IT IS the 29th century and Earth is a dump. Humans fled centuries ago after rendering it uninhabitable through insatiable consumption. All that remains is detritus: waste mountains as far as the eye can see.

This is fiction – the setting for the 2008 Disney Pixar movie WALL-E. But it may come close to reality if we don’t clean up our act. “We all know the challenge that we’ve got,” says Mary Ryan at Imperial College London. “We can find toxic metals in the Himalayan peaks, plastic fibres in the deepest reaches of the ocean. Air pollution is killing more people than the current pandemic. The scale of this is enormous.”

Back when WALL-E was made, pollution and waste were near the top of the environmental agenda. At the 2002 Earth Summit in South Africa, global leaders agreed to minimise the environmental and health effects of chemical pollution, perhaps the most insidious and problematic category. They set a deadline of 2020 (spoiler alert: we missed it).

Recently, climate change and biodiversity loss have dominated environmental concerns, but earlier this year the UN quietly ushered pollution back to the top table. It issued a major report, Making Peace with Nature, declaring it a third great planetary emergency. “Do I think that is commensurate with the risk? Yes, I do,” says Ryan.

“It justifies being right up there at the top,” says Guy Woodward, also at Imperial. The key question, though, is what pollutants we should be worried about. “Many are innocuous. Some aren’t. Some interact in dangerous ways. That is what we need to grapple with,” says Woodward.

Pollution, the waste by-product of our economic activities, is as old as civilisation itself. Ice cores from Greenland contain traces of lead and copper from ore smelting in Bronze Age Europe. The first synthetic chemicals ones that don’t exist in nature – were created in the mid-19th century.

But as with most planet-trashing human activities, the rate at which we created new pollutants and dumped our waste products into the environment began to rise exponentially after the second world war in a 70-year, ongoing bender that has been called the “Great Acceleration”.

Pumping out poison

Its waste products are many and various (see “What a load of rubbish“), but synthetic chemicals and their products in particular have become embedded in our lives like never before. In 1950, global production of plastics, for instance, was just 1.5 million tonnes. In 2017, it was 350 million tonnes. In 2050, it is forecast to reach 2 billion tonnes. Chemical industry output in developing economies increased more than sixfold between 2000 and 2010, says the UN report. According to the International Council of Chemical Associations (ICCA), a trade body, 95 per cent of goods rely on some form of industrial chemical process in their manufacture.

At every stage of their life cycles, synthetic chemicals can, and do, escape into the wild, potentially poisoning the environment, wildlife and us. “They are everywhere,” says Zhanyun Wang at the Swiss Federal Institute of Technology in Zurich. The most visible manifestation is plastic waste, but that is the tip of a huge iceberg, he says. “We release a lot of chemicals. But we really didn’t check them first.”

Pinning toxic effects on any one substance or group of substances is often difficult, but many chemicals in widespread use are known or suspected to be toxic to humans and wildlife. They include substances such as polychlorinated biphenyls (PCBs), a class of industrial coolants and lubricants that can be powerful disrupters of the endocrine system if ingested, and some per- and polyfluoroalkyl substances (PFASs) used principally to make stain-repellent coatings.

One particularly stark, well-documented example is a population of killer whales off the west coast of the UK that has failed to reproduce for almost 30 years and appears doomed to extinction. One mature female washed up dead on the shoreline of the Scottish island of Tiree in 2016 was found to have an undeveloped uterus and PCB levels 100 times the toxicity threshold for marine mammals. These are “astronomical levels”, says Paul Jepson at the Zoological Society of London Institute of Zoology.

It isn’t that we have stood entirely idly by as this has happened. Under the terms of the Stockholm Convention on persistent organic pollutants, which came into force in 2004, most countries around the world have committed themselves to outlaw or severely restrict the use of the most toxic chemicals. The original list comprised a “dirty dozen” of the worst offenders: eight pesticides (including aldrin, dieldrin, DDT and mirex), two industrial chemicals (PCBs and hexachlorobenzene) and two classes of industrial by-products (dioxins and furans).

But the chemicals it restricts are just a drop in the ocean. We don’t even know the number of synthetic chemicals that are, or have been, on the market, although that number is many tens of thousands at least. Chemicals phased out long ago may last in the environment for years, further complicating things. “Very persistent chemicals, like PFASs and like plastic pollution, will take hundreds or thousands of years,” says Wang.

Woodward points out that once the chemicals are in the environment, they can react with other compounds and be transformed by living organisms, forming mixtures and breakdown products that may have different effects. Take such factors into account and there are “orders of magnitude” more chemicals to worry about, says Leon Barron, also at Imperial. We know nothing about most of these.

This lack of knowledge is matched, or even surpassed, by our ignorance about what risks most of these chemicals might pose to human health and the environment. “For some of the newer chemicals such as pharmaceuticals and pesticides, we know very little about their health effects, certainly for humans. Very, very little,” says Barron. In advanced economies such as the European Union, manufacturers that want to introduce a new chemical must now convince regulators that it isn’t hazardous. The EU’s rules, known as REACH, came into force in 2007 and operate on the precautionary principle – a presumption that chemicals are guilty until proved innocent. But the rules don’t apply to chemicals released before 2007.

In other parts of the world things are considerably laxer. To make matters worse, in many cases manufacturers keep information confidential, citing intellectual property rights, or the documentation is ambiguous. And when you factor in mixtures and breakdown products, says Woodward, “the vast majority of chemicals we know virtually nothing about”.

Various organisations around the world maintain their own most-wanted lists. One of the most useful, says Barron, comes from the European Water Framework Directive and lists both well-established nasties and emerging concerns. This list is a useful guideline for research, and has some success stories under its belt, says Barron. It flagged up the danger of neonicotinoid pesticides to bees and other insects and set the ball rolling on a near-total ban in the EU agreed in 2018. But even with these known knowns and known unknowns, it is almost certain that there are unknown unknowns too, says Wang.

The current system for assessing chemical toxicity certainly isn’t up to the magnitude of the task. It typically takes a single chemical and investigates its effects on two or three organisms. There is no way we can do that for every single known synthetic chemical, let alone for breakdown products and mixtures of chemicals too. “The sun would die before we get there,” says Woodward. Another problem is that lab toxicology tests aren’t very informative about how a chemical will behave in a complex real-world environment, he says.

Many of the chemicals aren’t even necessary. Because of intellectual property conflicts, companies often invent new chemicals to do the same job as one already out there, says Ryan. Others are there for non-essential purposes. Plastic food packaging is often dyed black for aesthetic reasons, but the dye makes the plastic unrecyclable, says Wang; personal care products often contain bulking agents such as microplastics which are dirt cheap, but potentially harmful.

Even when we do find out that a chemical is harmful, cleaning it up often isn’t an option. “Unfortunately, with our current technologies, it is just impossible,” says Wang. “And also financially impossible. Even cleaning up PFASs in drinking water in the US is a trillion-dollar task.”

If that doesn’t sound bad enough, there is a fear that, if we continue pumping chemicals into the environment with little idea of what they are or what they do, we may reach a point of no return. The idea of chemical pollution tipping points has been around for more than a decade in the form of a concept called “planetary boundaries”. Formulated in 2009 by Johan Rockström at Stockholm University in Sweden, these can be thought of as limits to Earth’s habitability that we overshoot at our peril. One of the boundaries is chemical pollution, which is described as “a priority for precautionary action and for further research“.

As yet, it hasn’t even been possible to quantify where the boundary lies. “It is a wicked problem,” says Ryan. “Chemical pollution in totality is an extraordinarily complex system to try to come up with a sensible boundary on. I guess you could end up with a list of chemicals and what you think their boundary is, but even working out where those are is really hard.”

Wang agrees. “It is really difficult to assess where the boundaries are and it’s a daunting task,” he says. “But if we have more hold on how many chemicals have been produced, have been used and what they are, then there might be some methods to help us to understand.”

What we need, says Gregory Bond at environmental consultants Manitou View Consulting, is a global inventory that contains information about how, where and in what quantities chemicals are used, plus any known hazards. Wang goes further, suggesting an international body modelled on the Intergovernmental Panel on Climate Change (IPCC) to marshal and synthesise all the evidence on chemical pollution and feed it to policymakers. Biodiversity has such a body too, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. Creating one for pollution would be in keeping with its status as the third global crisis, says Wang. He and others laid out the argument in a recent opinion piece in the journal Science; an accompanying campaign for support has already attracted more than 1700 signatures from 80 countries.

This and other campaigns appear to be cutting through. The UN is gearing up for its biennial Environment Assembly in February 2022, which will set its agenda for the next few years. At a preparatory meeting in February 2021, leaders agreed that the priority must be to get a shift on with tackling the three planetary emergencies simultaneously. “The three crises are climate change, nature and biodiversity loss, and waste and pollution, the toxic trail of our economic development that is essentially poisoning and toxifying the planet,” says Inger Andersen, the executive director of the UN Environment Programme (UNEP). “Unless we tackle these with real sincerity and determination, it’s a future we cannot even contemplate.”

“These are interrelated crises actually, reinforcing each another,” says Ivar Baste, deputy director general of the Norwegian Ministry of Environment and a lead author of the UNEP Making Peace with Nature report. The connections between climate change and biodiversity loss are well established, and it is clear how chemical pollution causes both.

It also cuts the other way. Intact ecosystems are quite resilient against insults such as chemical pollution, says Woodward; ecosystem degradation weakens that buffer. Similarly, higher temperatures can multiply the impact of pollution. “The ways that chemicals react and degrade in the environment are typically a function of temperature,” says Ryan. “If your temperature fluctuations are now different because of climate change, then those pathways will be impacted.”

Pollution-free planet

Again, though, we simply don’t know enough. “There’s nothing really happening in that space, it’s a massive black hole,” says Woodward. “We don’t just need to know how chemicals operate in the world, we need to know how they’re going to operate in a warming world.”

The UN’s immediate goal on chemical pollution is significant progress towards a pollution-free planet by 2030. The ultimate goal might sound impossible, but that hasn’t stopped Ryan and her colleagues from setting up a project called Transition to Zero Pollution.

KNOWN NASTY: Asbestos

Asbestos is a group of silicate minerals used mainly as a fire retardant and thermal insulator in buildings. The damage it causes to our lungs if inhaled was recognised in the 1890s, but the first bans weren’t put in place until the 1960s. Most countries still allow its use, including the US.

KNOWN NASTY: Heavy metals

There is no universally accepted definition of a heavy metal, but most lists include lead, mercury, chromium, arsenic and cadmium. All of them can be toxic in certain forms, are widely used in industry and are released by the combustion of fossil fuels. Various efforts have been made to minimise exposure, such as the removal of tetraethyl lead from petrol, but even some sources that feel like long-solved problems are still with us.

A recent report by the UN Environment Programme, for example, flagged “lead in paint” as an ongoing concern. That same report also highlighted the dangers of cadmium and its compounds, which are highly toxic and carcinogenic at very low levels. Cadmium has myriad industrial uses including in batteries, alloys, pigments, solar cells and as an additive in PVC. It can also be a contaminant in food, because it is found in phosphate-rich rocks used to make fertiliser. Some countries and regions try to restrict its use. Global exposure to cadmium hasn’t fallen over the past decade, however.

KNOWN NASTY: Highly hazardous pesticides

In 1962, Rachel Carson drew the world’s attention to pesticide toxicity in her book Silent Spring. Back then, the World Health Organization estimated that about a million tonnes of pesticides were being used annually; that figure is now six times higher.

Compounds designed to kill or disable undesirable organisms have often turned out to be more widely toxic. A list of more than 300 “highly hazardous pesticides” is maintained by the global Pesticide Action Network. Earlier this year, it called for an urgent phase-out of these chemicals by 2030.

KNOWN NASTY: CFCs

Action against chlorofluorocarbons (CFCs) and other ozone-eating chemicals, used principally as refrigerants and aerosol propellants, is a rare success story showing what international action on chemicals can do. A multinational environmental treaty, the Montreal Protocol, which came into force in 1989, is slowly closing the holes punched in the atmosphere’s ozone layer by these chemicals. The ozone layer is projected to return to pre-CFC glory by about 2070.

KNOWN NASTY: Endocrine disrupters

Defined as chemicals that interfere with hormonal signalling, endocrine-disrupting chemicals or EDCs are a broad class. They include polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) used as flame retardants, bisphenol A and phthalates, which are both mainly used to soften plastic, and perfluorooctanoic acid (PFOA). PFOA belongs to a class known as per- and polyfluoroalkyl substances (PFASs) used as surfactants and stain retardants since the 1940s. They were originally regarded as inert and safe, but some are now known to accumulate in human tissues to toxic levels.

Some endocrine disrupters, including PCBs and PFOA, also belong to a list of “persistent organic pollutants” that are known to be carcinogenic and toxic to the reproductive, nervous and immune systems.

KNOWN NASTY: Environmentally persistent pharmaceuticals

Many drugs administered to humans, pets and livestock are by design highly bioactive and resistant to breakdown, and can adversely affect wildlife once released into the environment. The veterinary anti-inflammatory drug diclofenac, for example, is poisonous to vultures that scavenge on dead livestock and has almost wiped them out on the Indian subcontinent. The most common “environmentally persistent pharmaceutical pollutants” are certain painkillers, antibiotics, lipid-lowering drugs, epilepsy drugs and oestrogens from oral contraceptives. As yet, there is no global framework to assess their risks or restrict their use.

KNOWN NASTY: The rest…

The UN Environment Programme flags up a number of substances or groups of substances for which there is emerging evidence of risk, although not much in the way of detail or action. These include the neonicotinoid insecticides, the herbicide glyphosate, microplastics, organic tin compounds used as additives in plastics and pesticides, and the antibacterial agent triclosan used in many consumer products.

WHAT A LOAD OF RUBBISH

Humans have become prodigious producers of unwanted stuff, including synthetic chemicals, smoke, sewage, greenhouse gases, dust, scrap machinery, food waste, e-waste, metals, plastics, glass, paints, worn-out tyres, construction materials, agricultural waste, household garbage, old clothing and packaging, to name a few.

Airborne pollutants, including carbon dioxide, nitrogen oxides, ozone and particulate pollution, come from stuff we burn to power electricity generation and industrial processes, heat buildings, cook food and fuel vehicles – as well as being released by tyres rubbing on roads. Much of the rest of our polluting trail is just what is left over when we have used whatever we want to use.

“We take stuff out of the environment, and then we put it into the economy and society – which is a fine thing because it enables us to have the life we have – but when we’re done with it, we discard it as waste back into the environment,” says Inger Anderson, executive director of the UN Environment Programme.

Reliably quantifying these sources of waste is almost impossible. According to Imperial College London’s Transition to Zero Pollution programme, however, the world economy now consumes 100 billion tonnes of raw materials a year – mainly newly extracted minerals, metals, fossil fuels and biomass.

About half goes into making long-lasting products such as infrastructure, cars and machinery. The rest creates shorter-lived products such as food, clothing and plastics, which typically have a lifespan of a year or less and are then thrown away.

Only about 10 per cent of this waste is recycled. The rest goes to landfill or is dumped into the environment. A single piece of waste may contain many different types of environmental pollutant. Discarded electrical products, for instance, often contain heavy metals, flame retardants and other synthetic chemical pollutants. If these leach into soils or water courses, they can have untold effects on our health and the surrounding ecosystems.

HOW MANY CHEMICALS ARE OUT THERE?

Long-standing estimates for the number of different synthetic chemicals that humans have produced range from 25,000 to 140,000, with a widely quoted ballpark figure of 100,000.

In 2019, a study by Gregory Bond of environmental consultants Manitou View Consulting in Michigan and Véronique Garny of the European Chemical Industry Council trade body suggested the true number is probably towards the bottom end of that range. They estimated that between 40,000 and 60,000 industrial chemicals are currently being made and sold in Canada, China, the EU, Japan and the US. These five places collectively produce 75 per cent of the world’s chemicals and so probably account for the majority, says Bond.

But when Zhanyun Wang at the Swiss Federal Institute of Technology in Zurich and his colleagues looked further afield, at chemical inventories from the EU and 19 countries including Australia, China, India, Japan, Mexico, Russia, South Korea and Switzerland, they came up with a figure of 350,000. “We found a really surprising number,” says Wang. Many researchers think it isn’t far wrong.

Bond disagrees. He says this number includes about 260,000 chemicals that may no longer be manufactured or sold, and thousands more registered but never marketed. He suggests a comparable number from Wang’s study is closer to his own: 69,000. One thing we can say with certainty is that there are a lot of chemicals out there.