Thursday, February 26, 2015

Chemicals in fireworks (2)

In addition to the chemicals mentioned the previous post,  there are other chemicals in fireworks and support their functions

Combustion agents, which generate high temperature after the fireworks are ignited. The major chemical component of combustion agents include fuel and oxidants that support combustion. Besides black powder, some metals (Al, Mg, Fe, Zn), petroleum components, phosphor, sulfur organometal also serves as fuels of fireworks. The combustion of these fuels requires the support of oxygen. However, at the fast rate of combustion with fireworks, the oxygen in air is consumed faster than can be refilled by surrounding air. Therefore, different oxidants are also added to fireworks to support the abrupt chemical reactions.

The most common oxidizer is potassium nitrate, which decomposes to potassium oxide, nitrogen gas, and oxygen gas.

decomposition of potassium nitrate

Sometimes more explosive oxidizers, which produced temperatures of 1700 to 2000°C and made possible the creation of much more intense colors. These oxidizers are the chlorates and perchlorate

reaction of chlorates
reaction of perchlorates

decomposition of potassium nitrateThe chemicals as oxidants generally involve nitrate, chlorate, bromorate, and perchlorate.

Fireworks use chlorate and perchlorate as the oxidizer often include catalyzers . The function of catalyzers is to decrease the required temperature for certain chemical reactions. Catalyzers often include some transition elements, for example, CoO2, Cr2O5, CuO, TiO2, PbO2, Pb3O4.

Besides the chemical components that take part in chemical reactions during firework combustion, there are also other inner component such as sulfate, phosphate, carbonate and natural resin that make the different chemicals stay together.

Sometimes fireworks are used during the day time. In such case, smoke from fireworks plays a more important role than the light from fireworks. Such fireworks used during the day time also includes smoke generating agents which forms many aerosol particles with different sorption and refraction on the light to give different colors. Such chemicals that form aerosol particles include yellow phosphor, white phosphor, hexachloroethane, alumimum powder, zinic oxide, and dyes

With so many chemicals in fireworks, what's the environmental impact caused by these chemicals in fireworks? Let's continue next time.

Saturday, February 21, 2015

Chemistry of fireworks

This week unfolds the Lunar year of Sheep.  Lunar new year has been celebrated with fireworks for almost a thousand years. What's the science in fireworks. Let's explore by starting with black powder. 

Black powder was one of the greatest inventions of ancient China. It was invented  by alchemists experimenting with a naturally-occurring salt, potassium nitrate while looking for an elixir of immortality. But in handling and heating the sensitive substance they inevitably discovered its explosive properties. 

ancient book documenting how to make black powder

Although the first known account of the use of gunpowder as a weapon dates to 1046 in China, the use of black powder to make fireworks was documented during the Song Dynasty around the 1200s. 

There are various chemical components in fireworks. The major chemical component is the lighting agent. The ideal lighting agent requires a long time of lighting from chemical reactions. Flare of firework needs to be supported with heated solid and liquid microparticles that release energy via chemical reaction. The temperature of flare from lighting agents can be over 2000 Celsius. The effieciency of lighting agent depends on the content of magnesium. The most commonly used lighting agent in fireworks contains 55% magnesium, 40% sodium nitrate and ~5% synthetic resin. The time of lighting can last from 30 seconds to a few minutes.

Besides lighting agent, there is also a component called flashing agent in fireworks. Flashing agent generate bright light in a short time (0.1 s).  One type of flashing agent include aluminum-magnesium alloy, which is relatively safe. Another type of flashing agent additionally include potassium perchlorate (KClO4).

The other component of firework is called coloring agent. Coloring agents are comprised of different metal salts. Chemical reaction by the lighting and flashing agent generate large amount of heat. Such energy will excited the electrons of metal elements.  This high-energy excited state does not last for long, and the excited electrons of the elements quickly release their energy. The amount of energy released can be characterized by a particular wavelength of light and varies from element to element.  Higher energies correspond to shorter wavelength light, whose characteristic colors are located in the violet/blue region of the visible spectrum. Lower energies correspond to longer wavelength light, at the orange/red end of the spectrum.

The colors you see exploding in the sky are produced by the elements with the characteristic emissions listed in the table (source:

ColorCompoundWavelength (nm)
strontium salts, lithium salts
lithium carbonate, Li2CO3 = red
strontium carbonate, SrCO3 = bright red

calcium salts
calcium chloride, CaCl2
sodium salts
sodium chloride, NaCl
barium compounds + chlorine producer
barium chloride, BaCl2
copper compounds + chlorine producer
copper(I) chloride, CuCl
purplemixture of strontium (red) and
copper (blue) compounds
silverburning aluminum, titanium, or magnesium

More coming in the next post. ..

Friday, February 20, 2015

Chemicals associated with E-Cigarettes

Electronic cigarette is also referred as e-cig or e-cigarette, which is a battery-powered vaporizer which has a similar feel to tobacco smoking.

Third generation of e-cigarette that have organic light-emitting diode displays and buttons to adjust wattage or voltage.
Credit: Shutterstock/C&EN

Electronic cigarettes do not contain tobacco, although they do use nicotine from tobacco plants. They do not produce cigarette smoke but rather an aerosol. In general, they have a heating element that atomizes a liquid solution known as e-liquid.  E-liquid, also referred as e-juice or simply "juice", is a liquid solution that when heated by an atomizer produces vapor. The main ingredients of e-liquids are usually a mix of
propylene glycol (PG),

glycerin (G)

and/or polyethylene glycol 400 (PEG400),

sometimes with differing levels of alcohol mixed with concentrated or extracted flavourings;

E-cigarette fluid or “e-juice” comes in thousands of flavors, including pineapple custard and Scooby snack.
Credit: Associated Press

and optionally, a variable concentration of tobacco-derived nicotine.ingredients but without nicotine.

The solution is often sold in bottles or pre-filled disposable cartridges, or as a kit for consumers to make their own eJuices. Components are also available to modify or boost their flavour, nicotine strength, or concentration of e-liquid. Pre-made e-liquids are manufactured with various tobacco, fruit, and other flavors, as well as variable nicotine concentrations (including nicotine-free versions). Surveys suggested that the most liked e-liquids had a nicotine content of 18 mg/ml, and largely the favorite flavors were tobacco, mint and fruit. The flavorings may be natural or artificial.

Flavoring substances not identified in a natural product intended for human consumption, whether or not the product is processed. These are typically produced by fractional distillation and additional chemical manipulation of naturally sourced chemicals, crude oil or coal tar.

Most artificial flavors are specific and often complex mixtures of singular naturally occurring flavor compounds combined together to either imitate or enhance a natural flavor. These mixtures are formulated by flavorists to give a food product a unique flavor and to maintain flavor consistency between different product batches or after recipe changes. The list of known flavoring agents includes thousands of molecular compounds, and the flavor chemist (flavorist) can often mix these together to produce many of the common flavors.

Isoamyl acetate
Bitter almond
Ethyl propionate
Methyl anthranilate
Ethyl decadienoate
Allyl hexanoate
Ethyl maltol
Sugar, Cotton candy
Methyl salicylate

References and more to read:

Saturday, February 14, 2015

Caffeine chemistry

Caffeine, a methylxanthine alkaloid  closely shares chemical structural features with the adenine and guanine contained in deoxyribonucleic acid (DNA).


adenine                                     guanine

Caffeine is the world's most widely consumed psychoactive substances, but unlike many others, it is legal and unregulated in nearly all parts of the world.  Caffeine is classified as "generally recognized as safe" (GRAS) with toxic doses, over 10 grams per day for an adult. A cup  of coffee contains 100–200 mg of caffeine.

Caffeine can have both positive and negative health effects. It may confer a modest protective effect against some diseases, including Parkinson's disease and cardiovascular disease such as coronary artery disease and stroke. On the other hand, caffeine can cause sleep disruption, headaches, irritability, increased blood pressure and heart rate.

Decaffeination (decaf) is applied to remove caffeine from coffee beans, cocoa, tea leaves and other caffeine-containing materials. Decaffeinated drinks contain typically 1–2% of the original caffeine content, and sometimes as much as 20%.

In all decaffeination processes, coffee is always decaffeinated in its green, unroasted state. The greatest challenge to the decaffeination process is to try to separate only the caffeine from the coffee beans while leaving the other chemicals such as sucrose, cellulose, proteins, citric acid, tartaric acid, and formic acid at their original concentrations.  Since caffeine is a polar, water-soluble substance, water is used in all forms of decaffeination. However, water alone is not the best solution for decaffeination because it is not a selective solvent and therefore removes other soluble substances, including sugars and proteins, as well as caffeine. Therefore decaffeination processes use a decaffeinating agent such as methylene chloride, activated charcoal, CO2, or ethyl acetate.

Plastic Pollution in the World's Oceans

Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea.

A paper published in Science today on the estimation of mass of land-based plastic waste entering the ocean by linking worldwide data on solid waste, population density, and economic status. It is estimated that 275 million metric tons (MT) of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million MT entering the ocean. Population size and the quality of waste management systems largely determine which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025.

More information in the Report published in Science:
source of the graph:

Tuesday, February 10, 2015

Chemicals used for vector control

DDT has been used in malaria vector control because of its long residual efficacy when sprayed on walls and ceilings (6–12 months depending on dosage and nature of substrate).

Vector control is a method to limit or eradicate the mammals, birds, insects or other arthropods which transmit disease pathogens. The most frequent type of vector control is mosquito control using a variety of strategies.

DDT has been listed in the Stockholm Convention for persistent organic pollutants for international control. Recognizing that total elimination in many malaria-prone countries is currently unfeasible because there are few affordable or effective alternatives, the convention exempts public health use within World Health Organization (WHO) guidelines from the ban.

Today, about 3,000 to 4,000 tonnes of DDT are produced each year for vector control. DDT is applied to the inside walls of homes to kill or repel mosquitoes. This intervention, called indoor residual spraying (IRS), greatly reduces environmental damage. It also reduces the incidence of DDT resistance.
DDT (dichlorodiphenyltrichloroethane)


Saturday, February 7, 2015

Chlorofluorooctane sulfanate (ClFOS or Cl-PFOS) : metabolites or by-product during the production of perfluorooctane sulfanate?

Researchers from the National Research Centre for Environmental Toxicology of Australia used liquid chromatography quadrupole time-of-flight tandem mass spectrometry found some novel fluorinated surfactants in firefighters. The study was published this week at Environmental Science and Technology.

One of the novel chemicals is chlorofluorooctane sulfanate (ClFOS or Cl-PFOS), or one F atom in PFOS get replaced with Cl.

One hypothesis for the origin of Cl-PFOS is due to metabolism of PFOS-related compounds in human body.

On the other hand,  I think it is plausible that the novel chlorofluorooctane sulfanate is a by-product during the production of PFOS.  Check the analysis of chemical reactions during the production of PFOS:

Thursday, February 5, 2015

Polychlorinated biphenyls (PCBs) in silicone-based adhesives and chlorophenylsilanes

Chlorophenylsilanes are the intermediate substances in the manufacturing of phenyl silicones. As suggested by evidence found in a recent study by Katsunori Anezaki,Takeshi Nakano
polychlorinated biphenyls (PCBs) could be formed along with reactions to synthesize
phenyl silicone.
Silicones are typically heat-resistant and rubber-like, and are used in sealants, adhesives, lubricants, medicine, cooking utensils, and thermal and electrical insulation. Some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, and silicone caulk. Compared to methyl-based silicones, phenyl-based silicones have higher oxidation resistance, thermal stability and shear resistance. At elevated temperatures, phenyl-based silicones are more stable and resistant to thermal and oxidizing attack.

Wednesday, February 4, 2015

Historical used organochlorine termiticides

Organochlorine termiticides are a group of pesticides that were used for termite control in and around wooden buildings and homes from the mid-1940s to the late 1980s. These organochlorine pesticides included chlordane, aldrin, dieldrin, heptachlor, and dichlorodiphenyltrichloroethane (DDT). They
were used primarily by pest control operators in tropical urban areas, but also by homeowners, the military, the state, and counties to protect buildings against termite damage.

Chlordane as one of the most widely used termiticide before 1980s

In the 1970s and 1980s, the U.S. Environmental Protection Agency (EPA) banned all uses of these organochlorine pesticides except for heptachlor, which can be used today only for control of fire ants in underground power transformers.

Termiticides were commonly applied directly to soil beneath buildings or beneath slab foundations and around the foundation perimeter for new construction. They may also have been periodically applied underneath the building (if accessible) at occupied structures, around the perimeter of the foundation, or in trenches excavated around the foundation, or by injection through holes drilled next to the foundation or in the flooring at the periphery of walls.

These pesticides break down slowly in the environment, application rates were relatively high, and applications may have been repeated over time. As a result, these organochlorine termiticides may sometimes still be found in treated soils. The organochlorine termiticides contaminated soil becomes secondary source of the chemicals in he air.

Recommended  actions to limit or avoid exposure include:
 Plant grass or other non-edible vegetation
 Cover contaminated soil with some kind of surface material such as gravel (within several feet of the foundation) to act as a barrier to prevent soil exposure.
 Keep children from playing in dirt near the foundation and keep toys, pacifiers, and other items that go into children’s mouths clean.
 Locate pet enclosures away from the perimeter of the building foundation.
 Do not grow edible produce such as fruits and vegetables in potentially contaminated soils next to the building foundation. Cover the soil next to the foundation, or add clean soil and landscape with non-edible plants.
 Do not relocate soils from underneath the building or from the foundation perimeter to other areas of the property.
 To reduce exposure to soil, cover bare soil underneath the house with a barrier material such as gravel or plastic before you work or store materials underneath the house.

 Wash hands and face thoroughly after you work or play in soil near the building foundation, especially before meals and snacks.
 Avoid tracking soil from near the foundation perimeter into the home and clean it up right away if soil is tracked in. Remove work and play shoes before you enter the house. Keep pets from tracking
contaminated soil into your home.
 If you work with contaminated soil or soil that may be contaminated, you should wear gloves and
protective clothing (long-sleeve shirt and pants) to reduce exposure. A protective paper mask (N-95 type with two elastic straps) should be worn if airborne dust is present (such as when you are operating a weed-eater in contaminated or potentially contaminated areas). Working with contaminated soil may leave residues on your clothing, so change clothes and shower after you work with the soil and avoid spreading dirt from clothes or shoes into your vehicle or house.

Information retrieved from

Tuesday, February 3, 2015

UN Calls for Wastewater Focus

In my research, I focus on toxic chemicals that cannot be removed from wastewater treatment. And a lot of studies aim to develop advanced wastewater treatment technologies to remove more toxic chemicals in order to reduce loadings of toxic chemicals to the environment, which would affect ecosystems and in turn human health.


While developed countries such as Canada and the USA have over 90% of wastewater treated, sanitation of wastewater is still a big challenge faced by many low-income countries.  The global data indicate that only 20% of global wastewater is currently being treated. Wastewater in some developing countries is barely treated before released to the environment. Low-income countries possessing only 8 per cent of the required capacity to treat wastewater effectively. Such untreated wastewater is likely to contaminate water supplies and cause diseases. A UN-Water Analytical Brief, produced by the World Health Organization (WHO), the United Nations Environment Programme (UNEP) and UN-Habitat, on behalf of UN-Water, describes the damage being done to ecosystems and biodiversity as 'dire' and warns of the threat wastewater will increasingly pose to human health, economic activity, and water security if left unaddressed.

It is obvious that sustainable wastewater management will become a key task for the world to apply in the coming years.

UN and WHO officials pointed out  "Wastewater management has been neglected in the rush to commercialize drinking water production, a situation exacerbated by a fragmented water management system in many countries, and the use of different technologies that are often designed separately and retrofitted to existing systems."

"Around 70 per cent of industrial discharge in developing countries goes untreated. And eutrophication - from wastewater and agricultural run-off - has, according to recent estimates, reduced biodiversity in rivers, lakes and wetlands by about one-third globally."

"It is time to turn this environmental and human health challenge into an opportunity. Agriculture consumes 70 per cent of global water withdrawal, but agricultural irrigation from reclaimed wastewater is on the rise, and is being used to irrigate 20 to 45 million hectares worldwide. This is just a fraction of what is possible if policy and available technologies converge to ensure that wastewater and water quality are fully integrated into a more holistic water agenda as part of the post-2015 process,"

"To be successful and sustainable, wastewater management must be an integral part of the critical levers of urban planning and legislation resulting in productive, healthy and livable cities. The upcoming UN Conference on Housing and Sustainable Urban Development, Habitat III, will be an opportunity to underscore the importance of effective wastewater management and highlight the role of wastewater in the new urban agenda."

References and read more:

Monday, February 2, 2015

Health Risks from Inhaled Polychlorinated Biphenyls

Evaluating Health Risks from Inhaled Polychlorinated Biphenyls: Research Needs for Addressing Uncertainty

A recent article published in Environ Health Perspect by Lehmann et al. DOI:10.1289/ehp.1408564 describes some common sources of PCBs in indoor air and estimate the contribution of inhalation exposure to total PCB exposure for select age groups and identified some critical areas of research needed to improve assessment of exposure and exposure response for inhaled PCBs.

Air concentrations of polychlorinated biphenyls (PCBs) in some buildings can be orders of magnitude higher than background levels. The potential health risk posed by PCBs from indoor environment need to be assessed. To assess such risk we need to face some uncertainty.

Previous assessments of exposure and risk associated with PCBs primarily focused on dietary intake of contaminated food. With many recent studies suggested the importance of indoor PCB exposure, this article points out one important uncertainty for risk assessment of PCBs from indoor exposure.

The distributions of  PCB congeners in food and in indoor air are quite different. As such, toxicity of of PCB mixtures from indoor environment is likely to be different from toxicity due to dietary intake.

In addition to the uncertainty mentioned in the article, I think another uncertainty we need to face lies in the pathway from external exposure to internal exposure. Bioavailability/toxicokinetics of PCBs from inhalation would be quite different from dietary intake and need to be addressed.

Sunday, February 1, 2015

Roles of the human occupant in indoor chemistry

"Human occupants, through the reactive chemicals that they emit, have a large influence on
the atmospheric chemistry that occurs around them, ultimately impacting their own chemical
exposures and their health" --A recent article published in the journal Indoor Air by Charles J. Weschler from the Environmental and Occupational Health Sciences Institute, Rutgers University gives an overview on roles of the human occupant in indoor chemistry.

Clean up

As summarized by Weschler, a number of evidences suggested that there are pronounced influences of humans on chemistry within the indoor spaces they inhabit.

Occupants leave behind skin flakes, skin oils and body effluents on indoor surfaces and on their clothing. These human generated long-chain hydrocarbon involve unsaturated carbon bonds, which will react with indoor ozone and thus affect indoor chemical reactions involving ozone.

This review article also summarized the potential role of occupants on the levels of semivolatile organic compounds from indoor sources, which is based on a human uptake and exposure model coupled with an indoor chemical fate mass balance model that suggests human intake and elimination of a chemical (e.g., biotransformation, renal excretion, fecal egestion, hand washing, bathing)
influences its fate indoors. Such an impact varies according to chemicals properties (volatility, degradation, etc) as well as environmental characteristic (e.g., ventilation) and human behaviors (e.g. the frequency of cleaning. As mentioned by Wescler, this is an area that is potentially rich
for further exploration. Refer to this modeling study for more information.

Some facts summarized in the article:

  • lipids on skin surface of human are a combination of sebum secreted by sebaceous glands and lesser amounts of lipids from the stratum corneum
  • The chemicals that constitute skin surface lipids include triacyl glycerols (~25%), unesterfied fatty acids (~25%), wax esters (~22%), squalene (~10%), mono- and diacyl glycerols (~10%) and lesser amounts of sterol esters, sterols, phospholipids and other species 
  • squalene is responsible for roughly 50% of the unsaturated carbon bonds in skin surface lipids
Finally, the review article by Weschler provides a summary on the roles of the human occupant in indoor chemistry- "We have read the early pages of what promises to be a long and interesting book –interesting, in part, because the subject is us. This unfolding story promises to inform strategies designed to protect our health, our technical devices and our cultural artifacts"

References and more to read: