Don't worry, it's organic

According to public perception, organic food is the more heathy option. But is this always the case? Maria Burke looks at organic farming and explodes a few popular myths.

In Short
  • Organic farming is a multi-million pound industry that relies on the public's perception that organic food is more healthy
  • There is little evidence to suggest that organic fruit and vegetables are any healthier than conventional produce
  • Some forms of organic farming may introduce natural toxins into consumers' food  

Sales of organic produce are booming. Just look at the baby-food market, for example, where organics now account for 70 per cent of UK sales. The organic industry's message of safer, healthier food produced using farming practices that are gentler on the environment is falling on receptive ears. But critics take issue with many of the industry's claims, arguing that organic fruit and vegetables are more likely to be contaminated with potentially dangerous bacteria and mould toxins. And they point out that higher levels of natural 'pesticides' found in organic produce could be just as dangerous as synthetic chemicals if eaten at high enough doses. So just how safe are organic fruit and vegetables?

Several years ago, critics suggested that organic produce was more likely to be contaminated with bacteria that can cause food-poisoning and worse. Raw manure applied to soil can contaminate crops with pathogens such as Escherichia coliE. coli), shigella and salmonella, according to Mike Doyle, a microbiologist and director of the Center for Food Safety at the University of Georgia. They come from the stomachs of animals like sheep, cows and deer, and are shed in their manure. Once in the soil, they can transfer to the plants, or they can contaminate water used to irrigate or wash produce. Most farmers have developed antibodies to these infections, but they can kill the elderly or very young, or cause kidney damage.

Research conducted by Doyle's team has shown that E. coli O157 can persist in soil containing compost or contaminated water up to six months. 'The duration of contamination by E. coli O157 on produce grown in these fields varied depending on the type of produce. Greatest persistence (around 170 days) occurred on parsley and carrots, whereas least persistence (around 75 days) occurred on onions and lettuce', he comments.

Scientists have also shown that pathogens can get into the plant itself. Karl Matthews and his team at Rutgers University, US, showed how E. coli could transfer from manure and contaminated water into the inner tissues of organic lettuces, where it was protected from sanitising agents. The bacteria passed through the roots and entered the edible portions of the plant. However, the team introduced E. coli into the compost at rates far higher than would normally be found in nature.

Considering the amount of produce consumed, there is a significant risk to consumers, says Doyle. 'But if manure is properly composted or aged, then the risk of contamination of produce is likely to be low. Conventional farming that uses manure to fertilise fields poses the same risk as organic farming. The risk largely depends on how the manure is composted and handled before application to the soil.'

James Cleeton, policy project coordinator of the Soil Association, one of the UK's two organic accreditation organisations, believes organic produce has a lower risk from bugs like E. coli because organic farmers have to comply with manure-handling standards, but conventional farmers do not. Organic farmers in the UK are prohibited from spreading raw manure onto crops during the growing season. Composting - heating heaps of manure to 60 °C - greatly reduces pathogen loads, he says. 'All manure used on organic farms should be composted for a minimum of two months or stacked [left in piles] for three months prior to application, and there should also be a minimum three month period between application and harvest.'. He adds 'If fresh manure is used, organic farmers are directed to leave a six-month interval between application and harvest. If slurry is used, this is increased to one year.' In addition all organic farmers are inspected once a year by their accreditation organisation.

Caroline Smith DeWaal, Food Safety Director for the Center for Science in the Public Interest, a Washington DC-based consumer health group, agrees that organic growers' use of composted manure reduces pathogen risk dramatically. She says: 'Organic producers certified by the USDA [US Department of Agriculture] must use composted manure, although there are no similar requirements for other growers. The use of uncomposted manure on non-organic farms is not regulated in the US and it can clearly pose a significant risk.' The USDA's National Organic Standards Board states that raw animal manure can only be applied to land growing a non-food crop or if harvesting takes place 90-120 days after application, depending on the crop. There are detailed requirements for composting conditions, including the temperatures heaps should reach, how long the heap should be heated and how often the heap should be turned and aerated.

But are the regulations robust enough to prevent pathogen transfer? Mike Doyle's team has revealed that, under 'worst case scenarios', Salmonella and E. coli O157:H7 can survive in soil for around 210 days. 'This would suggest that harvesting vegetables 120 days after application of raw manure may not be safe under some circumstances,' he adds.

What's more, Tony Trewavas, a plant biochemist at the University of Edinburgh, points out that during composting, the required heat may not be maintained in the outside portions of the heap, allowing pathogens to survive. He also adds that when manure is composted, it can lose up to half of its nitrogen content as ammonia, reducing its fertilising powers and probably resulting in a reduced crop yield. 'Conventional farmers can use minerals to revitalise their soils so it matters less to them, but there may be a temptation for organic farmers to compost for less time. It all depends on trust.'

Any manure-based agriculture requires sophisticated analysis of produce for bacterial and mould toxin contamination, says John Hillman, director of the Scottish Crop Research Institute. 'Does composting work? I have grave doubts, but there is an absence of good quantitative data. We need robust monitoring. But this can be a problem as the bulk of organic produce is imported [to the UK] and it is easy to cheat.'

Trewavas believes that, while organic and conventional crops are probably equally at risk from pathogens in the UK, this is not the case in the US. 'Conventional farms in the US are traditionally much larger and farmers can't manure such huge areas,' he explains. 'There, the risk is, therefore, greater from organic crops because manure is mainly applied by owners of small organic farms.'

Dennis and Alex Avery of the not-for-profit Center for Global Food Issues, part of the Hudson Institute in Virginia, US, also think that the risk from manure is mainly associated with organic farming. When conventional farmers use manure, it is mainly on crops that are milled and cooked, they point out. They stress that while conventional farmers are not governed by national regulations, all states have manure-handling regulations for food crops. They worry that organic farmers may not comply with regulations, and doubt the efficacy and robustness of the US system of inspection by independent organic certifiers.

The official line
So are organic crops more likely to be contaminated with bacteria because growers use more manure, or less likely to be contaminated because growers abide by strict regulations for handling the stuff? According to the UK Food Standards Agency (FSA), there is no firm evidence one way or the other. It states: 'The microbiological safety of food depends essentially on controlling the hazards that arise in production and preparation. Good management of manures, including the use of composting and appropriate timing and application, can significantly reduce risks. This applies equally to organic and conventional agriculture.'

Another area of concern for organic-sceptics is contamination with toxic substances produced by moulds called mycotoxins. The Averys say this is more of a worry than bacterial contamination. Crops damaged by insects or weather are vulnerable to a range of moulds. These moulds can produce toxins that contaminate the crop, either as it grows in the field or in storage. The most toxic are aflatoxins, which can induce liver cancer at very low doses if ingested over a prolonged period of time.

'The risk from mycotoxins is much higher for organic produce,' say the Averys, 'because organic farmers use fungicides that are not as effective as the conventional equivalents.' What's more, organic farmers tend not to use any fungicides once the harvested crop is stored.

The Averys cite a FSA survey last year of 30 organic and conventional maize meal samples. It found ten samples were over the 'action limit' for a mycotoxin called fumonisin, six of which were organic samples. They were all withdrawn from the shelves. Two of the samples measured contained approximately 16,000 ppb of fumonisin. Currently, there is no legal limit, although a EU limit of 1000 ppb is under discussion. However, the FSA stresses that it was 'unlikely' that these products posed 'a significant risk to health'.

The organic lobby rejects the Averys' concerns. Cleeton argues that organic produce is less likely to be contaminated with mycotoxins because it is less prone to fungal attack. He explains: 'Conventional crops are fed nitrates. These have been shown to stretch plant cells, making them more prone to damage and more vulnerable to fungal growth. This is not the case for organic crops.'

The UN Food and Agriculture Organisation, which published a report on food safety in organic farming back in July 2000, also takes the line that organic farming does not lead to an increased risk of mycotoxin contamination. It stresses that good agricultural, handling and storage practices minimise the risk in both conventional and organic farming.

Once again, the FSA finds no evidence to support a higher risk from organic food. Furthermore, it adds that the EU's Scientific Committee on Plants has advised that there is insufficient evidence to show whether anti-fungal chemicals are effective in preventing moulds producing mycotoxins anyway. In the mean time, the FSA has commissioned a five-year study at Harper Adams University, UK, to examine the effect of environmental and agronomic factors, including organic farming, on the mycotoxin content of wheat, barley and oats.

Good phenols? Or bad?
Another contentious issue relates to compounds found in plants called secondary phenolic metabolites. Plants produce these natural toxins usually at very low levels to protect themselves against attack by pests or as a response to other sources of stress. Plant tissues may contain up to several grams per kilogram of these phenolic compounds, such as resveratrol, flavonoids, and furocoumarins. The organic lobby claims that their produce contains more phenolic compounds than conventional produce, and this makes their food better to eat. But the organic-sceptics argue that these natural pesticides may be a potential health risk and insist that there is no evidence to show health gains from organic food.

Cleeton quotes a raft of research showing that organic fruit and vegetables contain more phenolic compounds than conventionally farmed equivalents. Their theory is that because conventionally grown crops are protected by synthetic pesticides they don't need to rely so much on their own defence mechanisms, which include phenolic compounds. But others point out that, because of restrictions on pesticide and fungicide usage, organic farmers are more likely to select varieties with greater resistance to pests or disease. The farming practices employed may be irrelevant.

But the more contentious claim from the organic lobby is that because these phenolic compounds are antioxidants, organic fruit and vegetables are better at protecting the body from cancers and coronary heart disease than their conventional equivalents. 'The health benefits of high levels of antioxidants in the diet is well-documented,' insists Cleeton. 'There is a growing concern that levels of some phenolics may be lower than is good for human health in conventionally grown foods.'

Trewevas, meanwhile, is clear that there is just not enough evidence to demonstrate health benefits of phenolic compounds, or health gains from eating organic food. 'It is irresponsible for the organic lobby to make any such claims. Just because these products have antioxidant activity does not automatically make them useful. For example, flavonoids are phytooestrogens and will induce mutations in rodents at high concentrations. We don't know what they do in humans at the low levels we consume.'

The Averys agree that there is a lack of knowledge. 'The notion that phenolics are antioxidants, and therefore all phenolics are healthy is seriously suspect. When betacarotene, a plant-produced anti-oxidant, was administered to smokers to reduce cancer risks, they actually increased the risks and the study was halted early. We simply don't have nearly enough information to say that 20 per cent or 60 per cent more of 'phenolic' chemicals [a complex soup of many different phenolic chemicals with varying purposes] is healthier. We don't have enough information to state that diets high in 'antioxidants' are healthy. We don't really know what is in fruits and vegetables that makes them so healthy in our diet. That's what everyone is trying to find out. But there is no evidence that eating organic fruits or vegetables is any healthier than eating other fruits and vegetables.'

So what line does the FSA take? On the first claim, it says that there is insufficient data to prove whether levels of phenolic compounds in organic produce are greater and occur more frequently than in conventionally produced foods. It states: 'The presence of these chemicals in fruit and vegetables varies considerably, depending on a range of factors that include farming practices. For nutrients for which there is data available, the range of concentrations found tends to be both very wide and comparable for both organic and conventional produce.' On the second claim, it stresses that although phenolics are known to be antioxidants, they are also known to inhibit iron absorption. 'The impact of polyphenol consumption has not been fully evaluated. On the basis of current evidence, the overall FSA view is that organic food is not significantly different in terms of food safety and nutrition from food produced conventionally.'

There is some research that has raised concerns over the effects of phenolics, pointing out that some have potential mutagenic, carcinogenic and phototoxic effects. Take psoralens, for example, a group of furocoumarins found in celery, parsnips, dill, parsley and lime peel. Disease-resistant celery possesses high levels of furocoumarins concentrated in the leaf sap and stem sap. According to the US Center for Diseases and Control (CDC), contact with psoralens - or vegetables containing them - followed by skin exposure to sunlight can produce a variety of skin complaints ranging from burn-like blisters to eczema. While sunlight is enough to trigger this phytophotodermatitis, the artificial ultraviolet light in tanning salons makes it worse. However, there's little risk from eating furocoumarins, according to the UK Committee on Toxicity (COT). But it does recommend monitoring new strains of furocoumarin-containing plants.

At the moment, in the UK, organic producers are forbidden by both the FSA and Advertising Standards Authority to claim that their food is more healthy or more nutritious because there is no evidence to substantiate the claim. Nevertheless, this does seem to be what organic producers believe. On the other hand, the authorities also consider as unproven many of the concerns over the safety of organic food. But many critics remain adamant that science shows there is a significant potential for risk.

So the debate over organic food rages on. It is a highly contested and controversial area, encompassing, as it does, sensitive political issues, strongly-held personal convictions and substantial economic opportunities. But all the protagonists do agree on one important point: eating five pieces of fruit and vegetables protects against cancer. Perhaps, as Caroline Smith DeWaal points out, the over-riding message is that all produce - whether organic or conventional - poses a higher health risk than previously realised, a risk that is up there with the higher profile dangers associated with beef and poultry. As consumers, it seems the best we can do, while the two sides fight it out, is to tuck in to plenty of fruit and vegetables, and make sure we wash it all properly, organic or otherwise.


Maria Burke is a freelance science writer from St Albans, UK.


1. Karl Matthews et alAppl. Environ. Microbiol., 2002, 68, 397-400

2. Food Standards Agency

3.  Alyson Mitchell et alJ. Agric. Food Chem., 2003, 51, 1237-1241

4. Susanne Bugle et alJ. Agric. Food Chem., 2003, 51, 5671-5676

5. Otto Daniel et alEnviron. Health Perspect., 1999, 107(Suppl 1), 109-114

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