Is It Warm in Here?

May 18, 2013

The May 11 issue of The Economist has an interesting, though disturbing, short article on one measure of global climate change: the percentage of carbon dioxide [CO2] in the atmosphere.  This has recently reached a new high in recent history.

AT NOON on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts per million (ppm).

Now, 400 ppm does not sound very high; after all, it is only 0.04%.  However, as the article goes on to point out, this concentration of CO2 has not been routinely present since the Pliocene epoch, about 4 million years ago.

The data series  is from the observatory at Mauna Loa in Hawaii, run by the Scripps Institution of Oceanography, part of the University of California at San Diego.  This series (sometimes called the Keeling Curve in honor of the scientists who initiated the project) is of particular interest for two reasons:

  • The observation site is remote from large centers of human population, minimizing fluctuations due to temporary pollution spikes.
  • The observations have been made consistently, at the same place, since 1958.

There is a regular seasonal fluctuation in CO2 levels, tied to plants’ growth cycles.  In the northern hemisphere, levels tend to peak in May, and then fall until about October, as plants’ growth removes carbon dioxide from the atmosphere.

Carbon Dixoide Levels at Mauna Loa

Source: Scripps Institution of Oceanography

The seasonal pattern is clearly visible in the graph.  The more striking thing, of course, is the steady rise in the carbon dioxide levels, an increase of more than 25% over the observation period.  And there is no evidence that the rate of increase is getting smaller.

Triclosan Again

May 5, 2013

The Yahoo! News site has an article from the Associated Press [AP] about the US Food and Drug Administration’s [FDA] ongoing review of triclosan, an anti-bacterial and anti-fungal agent that is used in a wide variety of consumer products, including anti-bacterial soaps, toothpaste, deodorant, mouthwash, other cosmetic products, and household cleaning supplies.  The FDA’s original goal was to release the results of this review in April, 2011; clearly they are a bit behind schedule.   (According to the article, the results should be released later this year — or, at least, real soon now.)  Triclosan does have one use explicitly approved by the FDA: it is used in some toothpastes to help prevent gingivitis.  Its other uses have not, as far as I know, been subject to any formal approval process.

I’ve written here a couple of times before about the use of triclosan.  It is suspected, based on animal studies, of being an endocrine disruptor, boosting the effect of testosterone and estrogen, and reducing that of thyroid hormones.  Another animal study, reported last summer, suggests that triclosan can interfere with muscle function.   What is most striking, though, is that, for its main use, as an anti-bacterial agent in consumer products, there is essentially no evidence that it has any value at all.  As the FDA website, and other publications, have said for some time:

For other consumer products, FDA has not received evidence that the triclosan provides an extra benefit to health. At this time, the agency does not have evidence that triclosan in antibacterial soaps and body washes provides any benefit over washing with regular soap and water.

This is not to diminish, in any way, the importance on washing in  general, and washing ones hands in particular.  (The Centers for Disease Control have resources on hand hygiene.)  But, as the FDA’s note suggests, the evidence suggests  that ordinary soap and water work just fine.  As I wrote in an earlier post:

My own conclusion is that, since I have seen no evidence that these anti-bacterial products provide any benefit, and since there may be some risk, they are not worth using, especially since they cost more than plain old soap.

Apart from the possible negative effects of any particular chemical, there is a general argument for not using anti-microbial products indiscriminately.  There is a possibility that excessive usage may contribute to antibiotic resistance, and there is also a risk of disrupting the normal population of microbes that are part of our personal biosystems, which can lead to serious health problems.  It hardly seems worth much risk to use something, like triclosan, that in most cases doesn’t seem to work anyway.

Subterranean Rumblings

April 7, 2013

Especially in the winter months, first time visitors to New York City are often bemused by the sight of plumes of steam rising from manholes in the street (sometimes surmounted by jolly red-and-white “smokestacks”).  Where do they come from?  Are they byproducts of some subterranean “dark satanic mills”, or perhaps a covert entrance to Saruman’s workshops at Isengard?   Actually, they come from the Con Edison steam distribution system,which distributes steam from seven generating plants through underground pipes to most of Manhattan south of about 90th Street.  [Coverage map PDF]  The steam is used to provide heat, hot water, and other services; it serves around 100,000 commercial and residential establishments with more than 13.5 million tons of steam every year.  Since about 50% of the steam is produced as a by-product of electricity generation, the system as a whole is more efficient than individual building heating and hot water plants.  The system, the first parts of which went into service in 1882, works fairly well, though there have been some spectacular failures in the aging infrastructure, notably the 2007 explosion at 41st Street and Lexington Avenue, which left a crater in the street 35 feet wide and 15 feet deep.

Here in Washington DC, we have our own peculiar sub-surface activity: our manholes do not spout steam, but do occasionally explode.  Natural gas has been suspected as a cause of these explosions, but hard evidence for this has been scarce.  Now, the ScienceNOW news service of the AAAS reports that researchers have found high methane concentrations in the city, and very high concentrations in manholes.

Researchers who mapped methane concentrations on the streets of the nation’s capital found natural gas leaks everywhere, at concentrations of up to 50 times the normal background levels, they reported here last week at a meeting of the American Physical Society. The leaking gas wastes resources, enhances ozone production, and exacerbates global warming—not to mention powering the city’s infamous exploding manholes.

Methane [CH4] can come from a variety of sources, including landfills, swamps, cattle flatulence, and oil/gas production.  It is also the principal constituent of natural gas.  It is potentially an important source of global warming, since it is more than 20 times more potent as a greenhouse gas than carbon dioxide [CO2], the usual suspect.  The research team, headed by Robert Jackson of Duke University, suspected that natural gas leaks might be contributing to increased methane concentrations in the atmosphere; the results confirmed their suspicions:

… they drove along every street in the District of Columbia and regularly sampled the air, mapping the concentration of methane over a period of 2 months. They found thousands of places with air concentrations significantly above the 2 parts per million background level typically found in cities, with some areas as high as 100 ppm.

Methane itself is non-toxic and odorless (the gas company adds a chemical, typically a thiol like tert-butyl mercaptan, to make the gas stink); however, methane can promote the formation of ozone, which is a respiratory irritant.

The research team got more striking results when they sampled methane concentration in manholes.  In some locations, they detected methane concentrations of 100,000 ppm (or 10%).  My well-worn Handbook of Chemistry and Physics gives (approximate) explosive limits for methane / air mixtures at 5% and 15%, so the detected values are well within the danger zone.  The team suspects corroding iron gas distribution mains as the source of the leaks.  There are an average of 38 “manhole incidents” per year in Washington, so something is clearly amiss. (The same researchers have some similar data from Boston.)

It is of course sort of interesting to discover what may be causing incidents like exploding steam pipes or manholes, but these incidents reflect a larger issue.  There is a great deal of very old infrastructure in the US. much of which has not received very much in the way of maintenance.  (As another, unrelated, example, in August 2007, a highway bridge carrying Interstate 35-W across the Mississippi River in Minneapolis collapsed.)  For years, the American Society of Civil Engineers, has issued an annual report card on the parlous state of the nation’s infrastructure; it does not make for encouraging reading.

Fishy Business

March 3, 2013

Have you ever seen these places that feature “fish sandwiches”? I always think, “Well, that’s kind of general.” I mean, I wouldn’t order something called a “meat sandwich,” would you?
     — George Carlin

As the late comedian George Carlin pointed out, many menus, particularly in fast food restaurants, are not too informative about the ingredients of their fish sandwiches.  It may be, though, that their practice is more honest than that of some much tonier and more expensive establishments.

The Washington Post reported, in a recent article, that consumers buying fish run a considerable risk of getting something other than what the label says.   The ocean conservation organization, Oceana, conducted an investigation from 2010 through 2012, collecting more than 1,200 seafood samples from 674 retail outlets in 21 states to determine if they were honestly labeled.  The results, while not entirely surprising, are not good news for seafood lovers: on the order of one-third of the fish offered for sale in groceries and restaurants is mislabeled.

Ninety-five percent of the sushi restaurants, 52 percent of other restaurants and 27 percent of grocery stores surveyed sold mis­labeled seafood.

The study, in the interest of fairness,  did not identify the establishments surveyed, because it is in general not possible to determine where the mislabeling originated.  (You can download a copy of the study [PDF] from the Oceana site; there is also a summary [PDF] of key findings.)

Ordering some varieties of fish almost guarantees that the customer will get something else.  Fish labeled snapper was something else (often tilapia, a cheaper fish) in 87% of the samples tested.  Tuna was also frequently mislabeled, with 59% of the samples labeled tuna being something else.  The samples collected by Oceana included 46 varieties of fish; of these, 27 varieties were sometimes mislabeled.  Of the grocery stores, restaurants, and sushi venues sampled, 44% sold at least some mislabeled fish.  Of the outlets sampled, 18% of grocery stores, 38% of restaurants, and 74% of sushi venues had mislabeled fish.

Incorrectly labeled fish was found all over the US.  For example, 39% of the samples from New York City were mislabeled; in Chicago, the figure was 32%, in Denver 36%, and in Southern California 52%.  Every snapper sample from Washington DC was mislabeled, and every sushi venue sampled there had mislabeled fish.

Some questionable labeling may exist for historical reasons.   For example, some sushi establishments offer “white tuna”, which usually turns out to be a species called escolar; “white tuna” is not the name of any specific species of fish.  The term is also used to designate the kind of albacore tuna that comes in cans.  Sometimes, too, new names for fish species are introduced for marketing reasons.  The Post article cites the case of the Patagonian toothfish, which sold much better (and actually became a threatened species) once it was relabeled as Chilean sea bass.  Another change for marketing reasons was relabeling of the dolphin fish (Coryphaena hippurus or C. equiselis) as mahi-mahi, so that customers would not think they were eating Flipper.

There are some potential health implications of this widespread mislabeling, too  Escolar, the fish called “white tuna”, can cause severe digestive distress in some individuals.  Some of the substitute fish, such as tilefish and king mackerel, are identified by the FDA as being inadvisable for sensitive groups, on account of high levels of mercury.

Some of the problem, I think, comes from the American propensity to prefer food that is divorced, as much as possible, from its natural origins.  Even leaving aside frozen and packaged foods, most fresh meat and seafood in the US is sold wrapped in little plastic trays.  In contrast, the neighborhood fishmonger in London, where I lived for about six years, always had whole fish displayed for sale.  On business and holiday trips to France, I often ate in restaurants where the fish were laid out on ice in a display case; the diner was invited to inspect them and make a selection. In most US restaurants, you will not find anything resembling a whole fish,

These results, while disturbing, are not particularly surprising.  We have seen before that food products and medicines have been contaminated by ingredients from unscrupulous suppliers; bogus electronic parts have found their way into defense systems.  One of the unintended consequences of economic globalization has been the development of supply chains that are long and frequently rather opaque.  According to Oceana, more than 90% of the seafood consumed in the US is imported, and only a very small percentage of that is inspected by government regulators.

There are some efforts underway to address the problem.  One idea is to tag fish with a traceable ID number, so that prospective purchasers can determine its origin.  A seafood supplier in Washington DC, Profish Ltd., has its own tracing program called FishPrint that it offers to its commercial customers.  I hope these efforts will succeed.  If they do, not only will consumers be better informed, but conservation programs will also benefit.

DEET Resistant Mosquitoes

February 25, 2013

Most readers, I’m sure, are aware that mosquitoes are a transmission vector for a number of rather nasty diseases, including malaria, yellow fever, equine encephalitis, and dengue fever.  The standard advice, in regions where mosquitoes are common, is to keep one’s skin covered, to the extent possible, and to use insect repellent liberally.  One of the most common active ingredients in repellents is a chemical usually referred to as DEET (more formally as N,N-Diethyl-meta-toluamide or [IUPAC] N,N-Diethyl-3-methylbenzamide), an oily compound originally developed by the US military after the experience of jungle warfare in World War II.   Various ideas have been suggested to explain why DEET works; today, the consensus seems to be that insects just don’t like the smell.

However, a report at the BBC News site suggests that DEET’s effectiveness can be reduced because mosquitoes can adapt to it.  One type of adaptation is genetic.  There are always some individual insects that are less susceptible to DEET than average, and heavy use of the repellent creates evolutionary selection pressure favoring that lack of sensitivity.  (This is parallel to the evolutionary process leading to the development of antibiotic-resistant bacteria, or of herbicide-resistant weeds.)   This is a process that takes some time to occur, though mosquito generations are of short duration.

Some recent research indicates that there is another, shorter-term form of resistance that occurs.  Researchers at the London School of Hygiene and Tropical Medicine studied the effect of DEET on Aedes aegypti mosquitoes, which carry dengue and yellow fevers.  The mosquitoes were initially given the opportunity to feed from a human arm which had been covered with DEET; the repellent did, in fact, repel them.  However, when the same mosquitoes were presented with the same opportunity a few hours later, the repellent was significantly less effective.

To try to understand what was happening, the researchers measured electrical activity in the insects’ antennae (the location of the olfactory receptors).  Somehow, the first exposure to DEET de-sensitized the mosquitoes, so that their olfactory response was diminished.  According to Dr. James Logan,

We were able to record the response of the receptors on the antenna to DEET, and what we found was the mosquitoes were no longer as sensitive to the chemical, so they weren’t picking it up as well.

There is something about being exposed to the chemical that first time that changes their olfactory system – changes their sense of smell – and their ability to smell DEET, which makes it less effective.

The research paper [PDF available] has been published at the Public Library of Science, in the journal PLoS One.

More work will be needed to determine how long this short-term effect lasts, and whether it occurs in other species of mosquito.   Using repellents containing DEET is still a lot better than using nothing, but understanding these effects may help us develop even more effective protection.

Fuel Cell Development Agreement Signed

January 28, 2013

The BBC News has a report that a new agreement to develop fuel-cell technology has been reached by three major auto manufacturers: Ford, Daimler AG, and the Renault-Nissan alliance.   The aim of the joint project is to speed up the development of fuel cells as an automotive power source, and also to encourage the development of supporting infrastructure (e.g., hydrogen filling stations).

Ford, Renault-Nissan and Daimler have agreed to jointly develop a fuel cell system to try to speed up the availability of zero-emission vehicles.

The carmakers hope to launch “the world’s first affordable, mass-market fuel cell car” by 2017.

Fuel cells, which produce electricity by combining hydrogen and oxygen, are an environmentally attractive technology because their “exhaust” product is water.  To date, though, they have not seen widespread use, except in specialized applications like the space program, because the cost of manufacturing the devices is too high,  But Daimler, at least, has been interested for some time; back in 2009, I wrote about the development of prototype fuel-cell vehicles by Mercedes-Benz.  Work on the project will be carried out at several locations around the world.  The partners hope that their combined global presence will also increase the visibility and impact of the project.

The companies have issued a joint press release.

Update Monday, 28 January, 21:55 EST

Wired also has an article on this development, focused especially on the infrastructure issues involved.

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