Emerging Pollutants 2: Chemical CECs and the Regulation Gap

Chemicals dominate modern life. They're in the air we breathe, the food we eat, the products we use daily, and the rivers and soils that sustain us. Many are harmless or even helpful, but some present risks. For regulators, it's a daunting task to figure out which of the millions of compounds that swirl around us are potentially harmful. In this series of articles, 3E will help you navigate emergent pollutants to examine which substances are likely to attract regulatory attention in the future.

Chemical contaminants of emerging concern (CECs) are an increasingly urgent concern for regulators, scientists, and industry alike. Unlike biological CECs, such as antibiotic-resistance genes, or physical CECs, such as microplastics, chemical CECs are synthetic compounds at the molecular scale. They include pesticides, solvents, liquid crystal monomers, and many other substances that were not traditionally part of environmental monitoring but are now being detected in soil, water, and even human blood.

This is the second article in 3E's CEC series, and it looks specifically at chemical CECs: it discusses how scientists are tracking chemical CECs, the body of evidence behind their potential dangers, and the efforts of regulators and public health bodies to address the issue.

“Everything you put into your body, everything you clean your kitchen with, everything you spray on your pet - it all leaves a fingerprint,” analytical chemist Leon Barron, who leads the Emerging Chemical Contaminants team at Imperial College London, told 3E. “We live on a chemical planet. And yet, for most of the compounds we're exposed to every day, we just don't know what they're doing to us or to wildlife.”

An Ever-Growing Catalogue

The number of chemical CECs has been expanding for years. Part of this surge is thanks to technological advances. Laboratories like Barron's can now detect molecules at the parts-per-trillion level in river water or wastewater - that simply wasn't possible for most labs just a couple of decades ago.

Ludovic Bernaudat, who leads the Knowledge and Risk Unit at the United Nations Environment Programme, told 3E that industrial innovation has also played a role. Every year brings novel molecules designed for countless different applications. “We've lived for tens of thousands of years before synthetic chemicals,” says Bernaudat. “Once industry developed the opportunities and consumers saw the convenience, production exploded. Legislation and control didn't keep pace.”

Additionally, chemicals that have been in the market for a long time are coming under fresh scrutiny, pushing them into the chemical CEC category. For the sake of clarity, however, there is no official list of CECs. It is an informal term used in scientific literature to describe chemicals that could pose a threat to environmental or human health and could be subject to additional regulation in the future.

Despite the informal nature of chemical CECs, governments and their agencies are paying attention.

Chemical CEC Case Study: The Pet-Pesticide Paradox

Barron began seeing something peculiar in London's waterways a few years ago: imidacloprid, which belongs to the neonicotinoid family of pesticides that act on the central nervous system of insects. Imidacloprid is linked to declining bee populations and despite the UK- and EU-wide ban on the chemical for outdoor agricultural use, Barron kept finding it.

His team worked hard to track down where the imidacloprid was coming from and what they discovered makes for an interesting case study in how regulation can have unintentionally deleterious consequences. It also demonstrates that just because a chemical is already regulated, doesn't mean it can't also be a CEC.

The ban on imidacloprid did not include indoor domestic use and eventually, Barron and his colleagues traced the imidacloprid to antiparasitic medications used on pets. “It's a classic case of unintended consequences,” he says.

The UK, Barron explains, is one of the only countries in the world where cats and dogs are routinely given monthly flea and tick treatments, whether they show signs of an infestation or not. “The chemical doesn't stay neatly on the animal,” says Barron. “It spreads to bedding, furniture, even owners' hands. Every wash sends a pulse down the drain.”

The problem is not limited to the London area. A catchment-scale study led by the British Geological Survey and the University of Nottingham sampled water, sediments, fish, and invertebrates in two English rivers - one in the east of the country and the other in the west. Researchers found residues of imidacloprid in both rivers at concentrations high enough to pose risks to aquatic life. At some sites, levels exceeded chronic toxicity thresholds for river invertebrates, the foundation of aquatic food webs.

Even though imidacloprid is already controlled, regulatory loopholes have allowed the chemical to continue to find its way into waterways, albeit by different means. The growing body of evidence that imidacloprid is still making its way into the environment and that it poses risks means that it qualifies as a CEC because it could be subject to further regulation. Indeed, the UK announced in December 2024 that it was considering a total ban on the chemical.

As Bernaudat puts it, the “emerging” part of the CEC label isn't necessarily about novel chemicals. It also covers established compounds that are “emerging into concern.”

Need for a Regulatory Rethink: From Molecules to Families

Bernaudat says that current regulatory methods are slow and inadequate, allowing many chemical CECs to stay on the market in one form or another for too long. He advocates that regulators should change their tactics.

“Over the past few decades, we've regulated flame retardants individually,” says Bernaudat. “However, the sheer amount of innovation means that we can only play catch-up with this strategy.” He argues for a family-based approach: regulating an entire chemical class or tackling the issue from a sector-by-sector approach first, with appropriate and justified exemptions when no technically or economically alternatives are available. “It flips the burden of proof,” he says, and means policymakers can stop playing whack-a-mole.

For more information, read part 1 of this series:

Emerging Pollutants 1: Substances of First Step Toward Regulation