People are worried about pesticides. What are the facts?

    Many consumers are wary of pesticide residues in food and the adverse effects they could be having on their health. Given that these chemicals are added to food because of their ability to kill, it is perhaps unsurprising that consumers have these concerns and that the desire to avoid pesticide residues is one the reasons that some are prepared to pay more for organic produce. However, there is no evidence to suggest that pesticide residues in food are doing any harm to consumers.

    The important thing to understand about pesticides (and all potentially toxic compounds) is that their effects are dose dependant.  If you take a large dose of a pesticide and feed it to a rat, you may find that the rat develops cancer. This doesn't just apply to pesticides. Many naturally occurring plant compounds have also been found to cause cancer at high doses - about the same proportion of them as pesticides. These plant-produced compounds are a lot more abundant in our food than pesticide residues. It has been calculated that one cup of coffee contains more naturally occurring carcinogens (cancer causing chemicals) than most people consume as pesticide residues in one year. Plants naturally produce their own pesticides and these are in fruit and vegetables at concentrations hundreds of thousands of times higher than the concentrations of the pesticides added by farmers. The reason fruit and vegetables aren't killing us all is that the amounts of these compounds is too low to be harmful and the amount of our pesticides are even lower still.

    The toxicity of all pesticides is very thoroughly examined before they are licensed for use. A wide range of tests are performed (including testing on animals) to find a concentration low enough that the pesticide produces no harm. The maximum amount of pesticide residue that is legally allowed in the food is then set at a concentration much lower than this (usually about 1000 times lower) in order to be on the safe side.

    This doesn't mean, however, that we shouldn't reduce pesticide usage. While the amounts found on food are far too low to be harmful, the amounts handled by farmers when applying pesticides are much higher and there are cases of farmers being poisoned by pesticides.

    One way to reduce pesticide spraying is simply to stop spraying pesticides - the approach taken by organic farmers. The problem with this, however, is that with nothing stopping the pests the yield of the crop decreases. This means that more land has to be used to grow the same amount of food. This in turn drives up the cost of the food produced and is harmful to the environment, since more land needs to be used for agriculture. Most farmers in the developing world simply could not afford to do this.

    Another option is to use genetically modified (GM) crops. There are a group of GM crops called 'Bt crops' which have been modified to produce proteins called CRY proteins. These proteins come from a bacterium called 'Bacillus Thuringiensis' and they kill insects. Each CRY protein is very specific to a certain insect, so a plant can be modified to produce CRY proteins that kill its pests without harming other insects. CRY proteins have no effect on humans - they are broken down in our digestive system in the same way as most protein that we eat.

    There are multiple benefits of this 'Bt' technology. Firstly, the farmer saves money on pesticides. Secondly the yield is higher. Part of the reason bt crops are more successful than conventional crops sprayed with pesticides is that the CRY proteins are produced inside the plants, where sprayed pesticides will not reach. Also, the CRY proteins are not washed away by rain. In India, rural farmers choose to buy bt cotton seeds, rather than cheaper, conventional cotton seeds, because they more than make the cost back in the savings on pesticide and the increased yield. Finally, using bt crops means that farmers are less at risk of poisoning, because they are spraying less pesticides. A survey of cotton farmers in Northern China between 1999 and 2001 showed that the introduction of bt cotton had reduced the incidence of poisonings.

   In summary, we should seek to reduce the spraying of pesticides, because it is harmful and costly to farmers . However, we do not need to worry about pesticide residues on our food, because they are present at amounts far too low to harm us. One method that has been used to reduce pesticide spraying is the deployment of bt crops.


***Click here to see a video about bt cotton in India (you will have to select the video from the panel on the right)***

Genetic Modification is not natural. Does that make it morally wrong?

    First things first, I think it's important to define what I mean by 'natural'. If I was feeling suitably philosophical, I could try to argue that anything done by man is natural. After all, humans beings are living creatures and all of our decisions and actions are the results of biological processes in our bodies. However, I suspect that when most people hear the word 'natural', they don't immediately think of such human creations as aeroplanes, factories and skyscrapers, so I shall treat 'natural' as denoting something that would occur by itself - without human intervention.

    By this definition then, genetic modification of crops by people is not natural. My question, however, is this: what's so great about  'natural' anyway?

    It seems to me that there is a general consensus in society that we can become better, healthier people if we only consume things that occur naturally.

    The fact is however, if people had only ever done that most of us wouldn't even be here.  Pretty much all the food we eat is unnatural.  Agriculture is unnatural. Fields full of the same plant all growing in neat little rows are not a naturally occurring phenomenon.  The crops themselves are not even natural. They have all been subject to processes of artificial selection by humans for hundreds of years - we select the ones that have characteristics that suit our needs. Take the potato, for example, which has been bred to reduce the levels of poisonous glycoalkaloids. In fact most plants make poisonous chemicals, partly to stop them from being eaten and these poisons are all natural.

    Does this mean agriculture is evil? No, of course not. It may have its problems, just like any technology, but the fact is we wouldn't be able to sustain anything like the world's current population if we'd never applied science and technology to food production.

    GM is just the next stage of this. It is just a more elegant and precise way of manipulating plants for our own needs - just like we have been doing for millennia. You may disagree with GM because you are concerned about its safety or usefulness (I wouldn't agree with you, but I'll save that for another post), but saying that we should abandon GM because it is unnatural is wrong. Even without GM, we would still all eat unnatural food every day.

 

The Golden Rice Project

    Golden Rice is a genetically modified strain of rice, which has been created by Prof. Ingo Potrykus, Prof. Peter Beyer and colleagues with the specific aim of reducing the prevalence of vitamin A deficiency.  The name 'Golden Rice' comes from the golden colour of the rice grains. 

    The symptoms of vitamin A deficiency (VAD) include night blindness, blindness, xerophthalmia, poor growth, increased mortality and increased vulnerability to infection. The effects are particularly bad in children and pregnant women.  According to World Health Organisation statistics, VAD causes 250000 - 500000 children to go blind every year. More than half of these die within a year of going blind.  The countries in which VAD is most severe are shown in this diagram:

    

        VAD is linked to diet.  The best way to obtain vitamin A is to eat a balanced diet including meat, which is rich in compounds called retinyl esters; the body can convert these to retinal - the form of vitamin A which is important for vision.   Plants contain compounds called carotenes, some of which can also be converted to retinal by the human body.  The most abundant is beta-carotene, which is also known as provitamin A. 

    In many of the countries where VAD is most severe (particularly India and countries in south east Asia), the staple food is rice.  In Cambodia, for example, rice accounts for 76% of human calories.  Although the rice plant does produce beta-carotene, it does not produce it in the endosperm - the part which we eat.  This is because the plants use beta-carotene for light capture in photosynthesis and this process does not occur in the endosperm. Therefore, it is not surprising that in many countries where a lot of rice and little meat is consumed, there are high levels of vitamin A deficiency. 

    This is where Golden Rice comes in.  Golden Rice has been genetically modified so that it does produce beta-carotene in the endosperm.

    The pathway by which beta-carotene is usually synthesised by plants (i.e. the pathway missing from rice endosperm) is shown below in a simplified form. The words in black are the names of the molecules and the words in red are the names of the enzymes that catalyse each step.

    In the rice endosperm, only one of these enzymes is present: lycopene cyclase. Therefore, the creators of Golden Rice took existing rice and added genes which code for enzymes to replace those not found in the endosperm.  They added two genes. The first is a gene from daffodil which codes for phytoene synthase. The second is a gene from a soil bacterium which codes for an enzyme called phytoene double-desaturase. This enzyme can catalyse both the second are third step in the pathway.  The genes were put under the control of an endosperm-specific promoter, so that the enzymes would be produced in the endosperm.  The pathway found in Golden Rice endosperm is shown below:

   The first version of Golden Rice contained an average of 6.6mg of provitamin A per gram of rice.  Some critics - particularly anti-GM campaigners - pointed out that large amounts of the rice would have to be eaten for a person to gain their full requirement of vitamin A (if the person was only eating rice).  In 2005, a new version of Golden Rice containing 32mg/g was produced.  This was named Golden Rice 2.  Although some beta-carotene is destroyed during cooking and not all of it is absorbed into the body, the level of beta-carotene in Golden Rice 2 is comfortably enough to prevent VAD in people eating ordinary amounts of rice.

    Beta-carotene is a pigment, which gives the golden rice grains their colour.  Photographs of normal rice, Golden Rice and Golden Rice 2 are shown below:

    There is no reason why Golden Rice should be dangerous or harmful to human health.  Firstly, beta-carotene is abundant in many foods of plant origin. For example, it gives carrots their orange colour.  Moreover, there is no reason why the two enzymes that have been added should be harmful to humans and even if they were, they are irreversibly destroyed by the cooking process. Nevertheless, Golden Rice had to be tested for safety in humans, as is sensible with all new foods.

To be completed...