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This is the second in a series of posts that seeks to explain some of the detailed, crop-specific reasons that pesticides get used, and how that is actually important for true agricultural sustainability. In this post I’ll talk about a pesticide that is a main-stay of Organic farming and also widely used by other farmers.
Fire and Brimstone!
“Fire and Brimstone” is a biblical expression describing Hell that later became a derisive term for a style of Christian preaching. The term “brimstone” is the ancient name for the highly irritating element, sulfur, and it was a vivid image of why you wouldn’t want to end up in Hell!
It turns out that “brimstone” (sulfur), is not just a Biblical image of eternal suffering, it is an important and widely used pesticide active against certain diseases and against mites.
About Sulfur
Sulfur is exceptional in many ways:
- It is the oldest of all pesticides (~5000 years, to early Egyptian civilization)
- It is still the most heavily used pesticide in California (if represents 26% of the pounds of the top 100 materials used in CA – over 40 million pounds in 2008)
- While modern pesticides are used in the range of a pound to a few ounces/acre, sulfur is used at 4-10 lbs/acre and as frequently as every seven days
- It is the pesticide that leads to the most farm worker complaints (skin, eye and lung irritation )
- This pesticide has been predicted by a new risk model to cause significant “bird kill” at the rates at which it is commonly used – particularly on grapes (table, wine, raisin)
- It is by far the most widely used fungicide/miticide in “Organic” agriculture
OK, now I’m going to argue that sulfur (brimstone) is actually an important part of agricultural sustainability.
What!?
Considering the above information, you should probably be asking, “why in the ‘place with brimstone’ would you defend the ‘pesticide from hell?!'”
This is not an academic argument. Right now, I’m actually involved in a “broad stakeholder” process that is trying to define what sort of pesticide use is “sustainable,” and I find myself in the very unlikely position of defending sulfur. For instance, I am arguing that the model which says it kills birds needs to be validated before we can reach that conclusion.
I’m not really a likely candidate for this job of defending sulfur. I’ve spent enough time doing experimental work in sulfured vineyards to understand how irritating it can be. My consulting clients are not the companies that sell sulfur, they are the companies that invent newer, better alternatives. So, why would I defend sulfur?
A Walk in a Vineyard Without Sulfur (c 1980)
I remember being in an experimental vineyard plot around bloom in early June, probably around 1980. I was shocked to smell a pleasant fragrance – nothing like the acrid smell of sulfur that I had come to associate with any vineyard. This was an experimental block that had only been treated with the new, synthetic, DMI fungicide, Bayleton. It was the first real alternative to sulfur that the grape industry had ever seen. Grape flowers don’t even have any petals, they don’t need to attract pollinators, but with no sulfur around you could smell the wonderful fragrance that they produced (perhaps as some sort of evolutionary remnant? )
The Development of Pesticide Resistance
Well, that scent (whatever it represented) might have been noticed in a lot of California vineyards in the early 1980s as growers happily moved away from weekly sulfur dustings to applying Bayleton every three weeks. But quickly, the grape powdery mildew pathogen developed resistance because of the over-use of Bayleton. Because of that, Bayleton is no longer a viable tool for disease control for California grape growers.
Why Sulfur Is Still Important Today
Today, the grape industry has several other good alternatives to sulfur for powdery mildew control, but it still uses sulfur as a part of the seasonal control program. The sulfur serves to reduce cost, but most importantly, it serves to prevent resistance development as happened with Bayleton. So it turns out that the ‘pesticide from Hell’ is an important reason why the more benign options can be used in a sustainable fashion.
There are lots of other examples like this in other crops where relatively old, high use-rate products are still used because they help prevent the development of pest resistance to the newer alternatives. These chemicals don’t quite rise to the standard of ‘pesticide from hell’ but they are other examples of less-than-ideal options that serve to preserve the usefulness of much “softer” compounds. (I should also point out that sulfur is an important plant nutrient and is in some essential amino acids we require in our diet – it is just an issue of quantities).
Organic grape growers are pretty much limited to sulfur because even though the new synthetic fungicide options are safer, they do not fit under the “natural” limitation. By the way, some Organic growers in various crops use flame weeders for weed control, in which case they round out the entire ‘Fire and Brimstone’ image.
My next post in this series will be about “Pesticides that buy time.”
Air applied sulfur image from NARA/EPA, 1972 in the National Archives. Typically, sulfur dust would be applied with ground equipment.
You are welcome to comment directly on this site or to email me at feedback.sdsavage@gmail.com
Thanks for an interesting article, Steve. It’s refreshing to see a balanced view of these crop protection issues. I’ve mentioned your post in our blog http://www.pesticideinformation.eu/2010/04/organic-pesticides-and-integrated-pest-management/
cheers!
Gavin
Natural and Synthetic Pesticides
This document brings together the facts about natural pesticides in relation to synthetic pesticides. The aim is to help those involved with the current European plans to ban many synthetic pesticides on the basis of hazard and not on a risk assessment understand why the hazards posed by natural pesticides cannot be ignored and why they should forget about banning synthetic pesticides.
It is likely that many readers will be unaware of the existence of natural pesticides let alone their properties. It would seem that those in Europe planning the new ban are not aware.
1 Natural pesticides and their perception in the UK.
Q 1. What are natural pesticides?
A Natural pesticides are chemicals produced by plants that afford them protection against insect pests, bacteria and fungi. As every gardener knows not all plants in the vegetable and flower garden are attacked by the same pest. Some plants have natural protection others do not. In fact very few garden plants are attacked by pests and diseases which suggests that many plants have a formidable array of chemical and other defence mechanisms.
Some natural pesticides have been commercialised such as nicotine, pyrethrum (the forerunner of the synthetic pyrethroids) and strychnine.
Q 2. What are the concentrations and numbers of natural pesticides in food crops and how do they compare with the concentrations of synthetic pesticides?
A. Concentrations of natural pesticides can be expected to vary widely depending on many factors. The lower end of the scale probably starts at a few mg/kg e.g. benzopyrene in spinach at 7.4 mg/kg. Other examples are furfurol in cocoa and coffee at 55 to 255 mg/kg, caffeic acid at 50-200 mg/kg in apples, pears, plums and potatoes and at the top end of the scale are the pyrrolizidine alkaloids which occur in thousands of plants often at concentrations greater than10,000 mg/kg Ames (1990), Mattsson (2007). Any given plant is likely to contain several hundred if not thousand different natural pesticides.
The concentrations of natural pesticides are increased considerably when the plant is attacked by a pest or disease – a very significant feature.
In contrast the concentrations of synthetic pesticide residues in UK-grown crops are usually below the limit of detection. Concentrations seldom exceed 1 mg/kg. In the UK more than 200,000 pesticide/commodity combinations are analysed annually and the results compared with Maximum Residue Levels. The MRL is the maximum concentration that is likely to occur if the pesticide has been used according to good agricultural practice. MRLs are not health-based exposure limits and exposure to levels higher than a MRL does not imply a risk to health because of the built-in safety factor, normally of 100. MRLs are typically below 1 mg/kg and with a few values up to 5 mg/kg.
Over the last 8 years it has been found that 50 -70% of all samples analysed in the UK contained no residues and that less than 1% contained more than the maximum permissible level (PRC, 2000-2007).
Q 3. What are the quantities of natural pesticides in the diet?
A. Eleven years ago Ames and Gold (1997) in the USA reported that on average Americans ingest 5,000 to 10,000 different natural pesticides and their breakdown products each day totalling about 1,500mg. Data on the concentrations of natural pesticides in the UK and in Europe indicate that the same amounts would apply.
Q 4. Do natural pesticides pose a hazard and have toxicology studies been carried out on them?
A. Yes. By 1997, when Ames and Gold reported on the situation, 63 natural pesticides had been tested of which 35 (56%) were rodent carcinogens in acute studies. This is basically no different from all the chemicals (including synthetic pesticides) that have been tested. About half all chemicals tested (1275 by 1997) can be said, when supplied at a high enough dose and/or for long enough, to be rodent carcinogens and therefore potentially hazardous to man. It would be reasonable to assume that half of all natural pesticides will be carcinogens but it would be an enormous undertaking to study the thousands involved.
Long term or chronic toxicological studies have seldom been carried out on natural pesticides as they are routinely done for synthetic pesticides. This is a serious shortcoming in view of our lifetime consumption of fruit and vegetables.
Q 5. If all crop plants contain so many potentially harmful natural pesticides that might cause carcinogenic, mutagenic, teratogenic or genotoxic effects why are the adverse effects not seen on human health?
A. In view of our ignorance about natural pesticides – only a very few of the many thousands that are believed to exist have been isolated and studied -there can be no definitive answer to this question. It is likely that human metabolism copes with natural pesticides for example by breaking them down before they can cause any harm. Maybe the risk is much smaller than we have led ourselves to believe from the way we interpret and extrapolate the toxicology data on synthetic pesticide (see Q.15).
During evolution man has learnt not to eat poisonous plants such as deadly nightshade (a member of the potato, tomato and pepper family). A preparation from the roots and seed of hemlock (a member of the family that includes carrots and parsley) was used to kill Socrates. Brassicas (cabbage family) commonly contain harmful natural pesticides which most, but not all, humans can cope with. All that is natural is certainly not safe to eat.
Q 6. How do the amounts consumed and the carcinogenicity of synthetic and natural pesticides compare?
A. The amounts of natural pesticides consumed daily exceed the amounts of synthetic pesticides by at least ten thousand times. The numbers produced by Ames and Gold(1997) for daily consumption were 1,500 mg of natural pesticides and 0.1 mg of synthetic pesticides.
Natural pesticides have the same potential for harm as synthetic pesticides based on the data on all (432) synthetic chemicals that had been tested before 1997; 59% were found to be carcinogens to rats and mice compared with 57% of the naturally occurring chemicals (127 including 63 natural pesticides).
In other words natural pesticides pose the same hazards as synthetic pesticides.
Q 7. What is the public perception about natural pesticides?
A. There appears to be virtually no appreciation of the existence of natural pesticides let alone the possibility that they might be harmful. This is based on personal discussions and the lack of interest by the media despite their knowledge of and their preoccupation with synthetic pesticides. People seem to have a blind faith in anything natural. Logic and now toxicological studies show that natural chemicals are just as likely to be hazardous as any other chemical. Moreover because natural pesticides are consumed in very large quantities compared with synthetic pesticides and most pharmaceuticals we should be much more concerned about them than synthetic pesticides.
Q 8. Why is it that so little has been done to study the health implications of natural pesticides in Europe and the UK?
A. The answer to this is probably a combination of ignorance throughout society and Government, the emphasis given to synthetic chemicals and pesticides and a general belief in the goodness of all things natural. Only about 10% of toxicological tests have been done (most in the USA) on naturally occurring chemicals
The lack of information on natural occurring chemicals leads to a distorted view of the potential impact of chemicals on human health.
It would be stupid to suggest that we invoke the misused precautionary principal and should stop eating all fruit and vegetables until it has been proved that the natural pesticides they contain pose no risk of harm. There may however be cases (see Q. 9&11) where the natural pesticide content may have been raised to very high levels and invoking the precautionary principal may be appropriate.
The health-promoting benefits, particularly with regard to cancer, of fruit and vegetables are proven beyond all doubt so it would be very unwise to do anything that would limit their consumption.
2 The production and variation in the concentration of natural pesticides.
Q 9. What are the conclusions that can be drawn from our current knowledge about natural pesticides
A. Varieties of crops that have been bred or selected for better resistance to fungal or insect attack are likely to either contain more or have the capacity to produce more natural pesticides. Such varieties should not be permitted on the market until the chemicals responsible and their toxicology has been identified, studied and risk assessments made in the same way as they currently are for synthetic pesticides in the UK.
Where GM technology has been used to introduce the resistance factors it will have been an inevitable part of the development that a particular natural pesticide will have been targeted for which the genetic control will have been identified so facilitating a study of the toxicology. GM can provide a precise technique whereas conventional plant breeding leaves one completely in the dark about the reasons for resistance to a particular pest or disease.
Q 10. What are the conclusions that can be drawn about the use of insecticides and fungicides on crops and current EU proposals concerning banning many synthetic pesticides?
A. Crops treated with insecticides and fungicides contain less of the potentially harmful natural pesticides because their defence mechanism will not have been stimulated by a pest or disease attack. For example a study on parsnips showed that fungal infection increased the levels of a natural pesticide ( furocoumarins, which are carcinogens and mutagens and which are also found in carrots, celery, oranges and potatoes) by up to 100 times in (Mattsson, 2008).
In the absence of a risk assessment on the natural pesticides concerned it is clearly more sensible to spray the synthetic pesticide than not to and so minimise the amounts of natural pesticides in the crop.
This means that serious consideration needs to be given to these matters in Europe before irrevocable decisions are made by politicians in the European Union and member states to ban synthetic pesticides. At the time of writing it is said that the EU is planning to ban up to 80% of the synthetic pesticides used in the UK. If they go ahead with their ban it will show a lack of regard not only for scientific research but also for public health.
Q 11. What are the implications for organic farming?
A. It can be expected that crops produced by organic farmers will contain more of the potentially harmful natural pesticides than traditionally grown crops because synthetic pesticides are not used. Limited data that is currently available shows this to be the case for celery and parsnips but clearly much more data is required before this can be said to be generally true.
The potential hazard of fungal toxins both in growing and stored crops not protected by fungicides should not be ignored.
It is perhaps fortunate that the production of organic fruit and vegetables in the UK is very limited. However there are significant imports which need to be considered.
Q 12. What can be done to minimise the risk of harmful effects of natural pesticides?
A. Insects and fungi start their attack on the outer surfaces of a plant which means that the concentration of natural pesticides will be higher in such tissues than elsewhere. For example potato skins can contain 300-600 mg/kg of hazardous glycoalkaloids compared with the adjacent flesh 12-50 mg/kg. It would therefore seem to be advisable to cut away a considerable amount of the outer tissues of root vegetables before eating. Whether this is the case with fruit is not known but would be expected.
The outer layers of root vegetables and fruit can be excised but with the green vegetables and such cops as peppers and tomatoes this would pose problems.
3 Possible Future scenarios
Q 13. What are the implications of the EU banning synthetic pesticides because of the perceived hazard they pose and not on the basis of a risk assessments?
A. The total quantity of all ingested pesticides would be increased not decreased which is not what the EU want. Crop production will be hampered and farm economies seriously affected. A precedent will have been set for the EU to ban any chemical on the basis of perceived hazard. If one day the EU thought about assessing natural pesticides in the same way they would realise where their logicality has led them.
It is to be hoped that science and logic will prevail before too much damage has been done to the economy not only of European countries but also of the developing countries that take their lead from Europe.
If the hazardous natural pesticides in crops were judged in the same way as is proposed by the EU for synthetic pesticides then the consumption of all crops particularly fruit and vegetables would have to be banned. This is clearly ludicrous but it is the logical conclusion if the EU continues to use hazard and not risk assessment as the yardstick.
Q 14. What is the likely outcome if the EU does not ban synthetic pesticides on the basis of hazard?
A. The total burden of pesticides on humans would remain at current levels.
Farmers across Europe will be able to continue to control weeds, pests and diseases and thereby grow food efficiently which is especially important in times of global food shortages. Harvested crops will be protected to stop the formation of dangerous fungal toxins.
The EU will not have not backed itself into a corner with respect to matters of chemicals and health and it will have the opportunity to promote research (see Q. 15) and public understanding on chemicals and health.
Q 15. What needs to be done?
A. The dilemma exposed in this document by the consideration of the two different kinds of pesticide needs to be resolved.
The basic problem would seem to be related to our procedures for evaluating the potential impact of chemicals on health. Have we so repeatedly been bombarded by pressure groups with the notion that all chemicals and especially pesticides are bad for us that we are ready to accept the notion that just one or two molecules can have devastating effects?
It seems likely that not only is the “hazard” approach manifestly inadequate and misleading but that the interpretation of the toxicological tests and their extrapolation when setting acceptable chronic and acute exposure/ingestion levels may also be at fault.
In the UK a chemical is evaluated both on the basis of acute effects of high doses and as well as on the chronic effects of low doses. No-adverse-observed effect levels (NOAELs) are judged from the chronic toxicology tests and from these the acceptable lifetime daily intake (ADI) is set, normally at one hundredth the chronic NOAEL.
Maybe the safety margin of 100 is too generous.
In order to cast light on this it is suggested that a full range of toxicology tests followed by a risk assessment is carried out on some of the hazardous natural pesticides in say potatoes (and/or other regularly consumed vegetables) and acceptable daily lifetime intakes (ADIs) assessed using the safety margin of 100.
The results will show how the amounts we regularly consume in the vegetables compare with the ADIs evaluated using the safety margin of 100.
Such studies will have to be carried out in conjunction with studies on the effects of cooking and on the absorption and metabolism of the chemicals involved.
At present some European Governments are, for reasons which are not clear, more concerned with regulating minute quantities of synthetic pesticides and following the lead set by the media and badly informed pressure groups than with allowing science and logic to play its part.
Many eyes remain to be opened about the need to understand more about the very plentiful natural pesticides in our food if we are going to reduce our intake of hazardous chemical, which in the case of natural pesticides exceeds their synthetic counterparts by more than 10,000 times.
References
Ames,B. (1990). Dietary pesticides (99.9% all natural) Proc.Natl.Acad. Sci. 87,7777-7781.
Ames,B and Gold,L.S.(1977). Environmental pollution, pesticides and the prevention of cancer: misconceptions. FASEB 11, 1041-1052.
Mattsson, J.L.(2007)Mixtures in the real world: The importance of palnt self-defence toxicants, mycotoxins and the human diet. Toxicology and Applied Pharmacology. (in Press)
Mattsson, J.L.(2008). Spray for safer food. New Zealand Geograhic
(PRC, 2000-2007) Pesticide Residue Committee Annual and Quarterly Reports, published by DEFRA.
Victor M. Shorrocks M.A., D.Phil., C.Biol., M.I.Biol. 05.08.08