Contaminants of emerging concern (CECs) is a term used by water quality professionals to describe pollutants that have been detected in environmental monitoring samples, that may cause ecological or human health impacts, and typically are not regulated under current environmental laws. Sources of these pollutants include agriculture, urban runoff and ordinary household products (such as soaps and disinfectants) and pharmaceuticals that are disposed to sewage treatment plants and subsequently discharged to surface waters.[1][2]
Examples of emerging contaminants are 1,4-Dioxane, food additives, pharmaceuticals, and natural & synthetic hormones.[3] CECs have the ability to enter the water cycle after being discharged as waste through the process of runoff making its way into rivers, directly through effluent discharge, or by the process of seepage and infiltration into the water table, eventually entering the public water supply system.[4] Emerging contaminants are known to cause endocrine disrupting activity and other toxic mechanisms, some are recognized as known carcinogens by the United States Environmental Protection Agency (EPA).[5]
For a compound to be recognized as an emerging contaminant it has to meet at least two requirements:[according to whom?]
Emerging contaminants are those which have not previously been detected through water quality analysis, or have been found in small concentrations with uncertainty as to their effects. The risk they pose to human or environmental health is not fully understood.[citation needed]
Contaminants of emerging concern (CECs) can be broadly classed into several categories of chemicals such as pharmaceuticals and personal care products, cyanotoxins, nanoparticles, and flame retardants, among others.[6] However, these classifications are constantly changing as new contaminants (or effects) are discovered and emerging contaminants from past years become less of a priority. These contaminants can generally be categorized as truly "new" contaminants that have only recently been discovered and researched, contaminants that were known about but their environmental effects were not fully understood, or "old" contaminants that have new information arising regarding their risks.[6]
Pharmaceuticals are gaining more attention as CECs because of their continual introduction into the environment and their general lack of regulation.[7] These compounds are often present at low concentrations in water bodies and little is currently known about their environmental and health effects from chronic exposure; pharmaceuticals are only now becoming a focus in toxicology due to improved analytical techniques that allow very low concentrations to be detected.[7] There are several sources of pharmaceuticals in the environment, including most prominently effluent from sewage treatment plants, aquaculture and agricultural runoff.[8]
The growth of cyanobacterial blooms has been increasing due to the eutrophication (or increase in nutrient levels) of surface waters around the world.[9] The increase in nutrients such as nitrogen and phosphorus has been linked to fertilizer runoff from agricultural fields and the use of products such as detergents in urban spaces.[10] These blooms can release toxins that can decrease water quality and are a risk to human and wildlife health.[9] Additionally, there is a lack of regulations regarding the maximum contaminant levels (MCL) allowed in drinking water sources.[10] Cyanotoxins can have both acute and chronic toxic effects, and there are often many consequences for the health of the environment where these occur as well.[10]
Industrial chemicals from various industries are known to produce harmful chemicals that are known to cause harm to human health and the environment. Common industrial chemicals like 1,4-Dioxanes, Perfluorooctane sulfonate (PFOS) and Perfluorooctanoic acid (PFOA) are commonly found in various water sources.
Due to the large differences in transportability of compounds, there is a great level of variance contaminant to contaminant between the location of contamination and the place of occurring hazards. An example of the a contaminant which can have detected hazards at the point of origin is the effect of municipal solid waste on the environment through seepage and particulate pollution. On the other hand, the effects of water-soluble contaminants may be obscured a long time as they are washed far away from the contamination site and only slowly accumulate in oceans and groundwater to harmful concentrations.
There is an overlap of many anthropogenically sourced chemicals that humans are exposed to regularly. This makes it difficult to attribute negative health causality to a specific, isolated compound. EPA manages a Contaminant Candidate List to review substances that may need to be controlled in public water systems.[11] EPA has also listed twelve contaminants of emerging concern at federal facilities, with ranging origins, health effects, and means of exposure.[12] The twelve listed contaminants are as follows: Trichloropropane (TCP), Dioxane, Trinitrotoluene (TNT), Dinitrotoluene, Hexahydro-trinitro-triazane (RDX), N-nitroso-dimethylamine (NDMA), Perchlorate, Polybrominated biphenyls (PBBs), Tungsten, Polybrominated diphenyl ethers (PBDEs) and Nanomaterials.
The NORMAN network[13] enhances the exchange of information on emerging environmental substances. A Suspect List Exchange[14] (SLE) has been created to allow sharing of the many potential contaminants of emerging concern. The list contains more than 100,000 chemicals.
Table 1 is a summary of emerging contaminants currently listed on one EPA website and a review article. Detailed use and health risk of commonly identified CECs are listed in the table below.[5][15]
| Compound | Uses | Where it is Found | Health Risks |
|---|---|---|---|
| Trichloropropane (TCP) | Chemical intermediate, solvent, and cleaning product | TCPs are denser than water, so they sink to the bottom of aquifers and contaminate them, they also have a low capacity to be absorbed organically and leach into soil or evaporate, contaminating the air | Considered a likely carcinogen by NOAA |
| Dioxane | Stabilizer of chlorinated solvents, manufacturing of PET, manufacturing by-product | Often at industrial sites, and they move rapidly from soil to groundwater, although it was phased out as part of the Montreal Protocol it is very resistant to bio-degradation and has been found at over 34 EPA sites | Rapid disruption of lung, liver, kidney, spleen, colon, and muscle tissue, may be toxic to developing fetuses and is a potential carcinogen |
| Trinitrotoluene (TNT) | Pure explosive, military and underwater blasting | Major contaminant of groundwater and soils | Listed as cancer-causing by Office of Environmental Health, may cause carcinoma and bladder papilloma |
| Dinitrotoluene | Intermediate to form TNT, explosive | Found in surface water, groundwater, and soil at hazardous waste sites, and may be released into the air as dust or aerosols | Considered a hepatocarcinogen and may cause ischemic heart disease, hepatobiliary cancer, and urothelial and renal cell cancers |
| Hexahydro-trinitro-triazane (RDX) | Military explosive | Exists as particulate matter in the atmosphere, easily leaches into groundwater and aquifers from soil, does not readily evaporate from water | Decreased body weight, kidney and liver damage, possible carcinoma, insomnia, nausea, and tremor |
| Nanomaterials | Broad classification of ultrafine particulate matter used in more than 1,800 consumer products and biomedical applications | Released as consumer waste or spillage, may be airborne, found in food, or in many diverse industrial processes | May translocate into the circulatory system primarily through the lungs, exposing the body to an accumulation of compounds in the liver, spleen, kidney, and brain |
| N-nitroso-dimethylamine (NDMA) | Formed in the production of antioxidants, additives, softeners, and rocket fuel, and an unintended byproduct of the chlorination of waste and drinking water at treatment facilities | Broken down quickly when released into the air, but highly mobile when released into soil and will likely leach into groundwater, humans may be exposed by drinking contaminated water, ingesting contaminated food, or using products that contain NDMA | Probable carcinogen, evidence of liver damage, reduced function of kidneys and lungs |
| Perchlorate | Manufacturing and combustion of solid rocket propellants, munitions, fireworks, airbag initiators, and flares | Highly soluble in water so it can greatly accumulate in groundwater, also accumulates in some food crop leaves and milk | Eye, skin, and respiratory irritation and in high volumes corrosion. Potentially disrupts thyroid hormones |
| Perfluoro-octane sulfonate (PFOS) and Perfluorooctanoic acid (PFOA) | Used in additives and coatings, non-stick cookware, waterproof clothing, cardboard packaging, wire casing, and resistant tubing | During manufacturing, the compounds were released into the surrounding air, ground, and water, is resistant to typical environmental degradation processes and have been shown to bioaccumulate, found in oceans and Arctic, meaning they have a high capacity for transport | World Health Organization categorized possible carcinogen, may cause high cholesterol, increased liver enzymes, and adverse reproductive and developmental effects |
| Polybrominated biphenyls (PBBs) | Flame retardant | Detected in the air, sediments, surface water, fish and other marine animals, they do not dissolve so they are not mobile in water but are volatile and prevalent in the atmosphere | Classified by International Agency for Research on Cancer as likely carcinogenic, neurotoxic, and thyroid, liver, and kidney toxicity as well as an endocrine disruptor |
| Polybrominated diphenyl ethers (PBDEs) | Flame retardant and used in plastics, furniture, and other household products | Enter the environment through emissions, and has been detected in air, sediments, surface water, fish and other marine animals | Shown to be an endocrine disruptor as well as carcinogenic, also, may cause neural, liver, pancreatic, and thyroid toxicity |
| Tungsten | A naturally occurring element which exists in various household products and military manufacturing | Tungsten is water-soluble under certain conditions and may be found in dangerous quantities in water sources | May cause respiratory complications, and investigated as a potential carcinogen by the CDC |
| Diclofenac | Anti-inflammatory drug | Can be found in water treatment plant (WTP) effluents. Reported to be found in coastal waters as well | In large quantities can cause serious gastrointestinal toxicity. Severe ecotoxicity to selected breeds of animals |
| Bisphenol A (BPA) | Industrial plastic production (polycarbonate plastics and epoxy resins) | Found to accumulate in water treatment plant (WTP) effluents | BPA is cytotoxic and mutagenic. It exerts various adverse effects on reproductive, immune, endocrine and nervous systems |
| Sulfamethoxazole (SMX) | Antibiotics | Reported to be found in various freshwater systems | Common side effects include nausea, vomiting, loss of appetite, and skin rashes. It is a sulfonamide and bacteriostatic |
| Carbamazepine | Anticonvulsant | Reported to be found in various freshwater systems and WTP effluents. | Common side effects include nausea and drowsiness. Serious side effects may include skin rashes, decreased bone marrow function, suicidal thoughts, or confusion. |
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Further information: Water pollution |
Emerging contaminants are most often addressed as an issue concerning water quality. The release of harmful compounds into the environment which find their way into municipal food, water, and homes have a negative externality on social welfare. These contaminants have the capability to travel far from the point-source of their pollution into the environment and accumulate over time to become harmful because they have been left unregulated by federal agencies. These harmful compounds cause damage to environmental and human health, and they are difficult to trace therefore it is challenging to establish who should foot the bill for the damage done by ECs. Because these contaminants were not detected or regulated in the past, existing treatment plants are ill-equipped to remove them from domestic water.[22] There are sites with waste that would take hundreds of years to clean up and prevent further seepage and contamination into the water table and surrounding biosphere. In the United States, the environmental regulatory agencies on the federal level are primarily responsible for determining standards and statutes which guide policy and control in the state to prevent citizens and the environment from being exposed to harmful compounds. Emerging contaminants are examples of instances in which regulation did not do what it was supposed to, and communities have been left vulnerable to adverse health effects. Many states have assessed what can be done about emerging contaminants and currently view it as a serious issue, but only eight states have specific risk management programs addressing emerging contaminants.[23]
These are tactics and methods that aim to remediate the effects of certain, or all, CECs by preventing movement throughout the environment, or limiting their concentrations in certain environmental systems. It is particularly important to ensure that water treatment approaches do not simply move contaminants from effluent to sludge given the potential for sludge to be spread to land providing an alternative route to entering the environment.
For some emerging contaminants, several advanced technologies—sonolysis, photocatalysis,[15] Fenton-based oxidation[24] and ozonation—have treated pollutants in laboratory experiments.[25] Another technology is "enhanced coagulation" in which the treatment entity would work to optimize filtration by removing precursors to contamination through treatment. In the case of THMs, this meant lowering the pH, increasing the feed rate of coagulants, and encouraging domestic systems to operate with activated carbon filters and apparatuses that can perform reverse osmosis.[26] Although these methods are effective, they are costly, and there have been many instances of treatment plants being resistant to pay for the removal of pollution, especially if it wasn't created in the water treatment process as many EC's occur from runoff, past pollution sources, and personal care products. It is also difficult to incentivize states to have their own policies surrounding contamination because it can be burdensome for states to pay for screening and prevention processes. There is also an element of environmental injustice, in that lower income communities with less purchasing and political power cannot buy their own system for filtration, and are regularly exposed to harmful compounds in drinking water and food.[27] However recent treads for Light-based systems shows great potential for such applications. With the decrease in cost of UV-LED systems and growing prevalence of solar powered systems,[15] it shows great potential to remove CECs while keeping cost low.
Researchers have suggested that metal–organic frameworks (MOFs) and MOF-based nano-adsorbents (MOF-NAs) could be used in the removal of certain CECs like pharmaceuticals and personal care products, especially in wastewater treatment. Widespread use of MOF-based nano-adsorbents has yet to be implemented due to complications created by the vast physicochemical properties that CECs contain. The removal of CECs largely depends on the structure and porosity of the MOF-NAs and the physicochemical compatibility of both the CECs and the MOF-NAs.[28] If a CEC is not compatible with the MOF-NA, then particular functional groups can be chemically added to increase compatibility between the two molecules. The addition of functional groups causes the reactions to rely on other chemical processes and mechanisms, such as hydrogen bonding, acid-base reactions, and complex electrostatic forces.[28] MOF-based nano-adsorbent remediation heavily relies on water-qualities, such as pH, in order for the reaction to be executed efficiently. MOF-NA remediation can also be used to efficiently remove other heavy metals and organic compounds in wastewater treatment.
Another method of possible remediation for CECs is through the use of membrane bioreactors (MBRs) that act through mechanisms of sorption and biodegradation. Membrane bioreactors have shown results on being able to filter out certain solutes and chemicals from wastewater through methods of microfiltration, but due to the extremely small size of CECs, MBRs must rely on other mechanisms in order to ensure the removal of CECs. One mechanism that MBRs use to remove CECs from wastewater is sorption. Sorption of the CECs to sludge deposits in the MBR's system can allow the deposits to sit and be bombarded with water, causing the eventual biodegradation of CECs in the membrane. Sorption of a particular CEC can be even more efficient in the system if the CEC is hydrophobic, causing it to move from the wastewater to the sludge deposits more quickly.[29]