User:Cdodge415/Contaminants of Emerging Concern

Contaminant Classes
Contaminants of emerging concern (CECs) can be broadly classed into several categories of chemicals that have been found to significantly impact ecosystem and human health such as pharmaceuticals, cyanotoxins, personal care products, endocrine disrupting chemicals, nanoparticles, and flame retardants, among others. These classifications are constantly changing as new contaminants (or effects of existing contaminants) 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.

Pharmaceuticals
Pharmaceuticals, commonly antibiotics, steroids, anti-inflammatories, and antidepressants, are gaining more attention as CECs because of their continual introduction into the environment and their general lack of regulation. These compounds are often present at low concentrations in water bodies and little is currently known about their environmental and human health effects from chronic exposure; pharmaceuticals are only now becoming a focus in toxicology due to our improved analytical techniques that allow very low concentrations to be detected. There are several sources of pharmaceuticals in the environment, including most prominently compounds in effluent that are unable to be metabolized by microorganisms in urban wastewater treatment plants, aquaculture, and agricultural runoff. Improperly disposed of personal care products, over-the-counter and prescribed pharmaceuticals, and hospital waste also contribute to their presence in the environment. Because the doses of these compounds tend to be much lower than the effective dose, acute toxicity rarely occurs. Pharmaceuticals present in the environment can induce effects on aquatic organisms, such as possible metabolic changes, as well as increased antibiotic resistance in pathogenic microorganisms.

Endocrine disrupting chemicals
Many CECs can be classified as endocrine disrupting chemicals, or chemicals that mimic and alter the function of naturally occurring hormones in the body. These compounds are very common and are present in most manufactured products, including plastic bottles, cosmetics, and detergents. Reproductive effects in aquatic organisms and humans as well as immune deficiency, neurological impacts, and physiological effects can occur as a result of exposure to these compounds. There are a number of mechanisms through which endocrine disrupting chemicals can interfere with the body's natural hormone functioning that can be difficult to predict as these compounds often occur as mixtures.

Cyanotoxins
The growth of cyanobacterial blooms has been increasing due to the eutrophication (or increase in nutrient levels) of surface waters around the world. 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. Cyanobacterial blooms release toxins during cell death and as metabolic byproducts that can decrease water quality and are a risk to human and wildlife health. Additionally, regulations regarding the maximum contaminant levels (MCL) allowed in drinking water sources are currently lacking. Cyanotoxins can have both acute and chronic toxic effects from direct exposure including skin irritation, liver damage, and neurotoxicological effects. A derivative of mycrocystins, MC-LR, is one of the most highly researched cyanotoxins that has been found to promote liver cancer and has even resulted in human fatality. Cyanotoxin poisonings have also resulted in animal fatality in many domesticated animals such as dogs and cows and have been shown to bioaccumulate in aquatic food webs, posing a threat to human health through indirect exposure pathways as well.