Manure, crop–residues, ashes, cinders (pieces of coal), garbage (waste food), paper, card board and plastics. Plastics are the most important land pollutants. Rubber, leather, cloth, rubbish, bricks, sand, metal, broken glasses, demolished building, dead animals, discarded furniture, automobiles, insecticides, herbicides and other biocides and radioactive elements are some of the important land pollutants. The main sources of land pollution are pesticides, radioactive elements and fertilisers.

# Pesticides : Pesticides are chemicals used to kill pests like insects, rats, snails, fungi, herbs, etc. They are collectively called biocides because they kill life. They are of the following types :
 Insecticides : There are chemicals used to kill insect pests.
 Rodenticides : These kill rats.
 Fungicides : These kill fungi.
 Herbicides : These kill weeds.
 Helminthicides : These kill helminth worms.

# Chemistry of pesticide : Based on chemical composition, pesticides are divided into following main groups. They are :
 Chlorinated hydrocarbons : DDT (Dichloro diphenyl trichloroethane), aldrin, dieldrin, endrin, benzene hexa chlorids (BHC) and their close relatives form chlorinated hydrocarbon. They are very poisonous, very persistent, highly mobile and highly capable of dissolving in fat. As they have higher affinity for fat, they tend to move out of the physical environment and enter the living organisms. They are non–degradable pollutants.
 Organic phosphorus pesticides : These include arsenic and sulphur compounds. These are much less in use.

# Ecological effects of pesticides
 Mutation : Insecticides induce gene mutation in human beings (Wurster, 1974).
 Cancer : DDT produces cancer in human tissues.
 Congenital birth defects : Certain herbicides like diozan increase birth defects in both people and livestock.
 Sex hormones : DDT affects sex hormones in mammals and birds.
 Decline of reproduction : In Bermuda petral, a sea bird, the rate of hatching of eggs is much reduced because of the accumulation of DDT. If the accumulation increases further, there will be failure of reproduction in this species in future.
 Calcium metabolism : DDT interferes with calcium metabolism resulting in calcium deficiency. DDT causes hormonal disturbance resulting in delayed ovulation and inhibition of gonad development.
 Biomagnification : The pesticides are non–degradable. They have much affinity towards fat. Hence they tend to move into the living organisms. They are concentrated as they pass up the food chains. For example, at each trophic level, the accumulation of insecticides increases by 10 times. For example if the goat gets one part per million (PPM) of DDT from the grasses, it will have 10 ppm in its tissues. The man, eating the goat will have 100 ppm. The man-eating tiger will have 1000 ppm. If the food chain is still greater, the accumulation will still be higher. This increasing accumulations of insecticides in higher organisms is called biomagnification or biological amplification. DDT causes the pollution of air, water and soil.

# Control of pesticide pollution
 Minimum use : Pesticides should be used at minimum rates and that to only when required.
 Biological control : Pests should killed either by rearing predators or parasites.
 Sterilization : Juvenile hormones prevent metamorphosis and maturation in insects.
 Decoy plants : Pests can be minimised in high value crops by cultivating low value crops.
 Rotation of crops : Different types of crops should be cultivated in different seasons.