If we had to mention an environmental and health challenge of unprecedented magnitude, it would undoubtedly be that of emerging pollutants.
Their global presence and persistence, the lack of knowledge and regulatory standards surrounding them, and the harmful effects they cause to both humans and the environment make them the most pressing environmental threat.
What are emerging pollutants?
Emerging pollutants, also known as ‘contaminants of emerging concern’, are a heterogeneous group of chemical and biological agents whose effects are of growing concern in terms of the environment and health.
These types of pollutants are not new substances in the chemical sense, but have existed for decades. What is new, and why they are classified as ‘emerging,’ is their ability to be detected, quantified, and their effects understood thanks to advances in analytical chemistry in recent years.
According to the official definition of the Spanish Ministry for Ecological Transition, emerging pollutants are substances whose effects could not be quantified a few years ago due to technological limitations, but which can now be described in detail thanks to more sensitive and accurate analysis techniques.
Although the focus has traditionally been on the aquatic environment, the presence of these pollutants has been documented in water (surface, groundwater and drinking water), as well as in atmospheric air and soil:
- Emerging pollutants in water: this is the primary vector for transport and distribution. Urban wastewater is one of the most important sources, especially when it becomes clear that conventional treatment systems in WWTPs were not designed to remove these types of compounds. In addition, the natural hydrological cycle favours their transport and dispersion.
- Emerging pollutants in atmospheric air: although historically they have received less attention in atmospheric terms compared to water, the presence of these pollutants in the air is a documented reality. The airway favours long-distance transport, redistributing these compounds to regions far from their original sources.
- Emerging pollutants in soil: Soil acts as both a sink and a source of emerging pollutants. The massive accumulation of pollutants in soil from landfills, the use of sewage sludge as fertiliser, irrigation with treated or untreated wastewater, and the deposition of airborne particulate matter are particularly relevant as routes of contamination of the terrestrial environment.
Why are these pollutants a global priority today?
The concern stems not only from the presence of these molecules in the environment, but also from their biological behaviour. Unlike classic pollutants such as heavy metals, many emerging pollutants are pseudo-persistent, meaning that although their half-life is relatively short, their continuous emission and intensive use means that they are constantly present in ecosystems.
Perhaps the most worrying factor is their unprecedented global ubiquity, with emerging pollutants being documented in places where there should never have been any significant human activity.
The detection in Antarctica of pharmaceuticals, cosmetics and industrial additives shows that these compounds have achieved global distribution through atmospheric and oceanographic current systems.
Another defining characteristic of this type of pollutant is its resistance to environmental degradation. This persistence is exacerbated by phenomena of bioaccumulation, i.e., its accumulation in the fatty tissues of living organisms, increasing its concentration with each link in the food chain.
To make matters worse, wastewater treatment systems were designed decades ago with the aim of removing easily biodegradable organic matter, suspended solids and other pathogens.
Most emerging pollutants are not readily biodegradable, making conventional treatment systems ineffective. So much so that, rather than promoting their elimination, WWTPs essentially act as transport systems that release these pollutants directly into rivers and coastal waters.
Main types of emerging pollutants
The diversity of emerging pollutants of concern is one of the aspects that most complicates their regulatory management. According to various European regulatory bodies and scientific researchers, we can categorise them as follows:
- Pharmaceuticals and their metabolites
- Perfluorinated compounds or PFAS
- Endocrine disruptors
- Microplastics and nanoplastics
- Emerging pesticides and biocidal products
- Industrial additives and degradation products
Drugs and their metabolites
The impact of drugs as emerging pollutants goes beyond the mere presence of the original molecule in the environment.
According to recent studies, most drugs are not completely metabolised by the human or animal body, so a significant fraction is excreted in the form of original active compounds or metabolites through urine and faeces.
The danger of these substances lies in their ability to transform: once in the sewage system or aquatic environment, drugs undergo chemical processes that convert them into ‘secondary metabolites,’ making them more stable or even more toxic than the original substance.
For example, alarming concentrations of anticancer drugs have been detected in hospital effluents, which are resistant to conventional biological treatment in WWTPs.
Some of the drugs with high detection rates and emerging concerns are non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics (responsible for modifying antibiotic resistance genes in bacteria), beta-blockers and psychotropic drugs.
Perfluorinated Compounds or PFAS
PFAS represent a particular category of emerging pollutants that are especially problematic due to their virtually infinite environmental persistence, bioaccumulation, and documented effects on human health.
These compounds have exceptionally stable carbon-fluorine bonds that resist all known natural degradation processes, which is why they are known as “forever chemicals”.
PFOS (perfluorooctane sulfonic acid) and PFOA (perfluorooctanoic acid) are the most studied and most concerning PFAS. Originally used in industrial applications ranging from non-stick cookware coatings to stain and moisture protection for fabrics and papers, these compounds have become globally distributed, contaminating drinking water systems on multiple continents.
Endocrine disruptors
Endocrine disruptors are chemicals capable of altering hormonal health and normal endocrine functions such as metabolism, growth and development, sleep, and mood.
One of the best-known endocrine disruptors is bisphenol A (BPA), found in many polycarbonate plastics and epoxy resins used in cookware and food can linings.
Other disruptors of concern include oxybenzone, a UV filter found in sunscreens, and triclosan, an antimicrobial found in many personal hygiene products.
Many of these compounds have never been included in environmental control regulations because their effects on hormonal systems were not considered relevant in the original design of conventional pollution regulations.
At the population level, epidemiologists have documented consistent declines in multiple indicators of reproductive and developmental health over the past few decades, coinciding with the widespread commercialisation of emerging pollutants.
Microplastics and nanoplastics
Microplastics (plastic particles smaller than 5 mm) and nanoplastics (particles and fibres in the approximate range of 1-100 nanometres) are now considered one of the most worrying categories of emerging pollutants in water, air and soil.
Their origin can be primary—when they are intentionally produced at micro or nano size for cosmetic, textile, or industrial uses—or secondary, when larger plastic fragments slowly degrade in the environment until they reach these microscopic dimensions.
In terrestrial ecosystems, various studies indicate that most of the world’s plastic remains on land: it is estimated that around 98.5% of plastic waste remains in terrestrial environments and only a small fraction reaches the ocean. Once incorporated into the soil, nanoplastics alter porosity, water retention and the composition of microbial communities, reducing the soil’s ability to process organic matter and affecting the availability of nutrients for plants.
In the urban atmosphere, recent evidence is particularly disturbing: research by the Chinese Academy of Sciences, based on automated microanalytical techniques, has shown that concentrations of microplastics and nanoplastics in the air in Chinese cities are between two and six orders of magnitude higher than those estimated using classical methods. The particles float attached to dust, are carried by the wind and deposited by rain or dust fall. These data suggest that previous studies have significantly underestimated the actual amount of suspended plastic that inhabitants of large cities breathe in daily.
In the aquatic environment, all plastics tend, over time, to fragment into micro- and nanoplastics that are distributed throughout the water column and sediments, becoming a diffuse pollutant that is virtually impossible to recover.
In addition to their physical effect, micro- and nanoplastics act as vectors: they adsorb PFAS, pesticides, persistent aromatic compounds, heavy metals and pathogenic microorganisms on their surface, so that a single plastic particle can carry a whole ‘cocktail’ of pollutants.
Emerging pesticides and biocidal products
Unlike other emerging pollutants, pesticides and biocides do not enter the environment by accident or through uncontrolled waste disposal: they are deliberately introduced into the ecosystem.
Although some are already regulated under conventional environmental protection frameworks, several specific compounds have emerged as particularly significant concerns due to their environmental persistence and global presence.
Their high water solubility facilitates transport to runoff and aquifers, and many new-generation pesticides rapidly degrade into transformation products whose toxicity is unknown.
Industrial additives and degradation products
A lesser-known but equally important category of emerging pollutants is industrial additives.
These compounds are chemicals that are added to polymers (plastics), textiles or electronic components to give them specific properties.
However, these additives are not static, but migrate from the final products into the environment, whether air, water or soil.
The two main groups in this category are:
- Phthalates and bisphenols: these are the kings of the plastics industry as they provide flexibility and hardness (respectively). The problem is that they are released through simple use, heat or wear and tear on the material, causing hormonal disturbances.
- Flame retardants: these are present in almost all electronics and furniture to prevent fires. Once they leave the product, they are extremely persistent as they are not destroyed, but travel through household dust and end up in our fabrics.
Regulation of emerging pollutants
European legislation in this area is currently undergoing a process of monitoring and data collection that will enable environmental quality standards to be set in the future.
As many emerging pollutants are still poorly understood, the EU uses what is known as a ‘watch list’: a list of suspect substances (pharmaceuticals, pesticides, industrial compounds, etc.) that could pose a significant risk to the aquatic environment or human health and which Member States must measure over several years.
This list is updated by means of implementing decisions (the current one is Implementing Decision (EU) 2025/439) and is used to decide, based on actual data, which substances will later become ‘priority’ substances and will have mandatory limits in European legislation.
Spain applies these European rules through royal decrees and monitoring programmes. Royal Decree 3/2023 transposes the Drinking Water Directive and introduces a list of emerging contaminants to be monitored in drinking water, even if they do not yet have a mandatory limit value.
MITECO has launched a Monitoring Programme for the Watch List with sampling points at WWTPs, surface waters and drinking water catchments to measure these substances and send the results to Brussels.
In summary: Europe defines the framework and the list of substances to be monitored, and Spain adapts these regulations, measures them in its rivers, treatment plants and drinking water networks, and uses this data to decide which emerging contaminants will end up having strict legal limits in the coming years.
Conclusion
Emerging pollutants have become one of the major blind spots in modern environmental management. The science is clear: the presence of these substances in media as diverse as drinking water, urban air, soil and the adipose tissue of wildlife is not an isolated phenomenon, but a systemic consequence of our production and consumption model.
Although we are talking about very different substances (drugs, PFAS, endocrine disruptors, micro- and nanoplastics, etc.), they all share disturbing characteristics: they are persistent, travel far from their source, mix with each other and can have chronic effects on human health and ecosystems even at very low concentrations.
For this reason, the response cannot be solely reactive; it is necessary to narrow the gap between chemical innovation and our monitoring capacity in order to control and minimise exposure to these pollutants.
