Brian Dunning of Skeptoid.com gives the organic issue a thorough looking at on one of his episodes (#166).

Central to his points, is the position that the term 'organic' is quite arbitrary, much like the term 'natural'. It's a 'feel-good' term, not a scientific one, and can be misleading; much like natural flavorings vs. artificial flavorings in food, where the 'natural' product is often so refined from the 'natural' source as to contain only the one chemical, IDENTICAL to the one 'artificial' chemical alternative. It's simply the production method that is different.

To quote from that episode where Dunning is talking about fertilizers:

The biggest misconception is that organic farming does not use fertilizer, herbicides, or pesticides. Of course it does. Fertilizer is essentially chemical nutrient, and the organic version delivers exactly the same chemical load as the synthetic. It has to, otherwise it wouldn't function. All plant fertilizers, organic and synthetic, consist of the same three elements: nitrogen, phosphorus, and potassium. Referring to one as a "chemical fertilizer" and implying that the other is not, is the worst kind of duplicity, and no intelligent person should tolerate it.

The difference between the two is the source of the chemicals. To make the high-volume commercial versions of both organic and synthetic fertilizer, the source materials are processed in factories and reduced to just the desired chemicals, and the end product, these days, is virtually indistinguishable. Small organic farmers, and home organic farmers, might use fish meal, bone meal, bat guano, or earthworm castings. These are fine products and do indeed deliver the required nutrients. They're just not useful for high volume farming because they're (a) far too expensive, and (b) contain too much ballast, or inactive ingredient, that the crops don't use and merely increase the energy requirements of moving and delivering them.

Setting that aside and looking at pesticide risk in particular: are pesticides harmful? Yes, in sufficient levels. Are the amounts of pesticides in your fruit and veg harmful? Unlikely under regulated conditions. Conversely, are there risks from 'natural' contamination of your produce? Sure, and also unlikely under regulated conditions. Unclean produce can harbor bacteria from the soil. That's why government regulation such as health and safety standards are important, regardless of the method of growing or harvesting the food. It's also a good idea to wash them before consuming, which may reduce both bacterial and chemical contaminants.

So health issues being relatively equal, which should you choose? Organic agriculture may produce food that you find more flavorful to eat, if so that's a consideration you might bear in mind. But for general sustainability high-volume agriculture is much better at producing yield and efficiently harvesting and distributing the product. As a result, I have heard (edit - see earlier Skeptoid episode that has lots of good info and references) that in terms of carbon footprint and sustainability organic-style farming is not as good as standard agricultural practices.

And to finally address your specific question: here's another good article. Scroll down to the "Safer?" heading, and there is relevant info, in particular:

Do pesticides found in conventional foods pose a health threat? Does the difference in pesticide content warrant buying "organic" foods? Consumer Reports equivocates: "For consumers in general, the unsettling truth is that no one really knows what a lifetime of consuming the tiny quantities of foods might do to a person. The effect, if any, is likely to be small for most individuals—but may be significant for the population at large." But the editors also advise, "No one should avoid fruits and vegetables for fear of pesticides; the health benefits of these foods overwhelm any possible risk."

Manfred Kroger, Ph.D., Quackwatch consultant and Professor of Food Science at The Pennsylvania State University, has put the matter more bluntly:

Scientific agriculture has provided Americans with the safest and most abundant food supply in the world. Agricultural chemicals are needed to maintain this supply. The risk from pesticide residue, if any, is minuscule, is not worth worrying about, and does not warrant paying higher prices.

The Consumer Reports article cited is included in the references, and perhaps meets the criteria of a study you're looking for, although it's not exactly a peer-reviewed article.

Additional Reading:

Prompted to do more research by another answer, here are a couple more references:

• Organic produce does not appear to be nutritionally inferior to standard farming techniques.
• Although inorganic fertilizers are known to pose risks, organic fertilizers are not necessarily any safer.

What I've seen (at acsh.org and mayoclinic.com -- search for "organic" -- and others) basically says there's no hard evidence of any benefit of organics.

Organic proponents can find certain studies here and there that seem to indicate the organics are better, but it's not conclusive. There are plenty of other studies out there that show no difference in nutritional content or pesticide content.

The best advice I've seen from experts who have studied it is just to buy what you like best. If the organic tastes better (and based on 100 different factors, it might), then get organic. If the commercial tastes better, then get commercial.

Remember that even organics have pesticides on them -- it's just that they can only use certain ones, and that "natural ≠ safe".

I've never come across any studies. Soil association certainly avoids the direct claim.

I'd hope..that if any pesticides were found to have a direct link to public health that their use would be stopped. (eg DDT). But that also assumes actual testing is being done on previously approved pesticides.

On a related note, I personally disagree with the Soil Associations Organic standard as includes standards such as animal welfare, which I think are very important, whereas I do agree with using pesticides and GM.

The answer by Skrivener quotes a source saying this:

All plant fertilizers, organic and synthetic, consist of the same three elements: nitrogen, phosphorus, and potassium.

That is an entirely true and misleading statement. The same statement in nutrition:

All human foods, organic and synthetic, consist of the same three elements: fats, proteins, and carbohydrates.

The major argument for organic foods is holistic and evolutionary. This may seem like a contradiction in terms if you are used to the term holistic being used by idiots, but it's a useful term. Holistic is opposed to reductionist; both are useful. Reductionism, taking apart to the basic level, is how we gain further knowledge. It's also, however, really hard. Thus the entire century between discovering the three basic components of food (fats, proteins, carbohydrates), and realizing that they weren't sufficient nutrition. The same failure has happened in the context of plant nutrition. We know that plants need nitrogen, potassium, and phosphorous. And we can grow plants with just those three additions.

But they don't taste as good as the ones grown with compost, which is a holistic fertilizer in that it's not made of just those three things. It's made of primarily those three things, but there are trace other things that we don't know if they're important. It seems likely that they would be because evolution would encourage plants to make use of whatever was in their environment, and compost, not pure NPK fertilizer, is what would have been in their environment. Similarly, plants grown with compost, not NPK fertilizer, is what would have been in our environment, and so is likely what we expect nutritionally. We definitely know of calcium and selenium as things that plants need in very small quantities, and there are almost certainly others.

Tests of organic produce vs. conventional produce have showed higher yields of easily testable vitamins and nutrients. I would expect that less easily testable vitamins and nutrients would also be higher.

The critical thing is that this is not a rejection of reductionism or science, because it's easy to hear holistic and believe that. Some day, we may know about all of the vitamins and micronutrients that are in compost, and we may be able to generate a fertilizer that is as good or better for plants. But NPK is almost certainly not it. It's far too simple when the evolutionary landscape was certainly more complicated.

Now on to the argument of pesticides. The amount of pesticides you eat on a single piece of fruit are definitely not harmful. We can test that and determine it using trials. We cannot, however, easily test whether the amount you eat on every piece of fruit and vegetables over the course of your life is harmful. It's not that such a thing isn't testable, it's that testing it is expensive, time consuming, and depends on a stable environment. Pesticides are changed regularly as pests become used to it, so by the time we completed a sufficient test of pesticide consumption over your lifetime, we would be using completely different pesticides. So we guess that probably the pesticides aren't harmful. And they might well not be. They might also contribute to Alzheimer's and cancer. We just don't know, and until we have a systemic understanding of our bodies at the cellular level, we won't know.

I, personally, think they don't taste good. And I don't like washing fruits and vegetables because I think a bit of dirt is probably good for you. However, I'm skeptical of the organic rules because they've been systematically weakened. I think in many cases, organic fruits and vegetables grown by large companies are only barely organic. And organic is expensive.

Interesting question.

I'm going to declare an interest in that I am a soil association certified organic grower and, due to one of those fine ironies that makes life interesting I actually have a D.Phil in Plant Biochemistry and Physiology. I'm also South East Regional Horticultural Workforce champion so I've been talking to a lot of growers recently, both organic and conventional - although many of you may be surprised to know that its not uncommon for a grower to be both. Right - having got that out of the way let's look at the issues.

The question really is about what's the best way to produce tasty and nutritious food in large enough quantity to feed the population we've got without destroying the basis of agriculture in the process.

Until the last century all agriculture was organic - because it wasn't feasible to apply large quantities of chemical materials and pesticides hadn't been invented on any large scale.

Improvements came from the discovery of effective rotations and by breeding higher yielding varieties. Then it became commercially viable to supply NPK from chemical rather than from natural (ie farmyard manure) sources and agribusiness was born. Farmers tended to be rather trigger happy with the Nitrogen bottle and this led to lots of soft sappy growth which was prone to pests and had to be sprayed with lots of quite unpleasant chemicals.

What this neglects to take into account is the effect that intensive mechanisation and use of chemicals has on the soil ecosystem and structure. Basically it trashes it. It would be interesting to know Manfred Kroger's view about the fact that between one third and one half of the soil that was in North America when Columbus landed is now in the ocean as a direct result of the "scientific" approach to farming that he advocates. Trust me - the soil has been trashed by conventional farming. Even DEFRA's chief scientist was expressing concern on the Radio the other week. Believe me - if he's worried in public it must be 2 steps from being beyond repair.

Organic husbandry seeks to build the fertility of the soil by using organic materials (ie from animals) and by managing a systematic increase in the soil content of earthworms and benefical bacteria and fungi. So it focuses on keeping the soil in good heart so that yield is sustainable.

Proponents of "Scientific" farming seem to ignore this. (By the way the reason I keep putting the word scientific into quotations is to flag that I don't think this approach IS scientific in that the framework it uses is too limited). Yield is good but sustainable yield is a whole lot better.

People frequently raise the idea of GM as a panacea here by focusing on yield.

To some extent the issue of yield is a red herring. The UK govt is complaining about food waste at the consumer end but totally ignores the 30% that gets rejected by the supermarkets. If we fixed these two issues you'd be looking at a 60% growth in available food there and then. It takes quite a lot of plant breeding - GM or not - to achieve that.

I also think GM is quite dangerous for 3 main reasons - and not because think GM Maize is dangerous to eat - the probability of that seems vanishingly small to me.

1) It will reduce diversity in varieties. We are always hearing government wittering on about biodiversity while at the same time forcing through laws that force certification of seed in a way that is so expensive that most minor varieties are suppressed. This is a BAD thing.

2) The real nightmare is that we might accidentally create an inedible superweed that crowds out food crops.

3) Since we are in an era where food security is an increasing issue (the UK govt has just released its FOOD 2030 report) do we really want to be beholden to a multi national which is forever striving to achieve a legal lock-in on the use of its products? And if these things are designed to be used in a way that promotes the sale of more weedkiller then it's hardly in the national interest.

One thing that people seem to overlook is that if you routinely use pesticides all you get are resistant bugs - just like MRSA and c difficile.

Turning to the health issues. The recent report carried out by for the FSA by the school of tropical hygiene was a travesty. It so circumscribed its criteria that it was essentially meaningless and it totally ignored an EU study carried out at around the same time that came to opposite conclusions about the increased vitamin and mineral content of organic produce. And as a review there was no original scientific work carried out by its authors.

The truth as always is more subtle. The supermarkets have imposed a regime on growers as to varieties and they put a premium on appearance rather than taste and on the capacity of the vegetables to store well. There is some interesting recent evidence that these varieties take up essential trace minerals much less well that the traditional varieties do. So in that respect traditional organic food is likely to be better than organic produce grown for supermarkets because of the variety issue which applies equally to organic food in supermarkets. And of course it generally tastes better.

Ironically there is less difference in organic vs traditional today than there was 30-40 years ago when the battle lines were drawn up. The prevalence of the Greenwash approach to Corporate Social Responsibility has perversely meant that there is a great deal less pesticide residue in conventional crops PRODUCED IN THE EU than there used to be. There are also strict regulations about how much fertiliser you can use because run-off had been a real issue and something has been done about it. I'm even hopeful that we might do something on a national scale to rebuild soil structure as this is now becoming an issue visible on the radar.

The biggest problem growers face in behaving sustainably is the downward pressure on prices from the multiples which mean, for example that there's not enough cash in the kitty to replant orchards when they reach the end of their useful lives.

I know from talking to customers on the 2-3 farmers markets I do per month that people are only marginally concerned with organic. The are, however, very interested in locally produced, pesticide free produce that's healthy and tastes good. The easiest way to produce this is to grow organically since your production is certified.

What I see in the UK is an increased use of organic techniques into conventional farming alongside some highly mechanised and technical practices. The use of biological controls (predators) which is the mainstay of our pest control in the glasshouses is actually pretty mainstream stuff these days.

The organic standard as it is specified is really overkill in my opinion - but then the Soil Association has positioned itself as a consumer rather than a growers organisation. This is not to say that discipline of maintaining the standard doesn't benefit us as an organisation.

I'm sorry to have gone on for so long but this is an important issue and deserves being treated seriously.

If you're interested in this you might like to visit some of our sites.

FletchingGlasshouses.co.uk TheIntelligentGarden.com GrowingJobs.org