Recycling or reuse is in most instances environmentally preferable to disposal. Reuse of coal tar as an asphalt-pavement sealant for driveways and parking lots, however, has turned out to be an exception to this rule of thumb. See also: Asphalt and asphaltite; Pavement

Cafestol, C₂₀H₂₈O₃, is a compound, specifically a diterpene alcohol, found in coffee beans. It is extracted during the coffee-brewing process and may be present in coffee beverages, depending on the preparation method. Consumption of cafestol in coffee has been shown to produce both positive and negative health effects. See also: Coffee; Terpene

In an application of green chemistry, researchers reported in the journal Biomaterials (April 2018) the caffeine-catalyzed synthesis of a new class of polymer gels for drug delivery and other biomedical applications. These caffeine-catalyzed gels (CCGs) are easy to make and are customizable in terms of their chemical and physical properties, such as their composition, shape, solvent sensitivity, drug release, and mechanical strength. The gels have potential to be consumed as chewable and easier to swallow drug-delivery systems. They contain a small amount of caffeine but were found to be safe in toxicity tests. See also: Biomedical engineering; Caffeine; Catalysis and catalysts; Citric acid; Drug delivery systems; Gel; Green chemistry; Polymer

Handheld electronic devices with plastic casings, such as cell phones, may be exposing users to toxic organophosphate ester (OPE) flame retardants that leach out of these products. Researchers from the University of Toronto reported in Environment International (December 2018) that people in contact with cell phones showed evidence of hand-to-mouth and skin-absorbed OPE exposure. To test the relationship of these exposure pathways, the researchers measured OPE concentrations from air, dust, hand, electronic product, and urine samples. They detected OPEs as well as OPE urinary metabolites in more than 80 percent of the samples. In addition, they found greater evidence of OPE exposure from cell phones than from tablets, desktop computers, and televisions. See also: Fire technology; Flameproofing; Organophosphorus compound; Phosphorus; Polymer

Over the next 10 to 20 years, capturing carbon dioxide (CO₂)—a powerful greenhouse gas emitted from sources such as fossil-fuel-burning power plants, natural-gas processing plants, bioethanol plants, and cement plants—could become a significant method for mitigating climate change. Most of the captured CO₂ would probably be injected deep into the earth, a practice known as carbon capture and storage (CCS). The U.S. Department of Energy (DOE) estimates that the current cost to capture a ton of CO₂ is $60, which is cost prohibitive. With technological improvements, the DOE projects the cost to capture a ton of CO₂ could drop to a more affordable $40 in 10 years. See also: Carbon capture and storage; Carbon dioxide; Cement; Electric power generation; Global climate change; Greenhouse effect; Natural gas

If you think converting seawater to fuels that can power ships is a fantasy, think again. Researchers at the U.S. Naval Research Laboratory in Washington, D.C., have, in fact, accomplished this feat. In addition, the U.S. Navy has received a patent for an electrochemical device that removes carbon dioxide (CO₂) and hydrogen (H₂) gases from seawater, which together can be converted through a catalytic reaction to liquid hydrocarbon fuels that are similar to fossil fuels. Breakthrough technology aside, don’t expect to see U.S. Naval ships powered by fuels from seawater cruising the high seas anytime soon. Making significant quantities of this fuel requires processing a great deal of seawater, which, in turn, requires a large amount of electricity to drive the electrochemical process. Nevertheless, researchers expect efficiency improvements over the next 10 years to bring the concept closer to reality. See also: Carbon dioxide; Catalysis and catalysts; Electrochemical process; Fossil fuel; Hydrogen; Seawater

Due to their attractive properties, including high energy density and long cycle lives, lithium-ion batteries have become widely adopted in portable electronics and electric vehicles and continue to make inroads as renewable energy storage cells. However, as a raw material, lithium poses long-term economic and environmental sustainability concerns. These concerns include lithium's relatively high cost, looming scarcity, and negative environmental impacts from mining. As a potential alternative to lithium-ion batteries, researchers have been pursuing sodium-ion batteries (SIBs). Compared to lithium, sodium is significantly more abundant in Earth's crust, would be less expensive to obtain, and overall poses fewer environmental concerns. That said, sodium has proven far less tractable as a battery material. To address many of the issues that have stalled SIB advancement, researchers at Pusan National University in South Korea have developed new SIB anode materials. These new materials are efficient, are easily prepared, show high sodium-ion storage capacity, and have excellent cycle stability compared to their predecessors. The research team accordingly hopes that their technology can be used for large-scale production of sodium ion-based energy storage systems in the future. See also: Energy storage; Lithium; Mining; Sodium

Fentanyl is a synthetic opioid analgesic (pain reliever) that resembles morphine in its action. However, its drug potency is approximately 50 to 100 times more powerful than that of morphine, leading to high rates of both addiction and overdose deaths. In particular, the availability of fentanyl has increased dramatically since 2012, predominantly as the result of illegally manufactured and distributed quantities of the drug. According to the Centers for Disease Control and Prevention (CDC), fentanyl is the deadliest drug in the United States, surpassing heroin as the drug responsible for the greatest number of unintentional overdose deaths. Based on the CDC's latest analysis (covering the years 2011 through 2016 and reported in December 2018), the number of overdose deaths in 2016 as the result of fentanyl abuse was 18,335 (the number of heroin-related overdose deaths in 2016 was 15,961). This staggering number accounts for nearly one-third of all drug overdose deaths in the United States; in comparison, fentanyl accounted for only 4% of all overdose deaths in 2011. See also: Addiction and addictive disorders; Analgesic; Heroin: an addictive drug; Morphine alkaloids; Opiate; Pain

A class of chemicals known as per- and polyfluoroalkyl compounds (PFAS) are particularly worrisome in the environment because they do not biodegrade. For this reason, scientists often refer to PFAS as “forever chemicals.” PFAS’s staying power results from the carbon–fluorine (C–F) bond being one of the strongest and most stable bonds in organic chemistry. More than 5000 types of PFAS are used in a wide range of products, including nonstick pans, stain-resistant carpet, waterproof cosmetics, fast-food wrappers, dental floss, and fire-fighting foam. As a result of product use and waste released from manufacturing sites, PFAS occur widely in the environment, and, in particular, in drinking water—the most common exposure route. Because PFAS accumulate in the human body, exposure has been linked (in limited studies) to low infant birth weight, endocrine disruption, kidney cancer, and thyroid hormone disruption. Scientists have acknowledged that reducing the likelihood of PFAS exposure requires an effective water-treatment strategy. See also: Biodegradation; Chemical bonding; Environmental toxicology; Fluorocarbon

Atmospheric ozone plays a critical role in the biosphere by absorbing harmful ultraviolet radiation in the stratosphere—the layer of the atmosphere about 10 to 50 km (6 to 30 mi) above Earth’s surface. Since the adoption of the Montreal Protocol in 1987 banning chemicals that deplete this ozone layer, levels of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in the stratosphere have been declining. As a result, the ozone hole—an area of severely depleted ozone in the stratosphere above Antarctica—appears to be on schedule to recover sometime between 2040 and 2080. To avoid further delay in the ozone-hole recovery, scientists continually monitor the atmosphere for any new traces of CFCs or HCFCs. Much to their surprise, scientists reported in the Proceedings of the National Academy of Science, U.S.A. (February 2021) the discovery of three HCFCs that have no known use; that is, these chemicals should not exist according to manufacturing and emissions records worldwide. See also: Air pollution; Antarctica; Halogenated hydrocarbon; Ozone; Stratosphere; Stratospheric ozone