Author Archives: Karen O'Brien

Applying 21st century toxicology to green chemistry.

By Eddy Ball
October 2011

Scientists aiming to develop real-world solutions for problem chemicals gathered at a workshop on “Applying 21st Century Toxicology to Green Chemical and Material Design” Sept. 20-21, at the House of Sweden Event Center in Washington, D.C. The workshop was part of the National Academy of Sciences (NAS) ongoing series organized by the Committee on Emerging Science for Environmental Health Decisions sponsored by NIEHS. This workshop was unique in that it was co-hosted by the National Science and Technology Councils (NSTC) Committee on Environment, Natural Resources, and Sustainability (CENRS) Subcommittee on Toxics and Risks.

With more than 83,000 chemicals available for use in the U.S. today, there is rising concern about potential toxic properties these chemicals pose in relation to human health and the environment. This issue has given rise to the field of green chemistry — the science-based design of chemicals to minimize the use and generation of hazardous substances.

Visioning a green future

The workshop brought together chemists, toxicologists, and biologists to define common goals, identify knowledge gaps, and promote applied research aimed at expediting the application of new approaches to toxicology to the emerging field of green chemistry. As he opened the meeting, NIEHS Toxicology Liaison and co-chair of the NSTC Subcommittee on Toxics and Risks Christopher Weis, Ph.D., challenged participants to think of a future with safer chemicals and less need for regulation.

Paul Anastas, Ph.D., assistant administrator of the U.S. Environmental Protection Agency Office of Research and Development, who is often referred to as the father of green chemistry, then set the stage for the meeting’s three sessions with a presentation, titled “Vision of a Green Chemical Future.” Anastas told participants, “There are tremendous advantages — environmental, economic, and health-related — in implementing green chemistry into the design and production of the next generation of chemicals.”

The main focus of the sessions centered on identifying replacements for problematic chemicals and the emerging tools available for toxicology testing. Representatives from industry, academia, and government agencies discussed the utility of rapid assessment approaches in toxicology, including high-throughput biochemical screening, in vitro cellular approaches, and rapid assessments using aquatic organisms.

Putting the plan to action

During session three, Thaddeus Schug, Ph.D., a postdoctoral fellow on detail to the NIEHS Division of Extramural Research and Training, highlighted a collaborative project that is constructing a protocol for chemists to flag endocrine disruptors early in chemical development. “The protocol is not regulatory,” Schug emphasized, “but a guide chemists can follow as they develop a chemical, to give them confidence as to whether the substance is or is not an endocrine disruptor.”

Thaddeus Schug, Ph.D.
“What we propose to do is put the fastest, cheapest testing up front, the computational modeling, followed by high throughput screening and the zebrafish models,” Schug explained. The first-tier testing would be followed up with more specific testing as a chemical moves farther along the developmental process. (Photo courtesy of Steve McCaw)

The project, which is sponsored by the groups Advancing Green Chemistry and Environmental Health Sciences, publisher of Environmental Health News, has come up with a tiered system.

“The idea is if chemists hit a positive early on, they would either go back to the drawing board, or if that positive was in a specific area, such as an estrogen receptor in a high throughput assay, they’d follow that up with more comprehensive assays,” Schug continued. “A hit anywhere along the tiered system means chemists need to pull back, reanalyze, or throw the chemical out.”

The protocol is voluntary, explained Bruce Blumberg, Ph.D., a professor of developmental and cell biology at the University of California, Irvine. “We suggest this if you want to screen for endocrine activity in your chemicals and make them more green – this is the way we think you should do it. We’re providing an alternative approach interested parties can use to make the best chemicals they can,” he said.

Richard Denison, Ph.D., senior scientist at Environmental Defense Fund, welcomed the protocol’s development, saying, “It really flips the concept of tiered testing around.” Usually in tiered testing, a chemical only advances to the next level of testing if it is flagged for an effect at an earlier level. “[That] puts a huge question mark around the extent to which false negatives are being missed,” Denison added.

Christopher Weis, Ph.D.
“Dream big of a future in which green chemistry will move into the marketplace to the extent that this science will ultimately short-circuit the need for regulation,” Weis told workshop participants. “This will allow us to think ahead about potential chemical effects, rather than respond to problems that arise after chemicals are introduced.” (Photo courtesy of Steve McCaw)

Are Flame Retardants Safe? Growing Evidence Says ‘No’.

by Elizabeth Grossman: originally published 29 Sep 2011 in Yale360

Over the past 40 years, a class of chemicals with the tongue-twisting name of halogenated flame retardants has permeated the lives of people throughout the industrialized world. These synthetic chemicals — used in electronics, upholstery, carpets, textiles, insulation, vehicle and airplane parts, children’s clothes and strollers, and many other products — have proven very effective at making petroleum-based materials resist fire.

Yet many of these compounds have also turned out to be environmentally mobile and persistent — turning up in food and household dust — and are now so ubiquitous that levels of the chemicals in the blood of North Americans appear to have been doubling every two to five years for the past several decades.

Acting on growing evidence that these flame retardants can accumulate in people and cause adverse health effects — interfering with hormones, reproductive systems, thyroid and metabolic function, and neurological development in infants and children — the federal government and various states have limited or banned the use of some of these chemicals, as have other countries. Several are restricted by the Stockholm Convention on persistent organic pollutants. Many individual companies have voluntarily discontinued production and use of these compounds. Yet despite these restrictions, evidence has emerged in recent months that efforts to curtail the use of such flame retardants — a $4 billion-a-year industry globally — and to limit their impacts on human health may not be succeeding.
This spring and summer, a test of consumer products, as well as a study in Environmental Science & Technology, showed that use of these chemicals continues to be widespread and that compounds thought to be off the market due to health concerns continue to be used in the U.S., including in children’s products such as crib mattresses, changing table pads, nursing pillows, and car seats. Also this summer, new research provided the first strong evidence that maternal exposure to a widely used type of flame retardant, known as PBDEs (polybrominated diphenyl ethers), can alter thyroid function in pregnant women and children, result in low birth weights, and impair neurological development.

“Of most concern are developmental and reproductive effects and early life exposures — in utero, infantile and for children,” Linda Birnbaum, director of the National Institute of Environmental Health Sciences and the National Toxicology Program, said in an interview.

Read full post here.

ABOUT THE AUTHOR
Elizabeth Grossman is the author of Chasing Molecules: Poisonous Products, Human Health, and the Promise of Green Chemistry, High Tech Trash: Digital Devices, Hidden Toxics, and Human Health, and other books. Her work has appeared in Scientific American, Salon, The Washington Post, The Nation, Mother Jones, Grist, and other publications. In earlier articles for Yale e360, she explored how the Fukushima nuclear plant disaster could affect marine life off the Japanese coast and reported on recent studies suggesting a possible link between prenatal exposure to pesticides and the mental abilities of children.
MORE BY THIS AUTHOR

Scientists constructing tool for chemists to flag endocrine disruptors early in chemical development.

The reporter got the attribution for our project wrong (NIEHS is not financially supporting this work, but is supporting it in kind. AGC and sister organization, Environmental Health Sciences, are funded to do the project). Still though: we are glad people are interested.

Pesticide and Toxic Chemical News
Friday September 23 2011

A group of biologists and green chemists, supported by the extramural research division of the National Institute of Environmental Health Sciences, is developing a protocol for chemists to use to determine if the chemical they are developing is an endocrine disruptor.

Thaddeus Schug, who manages a portfolio of grants in the NIEHS Cellular, Organs and Systems Pathobiology Branch, highlighted the project during a panel discussion on practical approaches to integrating rapid testing into the chemical design process. The discussion took place Sept. 21, the second day of a workshop, “Applying 21st Century Toxicology to Green Chemical and Material Design,” which was sponsored by the National Academies’ Standing Committee on Use of Emerging Science for Environmental Health Decisions. Schug says the group has been working for the last year on developing a protocol, and the guiding principles behind it, to determine whether a chemical under development is toxic, and how and where testing should be performed.

“We focus on endocrine disruption, but our guiding principles and protocol could be developed to capture all forms of toxicity,” he said. The protocol is not regulatory, Schug said, but a guide chemists can follow – as they develop a chemical – to give them confidence as to whether the substance is or is not an endocrine disruptor.

The group, which includes non-governmental organizations, academics and green chemistry leaders, has come up with a tiered system. “What we propose to do is put the fastest, cheapest testing up front – the computational modeling, followed by high throughput screening and the zebrafish models,” Schug said. That would be followed up with more specific testing as a chemical moves further along the development process.

“The idea is if a chemist hits a positive early on, he’d either go back to the drawing board, or if that positive was in a specific area [i.e. an estrogen receptor in a high throughput assay], he’d follow that up with more comprehensive assays,” Schug said. “A hit anywhere along the tiered system” means the chemist has to pull back, reanalyze or throw the chemical out, he said.
“The idea is to do the fastest, cheapest test early on, so the chemist can weed out those problem chemicals early on in development so it’s not a costly procedure,” Schug said.

The idea of the protocol “arose from a great sense of frustration” in the endocrine disruptor community, Bruce Blumberg, a professor of developmental and cell biology at the University of California, Irvine who also is working on the project, said during the panel discussion. This frustration stemmed from “hearing things like, ‘Well, you can’t test for endocrine disruptors,’ which the American Chemistry Council says,” Blumberg noted. “We know very well how to test for endocrine disruptors, how to test for endocrine disruptor activities from in vitro all the way to animal studies,” he said. “So we said this is a gap that has to be filled, and we got together to fill that gap.”

The protocol is voluntary, Blumberg noted. “We suggest this if you want to screen for endocrine activity in your chemicals and make them more green – this is the way we think you should do it. We’re providing an alternative approach interested parties can use to make the best chemicals they can,” he said.

Richard Denison, senior scientist at Environmental Defense Fund, welcomed the protocol’s development, saying “it really flips the concept of tiered testing around.”
Usually in tiered testing, a chemical only advances to the next level of testing if it is flagged for an effect at an earlier level, “which puts a huge question mark around the extent to which false negatives are being missed.”

But in the case of the protocol, “you’re advancing things that don’t raise red flags to the next level [of testing], increasing the confidence that you didn’t miss anything,” Denison said. “I think that’s a really intriguing approach.”
(Read full article here.)
- Liz Buckley

A more sensitive material detects heavy metals at 100 times lower levels.

Synopsis by Wim Thielemans, Aug 04, 2011

Zhang, Y, Y Liu, X Ji, CE Banks and W Zhang. 2011. Sea cucumber-like hydroxyapatite: Cation exchange membrane-assisted synthesis and its application in ultra-sensitive heavy metal detection. Chemical Communications http://dx.doi.org/10.1039/c1cc10489f.

A nano-sized membrane that looks like a hard, hairy sponge can detect minute amounts of lead and cadmium in water, report researchers who devised a new method in the laboratory to grow the natural material – called hydroxyapatite – that makes up the membrane.

Hydroxyapatite has unique properties that are already being exploited in a variety of sensors in an effort to move away from using gold, mercury and other toxic substances. The new method – which is still being researched – takes its use even further by developing crystal-like protrusions and structures that increase the material’s surface area. Its higher interaction with the surrounding water dramatically improves the material’s sensitivity; it can measure levels up to 100 times lower than other available devices.

Heavy metals such as lead and cadmium are a major health and environmental problem. They contaminate soil and water and accumulate in plants and animals. People are exposed to heavy metals through many sources, including food, water, air and dust. In humans, exposure to heavy metal is linked to many disorders such as organ damage, developmental problems and psychological changes.

Governments regulate heavy metal emissions, but the metals still contaminate many streams, lakes and other water bodies. As regulation tighten, it is thus important to monitor for these pollutants at more sensitive levels in waterways, tap water and drinking water.

The researchers grew the hydroxyapatite – which is a major component of human teeth and bones – on a membrame for four to seven days to create a crystal-like material with a high surface area. A higher surface area allows for increased surface-water interaction.

The hydroxyapatite can efficiently exchange calcium from its own structure with lead and cadmium in the water. The metal content in the water is then determined by applying a varying voltage over the hydroxyapatite and measuring the electrical current that flows through it.

The detection limit for lead was determined to be 9 X 10-10 grams per liter (g/L) – that is, a decimal point followed by nine zeros and a nine. Cadmium was detected down to 3 X 10-9 g/L. These detection limits are on the order of parts per trillion. They could detect a single drop in the volume of 20 Oympic size swimming pools. This makes the innovative material 10 to 100 times more sensitive than other hydroxyapatite-based sensors.

The high surface area hydroxyapatite was formed by controlling its growth using a Nafion membrane. Nafion is a polymer that allows only positive ions to pass through it. Hydroxyapatite was formed by combining two reactants – calcium and phosphate – added on opposite sides of the membrane in water. Only calcium – with its positive charge – can pass through the membrane The hydroxyapatite forms on the membrane’s surface as calcium reaches the other side and combines with the water and phosphate.

The new method to prepare high surface area hydroxyapatite is very promising. However, applying it to detect heavy metals will take further work to optimise. For example, the authors only tested their device to detect a single metal. They did not yet report the effectiveness when several metals are present or when other non-metallic pollutants are present in the water.

The researchers will also need to optimise how to form the high surface area hydroxyapatite. For wide use, faster preparation methods will need to be developed.

See more science at Environmental Health News.

NIEHS scientists join forces with green chemists.

By Thaddeus Schug
April 2011

A representative diagram of the draft screening protocol  unveiled at the meeting
A representative diagram of the draft screening protocol unveiled at the meeting. The protocol is designed in a tiered approach, with rapid and cost effective screens conducted in the early phases and more extensive testing toward the end. (Slide courtesy of Pete Myers)

NIEHS/NTP scientists joined forces with leaders in the field of green chemistry in what may turn out to be a groundbreaking meeting, “Green Chemistry and Environmental Health Sciences — Designing Endocrine Disruption Out of the Next Generation of Materials,” held March 21-23 in Sausalito, Calif.

The challenges facing scientists trying to design such new materials are daunting. Say a chemist has developed a compound that he or she believes could be a replacement for bisphenol A (BPA). How will the scientist determine if the molecule is safer to human health and the environment? What testing will need to be done and what will guide scientists through this process?

The goals of the meeting in Sausalito were ambitious — to develop a consensus statement on the principles that guide the science needed to assess risks of potential endocrine disruptors, and to develop a reliable and rational testing protocol to aid chemists as they develop and bring the next generation of chemicals into the marketplace.

The intersection of green chemistry and environmental health science

Karen O’Brien, Ph.D., from Advancing Green Chemistry (AGC) and Pete Myers, Ph.D., of Environmental Health Sciences (EHS), welcomed participants to the event, which brought together an equal mix of biologists and chemists. Representatives from NIEHS and NTP included Division of Extramural Research and Training (DERT) program administrator Jerry Heindel, Ph.D., and Kristina Thayer, Ph.D., director of the NTP Center for the Evaluation of Risks to Human Reproduction (CERHR).

Following a social ice-breaking exercise on the evening of March 21, the first full day of the meeting opened with presentations from Terry Collins, Ph.D., the Teresa Heinz Professor of Green Chemistry at Carnegie Mellon University, and John Warner, Ph.D., president and founder of the Warner Babcock Institute for Green Chemistry.

Both Collins and Warner stressed the need for fundamental changes in the way that scientists design new chemicals and the process of bringing them into the marketplace. “We must also pay close attention to the environmental impact and the effects on human health posed by these chemicals, and for those reasons chemists need to work hand-in-hand with biologists,” said Warner. He also stressed that chemists generally have no background in toxicology, but that they need to be able to test the chemicals being developed for endocrine activity and to do it early on in the product development process.

Designing a chemical screening protocol

The remainder of the day was divided into discussion sessions covering each phase of a newly developed screening model, designed by a science advisory board formed by meeting organizers that met monthly, via teleconference, for six months prior to the workshop. The protocol is geared towards identifying a wide-range of endocrine-active chemicals, such as atrazine, BPA, brominated flame retardants, organotins, perchlorates, and phthalates. The Board conducted  interviews with scientists with expertise in specific areas of toxicology, endocrine disruption, and assay development.

The testing paradigm proposed involves a five-tiered approach, starting with the fastest and cheapest assays and working through more specialized tests to determine whether a new chemical has endocrine disrupting characteristics. The initial two phases rely on predictive computer modeling and high-throughput screening to quickly weed out problem chemicals. These tests are followed by more specific in vitro cell-based screening assays with a mind to refining, reducing, and replacing animal testing as much as possible.

The final two phases involve use of fish, amphibian, and mammalian in vivo modeling systems. Overall, the protocol is intended to help green chemists establish a high degree of confidence that the replacements they are developing are unlikely to be harmful to humans or the environment.

The next steps

The meeting wrapped up with discussion on how to proceed with development of the testing protocol as well as plans for implementation. The advisory board plans to use input from the meeting to develop and publish a white paper outlining guidelines that chemists can use to assess the quality of protocols and tests used to assess endocrine disruption.

(Thaddeus Schug, Ph.D., is a postdoctoral research fellow currently on detail as a program analyst in the NIEHS Division of Extramural Research and Training. He was part of the NIEHS/NTP delegation and a presenter at the meeting.)

 

Left to right, Collins, Heindel, and Warner mix ingredients  for a batch of salmon tartare.
Left to right, Collins, Heindel, and Warner mix ingredients for a batch of salmon tartare.  The cooking exercise was used as an ice-breaking event to demonstrate how environmental health scientists and chemists can work together to solve complex issues. (Photo courtesy of Pete Myers)

Laura Vandenberg, Ph.D., left, contributes to the discussion  on assay development, as Tom Zoeller, Ph.D., center, and Wim Thielemans, Ph.D.,  look on.
Laura Vandenberg, Ph.D., left, contributes to the discussion on assay development, as Tom Zoeller, Ph.D., center, and Wim Thielemans, Ph.D., look on. Vandenberg, a postdoctoral fellow at Tufts University, studies the developmental effects of endocrine disrupting chemicals. (Photo courtesy of Pete Myers)

Left to right, Bruce Blumberg, Ph.D., Thayer, and Andreas  Kortenkamp, Ph.D., served as panel members for a discussion on in vitro screening assays.
Left to right, Bruce Blumberg, Ph.D., Thayer, and Andreas Kortenkamp, Ph.D., served as panel members for a discussion on in vitro screening assays. (Photo courtesy of Pete Myers)

A group photo of the meeting attendees.
A group photo of the meeting attendees. The meeting was held at the Cavallo Point Lodge, which sits adjacent to the Golden Gate Bridge. (Photo courtesy of Pete Myers)

NIEHS  grantees Andrea Gore, Ph.D., left, and Frederick vom Saal, Ph.D., were among  panel members for the discussion on in  vivo assays.
NIEHS grantees Andrea Gore, Ph.D., left, and Frederick vom Saal, Ph.D., were among panel members for the discussion on in vivo assays. Both Gore and vom Saal are members of  the project’s scientific advisory board. (Photo courtesy of Pete Myers)

 

Emerging Environmental Health Science in Green Chemistry

NIEHS Senior Advisor for Public Health John Balbus, M.D., attended the inaugural symposium March 24 for the new University of California, Berkeley Center for Green Chemistry, entitled “Green Chemistry: Collaborative Approaches and New Solutions.” Balbus’ talk, “Incorporating Emerging Environmental Health Science in Green Chemistry,” outlined some of the challenges of applying 21st century science to protect public health.

  • How do we harness the potential of unlocking the genome?
  • Can we more accurately predict which chemicals are likely to cause harm?
  • How do we implement our understanding of susceptibility and non-chemical stressors to enhance human health?
  • How can we better incorporate new methods and technologies into science policy?

Balbus proposed that the newly developed Tox21 (http://ntp.niehs.nih.gov/index.cfm?objectid=06002ADB-F1F6-975E-73B25B4E3F2A41CB), an interagency high throughput screening initiative, is aiming to meet many of these challenges and could be a valuable tool for green chemists. Demonstrating its utility in screening chemicals for disruptions in insulin signaling, Balbus concluded, “Advancements in programs such as Tox21 will eventually allow us to accurately predict how chemicals will impact human health before they are brought into the marketplace.”

Novel ‘Green’ Chemical Endocrine Screening Protocol Looks Beyond EPA’s

Inside EPA: Risk Policy Report – 07/12/2011
By Jenny Hopkinson

A group of private and government scientists is moving closer to completing a testing protocol for determining whether new “green” chemicals entering the market are safer than those they are intended to replace and do not pose endocrine disruption risks, an effort that extends beyond EPA’s screening program, which focuses on existing chemicals.

Advancing Green Chemistry (AGC), the non-profit group leading the efforts, has joined with National Institute of Environmental Health Sciences (NIEHS), Environmental Health Sciences, Inc and other private sector groups, to develop a five-tiered testing protocol that will eventually be available free to chemical producers to determine whether their products may disrupt human endocrine systems, an outcome that has been linked to a slew of health problems including obesity and breast cancer.

An AGC source says the protocol is close to being submitted for peer review and developers hope it will be completed in about another year.

The protocol is designed to address concerns that newly developed green chemicals — which are intended to be safer alternatives than existing substances — may not be much better for the endocrine system, which regulates the body’s hormones, than the existing chemicals they are being created to replace.

While EPA is required by law to test a slew of existing chemicals under its endocrine disruptor screening program (EDSP), so far the agency has been “stuck” in what it can get done and has been struggling for almost two decades, the AGC source says.

Delays with the EPA program have long been a concern. For example, former House Rules Committee Chairman Louise Slaughter (D-NY) last year pushed legislation that would have created a new endocrine screening program at NIEHS, in part because EPA had been slow to establish its program. “While EPA does have the EDSP they’ve been more focused on toxics and only in the past few years focused on endocrine disruption,” her spokeswoman said (Risk Policy Report, Dec. 22, 2009).

Similarly, the AGC source says EPA is “snarled up in the morass of trying to regulate existing chemicals, and that hamstrings people.” Testing for endocrine disrupting effects “is something the government should be doing, but it just doesn’t seem to be something that’s happening,” the source says.

The source puts the blame on industry for the delays in EPA’s program. “There’s a lot of vested interest in the chemicals on the market” by their manufacturers, and that is slowing down the process, the source says. So far the agency “hasn’t been able to sort that out.” Rather than get bogged down in attempts for regulation of the chemicals, “we are trying to just look forward,” the source says.

But that is not to say that EPA hasn’t shown interest in the protocol. Paul Anastas, head of the Office of Research and Development, has been involved with developing the system, although the source says while he has been “constructive and supportive,” there has been no indication that EPA will adopt the methods. “But if they want to take over our project, great I think that would be better for all of us,” the source adds. “This should just be the way we test chemicals, period.”

A second source, however, argues that EPA’s programs aren’t capable of looking at such sensitive effects of chemicals. “Unfortunately there are people still working in the lab in EPA . . . who will say none of this work has any value,” the source continues. “They are stuck with toxicologists who are still doing old school toxicology.”

As a result, AGC, about a year ago, brought together a group of chemists, toxicologists and other government and private scientists to examine what the source describes as a “burgeoning wave” of new science on endocrine disruption with the goal of developing a tool for chemical makers to ensure in the development process that a chemical will not have effects on hormones.

The result is a five-tiered protocol that begins with what the source described as “quick and easy” Quantitative structure-activity relationship (QSAR) modeling and looking at a chemical’s structure, followed by in vitro high-throughput screening assays, validated and specialized cell-based assays, amphibian and fish tests, with the final tier being mammalian testing.

While chemical producers can run a new substance through as many or as few tiers as they choose, if a chemical passes through all the tiers, then it is quite likely to be safe, said Thaddeus Schung, a postdoctoral research fellow with NIEHS, speaking at the American Chemistry Society’s 15th Annual Green Chemistry and Engineering Conference in Washington, DC, June 22.

Schung said that the system aims to be a logical, consensus based tool to determine endocrine activity based on sound science. “Were trying to use this brain power here to come up with a sensible effort to . . . predict chemical toxicity.” Our hope, Schung said, is to “kick some of these chemicals out of production and make way for some new chemicals that are being developed by green chemistry.”

The AGC source echoes this, saying the protocol will provide an important new tool for chemical producers. As chemists develop these new materials “it’s really hard for them to know whether or not what they’ve designed has the potential to be an endocrine disruptor.”

“Green chemists are being asked to design the next generation of benign chemicals and they don’t have the tools to do it,” the source continues, adding that chemists are not toxicologists. “This is the new design criteria — you want to make chemicals that don’t act like hormones and don’t rewire people’s systems.”

And another source says that given the public backlash on products containing such endocrine disrupting chemicals such as bisphenol A (BPA), “industry is staying ahead of this now,” the source says. “They realize that this is the way we have to go.” – Jenny Hopkinson

Sustainable method naturally divides wood’s parts.

Synopsis by Wim Thielemans and Wendy Hessler, Jul 22, 2011

vom Stein,T, PM Grande, H Kayser, F Sibilla, W Leitner and P Domınguez de Marıa. 2011. From biomass to feedstock: one-step fractionation of lignocellulose components by the selective organic acid-catalyzed depolymerization of hemicellulose in a biphasic system. Green Chemistry http://dx.doi.org/10.1039/c1gc00002k.

 


2011-0717poplartrees
timabbott/flickr

A single-step process using only natural materials may transform the way lignocellulosic biomass is separated into its prized parts of cellulose, lignin and hemicellullose.

All three are valued raw materials for a wide variety of products and processes, including the cellulose for biofuels. The sustainable procedure can run continuously and is being considered for industrial use.

Current methods to separate the trio use harsh conditions that damage part of the end products and produce too much waste.

 

Context

Plants are a complex mix of materials that differ among various vegetative groups. Corn, wheat, trees and other woody plants contain lignocellulosic biomass. This is made up of three major components: cellulose, lignin and hemicellulose.

Cellulose is a water friendly part of these plants. It provides strength and structure and helps transport water from the roots to the leaves. Lignin is like a water tight glue that binds the cellulose together. It also protects cellulose from degrading under the sun’s ultraviolet rays and decomposing from microbes, bugs and fungi. Hemicellulose binds the cellulose and lignin, which are not very compatible.

Plants naturally make cellulose in staggering quantities, with some estimates topping several hundred billion tons per year. Since cellulose is abundant, it is an obvious target as a source for renewable feedstocks – the raw materials used by industry to produce products. Once processed, cellulose – more commonly known as pulp – is used widely in paper products, cellophane, as food additives and, more recently, in the production of bioethanol.

Lignin currently has only minor industrial uses, for example as dispersants and a feed additive. The majority of lignin is burned to recover the energy that os used in separating it from the biomass. However, it is the only natural source of large amounts of aromatic compounds, which are vital for making plastics – such as polystyrene – and drugs. Therefore,  a large amount of research is focusing on breaking down pure lignin into these aromatic compounds.

Industrial use of lignocellulosic biomass to make chemicals and fuel is hindered by its complex mix of cellulose, lignin and hemicellulose, which are difficult to separate. Harsh processes – high temperatures and caustic chemicals – that degrade the raw materials and make waste are commonly used.

What did they do?

In this study, researchers from Germany describe a very clever way to separate cellulose, lignin and hemicellulose in a single process.

They mixed lignocellulosic biomass – which can be wood, corn or wheat stalks or other cellulose and lignin containing materials – with three natural, benign additives. The additives were: water; oxalic acid – an acid obtained from the simple sugar glucose and found in many plants, including black tea; and 2-methyltetrahydrofuran (2-MTHF), a solvent that can be obtained from biomass.

The concoction was heated to an industrial low temperature of 140 degrees Celsius.

What did they find?

The enzymes and low temperatures work together to separate the lignocellulosic biomass into its component parts. During the process, the oxalic acid breaks down the hemicellulose and turns it into water-soluble sugars. The lignin and cellulose are not affected.

Since lignin and cellulose are very different, they spontaneously separate when the hemicellulose the glue that holds them together is degraded. The cellulose remains as an insoluble pulp that can be filtered off and used as a feed to make bioethanol or other chemicals. The lignin is extracted from the water-oxalic acid mixture using 2-MTHF.

Lignin is recovered by boiling off the 2-MTHF via distillation. This also allows recovery of the 2-MTHF, which is recycled in the process of extracting the lignin.

Equally, the oxalic acid can easily be recovered from the water-sugar mixture. It is recycled back into the process again to break down hemicellulose anew.

So in the end, the process yeilds an inlet stream of lignocellulosic materials and three outlet streams: lignin, cellulose and a mixture of water and sugars.

What does it mean?

Natural additives and lower temperatures offer a more sustainable way to divide certain types of plants into three main components. These lone parts are valuable starting products for many industrial applications.

This process is a very important development since it shows that it is possible to separate lignocellulosic materials using benign conditions and in a straightforward manner. It solves many of problems that plague current methods, such as high temperature, waste generation and product damage.

The researchers also designed the process so it can run continuously. This is a major advantage for industrial use and may make the process very attractive to industry.

However, this is a small scale study and further work will be needed to investigate whether it works as well on a very large scale and for a wide variety of different materials.

Resources

Taherzadeh, MJ and K Karimi. 2009. Pretreatment of lignocellulosic wastes to improve ethanol and biogas production:  review. International Journal of Molecular Sciences, http://dx.doi.org/10.3390/ijms9091621.

Toward more sustainable fungicides.

De Sousa, R, C Thurier, C Len, Y Pouilloux, J Barrault and F. Jérôme. 2011. Regioselective functionalization of glycerol with a dithiocarbamate moiety: an environmentally friendly route to safer fungicides. Green Chemistry http://dx.doi.org/10.1039/c1gc15053g.

Synopsis by Wim Thielemans,

Jul 07, 2011

A new approach devised by chemists promises to clean up the dirty business of making and using fungicides. The approach relies on a naturally-available source material called glycerol instead of the traditional metal-releasing compounds used today.

Fungicides kill or inhibit growth of molds, mildew and other fungi. Their use on food crops by the agricultural industry is omnipresent and has increased fourfold during the last 50 years. In 2007, fungicides accounted for $33 billion in sales.

With the growing population and the increased strain on food resources, the use of fungicides is set to continue to increase. This new work is a big step toward reducing the environmental impacts associated with producing and using the pesticides. It also opens the door to making other chemicals with the same starting chemical – the naturally-occurring glycerol.

Fungicides are generally prepared as water-soluble salts – in chemistry, salts are a  products made up of a positively and a negatively charged molecule that form the neutral salt. The salt products used for fungicide production also contain metals that contaminate soils, rivers and underground water. In addition, the breakdown products can be highly toxic.

It is thus very important to prepare safer fungicides through environmentally friendly processes.

A recent study published in the journal Green Chemistry reports a possible way to make safer, water-soluble fungicides without metal salts. The chemists describe making a specific class of fungicides – called dithiocarbamates – using a previously reported method that relies on glycerol instead of the salts. Glycerol forms part of plant oil molecules and is used as a sweetener and low fat filler in food and as a thickener in liqueur. It is also used in a variety of pharmaceutical and personal care products such as toothpaste, soap, mouthwash and cough syrup.

It turns out, the process is  more efficient and potentially cheaper than current methods. The chemical pathway releases only ethanol and CO2 as waste. All sulphur and nitrogen in the reactants was included in the final material, which is a major achievement. In addition, the researchers were able to scale up their process to produce larger quantities at one time.

The success of fungicides derived from this method is being tested in field studies on sunflower, wheat and soy crops. These studies will decide the real impact that this work can make on safer fungicide production.

Can synthetic silk beat nature’s own?

 

Kinahan, ME, E Philippidi, S Koster, X Hu, HM Evans, T Pfohl, DL Kaplan and J Wong. 2011. Tunable silk: using microfluidics to fabricate silk fibers with controllable properties. Biomacromolecules http://dx.doi.org/10.1021/bm1014624.

 


Jul 09, 2011

 

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CameliaTWU/flickr
A silkworm (Bombyx mori).

For the first time, people can do what only spiders and silkworms can do: spin silk fibers to specific specifications.

The new technique opens the door to customizing fibers to use in medicine, engineering and – of course – clothing. It relies on a special device to build silk protein chains that are then spun together into fibers with predicted and controlled strength, rigidity and width.

The researchers will continue to refine the method that may lead to a cheaper and more directed silk product than spiders and silkworms currently provide. The innovative method to make synthetic silk is explained in the journal Biomacromolecules.

Context

Silk is a very attractive material for clothing and other textiles due its smooth, cool and comfortable qualities. Manufacturers also find silk tantalizing. Silk’s mechanical properties – it is as strong as steel yet six times lighter – and ecofriendliness – it is biocompatible and biodegradable – make it an attractive material for biomedical and engineering applications. In fact, silk is used for suture threads and in tissue grafts.

In all the world, only silkworms and spiders can make silk. A mysterious spinning process produces the strong threads that are weaved together into webs and cocoons. The animals make the unique silk protein and spin it together in just the right way to form a special structure that gives the fiber its desired properties. The invertebrates do this with apparent ease. More so, they can control its properties, depending on where and for what purpose the silk thread will be used.

Obtaining natural silk for consumer uses, then, comes with a set of problems. The properties of natural silk – its strength, width, length – is determined by the specific species of spiders and worms. Basically, people get what the animals produce. It is also expensive and laborious to keep the silk-producing creatures – normally silkworms – and harvest the product.

So, there is need for a rapid method to fabricate silk and control its mechanical properties. The first step in this process has already been solved. A variety of other organisms – ranging from bacteria to goats – have been genetically modified and can produce silk proteins. The type of silk protein can be easily varied. It can also be produced in large quantities. However, the second challenge of how to spin those proteins into fibers with the desired properties remains.

What did they do?

Researchers from Boston, Mass., and Göttingen, Germany, used a microfluidic device that mimics the silkworm glands by extruding silk proteins from an aqueous solution. The solid device is infused with two crossing channels similar to the thickness of a human hair. Liquids can flow through the channels, which come together to allow a very small point of mixing. Through one channel flows the aqueous silk protein solution. Through the two intersecting channels flows an acidic solution of polyethylene glycol. Where the two channels meet, the fluids mix. Polyethylene glycol is a benign molecule  – a polymer – that envelops the active drug ingredients and acts as a lubricant in a variety of medicines.

Several different flow speeds and ratios of silk protein to polyethylene glycol solution were tested. The ensuing mechanical properties of the spun fiber – such as strength, strain and stress failure – were measured.

What did they find?

The device created a single strand of silk fiber with very well-defined properties. The fiber’s properties were altered by varying the spinning conditions, such as flow speed and the speed with which the dry fiber was drawn out of the device.

A small amount of original material was required – as little as 50 microliters, which is about the volume of a drop of water. This makes it a very interesting tool to screen different processing parameters and determine their effects on the spun fiber properties.

The authors related the flow characteristics inside the device to the fiber’s mechanical properties – strength, rigidity – and the internal structure formed by the silk proteins inside the fiber. They were able to control the fiber diameter and fiber strength. They even could vary the diameter of the fiber as it was spun.

While they did not yet match the properties of natural silk in this work, the control they showed over properties is very promising.

What does it mean?

The researchers designed a device that can rapidly produce synthetic silk fibers from silk proteins. The spinning conditions are easily controlled to determine the effect on the properties of the spun fibers.

This new technique opens up the possibility to customize fiber properties so they be used for specific applications. Of several methods being investigated to produce synthetic silk, this one is closest to the natural process, so it offers a very clean method to produce silk fibers on a large scale. No real waste is generated, and the polyethylene solution can be recycled.

More generally, the process is an example of how green chemists can develop a clean manufacturing process straight away and avoid creating pollution problems right from the start.

This work has a great potential to improve understanding of how to make synthetic silk fibers and possibly make them stronger, softer, more stretchable or thinner than natural silk. Different silk proteins can be produced from bacteria, goats and other animals – or even synthetically in the lab – so it is now possible to study the effect of spinning conditions and variations on the silk fibers that are produced. The small starting volume reduces the amount of silk protein required making the tests cheaper and faster to run.

The authors investigated only two processing parameters, but their new device can easily be used to screen all others quite rapidly. The process will no doubt increase understanding of both synthetic and natural silk production.  More importantly, the device may produce better, designer silk fibers.

Resources

Silkworm information. Center for Insect Science Education Outreach. University of Arizona.

Gold, palladium team up to clean up chemical-making process.

 

Kesavan, L, R Tiruvalam, MH Ab Rahim, MI bin Saiman, DI Enache, RL Jenkins, N Dimitratos, JA Lopez-Sanchez, SH Taylor, DW Knight, CJ Kiely and GJ Hutchings. 2011. Solvent-free oxidation of primary carbon-hydrogen bonds in toluene using Au-Pd alloy nanoparticles. Science http://dx.doi.org/10.1126/science.1198458.

 


Jun 07, 2011

 

2011-0606audreyshand
Audrey Moores
Chemists report a cleaner way to produce a much-used compound called benzylbenzoate.

A team of researchers have cleaned up the process to produce a versatile compound – called benzylbenzoate – that kills disease-causing mites, stabilizes fragrances and is a building block for pharmaceuticals. Benzylbenzoate is made from toluene – a cheap and readily available chemical in crude oil. The new process applies oxygen gas and toluene to a material made of carbon and tiny particles of metals gold and palladium. No solvents are used, and no waste byproducts are generated. The finding is also important because it is a stepping stone to a method to convert natural gas into a useful fuel like methanol.

 

 

Context

Adding an oxygen atom to a molecule – called oxidation – in a controlled fashion is a long sought but challenging goal of chemistry. The procedure is important because most molecules used in industrial and consumer applications have unique properties due to the exact position on the molecule of specific groups of atoms – their chemical functional groups. Many of these functional groups are oxygen based.

For example, introducing one oxygen atom would convert methane – the main component of natural gas and an abundant resource – into methanol, which could be used as a liquid fuel. While simple on paper, the actual transformation is challenging. It often leads to more than one oxygen attaching and ultimately, to the complete burning of methane into carbon dioxide.

More generally, the chemical industry heavily relies on molecules that contain oxygen at key positions. They are used as bulding blocks to make other chemicals. Among them, benzyl alcohol, benzaldehyde, benzoic acid and benzylbenzoate have important economical impacts. They constitute starting points in the manufacture of important products, such as pharmaceuticals, dyes, solvents, perfumes, plasticizers, preservatives and flame retardants.

But, harmful chemicals are needed to make this family of molecules. The process starts with a simple, carbon-based molecule called toluene. Toluene is a component of crude oil. Its transformation currently requires harsh processes involving chlorinated chemicals, acidic solvents or toxic metals. The process has very poor yields (around 15 percent) and generates copious quantities of waste.

Alternatives starting with biomass are desirable and intensely researched, but to date, no alternative process exists to create this important family of compounds.

Current research on oxidation reactions focuses on three key points. First, any required additive needs to be solid to ease separation. Second, the oxygen atom introduced should preferably come from oxygen gas present in air, as opposed to more wasteful or toxic sources. Third, the process must be very efficient – that is, yield a lot of material– and selective – create only one molecular product and thus limit separating the wheat – what’s wanted – from the chaff – what’s not – after the reaction.

What did they do?

The research team from the United Kingdom and the United States exposed toluene to oxygen at 160 degrees Celcius and 10 bars of oxygen – equivalent to 10 times normal atmospheric pressure – for two days. Under these conditions, a very small fraction – 2.9 percent – of toluene was converted into a mixture of benzaldehyde, benzoic acid and a small quantity of the desired benzylbenzoate.

Then, they tested several materials for their ability to improve the reaction. One was gold nanoparticles deposited onto titania, because it actively promotes oxidation of alcohols and carbon monoxide.

Gold nanoparticles deposited onto carbon – similar to porous charcoal – was also tested.

In another approach, they deposited tiny particles of gold and palladium inside the carbon pores. In this setting, gold and palladium form an alloy that has unique properties, different from both pure gold and pure palladium.

They also varied the proportion of gold and palladium in the system and measured how it was impacting the chemical process.

Each system was analyzed using two criteria: 1) conversion – the number of toluene molecules transformed – and 2) selectivity – Did one toluene transform into one or several kinds of molecules?

What did they find?

The gold and palladium nanoparticles on the porous carbon offered the best materials to spur the difficult reaction that transforms toluene to benzylbenzoate.

About half of the toluene was converted with this media. The process was very selective – 94.3 percent of the product was benzylbenzoate. This process required 6,500 times less metal than toluene.

The authors then tried to improve toluene conversion by altering the amount of metal. By adding more metal – 1,650 times less metal than toluene – they reached a conversion of 94.4 percent.

Researchers found that the other materials were not as good. Gold nanoparticles on titania did not perform well despite its other successes. Gold alone on carbon was not very active, either.

The mixture of the gold with palladium inside each nanoparticle proved essential to activity. The optimum proportion was 1 gold atom for 1.85 palladium atoms. Size mattered too, and a small size particle was critical to obtaining high conversion.

What does it mean?

In this work, researchers developed a novel material that takes oxygen from the air to transform toluene into the valuable benzyl benzoate. The material is composed of carbon, gold and palladium at specific ratios for optimum performance.

This research is very important because it brings chemists closer to defining the reaction that could convert methane from natural gas to methanol. Such a  process could allow two important developments.

First, methane is a flammable gas and is thus impractical and dangerous to use as a fuel for vehicles. Methanol, on the other side, is a liquid similar in properties to ethanol. Ethanol currently makes up a small fraction of automobile fuel sold in the United States.

Second, methanol has other important applications in the chemical industry. It is used as a solvent, as an antifreeze and as a building block for a host of commodity chemicals.

The new reaction is also remarkable because of its high yield, chemical selectivity, low waste and use of available resources. The use of a very simply reagent – oxygen gas from air – generated no waste.

The material was very convenient to use. After the reaction, the ending product separated completely from the starting material and was simply filtered off. This allows for two good things: 1) no metal or carbon ended up in the product and 2) the material can be reused in subsequent reactions. The materials was reused four times without measuring any alteration of reactivity.

The porous carbon support played an important role in the success of the reaction. The same material based on porous titania was less active. The researchers suggest the improved performance originates from the difference in surface structure between the carbon and titania based nanoparticles. They believe carbon causes the metal particles to be rougher and thus more reactive with the oxygen.

In all cases, the chemists did not detect any carbon dioxide waste. This means that the oxidation reaction – that is, adding an oxygen atom to the starting carbon, gold and palladium materials – proceeds well. Only one atom of oxygen is added, not several, which happens during complete combustion. This process affords a valuable chemical from toluene without burning toluene itself.

More development and studies are needed to turn this discovery into an industrial process.

Resources

Edwards, JK, B Solsona,E Ntainjua, AF Carley, AA Herzing, CJ Kiely, and GJ Hutchings. 2009. Switching Off Hydrogen Peroxide Hydrogenation in the Direct Synthesis Process. Science 323(5917):1037-1041.

Enache, DI, JK Edwards, P Landon, B Solsona-Espriu, AF Carley, AA Herzing, M Watanabe, CJ Kiely, DW Knight and GJ Hutchings. 2006. Solvent-Free Oxidation of Primary Alcohols to Aldehydes Using Au-Pd/TiO2 Catalysts. Science 311(5759):362-365.

Konietzni, F, U Kolb, U Dingerdissen, WF Maier. 1998. AMM-MnxSi-catalyzed selective oxidation of toluene. Journal of Catalysis 176(2):527-535.

Partenheimer, W. 1995. Methodology and scope of metal/bromide autoxidation of hydrocarbons. Catalysis Today 23(2): 69-158.

Saravanamurugan, S, M Palanichany, V Murugesan. 2004. Oxyfunctionalisation of toluene with activated t-butyl hydroperoxide. Applied Catalysis A General 273(1-2), 143-149.

Sheldon, RA, and JK Kochi. 1981. Metal-catalyzed oxidations of organic compounds. Academic Press:New York.