There are, however, problems attached to the uses of pesticides. Although some pesticides break down in the environment quickly, such as herbicides that break down rapidly and are only poisonous when ingested at high concentrations thus cause problems very occasionally, others do not.
For example fungicides can be important pollutants. Many of them contain either Copper or Mercury, as fungi are very sensitive to these two elements. Mercury is toxic to humans. Cases have arisen, for instance in Japan, where people have died as a result of eating fish and molluscs, which had accumulated high concentrations of Mercury (Advanced Biology, Michael Roberts, 2000).
In addition, some insecticides are not broken down completely or very quickly once they have been applied. They remain in the environment for a long time this is known as persistence. When insecticides are not broken down they may persist in food chains. As the chemicals pass from one trophic level to another, they become concentrated, particularly in fat deposits of top carnivores such as birds of prey. This is called bioaccumulation.
Bioaccumulation of pesticides occurs as you move up the food chain.
- Bioaccumulation of pesticides is a serious problem, especially with chlorinated hydrocarbons which are stored in fat (example of bioaccumulation)
This diagram represents bioaccumulation of DDT in a food chain. Note that the concentration is highest in the final predator (ppm = parts per million) (6)
The effect may be quite dramatic, as with DDT, which is now found in virtually all animal tissue, in every food chain, and even the Antarctic snow (Food, Farming and the Environment, Damian Allen and Gareth Williams, 1997). However thanks to its use, millions of people survived who would other wise have died of malaria or starvation (Biology: Principles and Processes, Michael Roberts, 1993).
Although this case is an extreme circumstance, laws have now been put in to place to stop these dangerous chemicals from coming on the market again, although there is still a question about the amount of pesticides used on crops. A person may consume 1.5g of natural toxins per day in foods such as coffee, potatoes, tomatoes, whole wheat and brown rice. This is about 10000 times the average amount of pesticide residue consumed. (Charles, New Scientist)
Another problem, that that may arise is if a particular pesticide is used a lot the pest may eventually become resistant to it. The pesticide no longer kills the pest and so a new one has to be developed at all times which results in more resources and cash flow being ploughed into developing and testing.
An alternative method to chemical pesticide use is using biological pesticides or Bio-pesticides. Bio-pesticides are certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals. An example of this is using other animals to get ride of pests. Examples of include using ladybirds to control aphids, using cactus moths to control prickly pear cactus, using the parasitic wasp Encarta to control whitefly in greenhouses, using myxomatosis to control rabbits in Australia etc.
Advantages of these would be that they are specific as they only target the pest species, the pest are unlikely to develop a resistance to the predator and once introduced, there is no need for further reintroduction. Nevertheless, the disadvantages to having many living organisms are they have to be bred and packaged in special greenhouses using special methods. This makes it very expensive to use in an open environment such as a field. Although the biological method is widely adopted in the greenhouse market, due to being in a situation which organisms can not fly away and migrate but are kept in a closed system. Furthermore, it stops eutrophication and bioaccumulation. However, because of its expense and uncontrollable application, it is a way of keeping numbers of pest down, not eradication of the pests. This is why a mixture of both is one possible technique. (1)
The second method is conservation; conservation of natural enemies is an important part in any biological control effort. This involves identifying any factors that limit the effectiveness of a particular natural enemy and changing them to help the beneficial species. Conservation of natural enemies involves either reducing factors, which interfere with the natural enemies, or providing needed resources that help natural enemies. (3)
We must also consider an ethical viewpoint upon modifying plants. Religious groups such as the Sikhs and other conscious individuals are vegetarians. It may be improper for them to eat fruit and vegetables that have been modified to contain pesticides that alter the natural production of plant crops and fruit. Some Christians object in principle to modified food, as an unacceptable intervention in God's creation violating barriers in the natural world. Environmental activists also agree the most vulnerable populations are children, the developing foetus, the elderly and ill. Most worrisome from a public health perspective are chronic health affects such as cancer, infertility, miscarriage, birth defects and effects on the brain and nervous system. (4)
Overall when using pest controls there are a number of factors to consider, to get maximum effect and sustain pest control. The important factors to consider are how efficient each method is at controlling the pest, the cost, damage that might be caused to the environment, and possible health hazards. In a survey of the 200 commercial grain storage premises contacted in 1995, 114 stored grain and 104 were visited to obtain data on pesticide usage. Ninety three percent of those visited were found to use pesticides. (7). In addition in the developed world we have become increasingly concerned about the long-term effects that chemical pesticides and herbicides may have on us as we eat our well-sprayed food. Even with the latest technology farmers will still resort to using pesticides, agreeing with the predicted US demand for pesticides in 2006 will reach $10.6 billion (8)
We have also become progressively greener over recent years; with more and more people expressing concern over the future of the earth and our effect on it, hence the reason for many people turning to organic based products. The Organic Trade Association states that nearly 10% of cropland in Europe is dedicated to organics. (9) Substituting biological control for chemical intervention therefore seems like a very good idea. However the use of pesticides is integral to the framing industry and is important to our world as it revolves around price and quality of such indispensable goods such as crop.
Bibliography
Bill Indge, published in 2000, "A New Introduction to Biology", page 211-212
www.defenders.co.uk
Class notes from AQA exam board
Pesticides, Report No. 636 (The Fredonia Group, Cleveland, Ohio, 1994) as cited in AGRO, No. 225 (1995), p. 16.
Members.aol.com/Tenaya21/Ecology/ LectureNotes/lec24.html
Thomas, M. R.,Garthwaite, D. G. & Norris, L. N ,Commercial grain stores in Great Britain/1998
Clorox Company Report
As the Demand for Organic Produce Grows, So Does Supply - Or Does It?
Tess Osborne
Arun Joshi
