How Contaminants of Emerging Concern Challenge Ecotoxicology
Imagine pouring a single drop of red food coloring into a liter of clear water. At first, the concentrated color is obvious and vivid. But if you continue adding water—a gallon, a bathtub full, an entire swimming pool—that original drop becomes increasingly diluted until it disappears from view entirely.
Now consider that scientists are finding traces of pharmaceuticals, personal care products, and industrial chemicals in rivers, lakes, and oceans at similarly infinitesimal concentrations. Despite being measured in parts per trillion, like that invisible drop in a swimming pool, these contaminants of emerging concern (CECs) are causing significant disruptions to aquatic life and potentially threatening ecosystem stability .
The term "contaminants of emerging concern" describes a diverse group of synthetic or naturally occurring chemicals that aren't yet regularly monitored in the environment but may pose ecological or human health risks 7 .
What makes them particularly challenging is that they include substances we use daily: medications, sunscreens, cleaning products, and plastic materials that eventually find their way into waterways through wastewater treatment plants, agricultural runoff, and other pathways 3 .
With over 350,000 chemicals and chemical mixtures registered for commercial use globally, and thousands more introduced annually, environmental scientists are facing what some have called a "second chemical revolution" 7 .
Registered Chemicals
Emerging contaminants encompass a remarkably diverse array of substances that share one common characteristic: they're being detected in the environment with consequences we're only beginning to understand.
Allows products to remain effective but resists degradation in ecosystems.
Makes them highly mobile in water, enabling spread far from original sources.
Can cause biological effects even at extremely low concentrations.
These challenges are compounded by the limitations of traditional wastewater treatment plants, which were designed to remove conventional pollutants but often allow emerging contaminants to pass through virtually unaffected 2 . One study of parabens (preservatives used in cosmetics) found that while wastewater treatment reduced concentrations, these compounds remained detectable in effluent and were subsequently found in surface waters 2 .
Traditional ecotoxicology has typically focused on studying single chemicals in isolation, but emerging contaminants rarely exist alone in the environment. Instead, they form complex chemical cocktails that can interact in unexpected ways.
Combined effect is greater than the sum of individual effects 9 .
One chemical reduces the toxicity of another 9 .
These interactions occur through various mechanisms. Some chemicals might compete for the same binding sites in organisms, while others might enhance cellular uptake or inhibit detoxification systems.
Another critical concern with emerging contaminants is their potential to bioaccumulate in organisms and biomagnify up food chains 6 .
Low concentrations in aquatic environments
Accumulation in bivalves, polychaetes, and small organisms
Concentration increases at each trophic level
Highest concentrations in apex predators
Research on Saunders's gulls in Yellow Sea coastal wetlands demonstrated that PFAS compounds were transferred maternally and accumulated through the food chain 1 .
To understand how scientists study these complex interactions, let's examine a specific experiment that investigated the combined effects of microplastics and pharmaceutical products. Researchers were particularly interested in whether microplastics might influence the toxicity of statins (cholesterol-lowering medications) on marine benthic nematodes 1 .
The scientists set up multiple test conditions to isolate different factors:
The findings revealed unexpected interactions between these two classes of emerging contaminants. As anticipated, both PVC microplastics and Lipitor alone significantly reduced nematode abundance, biomass, and diversity.
The surprise came from the combined exposure: rather than increasing toxicity, the presence of PS-microplastics with Lipitor actually attenuated the toxicity. The researchers discovered this was due to physical adsorption of the statin onto the microplastics, reducing the bioavailability of the pharmaceutical to the nematodes 1 .
This suggests that in some circumstances, microplastics might act as carriers that potentially reduce the immediate biological impacts of other contaminants—though they might still transport these adsorbed chemicals through ecosystems.
Less toxicity in combined exposure compared to individual contaminants
| Contaminant Category | Concentration Range |
|---|---|
| PPCPs | ng/L to μg/L |
| PFAS | ng/L to μg/L |
| Microplastics | 1-1000 particles/m³ |
| EDCs | ng/L to μg/L |
Studying contaminants that often exist at trace concentrations requires sophisticated approaches. Modern ecotoxicologists employ an array of advanced tools to detect, quantify, and understand the effects of emerging contaminants.
The ability to measure emerging contaminants at environmentally relevant concentrations (sometimes as low as parts per trillion) has only become possible with advances in analytical technology.
Beyond chemical detection, ecotoxicologists need to understand biological impacts.
Detects biologically active contaminants through antibody recognition .
Framework connecting molecular events to ecological impacts 9 .
Genomic, proteomic, and metabolomic methods revealing molecular responses 9 .
Detect biologically active compounds in environmental samples .
The challenges posed by emerging contaminants are driving innovation in ecotoxicology. Researchers are increasingly adopting a "One Health" perspective that recognizes the interconnectedness of human, animal, and environmental health 7 .
There's also growing emphasis on green chemistry principles that aim to design chemicals and processes that reduce or eliminate the generation of hazardous substances 7 .
Detection and characterization of individual CECs
Understanding mixture effects and transformation products
Development of predictive models and advanced treatment methods
Implementation of green chemistry and circular economy approaches
Perhaps the greatest hurdle is translating scientific understanding into effective regulation. The current chemical-by-chemical regulatory approach struggles to keep pace with the thousands of new substances introduced annually 7 .
Groups chemicals with similar properties for more efficient oversight
Requires demonstration of safety before widespread use
Coordinated global action through initiatives like the UN Science-Policy Panel
Contaminants of emerging concern represent a profound challenge to ecotoxicology, forcing a reevaluation of traditional approaches to environmental protection. These invisible pollutants, with their complex interactions and subtle effects, remind us that what we can't see can still harm us—and the ecosystems we depend on.
References will be listed here in the final version.