Emerging Contaminants - What, Where and How to Tackle

Chemical compounds are a natural phenomenon in the natural world. However, the proliferation of human industry and activity over recent millennia – and, in particular, over the last 200 years – has seen a multitude of synthetic compounds enter the picture. For many years, it was believed that this abundance of chemicals would not cause any long-term problems for the planet or its inhabitants, since “dilution is the solution to pollution” was a widely held mantra.

However, the discovery that many of these substances have the ability to persist in the environment for a significant amount of time (decades, centuries or perhaps even longer) has caused concern in scientific circles. This has led to many of them being dubbed emerging contaminants or contaminants of emerging concern (CEC), since little is known about them and regulation surrounding their emission and control is sorely lacking. In this introductory article, we’ll take a closer look at what the term means, where they are found and how they can be dealt with, among other questions pertinent to the topic.

How many emerging contaminants are there?

According to figures provided by the Environmental Protection Agency (EPA) in the US, there are currently more than 86,000 chemical compounds in active circulation in the world today. Such a large figure makes it virtually impossible to ascertain atmospheric or environmental concentrations of all of them – or even more fundamentally to understand how they affect the natural world around them.

As our ability to analyse water samples has evolved and our awareness over the potential problems that this could cause has increased, we have begun to pay closer attention to certain chemical compounds in particular. Perhaps the first substance to be named as an emerging contaminant was DDT, widely used as a herbicide and pesticide throughout much of the 20^th century. However, research by an American marine biologist Rachel Carson in the early 1960s led her to theorise that DDT could hold devastating effects for the wider ecosystems surrounding the fields where it was sprayed.

Her hypotheses were rubbished at the time, though scientists would later come to agree with her findings and the substance was eventually outlawed. Today, it’s possible to see something similar happening with agricultural additives containing substances like glyphosate and neonicotinoids, although it’s not yet clear how the current furore will play out. As such, the face of emerging contamination is a forever changing one and it’s extremely difficult to quantify exactly how many there are today.

According to the official tally compiled by the EPA, there are over 1,000 emerging contaminants on their register. However, such a figure is believed to be at least 10 times too conservative. The sheer number of substances present in the environment, alongside the logistical and financial difficulties involved in monitoring and researching them all, means the subject is an especially difficult one.

Emerging contaminants vs contaminants of emerging concern

It should also be noted that just because some of these compounds are termed as emerging contaminants, that doesn’t mean that they are new additions to the planet. Of course, there are new chemicals entering the marketplace on a regular basis, which complicates the issue further. On the other hand, many contaminants have been around for millennia.

Take the aforementioned DDT issue, for example. The substance was in use for decades prior to its dangerous properties being discovered, and there was significant pushback after the fact. Even before DDT, other chemicals (such as arsenic) had been used as a rudimentary herbicide for centuries, while lead – often considered the oldest contaminant on the planet – was widely used by the Ancient Greek and Roman Empires long before it was regarded as harmful.

Therefore, it makes sense to distinguish contaminants of emerging concern (those which have been around for a long time, but about which we have only relatively recently harboured concerns) from emerging contaminants (those having just entered the marketplace in recent times). Regardless of which definition is used, the problem is a concerning one.

Where are emerging contaminants found and where do they come from?

That’s because emerging contaminants and CECs are found throughout the natural world. They are present in our soil, where they can compromise the quality of the terrain and negatively impact the cultivation of crops upon it. They can leach into surface water, groundwater and underground aquifers, potentially disrupting the natural rhythms of these habitats and deteriorating the water quality. And they’re often found in both wastewater and drinking water, spelling dire news for the human populace as well. They can even infiltrate the air.

They reach these locations via a variety of sources and means. Chemicals are virtually omnipresent in our daily lives; they are used in products we consume on a daily basis, they’re employed in a  variety of industrial processes and they are a by-product of the modern way of living. As such, they’re washed down the plughole or excreted through our systems, agricultural runoff sees them swept into streams and lakes and they’re improperly disposed of and can leach into the surrounding environment.

Of course, these sources emit the pollutants in initially microscopic concentrations, which led scientists to believe their impact on the planet to be negligible for many years. However, their extremely long half-lives mean that they can bioaccumulate in soil, water, crops, animals and humans, potentially reaching concentrations that could eventually be damaging.

What are the impacts of emerging contaminants?

By definition, the complete characteristics and effects of emerging contaminants are not yet fully understood. However, there is an increasing amount of research being conducted into how they impact environmental and human health, which points to the fact that they could be potentially disastrous for both over a prolonged period of time.

That’s because certain emerging contaminants have been confirmed as carcinogenic, meaning that exposure to them could increase the chances of humans and animals contracting cancer. Meanwhile, others are endocrine disruptors, which interfere with the normal functioning of the hormonal system. In animals, this has been observed to negatively impact the reproductive and breeding habits of some aquatic organisms. In extreme cases, it has even changed the sex of animals altogether.

Certain chemicals are also hugely dangerous for underwater ecosystems due to the nutritional imbalance they introduce. For example, many agricultural fertilisers contain ammonia, nitrogen and phosphate in order to optimise crop yields. However, when these chemicals are allowed to infiltrate streams, rivers, lakes and the suchlike, they can disrupt the delicate balance that is necessary to maintain the status quo.

In practical terms, this can manifest itself in the rapid growth of some species over others. For example, an excess of nutrients can lead to a process known as eutrophication, whereby algal blooms spread out over the surface of the water rapidly. Not only do these flora consume more of their fair share of oxygen, but they also prevent the sunlight from reaching the depths beneath them. In this manner, they deprive other organisms of resources vital to their survival.

Of course, these adverse effects could (and likely do) represent just the tip of the iceberg when it comes to understanding the full ramifications of allowing such contaminants to accumulate in the environment. As research progresses and our understanding grows, the fears become ever greater. For that reason, it’s imperative we detect and monitor contaminant concentrations, removing them from the environment where possible.

How can we detect emerging contaminants?

However, with so many tens of thousands of chemical compounds at play – and more entering the environment all the time – classifying, identifying and monitoring them is far easier said than done. Traditionally, pollutants are monitored by the use of targeted screening, which analyses a sample with the specific purpose of finding one or more chemical compounds that are known to be dangerous. In this manner, we can keep tabs on the highest profile offenders.

When it comes to emerging contaminants, on the other hand, it’s an altogether different proposition. With little known about these substances and next-to-no legislation in place to administer their circulation, sites are usually not required to detect for them. As a result, it must fall to the scientific community to develop methods of doing so, as well as putting these into practice in the field to learn more about real-world behaviours and effects of the contaminants in question.

Two methods have been particularly effective in doing so. Non-target screening (NTS) and suspect screening rely on sophisticated analytical techniques such as high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) to break down a sample into its constituent parts. Electrospray ionisation (ESI) is then used to isolate each compound individually, with its unique properties cross-referenced against a pre-existing database. In this manner, researchers are able to arrive at a reasonable classification and quantification of the emerging contaminants in a sample.

Can we remove emerging contaminants?

Of course, understanding the scale of contamination is only half the battle. Ideally, we must remove these CECs from the environment altogether so as to prevent their bioaccumulation from spiralling out of control. Again, this is unfortunately much harder to achieve in practice than might be supposed in theory.

That’s because conventional wastewater treatment systems were simply not designed with emerging contaminants in mind. As a result, many of them pass through filtration systems entirely unscathed, after which point they are allowed to freely enter the natural world once more. Although there are new and innovative techniques to tackle emerging contaminants and CECs, certain substances require different approaches. Therefore, the costs and time commitments involved in a comprehensive removal of emerging contaminants make such a proposition unfeasible at the present time.