Introduction Over the last 60 years farmers and growers have changed the way they produce food in order to meet the expectations of consumers, supermarkets and Governments. In doing so they have made many changes to the way they farm. This often includes the use of pesticides.

What is a pesticide? A pesticide is any substance or mixture of substances intended for: preventing, destroying, repelling, or mitigating any pest. Under United States law, a pesticide is also any substance or mixture of substances intended for use as a plant regulator.

What is a pest? Pests are living organisms that occur where they are not wanted or that cause damage to crops or humans or other animals. Examples include: * insects * mice and other animals * unwanted plants (weeds) * fungi * microorganisms such as bacteria and viruses

Types of Pesticides Common misunderstood: to refer only to insecticides, the term pesticide also applies to herbicides and fungicides. Pesticide use is now common practice worldwide. Herbicides control weeds. Insecticides control insects. Fungicides control diseased crops.

Household Products- Pesticides Many household products are pesticides. For example: * Cockroach sprays * Insect repellents for personal use * Rat poisons * Kitchen, laundry, and bath disinfectants and sanitizers * Products that kill mold * Some swimming pool chemicals.

Benefits / Risks Pesticides can cause harm to humans, animals, or the environment because they are designed to kill or otherwise adversely affect living organisms. At the same time, pesticides are useful to society - can kill potential disease-causing organisms and control insects, weeds, and other pests.

Other Risks Pesticides are among the most widely used chemicals in the world, and also among the most dangerous to human health Cancer Neurological damage Miscarriage

Introduction DDT When people hear the word, "pesticides," they often associate it with something very negative. And many times, they'll soon think of DDT. DDT is one of the most famous pesticides in the world, and it has been with us for quite a long time. It was first made in a laboratory in 1873, but it was not until 1939 that Paul Muller of Geigy Pharmaceutical in Switzerland discovered the effectiveness of DDT as an insecticide.

Chemical DDT DDT stands for dichloro, diphenyl trichloroethane. It is a chlorinated hydrocarbon. DDT is a chemical used mainly as a pesticide. DDT was one of the most widely used chemicals for controlling insect pests on agricultural crops.

Chemical DDT Ingestion and other exposures to the chemical can cause various symptoms. The chemical may be absorbed through the skin. The type and severity of symptoms varies depending on the amount of chemical involved and the nature of the exposure.

Symptoms # Skin irritation # Headache # Eye irritation # Weakness # Anxiety # Dizziness # Headache # Weakness # Fatigue # Nausea # Vomiting

DDT Effects So far, we have learned that DDT is an extremely persistent chemical. It gets into the fats of organisms, and it stays there. Even small amounts of DDT can affect small microorganisms. This is especially true for microorganisms that live in the water. As an example of this high sensitivity, water that contains only 0.1 gram of DDT per liter can slow down growth and photosynthesis in green algae.

History As a pesticide, DDT was first used during WWII. It was so effective as an insect killer that some called it the "atomic bomb" of pesticides. After WWII, we realized that DDT could also be used on farms to control some common agricultural pests.

Real Life Situation DDT and malaria It was found to be particularly effective against insects which carry disease - especially the mosquitoes which carry malaria. Even today, every year 300 million people catch malaria and more than a million of them die. Using DDT to kill the mosquitoes has almost eliminated malaria from more than 20 countries with a total population of more than a billion people. The effect of using DDT is well illustrated by the example of India. Before the use of DDT, there were more than 75 million cases of malaria every year, and about a million deaths. Using DDT has reduced this to 5 million cases a year, and only 5000 of these result in death.

The environmental case against DDT In 1962 an important book was published called "Silent Spring" by Rachel Carson. The name came from a worrying fall in the numbers of some birds. This was found to be caused by pesticides like DDT which are only broken down very slowly in the body or in the soil. They are described as "persistent organic pesticides" or POPs. DDT has now been found all over theworld, even in the Arctic - far from where it was used. DDT is a chlorinated hydrocarbon. These are very stable and are stored in body fat. Animals and birds can accumulate more DDT from the food chain faster than they can get rid of the DDT they already have in their bodies. The levels of DDT in the body increase over time. One of the effects of this in birds is that it causes them to lay eggs with very thin shells. These break easily before the eggs can hatch.

The environmental case against DDT Animal studies using rats and mice have shown some harmful effects of DDT including a possible link with cancer and possible effects on the immune system and the reproductive System. On the other hand there is no definite proof of any harmful effects on humans although DDT has been found in human blood and breast milk. This is despite the fact that millions (or even billions) of people have been exposed to it over long periods of time. Some studies have shown that there may be effects on human development. Exposure may result in low birth weights or reduced heights in children.

The environmental case against DDT South Africa stopped using DDT because of worries about high levels of DDT in blood and breast milk in the population. They used other insecticides to control the malarial mosquitoes instead of DDT. Unfortunately, the mosquitoes quickly became resistant to these other insecticides. South Africa had to start using DDT again to avoid large numbers of deaths from malaria.

Questions Questions 1. DDT is a chlorinated hydrocarbon. What do you understand by this term? 2. When India started to use DDT to control malarial mosquitoes, the number of people getting malaria fell from 75 million cases a year to 5 million cases a year. Thenumber of deaths fell from 1 million to 5000 a year. Can you suggest any reasons why the number of deaths fell faster than the number of people catching the disease? 3. Using chlorinated hydrocarbons like DDT resulted in a fall in numbers of some birds. This was especially true of birds of prey like sparrow, hawks and peregrine falcons. Why do you think that these were particularly affected? 4. There is disagreement among scientists and others whether DDT should be banned completely. Make a list of the reasons why DDT should continue to be used, and a second list of the reasons why it should be banned.