To Spray or Not to Spray

Part II

by M.J. Harvey  October 2004


I was raised in the North of England which, according to the Southern English, is all Dark Satanic Mills (the Battle of Hastings, 1066, is not over yet), but Doncaster, named by the Romans, was a pleasant, small market town which developed at a major crossroads in trade.  Nowadays the nearby coal mines and the steel mills of Sheffield are all closed, the houses are heated with natural gas and cutlery comes from China.


By the 1950’s chemical manufacturers were favouring green-field sites for new developments and by coincidence two plants about 30 km on either side of Doncaster were responsible for famous industrial accidents which went into the record books, at least of chemical engineers.  Flixborough to the east I will mention only in passing since it had no lasting consequences.  It manufactured nylon monomers from cyclohexane and one night a pressure tank ruptured liberating an enormous cloud of gas which hung over the site until it found a spark and caused what is termed a Blevy (Boiling Liquid Expanding Vapour Explosion – or something similar) which flattened it to a couple of metres high.  I drove out to see it – very impressive.


More to the point, Bolsover to the southeast is a small town in Derbyshire and was chosen to manufacture 2,4,5-T (2,4,5-triclorophenoxyacetic acid) which is produced similarly to 2,4-D but adding more chlorinating precursor and using higher temperature and pressure.  In vegetation control 2,4,5-T has a wider spectrum of action than 2,4-D and in particular will kill the seedlings of trees which often germinate on roadside verges (antique word).  One formulation is called ‘Brushkill’ from this very property.  It became very popular with rural councils in the 1960’s because it was quicker and cheaper than mowing the weeds and lasted longer.


When a chemical engineer is designing a plant to manufacture a particular chemical there is often a choice of a continuous-flow process in which the precursors are mixed together in a pipe system and react as they flow along, or alternatively a batch process in which the ingredients are mixed in a container and allowed sufficient time, temperature and pressure to finish reacting, after which the product is drained off.  Bolsover had a very large, very expensive steel vessel in which to produce 2,4,5-T.  One day the reaction ran away.  In other words the heat produced during the reaction caused the reaction to accelerate, the pressure rose and it boiled over.


When the engineers cooled the vessel down they found a witches’ brew of chemicals had been produced.  The extra heat and pressure had gone beyond 2,4,5-T and synthesized, among many other chemicals, several kilograms of a class of polychlorinated polycyclic compounds collectively called dioxins.  These are among the most toxic compound known to man producing cancers and mimicking and interfering with the action of hormones.  Dioxins are fat-soluble and hence tend to accumulate in fat deposits in the body from where their rate of elimination is slow.


The mixture was drained off and destroyed and after an extensive public enquiry the owners decided to put their valuable reactor vessel back into service.  To clean it they suited-up some men in the then best available protective gear, gave them pressure cleaners and sent them into the already pretty clean vessel.  These men came down with a disfiguring skin complaint called chloracne which is specifically caused by the action of dioxin on the skin.  At this point it became obvious that while the amounts of dioxin remaining were extremely small, their effects were severe.  Bolsover was one of the first events that gave notice to the world of just what dealing with dioxins involved.  The owners gave up on the reactor, dumped it into the pit of a nearby disused magnesian limestone quarry and buried it for good.


Now Bolsover made no impression over in North America but shortly after, a series of events coincided which have influenced public opinion ever since.  The event was the Vietnam War.  If I can summarise the Vietnam War in a sentence – it was a civil war involving a conflict of visions:  Ho Chi Minh wanted to organize the largely peasant population into a Peoples’ Paradise while the southern elite were intent on setting up an Industrial Kleptocracy, with America supporting the latter fearing – on the basis of the Domino Theory – that if the communist hordes were not stopped dead their next landing would be on the coast of California.  In charge of the northern forces was General Giap, one of the great generals of the twentieth century (a minority opinion).  Since the US forces had complete control of all air, sea and road transport, General Giap had the problem of transporting a large amount of materiel up to 1000 km without using trucks, ships or planes.  He did this using human transport through a network of forest trails in the mountains.


The Vietnam forest are a tropical/subtropical evergreen forest very rich in tree species and epiphytes.  Some of the genera will be familiar to northern readers – oaks, magnolias, (few rhododendrons), but in the form of small-leaved evergreen species quite unlike the northern versions.  When it became obvious that armaments were leaking to the south through an invisible trail system the US Army decided to cut these routes with a combination of 1000 lb bombs and herbicides, the latter being the notorious ‘Agent Orange’.


Agent Orange was a mixture of products, mainly 2,4,5-T.  The US Army wanted large quantities and, in consideration of the US taxpayers, they wanted it cheap with the result that purity and in particular, dioxin content, were not at the top of the list of specifications.  Over many years Agent Orange was sprayed over the Vietnam forests to defoliate the trees and on paddy fields to deprive the inhabitants of food with disastrous results for the health of the Vietnamese, but it was American veterans who started to complain of impotence, cancers and deformed fetuses that led to public awareness of the problems that dioxin can cause.  From the years of publicity regarding the US veterans fight for compensation for the long-term effects of Agent Orange can be traced much of the current opposition to spraying of any kind.  The public perception of ‘chemicals’ has to a large extent been moulded by the Agent Orange series of lawsuits, driving in part the organic food movement.


So how did individual chemists and the chemical industry react to many years of bad publicity?  And please get away from the popular image of scientists as drooling Frankensteins – real life isn’t made up of Hollywood and cartoons.  Actually the problems were understood very well.  The persistent organochlorine compounds were withdrawn and long persistence was seen as a drawback, not an asset.  The aim became to produce modern alternatives that decomposed to harmless components in the environment after doing their job.  At the time DuPont, one of the better companies, had as their slogan ‘Better Life Through Chemistry’ (visit their open-air museum in Delaware of you ever get the chance). 


You might be thinking, why not use natural products?  The commercial drawback to natural products is that they are not patentable, hence your price could be undercut by anyone at anytime.  Consider a natural insecticide that the chrysanthemum group of plants produce – the pyrethrins.  These are excellent quick-acting knockdown chemicals on many flying and chewing insects.  Just don’t spray them near your goldfish because they are also fish poisons.  What could the companies do?  Why not synthesize a similar molecule and patent it?  Call it ‘Permethrin’.  Lovely stuff, non-persistent, decomposes, low mammalian toxicity, non-accumulating in tissues.  So that was one solution to the problems that had arisen during the previous twenty years.


Another approach has been to use biological control.  For instance there is a natural soil bacterium that attacks and kills some leaf-eating caterpillars.  This is Bacillus thuringensis, abbreviated Bt.  It does not infect humans or other mammals, or birds, or indeed, most insects.  You would think that this would be welcome as a refreshing new approach a world apart from the old chlorinated pesticides, but no, not in Victoria, the old suspicion of anything sprayed, particularly by the government, especially from planes, remains.  The shadow of Vietnam and Agent Orange is still hanging over us.