolved.
  • The overall effectiveness of carbon sequestration.

We now have the full report from the WRc.  Overall, the impact of this trial is considered low risk.  WRc has made recommendations to Planetary and the key ones are summarised below:

  • Additional sampling of the source material.  This is because, at the moment, we have not got satisfactory information on the whole supply chain, so alternative sources or better documented assurance will be needed in future.  Planetary already has enough magnesium hydroxide, in the form of brucite, for the trial and have committed to resampling it to assure its content. They have already committed to finding a fully traceable source of magnesium hydroxide if they decide to expand this to a full-scale activity.
  • Overall, the WRc were satisfied that the dispersion modelling and calculations of dissolution rates were a good representation of what might actually happen - this trial will verify those modelled calculations.
  • Some additional monitoring is necessary to detect impacts and help confirm modelled dissolution rates.
  • The WRc recommends that Planetary refine their calculations of the suitable concentration of Mg(OH)2 to use, using long-term data on multiple appropriate marine species.  Please see our FAQs for more information about this point.

Planetary is now considering these changes and will need to resubmit its proposal to us once it has made them.

We will base our decision on the updated LEP proposal from Planetary Technologies and South West Water.  We cannot and will not make any decision until we have received this.

Although the WRc report is a technical document produced for the Environment Agency, and written as such, we have decided to make it available for you to download and read.  You can download it using the link at the bottom of this page.

If you have any questions for the WRc, please direct them to us at the Environment Agency at


Frequently Asked Questions:

Are you consulting on this decision?

No. A local enforcement position is a decision relating to enforcement.  These decisions are based on public interest and potential harm to people and/or the environment and are not subject to consultation.  We may use local enforcement positions when proposed research or trials that involve the development of new ideas, techniques and processes aren’t covered by permits.  A local enforcement position would only be used for a short duration and where environmental risks are low.

However, this doesn’t mean we don’t value your opinions, views and questions and we do want you to feel able to contact us and ask us questions.  We are committed to being open and transparent throughout this process.

If Planetary and South West Water decide to apply for a full environmental permit, then we will, and are required to by law, hold a formal consultation in line with public sector consultation principles.  We will let you know how to take part in this, through our mailing list and this information page.  

What is the government position on ocean alkalinity enhancement?

The UK Government recognises that to address climate change a range of actions are needed, including removing greenhouse gases from the atmosphere and reducing our emissions.  They recognise that engineered Greenhouse Gas Removal (GGR) technologies will play a vital role in tackling climate change and achieving the UK’s net zero target.  The Department for Energy Security and Net Zero (DESNZ) recognise the potential for ocean-based carbon dioxide removal and have funded two ocean-based GGR projects through Phase 1 of the direct air capture and GGR removal programme. 

Why is climate change important?

The World Meteorological Organisation (WMO) recently stated there is a 50% chance that average global temperature will reach 1.5 degrees Celsius above pre-industrial levels in the next 5 years.

Climate change is affecting the South West now.  Through 2022 and 2023 we experienced a period of drought lasting for 13 months, following 2022's summer of exceptionally low flows in our waterways, and changing rainfall patterns through the winter.  During this time, communities in Devon and Cornwall alternated between conflicting conditions of flooding or hosepipe bans.

What is the Environment Agency's role in climate change?

Climate change will significantly affect our lives and the Environment Agency’s work. The Environment Agency is responsible for:

  • acting to reduce greenhouse gas emissions.
  • regulating low carbon and renewable energy schemes.
  • helping people and wildlife adapt to the impacts of a changing climate. You can read more about this here: Environment Agency and climate change adaptation

The Environment Agency protects our air, land and water. Our regulation enables the UK’s transition to carbon net zero, ensuring we are sustainable and resilient to climate impacts.

We understand that innovative greenhouse gas removal techniques that are safe for people and wildlife need to be considered as part of the solutions to the climate emergency.  We need to ensure any trials are well regulated and happen in an incremental way to understand the risks to the environment.

We will ensure that novel technologies are subject to proportionate and risk-based regulation to provide the necessary level of environmental protection.

We have obtained information from Planetary and WRc to better understand and manage any environmental risks associated with Planetary’s proposal, and to better understand the greenhouse gas removal potential.

What is the London Protocol?

The UK government is a signatory to the London Protocol.  The London Protocol was originally formed to address dumping waste or other discarded material at sea.  We are waiting for Defra to confirm whether or not the London Protocol applies to this project.  The relevant amendment to the London Protocol is available for download at the bottom of this page.

I’m concerned that South West Water are involved in this trial, considering their performance in the recent Ofwat Water Company Performance Report 2022-23. Will their performance score affect your decision?

We recognise South West Water (SWW) has been scored for being non-compliant with its permits at various sites across Devon, Cornwall and the Isles of Scilly.  Our regulatory officers are working hard to address these issues with SWW to ensure SWW is permanently compliant with its environmental permits.

Although Planetary are using SWW’s long sea outfall pipe and its associated environmental permit, Planetary will be controlling the magnesium hydroxide dosing. When we consider the proposal we will take account of the control measures Planetary propose and whether they, and any LEP conditions, are likely to be complied with when making our decision whether to issue an LEP. If we decide to issue an LEP, we will commit to actively regulating the activity.

If we agree to issue a Local Enforcement Position (LEP) we will require that the magnesium hydroxide dosing will be paused immediately if SWW’s storm tanks spill as the input of untreated sewage to St Ives Bay may affect the trial results.  We will ask for evidence that SWW and Planetary have set up a rapid communication pathway to ensure the trial is paused quickly.  The new event duration monitoring equipment installed on all combined sewer overflows in the country will also help with this.  This will enable Planetary to be confident that their results are not affected by untreated sewage in St Ives Bay.

Why have Planetary chosen to carry out this trial in Hayle?

The point where the magnesium hydroxide enters the ocean is just outside St Ives Bay, approximately 2.4km offshore, near Godrevy lighthouse.  The location is ideal because of the high mixing potential in the ocean at Hayle as well as good access to the harbour and outfall.

More information can be found on Planetary’s website.

Is this the right technology to sequester carbon? Wouldn’t planting sea grass be better?

We are supportive of the need to take carbon dioxide out of the atmosphere and it is likely that a range of different techniques will be required to remove carbon dioxide from the atmosphere. This trial would improve understanding of ocean alkalinity enhancement as a greenhouse gas removal technique. We are also leading on an ambitious, cross-Defra estuarine and coastal habitat restoration initiative known as Restoring Meadows, Marshes and Reefs (ReMeMaRe)” (pronounced “re-memory”), with a focus on restoring three priority habitats; seagrass meadows, saltmarsh and native oyster reefs.   

With the restoration of these habitats, we restore the multiple benefits that they provide, including biodiversity, flood defence and coastal resilience, carbon storage, water quality, human health and wellbeing, recreation and fisheries. In doing so, we help address the twin crises of climate change and biodiversity loss.

We assess all applications to the Environment Agency in a fair, independent and objective way, based on their merits and the evidence presented to us in the application.

What would happen after the trial?

We would need to consider the monitoring data and undertake a review.  We would share as much information as we can with you.  Approval would only cover this trial and any future projects would need to go through a new application process.  We are not aware of any next phase or stage currently.  We would objectively consider any further proposals we receive, as we are required to by the Regulator’s Code.  We would hold a full and extensive consultation on any application to vary the permit.

What safeguards and monitoring will be in place to protect the environment and sensitive species?

We are awaiting proposals from Planetary on their monitoring plans.  These will be considered when deciding whether to issue an LEP.  It is important to appreciate that Mg(OH)2 is of low toxicity and the quantity planned to be introduced is low.  It is likely that the risk to marine species from Mg(OH)2 in this trial is very low.  We will need to be satisfied that the proposed monitoring is designed in such a way that any impacts on species and the environment are detectable.  The trial aims to test how the magnesium hydroxide will be dispersed and dissolved, rather than increasing dosing and carbon sequestration.

In making our considerations we also need to account for adverse weather and consider any contingencies if monitoring is impacted.

If the trial goes ahead, we will require that Planetary carry out careful monitoring and reporting in accordance with specified conditions set out in an LEP. They have stated they will make the results of this monitoring available to the public.

What do the WRc mean when they recommend that Planetary refine the toxicity assessment for Mg(OH)2 by generating long-term toxicity data for other aquatic or marine species?

When conducting their investigation, WRc aimed to calculate the concentration of Mg(OH)2 that would not impact marine life or organisms. This is called the Predicted No Effect Concentration (PNEC). It is calculated from data obtained for the most sensitive species, therefore protecting other marine organisms.

There was limited marine species data on magnesium hydroxide, so WRc used data from only one taxonomic group to calculate the PNEC. This included:

  • Acute data for the most sensitive freshwater species.
  • Long term-data for the most sensitive marine species.

This has led to the prediction of a highly precautionary PNEC value.  This concentration can be changed when long-term data on other marine species are made available.

Taking this into consideration, as well as other factors like:

  • the fate and behaviour of Mg(OH)2 in the environment
  • its low short-term toxicity to organisms such as crustaceans and fish that are more sensitive than larger species like seals,

It is likely that the risk to marine species from Mg(OH)2 in this trial is very low.

What might be the impact on marine life, the fishing industry and tourism?

We regard this trial to be very low risk given the scale, low dose rates proposed and the protective measures we will require to be put in place should the trial go ahead.  We do not envisage any impact on marine life, fishing, or tourism.  We will require the monitoring to be designed in a way to detect any impacts.  If Planetary’s monitoring is not adequate or identifies a problem, then the dosing will be stopped immediately.

Which fish are in St Ives Bay and will be affected by the trial? How will that affect the seals?

We understand there is concern about the impact this trial may have on the wildlife of St Ives Bay, particularly it’s seal population.

We have asked for advice from the Water Research Centre. It is intended that their final report will provide reassurance that we have investigated this in detail.

When conducting their investigation, WRc aimed to calculate the concentration of Mg(OH)2 that would not impact marine life or organisms. This is called the Predicted No Effect Concentration (PNEC). It is calculated from data obtained for the most sensitive species, therefore protecting other marine organisms.

There was limited marine species data on magnesium hydroxide, so WRc used data from only one taxonomic group to calculate the PNEC. This included:

  • Acute data for the most sensitive freshwater species.
  • Long term-data for the most sensitive marine species.

This has led to the prediction of a highly precautionary PNEC value.  This concentration can be changed when long-term data on other marine species are made available.

Taking this into consideration, as well as other factors like:

  • the fate and behaviour of Mg(OH)2 in the environment
  • its low short-term toxicity to organisms such as crustaceans and fish that are more sensitive than larger species like seals,

It is likely that the risk to marine species from Mg(OH)2 in this trial is very low.

Will there be a visible plume from the outfall

Given the low dose rates, it is highly unlikely that there will be any visible difference around the outfall.  In the unlikely case that a change could be detected, it would be small, very limited in scope and temporary.  Please contact Planetary for further information on this issue.

Will the Mg(OH)2 not drop out of solution and cover the floor of the sea with deposits impacting wildlife?

This could theoretically happen but would only occur if dosing rates were too high or mixing is inadequate.  The deposition would be undissolved calcium compounds, which are of very low risk to marine organisms, but it is one of the issues we need to consider.  We will require unexpected settling to be strictly monitored as part of this trial should it go ahead.  Monitoring of both dose rates and the area around the outfall would ensure the risks are minimised and any deposits are detected at an early stage.  Planetary consider that, given the highly turbulent environment and the low dosing rates, the risk of any substantive seafloor deposition is very low.

Will this trial impact on the wastewater treatment works?

We are confident that there will be minimal impact on the wastewater treatment works and final effluent quality because dosing will be after treatment.  SWW are still required to comply with all permit conditions.  We will also require that dosing is stopped immediately if there are any pollution incidents or storm tank discharges as these events may interfere with monitoring results.

Will there be any traffic impacts from this trial?

There are some vehicle movements that will be associated with this trial but this is not expected to be significant.  Any concerns about traffic should be addressed with the Local Authority.

Are SWW and Planetary making money out of this trial and technique and how is it being funded?

We are not party to any financial arrangements between Planetary and South West Water, but we understand Planetary are funding this trial.  Please contact them with any questions regarding funding.

What is the overall carbon footprint of this trial given that the magnesium hydroxide is shipped from China?  How might this be calculated and assessed?

Please refer to the WRc report for information about the carbon footprint of the trial and direct any further questions to Planetary.


Have a Question?

If you would like to ask us a question you can email us at

To help us manage your enquiry, please state in your email which category your question falls into:

  • Supportive of the project
  • Financial benefits to Planetary and/or SWW
  • Impact on the wildlife
  • London Protocol
  • Carbon footprint
  • Activity monitoring, regulation and/or control
  • SWW's permit compliance
  • Economic impacts in the local area


  • Other

This is our preferred way for you to contact us, but please let us know if you would prefer to communicate with us in a different way.  Please also phone us on the below phone number if you need a paper copy of any of our documents.  We may charge for copying costs.  We are committed to being an inclusive, open and transparent organisation.

We promise we will read your comments and respond to your questions as soon as we can.  It may be that we are able to answer your questions in the decision document we will develop if we decide to issue the LEP; we will let you know if this is the case.  If Planetary and South West Water apply for a full environmental permit, we will hold a full and extensive consultation and we will let you know how you can have your say.

  • Sign up to our mailing list.  You can receive updates from us this way as well as on the online portal.
  • Ask for help accessing the online portal.
  • Request information in a paper format.
  • Submit a Freedom of Information request.
  • Ask more general questions about our role as a regulator or anything else the Environment Agency does.

You can also phone our National Customer Contact Centre on 03708 506 506 and ask for someone in the Devon, Cornwall and Isles of Scilly area to phone you back about the Planetary Ocean Alkalinity Enhancement Trial.

Please direct your technical questions about the ocean alkalinity trial to Planetary Technologies by emailing


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