The variety and sheer volume of waste that has been, and continues to be, created and accumulated by global industrial civilisation is truly enormous. One particular category of waste stands out from the rest however, mainly in terms of the negative perception and fear it induces, namely, the accumulated radioactive wastes which have been generated by the nuclear industry across the world. In coming years and decades a number of national governments will embark on a parallel series of megaprojects to implement deep geological disposal, which will see these wastes buried in engineered facilities in stable rock formations at great depth. Operating and eventually closing geological repositories will be amongst the most complex and longest-term infrastructure projects attempted by these nations. These facilities will consume significant financial and physical resources, energy and human expertise on multi-decadal timescales (likely well into the 22nd century), akin perhaps to the building of cathedrals in the Middle Ages.
The main gain this approach brings is passive (i.e., without ongoing active intervention or action from people) isolation of toxins from the surface environment over very long periods of time by taking advantage of both engineered containment and barriers, and the distance and dispersion provided by very large masses of overlying rock. Radioactive wastes will be managed via this high tech and elaborate approach because it is considered commensurate with their hazard and longevity. Put another way, these wastes are judged by governments and society at large to be sufficiently toxic to justify the effort and resources required to implement geological disposal.
Radioactive wastes, along with many of the other types of waste material which have been accumulated, landfilled (which is a shallow and relatively lightly-engineered form of geological disposal) and dispersed into the global environment, contain/comprise substances described under the Planetary Boundaries (PB) framework (defined by the Stockholm Resilience Centre) as Novel Entities (NEs). This category describes “new substances, new forms of existing substances and modified life forms, including chemicals and other new types of engineered materials or organisms not previously known to the Earth system as well as naturally occurring elements (for example, heavy metals) mobilized by anthropogenic activities”.
A very wide variety of industrial, military and consumer activities have generated a huge array of NE-bearing waste substances. These NEs include various metals (including copper, aluminium, silicon, gold, nickel, cobalt, neodymium, lithium, silver, lead and titanium, which do not participate in large scale biosphere processes, making their mass release from the geosphere a hallmark of human activity) along with various organic materials (such as organochlorine pesticides, polychlorinated biphenyls, dioxins, and phthalates), Per- and Poly-fluoroalkyl Substances (PFAS, a large group of ‘forever’ chemicals based around the artificial and nearly indestructible carbon-fluorine bond), the millions of tonnes of plastics that are emitted to the environment annually (and the micro- and nanoplastics that have consequently dispersed into every part of the Earth System), nanomaterials such as graphene, and of course the exotic radionuclides generated by anthropogenic nuclear processes.
The aggregate impacts of this cocktail of NEs at different scales is as-yet only partially understood. There is however growing concern and evidence that their growing ubiquity in the global environment may be increasingly driving a range of systemic effects, pressures and disruptions to human health and fertility, the functioning of the Earth System, and the health of the biosphere, which together could in time become comparable with other global systemic threats such as climate breakdown. Because they contribute to these large-scale risks, and are potentially on par with the hazards associated with radioactive wastes, it has been previously suggested (and is also the proposition made in this article), that management at scale of the most toxic and persistent NEs via geological disposal may be justified. Some hazardous wastes are already managed in this way, though the extent of this is limited to a few locations worldwide and only for certain materials. Therefore, a coordinated effort to extend geological disposal to a much wider range of wastes, which (for now at least) lack the ‘fear factor’ of nuclear wastes, would represent a major paradigm shift.
A large number of practicality, economic and engineering factors would need to be addressed to enable this; a few of the most significant ones are considered here. The first of these considerations is how wastes containing NEs could be made compatible with geological disposal; namely concentrated within robust containers and immobilised or solidified (likely in cement or epoxy resin, or by vitrification into glassy material). This segues to the next challenge, namely the ‘diffuseness’ of many NEs relative to radioactive wastes. The products of nuclear processes are generally concentrated and contained at the point of generation as far as possible, making them ready to be immobilised. Some of the NEs of greatest concern (including metals such as mercury and lead, lipophilic organics such as dioxins, and PFAS and microplastics) do exist in concentrated form in waste materials, but a large proportion has also been dispersed in an uncontrolled manner into the environment, so largely exist in well mixed, high-entropy states.
There could be scope to retrieve a proportion of these toxic substances where they become relatively concentrated (e.g., in landfill leachates, sewage sludges, biomass, and in soils and watercourses), potentially via innovative filtration, adsorption and phytoremediation techniques. However, the energetic and practicality challenges of concentrating and containing already-dispersed pollutants may drive the focus towards legislating and designing systems for ensuring that NEs are concentrated and contained at the point of use and disposal as far as possible going forward. The next consideration is the work taking place to develop the means to cheaply and effectively treat and destroy many of the NEs of greatest concern, which could nullify the potential economic case for expensive geological disposal.
Currently, energy-intensive high temperature incineration is the only practical approach for destroying PFAS, but innovative new techniques are under development which could reduce the cost of PFAS destruction. Enzyme-based biotechnology approaches are also under development for the destruction and recycling of plastics in the environment. However, treatments of this type are applicable only to some NEs (PFAS and plastics have been a focus to date, but there is no means to destroy elemental pollutants such as heavy metals) and are not passive solutions. More specifically, these approaches would rely on stable economic and high-tech industrial systems being in place to actively process past and future burdens of NEs on an open-ended basis (which contrasts with passive nature of geological disposal).
Another significant consideration would be around the fundamental nature of the ‘safety cases’, which are the structured sets of arguments that demonstrate long term safety and therefore underpin geological disposal. For radioactive wastes, the central basis of the safety case is around delaying and attenuating the escape of the radionuclides from the facility back to the environment for a sufficiently long time (>100,000 years) such that radioactive decay will substantially reduce the overall hazard. This is because the engineered barriers that contain the radioactive wastes are not intended to nor could credibly maintain their integrity forever. They will degrade over extended timescales allowing radionuclides to escape into the surrounding ‘host geology’ and eventually migrate the surface environment and biosphere; however, if the radioactivity hazard has diminished during that time, the repository will have done its job.
In contrast, for substances which are stable (with an effective infinite half-life) such as chemical elements and very persistent compounds, the hazard will not diminish with time and therefore different approaches to demonstrating protection of future generations may be needed. Repositories at great depth (which provide long and tortuous pathways for migration to the surface, and large rock masses into which pollutants may disperse) and/or which are located in very dry subsurface conditions (without the groundwater flows which could transport pollutants back to the surface) could potentially allow robust safety cases to be made for stable pollutants. However, if the intent was to co-locate NE-bearing wastes in an already-planned or -built radioactive waste repositories (a more credible theoretical proposition than the building of dedicated NE-bearing waste repositories), or alternatively to use existing infrastructure such as redundant mine workings, the safety cases and engineering requirements would need careful consideration.
The key question is: is this proposition realistic? As the profundity of the threat to people and the environment from chemical pollution at global scale becomes better recognised (research highlights the NE-PB as highly transgressed yet incompletely understood), we may need to collectively start thinking about more ‘extreme’ approaches to address this. Although extending geological disposal at scale beyond nuclear wastes would likely generate major challenges from technical, cost/economic and policy quarters, it could also be just the sort of ‘out of the box’ type thinking needed. Other more fundamental open questions remain as well; notably just how deliverable multiple deep geological disposal projects are likely to be in coming decades. This is in light of potential future global polycrisis predicaments which could increasingly challenge the ability of many nations to maintain even critical functions, much less hugely complex and costly ‘gold-plated’ remedial projects. Whatever the obstacles, the waste and pollution we have collectively spewed into the global environment in the pursuit of convenience and profit isn’t going anywhere without some form of decisive and assertive action; perhaps the mentality of into eternity is the solution which may match this challenge.
