Evidence that VOCs may be the cause of symptoms
It is quite bewildering to note that volatile organic compounds (VOCs) were suspected of causing symptoms twenty years ago and yet to date, none of the research projects have attempted to investigate this extremely important hypothesis.
Interestingly, Aberdeen University appear to have released several press statements confirming their intention to investigate this concept, but sadly their research was for some reason curtailed to a partial environmental study that merely recorded the presence of VOCs in the airspace near to rape fields.
The following list outlines both anecdotal and scientific evidence which previously suggested that VOCs from oilseed rape could be the cause of symptoms:-
In 1987, an article published in the Times newspaper suggested that the VOCs from oilseed rape could be the cause of symptoms in horses.
In 1988, Tollsten reported; In the headspace of whole plant [Brassica & Sinapis] samples we identified a total of 34 volatiles. In four of the species, terpenes were the major compounds of whole-plant samples. These terpenes are flower-fragrance components. The Crucifer species investigated produce characteristic odours, with interspecific differences evident in both flower fragrance (terpenes and benzenoids) and Glucosinolates breakdown products (ITCs and nitriles).
In February 1989, Cameron of Angus District Council reported during his presentation at Kew Gardens that terpenes could not be ruled out as the cause of symptoms.
In April 1989, Mayer reported that oilseed rape produced volatile isothiocyanates that were well recognised as bronchial irritants. Mayer also observed a correlation between the acreage of oilseed rape in the Essex Region and asthma admissions at a local Hospital.
In September 1989, McFarlane-Smith of the Scottish Crop Research Institute said that rape also gave off toxic and volatile oils known to cause irritation to the skin and mucous membranes.
In February 1990, The Scotsman newspaper announced that the 3 year Aberdeen study would carefully monitor to see what extent chemicals contributed to peoples allergies.
In 1990, Ninan reported that the strong perfume emitted [from oilseed rape] may well have caused symptoms.
In 1990, McGoram reported that the VOCs from oilseed rape could be the cause of symptoms in horses.
In 1991, Fell reported that the VOCs from oilseed rape could be the cause of symptoms in humans. Th inhalation of volatile material which may be attached to the pollen grain itself is clearly important in the elicitation of nasal symptoms in both atopic and non-atopic subjects [both immunological and non-immunological mechanisms].
In May 1992, Seaton advised the press that oilseed rape produced a chemical, which may be the irritant that is causing the symptoms.
Perry of the Scottish Crop Research Institute (SCRI) advised the press that the SCRI had been given a grant to trap the volatile chemicals which could be tested on individuals to see if they produced a reaction. Perry concluded that the chemical theory was highly plausible.
In 1992, McSharry reported that the volatiles given off from the plant [oilseed rape] have the ability to produce compounds that have the potential to cause toxic, non-specific [cell-mediated] reactions, as well as IgE antibody-mediated reactions.
In 1992, Seaton reported in the Thorax journal that subjects whose respiratory symptoms coincided with the oilseed rape flowering season simultaneously developed an increase in bronchial reactivity, and that the increase in reactivity was likely to be mediated by factors other than IgE antibody-mediated [i.e. cell-mediated]
In March 1993, Seaton issued preliminary findings of the Aberdeen University three year study, through the placing of a letter in the Scotsman newspaper. Seaton reported that in the oilseed rape area a proportion of the interviewees attributed their symptoms to oilseed rape crops. Seaton thought that it was likely that in many cases they were correct, but the symptoms were not classified as classic Type 1 antibody-mediated. Seaton concluded that he hoped that his continuing work would shed light on the different [non-immunological] concepts.
In March 1993, In a press statement Aberdeen University advised that high levels of terpenes which can cause skin and respiratory complaints were detected in the early season and more research was being carried out in that area.
In April 1994, Seaton advised the press that he was in no doubt that oilseed rape did cause irritant symptoms like tickling of the eyes and headaches. However, Seaton dismissed these symptoms on the basis that as soon as you passed the field, the symptoms disappeared, and also because the symptoms did not fit the classic Type 1 allergy symptoms. Seaton concluded that chemical attractants released by the plants were probably responsible for causing the irritation.
In April 1994, Soutar reported in the Thorax medical journal that the symptoms attributed to oilseed rape were likely to be irritant, probably caused by volatile organic compounds released by the plant. Oilseed rape was shown to give off terpenes and these were detected close to fields. Soutar goes on to say that; As oilseed rape is largerly insect pollinated and gives off a number of chemicals, at least partly acting as insect attractants, it is possible that these, rather than pollen, are the cause of symptoms.
In April 1994, Seaton was interviewed on a BBC radio programme and advised that in his opinion there was a case for not planting it [oilseed rape] very close to peoples homes. Seaton would not say what distance was appropriate, but advised that in his studies, the researchers found next to no problem in the air 100 metres from the edge of the oilseed rape fields.
Seaton advised that as a general rule, it was probably unwise to have these crops (or indeed other crops) planted very close to peoples homes, and concluded that in his opinion, most crops have the potential to cause irritant and allergic symptoms in people living close to them. [Seaton unfortunately did not expand on his comments about most crops].
In May 1994, Brostoff co-author of the 1991 Oxfordshire oilseed rape allergy paper, confirmed that the Oxfordshire research team also felt further research on the volatiles was important.
In June 1994, Butcher reported that; since oilseed rape is extensively grown on arable land in dense monoculture it may be found that that the levels of these common volatiles are much greater in close proximity to the crop than would normally be experienced, perhaps sufficient to act as irritants or allergens. Butcher goes on to say that his study found that there was a fourfold increase in the total quantity of volatiles emitted as plants progressed from the pre-flowering stage to the peak flowering stage. This was paralleled by an increase in the number of volatiles detected from 6 up to 20.
In June 1995, Parratt of the Tayside research team reported that; The comparison of symptoms in the two years shows clearly that living in close proximity to oilseed rape is associated with increased reporting of symptoms which is coincident with peak flowering of the crop. Statistical testing showed that symptoms were significantly increased during the ‘middle’ period of our study; that is - the period of maximum flowering of the crop. This is the first clear evidence that heavy exposure to oilseed rape causes symptoms and confirms the general public’s perception of the problem.
In September 1995, Soutar reported; People who complained of symptoms in relation to the flowering of oilseed rape were rarely allergic to the plant and fewer than half were atopic. Nevertheless, they usually showed increased bronchial reactivity during the season, which may have been due in some cases to other allergens but in others to non-specific irritant effects of the air. Whether these are due to chemicals released by the crop, to rising summer ozone levels, or to other factors remains unclear.
In August 1997, Anto reported via a letter in the Lancet that; As pointed out by Hemmer, despite 20 years of increasing production and industrial use, only a few studies have been conducted on oilseed rape allergy, most of them in the UK. The results of these studies have shown that a proportion of people living in close proximity to rape crops is likely to be sensitised and/or have respiratory and irritative [non-immunological] symptoms
Anto concluded; the case of health effects resulting from exposure to either particulate or volatile emission from oilseed rape crops illustrates once more the urgent need of a proactive approach based on large longitudinal studies able to evaluate which changes in quality of life and function will result from transformations in agriculture or industrial processes.
In May 1998, Hemmer advised by the placing of an article in the British Medical Journal that the 1997 report published by the British Medical Research Council stated that there is evidence of health effects associated with the cultivation of oilseed rape. Some of the VOCs detected from oilseed rape, such as terpenes, aldehydes and organic disulphides, may theoretically account for adverse health effects through by their irritant action on mucous membranes. Higher prevalences of headache, cough and wheezing - at the borderlines of statistical significance - have been described from areas of oilseed rape cultivation.
Hemmer concludes his article with a rather curious, almost denigrating and unwarranted comment [in my opinion; not suitable for a learned journal of such high stature] aimed at the general public. Hemmer goes on to say; ...or do people simply dislike its intense smell and flashy yellow flowers? Scientists must never ignore potential health hazards, but so far there is little evidence to incriminate a versatile crop of economic importance as a cause of ill health.
In July 1998, Parratt retorted in a reply to Hemmer’s article; Hemmer has addressed the question of allergy or atopy to oilseed rape and particularly its pollen. We agree that true allergy to oilseed rape pollen is uncommon if defined as positive skin reactivity or a positive RAST test associated with appropriate symptoms. However, in our studies, we have shown that up to 40% of persons in rural communities suffer from symptoms such as eye irritation, runny nose, cough and wheeze. We consider there are two types of presentation: (1) true allergy [immunological] which is uncommon and (2) an irritant effect [non-immunological] on the respiratory tract and eyes which is more common and does not fit the classical definition of allergy. Hemmer fails to make this distinction which we believe is important.
We have sought EU support to compare the putative causes of oilseed rape allergy/irritancy in European countries and the UK. No funding was forthcoming. Until such studies are undertaken there can be no satisfactory resolution of the public concern that oilseed rape is a genuine cause of ill health.
In 1998, McSharry stated; oilseed rape allergy or sensitivity is a public health concern with economic and political interest. This subject still needs more work. Probably the best prospect will be a co-ordinated multi-disciplinary approach, with respiratory physicians, clinical scientists and plant biologists who have the confidence of the community and local authority in the areas studied. It is important that sensitization among farmers is investigated since they are at the front line of contact with oilseed rape. The role of VOC in the exacerbation of asthma symptoms, analogous to traffic pollution, will need clarification.
In 1998, McEwan highlighted the diversity of VOCs emitted by oilseed rape and confirms field emissions to be broadly similar to those found previously in laboratory studies.
In 2000, Galloway reported that a study from the Grampian area of Scotland concluded that subjects whose respiratory symptoms coincided with the oilseed rape flowering season simultaneously develop an increase in bronchial reactivity and that this increase is mediated by factors other than IgE [non-immunological].
Galloway goes on to advise; In light of all the above evidence, it would appear that although there is a definite reaction to oilseed rape crops, not all of this is allergic [immunological] and in the absence of atopy, individuals who exhibit symptoms and increased bronchial reactivity could be reacting to VOCs in the air [by non-immunological mechanisms]. Whatever the reason, the effects of this crop cannot be easily accounted for by common immunological explanations.
Author - Armitage; copyright 2007