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BAD BOYZ 2.0. Emerging environmental contaminants

Original article:

Richardson, S.D., and Kimura, S.Y. (2017). Emerging environmental contaminants: Challenges facing our next generation and potential engineering solutions. Environmental Technology & Innovation 8, 40–56. https://doi.org/10.1016/j.eti.2017.04.002

On the morning of August 5, 2015, the Animas River, located between the cities of Silverton and Durango in Colorado, turned orange. Onsite U.S. Environmental Protection Agency (EPA) projects at the Gold King Mine, situated a few miles north of Silverton, triggered an uncontrolled release of approximately 3 million gallons of acid mine water into the Animas. This outflow, commonly referred to as a “mine blowout”, carried iron-oxyhydroxide sediments soaked in heavy metals which had been deposited in the mine. The acid water is what caused the orange coloration of the Animas river (Fig 1). Eroding rocks, soil, and road embankments on its way downstream, the flow continued depositing small amounts of soil particles mixed with orange-brown iron-oxyhydroxide, cadmium, lead, and arsenic. Moving from the Animas and San Juan Rivers, the plume ultimately reached Lake Powell in Utah on August 14, 2015.

Fig 1. The Animas river, as viewed after spillage of mine waste in August 2015. (Wikimedia Commons)

Catastrophic contamination from traditional means such as heavy metals, pesticides, industrial waste and polychlorinated biphenyls (PCBs) are a recognized environmental issue. However, recent research efforts have revealed that there is an abundance of environmental contaminants that were previously unrecognized. This could be because many of these “emerging” contaminants do not exert the same kind of acute toxicity as well-known contaminants, instead using subtle, non-traditional disruptive mechanisms. Also, despite being termed “emerging,” a number of these substances have been present in the environment for decades, but were undetected due to lack of sensitive and appropriate instruments. Many of these pollutants impact human health, but they are particularly harmful for aquatic life, and therefore require intensive investigation.

So what are some of these emerging newbies? How do they work and what are some possible solutions for removal?

Prescription required

Pharmaceutical contaminants are gaining increasing relevance due to their widespread presence in several countries, including U.S., Germany, London and Spain. Many have reported the presence of drugs such as ibuprofen and acetaminophen in drinking water following wastewater treatment. However, apart from their introduction into ocean waters from human use, a variety of medications are given to livestock, poultry and fish farms. Although these drugs are found at the lowest observed effect concentration, there is a persuasive case to be made for their long-lasting deleterious impact on wildlife.

In 2003, wildlife epidemiologists began to investigate the mysterious death of millions of vultures in India. Reports finally confirmed the culprit: the anti-inflammatory drug diclofenac, which was being used as a painkiller for cattle. By consuming their carcasses, vultures were building up toxic levels of the substance, effectively poisoning them to death (Fig 2). Another tragic study came from the Experimental Lakes Area in northwestern Ontario, Canada, wherein a group of researchers introduced EE2, a synthetic version of estrogen used in birth-control pills, to assess reproductive effects on a wild fish species called fathead minnow. Their data revealed that chronic exposure to EE2 not only feminized the males through altered gene and protein expression, but also led to changes in egg-production in females. Ultimately, the minnows experienced near-extinction from the lake, demonstrating that even low doses of various drugs can damage wildlife and aquatic populations.

Fig 2. Painting of black vultures feeding on a mule deer carcass. More than 95% of the vulture population in India has been decimated by diclofenac poisoning, a common anti-inflammatory drug given to cattle. (Wikimedia commons)

Drugs afloat

From discovery of methamphetamine and ecstasy in U.S. waters in 2004, to finding cocaine in waters from Italy in 2005, illicit drugs are commonly reported to be present in aquatic ecosystems of various countries. A study on tap water across the globe determined the presence of cocaine, methadone, and their metabolites, benzoylecgonine and EDDP. Levels of benzoylecgonine present in wastewater have been reported to be toxic to zebra mussels. Interestingly, THC, the main psychoactive ingredient in marijuana, is absent from surface and groundwaters. Instead, THC and other cannabinoids are found in sewage sludge. Whether this is because marijuana is an organic substance, as compared to other synthetic drugs, is yet to be understood. Although not impacting aquatic life directly, sludge is commonly used as a fertilizer, which suggests other potential routes for exposure to THC.  

Unseen threats     

Use of engineered nanomaterials has blown up in almost all research and development sectors, with a plethora of products manufactured using them for various parts. Nanomaterials are around 1-100 nm in size, and advantageous because of their strength, stability at high temperatures and low permeability. However, with such high usage, there is a growing concern regarding their toxicity, transport, and removal from environmental waters. Presence of buckminsterfullerene and C70 fullerenes have been reported in river water, soils and suspended wastewater sediments (Fig 3). These “buckyballs” are used in solar cells, molecular wires and as drug carriers and even precursors to diamond!

Fig 3. Structure of buckminsterfullerene. An allotrope of carbon, it is commonly used in nanostructures as a strengthening material. (Wikimedia Commons)

Other examples include nanosilver-treated clothing, shampoo, toothpaste, detergents, and zinc nanoparticles in sunscreen. Both nanomaterials can accumulate in the blood and urine, but long-lasting effects still need to determined.       

Looking ahead

Much progress has been made in identifying, quantifying and understanding how contaminants affect the fate of the environment. Traditional water treatment plants utilizing three main stages: coagulation, flocculation, and sedimentation are being used to remove pollutant particulates (Video 1).  Advanced oxidation processes with ultraviolet (UV) and hydrogen peroxide (H2O2) are enabling inactivation of compounds such as diclofenac, ibuprofen and other pharmaceuticals. Nevertheless, contaminants can linger and/or transform in the environment. In the case of the Animas river, traditional metals deposited by the Gold King Mine have sedimented. However, they can be resuspended during storm events and spring runoff, thereby further decreasing water quality of the river. Emerging pollutants, on the other hand, could transform due to processes such as microbial degradation, hydrolysis, and can react with disinfectants in drinking water or wastewater treatment to form disinfectant by-products. Therefore, there is a need for speedy detection and identification of molecules and their properties. This is certainly a daunting task, considering the immense number of chemicals present in the environment. Ongoing engineering solutions and toxicology studies will aid in getting a clearer picture of the potential human and ecological effects of known pollutants and yet-to-be-determined toxic products.



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