Emerging Contaminants in Water: Sources, Effects and Treatments
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Few could argue that water is not one of the most precious resources on the planet, and certainly none could argue that it is possible to live without it. This means that when a water source is contaminated with potentially harmful matter, it can cause widespread damage to the local human and animal populations that rely on that water source, unless action is taken to prevent this.
So, what is an emerging contaminant?
While there are no formal benchmarks for something to be labelled an emerging contaminant, or “a contaminant of emerging concern”, the general consensus seems to agree on the following three definitions:
• The material concerned should be recently discovered or synthesised
• The material can already be known, but its environmental hazards were not previously studied
• The material can already be known, and its risks already studied, but new information has indicated a potential for a review of its environmental effect.
Following this, it is clear to see why lead metal which has caused problems since the time of the Greek and Roman Empires1, cannot be classed as an emerging contaminant. However, something like tungsten, which was formally studied in the late-2000s2, despite being widely used in electrical and aerospace industries for decades, can be.
Pharmaceutical waste in drinking water supplies
Pharmaceuticals and personal care products (PPCPs) most likely fall under the second set of criteria. The earliest simple pharmaceuticals have been in circulation since the late 18th century, as the American Civil War created huge demand for the synthesis and production of painkillers and antiseptics3. However, despite being discovered so long ago, it is only recently that the interaction of these PPCPs with the environment has been studied.
Most commonly, PPCPs enter the water supply via the excretions of humans and animals, or through the wastewaters from the pharmaceutical production plants4.
Once PPCPs are in the water, they can be extremely challenging to remove effectively. Professor José Rivera-Utrilla, of the Inorganic Chemistry Department at the University of Granada, studies the problem. He explains that, “As conventional wastewater treatment plants primarily use physio-chemical treatments to purify water, here they have a limited capacity to remove pharmaceutical products from urban wastewaters, since most of the compounds cannot be metabolized by microorganisms.”
While the effects of PPCP contamination on human health are still largely unknown, research into how to remove them from the water supply has gone ahead regardless in a bid to head off any potential threat. A combination of strong UV radiation and the presence of activated carbon has been shown5 to degrade pharmaceuticals into simpler molecular chains that can be easily removed from water using the existing purification methods.
Nanomaterials and nanoparticles in the environment
The term “nanoparticle”6 describes any particle between 1 nm and 1 μm in size, irrespective of its origin or chemical composition. This small size gives a high surface area-to-volume ratio, which can lead to unusual properties not usually seen in larger materials of the same nature. Predicting the chemical properties and potential toxicities of nanoparticles can therefore be extremely difficult, even if the properties of the larger bulk material are already well-known.
A high surface area-to-volume ratio also causes nanoparticles, in general, to be extremely reactive. Their reactivity is one reason the particles can do so much harm to living beings and whole ecosystems, but it also facilitates a rather simple method of removing nanoparticle contaminants from water sources. Many of the most common nanoparticles are metals and metal oxides. When they come into contact with metallic quantum dots7 they start to agglomerate to form much larger particles which can then be easily filtered out from the water in a traditional water treatment plant.
It is worth noting that in some cases the unusual properties displayed at the nanoscale are actually beneficial. Carbon nanotubes and nanoparticles of titanium oxide are of particular interest due to their antimicrobial properties8. Early experiments9 indicate they could be a low-cost way to treat water supplies in third world countries, which are often contaminated with water-borne viruses and bacteria.
Endocrine disruption linked to perfluoroalkyl exposure
From water-resistant clothing, to cookware, to packaging, perfluoroalkyl compounds are deeply integrated into our day to day lives10. Reflecting the increasing number of applications over past decades, the amount of perfluoroalkyl compounds detected in water has also increased. Although perfluoroalkyls are for the most part non-toxic, they are difficult for humans and animals to metabolise, resulting in a build-up of the chemical in the body. At high enough levels, perfluoroalkyls can disrupt the endocrine system of the organism it is accumulating in.
Professor Sébastien Sauvé at the Université de Montréal studies the effects of these emerging contaminants. He explains, “There are clear impacts of endocrine disruption in humans with an ever precocious age for puberty in young girls, drastically lower levels of male fertility, higher occurrence of a variety of thyroid-related issues or other endocrine disruptions"11. However, he also stresses that this is a complex issue that cannot be reduced to a simple cause and effect, “We are chronically exposed to a range of low concentrations of a large suite of endocrine disruptors that have many different routes to impact our health. Those contaminants will also have some interactions among themselves; sometimes additive, competitive, synergistic – all of which are possible and further complicate our understanding.”
Despite studies on the health effects of perfluoroalkyls being in relative infancy, they are clearly chemicals of concern, and consequently work is already underway to establish ways to remove them from water. Similarly to the removal of pharmaceuticals, the use of activated carbon is proving effective12 through absorbing the perfluoroalkyls onto its surface. This sorption technique has also been shown to work using ion-exchange resins, calcium fluoride salts, multiwalled carbon nanotubes, and more in laboratory conditions13. No full-scale pilot programs of these techniques have yet been tried but it would appear to be the next logical step for many researchers.
The creation of dedicated bodies, such as the Environmental Protection Agency14 in the US and the Department for Environment, Food and Rural Affairs15 in the UK, stokes a central effort to improve environmental conditions. Guaranteeing access to safe drinking water worldwide remains one of the most important targets for agencies like these, ensuring that research into the effects of emerging contaminants and their removal continues to be a key priority.
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