Agrochemicals
The artificially synthesised chemicals used in agriculture are called agrochemicals: mainly chemical fertilisers, insecticides, weedicides and fungicides. Used in the hope of short-term gain, their effect on the environment and on health has been very great.
Pesticides and the lethal dose
Weedicides, insecticides and fungicides are known together as pesticides. Their strength is given by the lethal dose, LD50: the dose of chemical needed to kill 50% of a population of a pest species.
Assignment 15.6
For a crop in your area, list the agrochemicals used from the start of cultivation until harvest. Avoid touching agrochemicals.
Banned in Sri Lanka
By a gazette notice issued by the government on 23 December 2014, the sale and use of the agrochemicals glyphosate, propanil, carbaryl, chlorpyrifos and carbofuran were banned.
Figure to be added
Why a smaller LD50 means more danger
LD50 is the dose that kills half the test population, so a chemical with a small LD50 needs only a little to kill — it is more poisonous. The trouble is that pests are not the only living things exposed. The same spray reaches bees and earthworms, washes into streams where it kills fish, and stays on food. The farmer who sprays without gloves or a mask breathes and absorbs it, and, as the pages on chronic kidney disease show, heavy use of agrochemicals is linked to serious illness among Sri Lanka's farmers. Pests can also become resistant, so ever more is needed.
Short-term gain, long-term harm
Agrochemicals — fertilisers, insecticides, weedicides, fungicides — harm the environment and health; LD50 measures a pesticide's strength.