Skeletal Formulas and the Export of Occupational and Environmental Hazards

Whether it’s a scientific discipline, plumbing or a sport, every specialised field has its own terminology—words that don’t often enter into everyday vocabulary but which are used without a blink among specialists. The term for such in-crowd words and expressions is jargon. But in many subject areas,  jargon can also come in the form of images. Even the rare person who remembers their introductory chemistry courses would still be taken aback by the following skeletal formula:

the skeletal structure of ethanol

Ubiquitous in online data bases (Chem Spider, Merck Index or CRC handbook), a skeletal formula is what I call image-jargon. The common atom in organic compounds, carbon, is often symbolised by an angle or a corner. Since it is assumed that the person looking at the structure knows that, except in radicals, carbon will make four bonds, some of the hydrogen atoms are also hidden. For example in the above skeletal formula of ethanol, the alcohol found in wine, beer and spirits, there is one angle representing a carbon and that “hidden” carbon is bonded to an OH group and to a methyl group (CH3). That’s only two bonds so far, so there have two be two more hydrogens for a total of six. The molecular formula of ethanol represented by that skeletal structure is C2H6O. In other words the above skeletal structure is equivalent to this three dimensional model of the molecule:

C2H6O or ethanol

For compounds containing only carbon, hydrogen and /or oxygen and/or nitrogen and/or halogens, there’s a nice formula  we can use to verify that we are putting in the right number of hydrogens. (If you think the conditions are restrictive, compounds with the mentioned elements include the majority of carbohydrates, fats, alkaloids, amino acids  and all terpenes, esters,  and petroleum products—-literally millions of known compounds in total

C + 1 – (H- N+ X)/2  = degree of unsaturation (d.u.),

where C = number of carbons; H = number of carbons, N = nitrogens and X = number of halogens such as fluorine, chlorine, bromine and iodine. Notice that the number of oxygen atoms have no impact on the degree of unsaturation. .

What raises the degree of unsaturation from zero is any “ring” system (closed loop structure; it could be triangular, hexagonal, etc) or a double bond, which looks like an equal sign. A triple bond raises the d.u. by two.

So for our ethanol structure, there are no such double bonds or ring structures, so d.u. = 0. Since C =2, then

2 + 1 – (H-0 + 0)/2  = 0

Solving for H, we obtain H = 6

Let’s look at one more:

benzidine, a group I carcinogen

Here we have 12 angles (6 in each hexagon) for a total of 12 carbon atoms. The degree of saturation is raised to 8 by the presence of 6 double bonds and two hexagons.

C + 1 – (H-N + X)/2  = degree of unsaturation

12 + 1 – (H-2 + 0)/2  = 8

H = 12, which implies that 8 hydrogens are hidden by the skeletal formula, one at each carbon(corner) to give each carbon four bonds.

Benzidine is no longer sold in the United States, Canada or Europe. This has been the case since the mid-1970s. It was mainly used in the production of dyes found in cloth paper and leather. It is a class 1 carcinogen, increasing the risk of bladder cancer in humans, especially for who worked in an occupation that exposed them to such dyes.

Unfortunately that is not the end of the story. There are still benzidine derivative compounds, which are not group I carcinogens but  group 2 substances, which probably causes cancer in humans. One such compound is 3,3′-dichlorobenzidine.

3,3-dichlorobenzidine, a group II carcinogen

Although it is not made here in Canada, we import 100 tons of it every year from Asia because the compound is used as an intermediate to make yellow to yellow green pigments for printing inks, textiles, paints, plastics and crayons. Health and Welfare Canada is not worried about trace amounts of the substance because of the concentrations involved and because the compound is not used in any edible products. Unfortunately no one has ever gathered evidence for the combined effects of the cacophony of trace carcinogens we are exposed to in modern life. Moreover, especially since safety standards for workers are typically lower in Asia, it is unfair to them if we persist in consuming such large quantities of the compound. Like all aromatic amines, 3,3′-dichlorobenzidine is easily absorbed through the skin and lungs. According to the Center for Disease Control and Prevention,

Employees engaged in handling operations involving compounds in the list below(which includes 3,3′-dichlorobenzidine)  must be provided with, and required to wear and use, a half-mask filter-type respirator (SOHA standards) for dusts, mists, and fumes.  A respirator affording higher levels of protection than this respirator may be substituted.

Even in the United States , the OSHA Respirator Standard has been known to be violated by almost half of companies surveyed in 2000 to 2002. More recently a significant number of violations persisted. One could only imagine what safety practices are like in India, which, worldwide,  has the most chemical plants , specifically 6,  producing this substance.

Coincidentally, this morning a few hours after I paused writing this article, The Current on CBC interviewed a medical doctor, Paul David Blanc, who was discussing a parallel situation involving carbon disulfide (CS2). This reagent is used in the second last step in the production of  viscose, also known as rayon. According to WHO, for every kilogram of viscose produced, about 20-30 g of carbon disulfide and 4-6 g of hydrogen sulfide are emitted . The highly volatile carbon disulfide, if not diverted, fills factory workrooms with fumes that can have long term effects such as depression, mental illness and suicide. Other side-effects include blindness, impotency, and malfunctions of the vascular system and other organs. Rayon is no longer produced in North America after claiming many victims in the late 19th and early 20th century. In Europe the vapours are recycled, keeping levels safer for workers. But such is not always the case in Bangladesh and elsewhere in Asia. Yet we import these goods, ignoring the consequences suffered by producers.
Rayon is  not the only commercial product made with carbon disulfide. A more complete list includes cellophane, sponges, sausage casings, pesticides and carbon tetrachloride. In one of the most unethical examples of greenwashing, marketers label “bamboo fabrics” as being “green”. But the manufacture of these products again relies on carbon disulfide  and takes place in China where laws  protecting labourers and the environment from  CS2‘s toxicity are either less stringent or non-existent.

The recent election in the United States was won by Donald Trump, who among other things, exploited a populist resentment of free trade. But the focus was entirely on the loss of American jobs. It’s not a coincidence that the anti-environmental winning candidate did not use imported dyes and rayon as part of his argument. Given that automation is also a cause of job-loss in the Western world, the solution is not to take manufacturing jobs away from Asian countries. Instead what’s needed is to incorporate occupational and environmental regulations into the free trade arguments. Otherwise the Western world will continue to export occupational hazards and pollution to Asia.

Other Sources:


Fake Silk The Lethal History of Viscose Rayon. Paul David Blanc. Yale University Press. 2016. 325 pp.


Marcel Laurin Woodland Park

The Marcel Laurin Woodland Park is all too easy to under-appreciate. Drive or cycle by it too quickly, and it could easily go unnoticed because of its size–it’s not one of Montreal’s largest regional wooded areas. But once inside the woods, one realises that it is a special part of Montreal’s parks and protected woodlands, which combine to hold 75% of the city’s approximately 1.2 million trees. It gives citizens easy access to wildlife, which is key since not all can afford to travel far to experience it. Still a long way to becoming a mature forest, the woodland  is in part a wetland . Especially in the springtime,  the water that it collects allows dead leaves and other lingering organic material to decompose, increasing the availability of nutrients. These lead to a diversity of fauna and flora.

Some of its Fauna


Source Wikipedia

The common garter snake (Thamnophis sirtalis), like all reptiles in Quebec, is not poisonous to humans. It’s a good thing because after ignoring my advice, a student of mine once picked up a baby garter and was lightly bitten on the thumb. When defiant students are not around 🙂 ,  the snakes feed off the woodland’s slugs and toad-eggs. The adults form a mating ball consisting of several males competing for a single female, which eventually gives birth to live offspring. They were considerably widespread on the island as far back as the 1960s when I remember seeing garter snakes on a weekly basis during my childhood in St. Leonard. But that suburb of Montreal, like the rest of the city, has lost most of its wetlands. A stream that once ran through the former St-Leonard site has totally disappeared and though memories of some citizens have not yet faded, the biological diversity in many areas is long gone.


This 1832 map shows two areas of Montreal including (1) the current site of Marcel Laurin Woodland and (2) St-Leonard described in the text. Large sections of the island had already been deforested for the sake of agriculture. But we can see persistent streams(highlighted) and associated wetlands that no longer exist but which influenced the type of vegetation and animal life on our island. Source: James Wyld (1812-1887), David Rumsey collection

The availability of nutrients in the wetland makes the area rich in insect life which attract a variety of birds. In the Marcel Laurin Woodland, I’ve seen cardinals throughout the year along with wood peckers, birds that are rarely seen by citizens in the more densely urbanised sections of the island. Thanks to the efforts of amateur ornithologists who reported their sightings to Regroupement Québec Oiseaux, the organisation was able to include them in the ÉPOQ database.  Here are some of the ones people and I have spotted in the woodland. From left to right are the the black-capped chickadee (Poecile atricapillus); the eastern kingbird (Tyran tritri); magnolia warbler(Setophaga magnolia); hairy woodpecker (Picoides villosus); and the least flycatcher (Empidonax minimus). (The first pic is mine and was taken in Marcel Laurin; the rest are from Wiki)

The city’s website reports that

the woodland holds a certificate from the University of Kansas’ Monarch Waystation Program, and in 2009 it received significant support numerous partners for the planting of native grasses and milkweed necessary for the Monarch butterfly’s feeding and reproductive needs.

I have yet to see monarchs in the park, which does not necessarily mean they don’t come by, but I also noticed some replanting of milkweed late in the summer of 2016.  Thus the project described above is still a work in progress.

Some of its Flora and an Unwelcome Guest

Drawn to the borders of the Marcel Laurin’s stream are two dominant species, the silver maple and the red ash. One of the drier areas also has a small strand of at least 20 scattered beeches. A few years ago, invasive species such as the European and adler buckthorn were removed to help indigenous species such as the ash and maple, when suddenly the former was invaded by the Emerald Ash Borer (EAB), an insect whose larvae can girdle and kill trees. The threat is serious because 1 in every 6 trees in Montreal (and the majority of trees in Marcel Laurin Woodland) is an ash. In the past two years the city of Montreal has been forced to cut almost 8000 thousand severely infected ashes on the island. In that same time period, 37,000 infected trees have been treated with TreeAzin


(A) egg (B) larva (C) the EAB adult. Source: Phil Geib, Chicago Tribune

The insecticide consists of a 5% solution of azadirachtin, a compound found in neem seeds.


azadirachtin from chemSpider

It is biodegradable and shows very low toxicity to mammals. It actually doesn’t kill the insects; it prevents the destructive larvae from developing. The reason that the larvae are so destructive is that until the late 1990s EAB was only found in eastern Russia and China, where the insect and ashes coevolved. Continuous election created a balance where EAB could complete its life cycle without killing trees. But in North America, in only about a decade, EAB has spread like wildfire from Michigan to Quebec and all the way to Texas. Out continent’s ash trees lack defensive mechanisms and compounds that are used by trees in Area where the insect is indigenous. In addition, our ash trees on this continent release compounds like hexanal, linalool and 13 other volatiles whose signals are picked up by the antennae of adult EAB , facilitating insect-movement from one host to another. This happens when they are chewing on the leaves. As the larvae develop they  feed off the phloem, tissues that transport sugars from the leaves to the roots. The bark of the ash tree releases sequiterpene-compounds like α-cubebene, which also helps EAB adults locate a tree. And with more guests invited, enough tissue can be damaged to kill the tree.

What has not helped Montreal ash trees in the face of this EAB epidemic is climate change. Drought weakens trees, making them more vulnerable to insects. Winter temperatures below -33 º C are needed to kill dormant eggs. Montreal’s winters have been milder in recent decades. Environment Canada records indicate that we have not seen -33 º C in February since 1994; December  temperatures have been above -33 º C since 1980, and in the last four years, the coldest January temperature was only -24.6 º C.

Other Sources:

Review of the emerald ash borer (Coleoptera: Buprestidae), life history, mating behaviours, host plant selection, and host resistance
Therese M. Poland, Yigen Chen, Jennifer Koch, Deepa Pureswaran.  The Canadian Entomologist. 147(03): 252-262.