A pesticide is a poison used to kill an insect ,an animal ,or a plant which is considered as a pest. Besides pests, they can be harmful to persons involved in sale, transportation, handling and use, animals in the field where pesticides are used and it affects the environment as a whole. About 75% pesticides use occurs in developed countries, 3 million people suffer from pesticide poison every year and 20,000 may die every year. Majority of deaths occur in developing regions , including Africa. It means that from manufacture to disposal, all pesticides must be handled in a manner so as not to pose unnecessary risk to humans and the environment.

Desirable characteristics in a pesticide:
i) Only a small amount is needed to kill targeted pests(specific)
ii)Has low  toxicity to non-target species.
iii)Has a lifetime long enough to kill target pests (doesn’t persist in the environment)
iv)Degrade into benign products
v)Doesn’t  bio accumulate
vi)Doesn’t run-off with water from application site
vii)Pests are slow to develop resistance to it.

Benefits of pesticides :
i)Improving productivity
ii)Protection of crop losses/yield reduction
iii)vector disease control
iv)Quality of food: In countries of the first world, it has been observed that a diet containing fresh fruit and vegetables far overweigh potential risks from eating very low residues of pesticides in crops
v)Other areas-transport ,sport complex, building :The transport sector makes extensive use of pesticides, particularly herbicides .Herbicides and insecticides are used to maintain the turf on sport pitches, cricket grounds and golf courses. Insecticides protect buildings and other wooden structures from damage by termites and wood boring insects.

Hazards of pesticide:
i) Direct impact on human: Certain environmental chemicals ,including pesticides termed as endocrine disruptors,  known to elicit their adverse effects by mimicking or antagonizing natural hormones in the body and it has been postulated that their long-term ,low dose exposure is increasingly linked to  human health effects such as immune suppression, human disruption, diminished intelligence ,reproductive abnormalities and cancer.
ii)Impact through food commodities: Cucumbers, apples, tomatoes , lettuce, strawberries ,mandarins ,pears ,bananas ,beans and potatoes are many of the food commodities with extensive pesticide use such as acephate, carbendazin, chorothalonil, choloropyriphos, DDT, diazinon, endosulfan, methamidophos,iprodione ,metalaxyl,methidathion,thiabendazole, triazophos.
iii)Impact on environment :Pesticides can contaminate soil, water ,turf, and other vegetation. In addition to killing insects or weeds, pesticides can be toxic to a host of other organisms including birds ,fishes, beneficial insects and non- target plants .Insecticides are generally the most acutely toxic class of pesticides, but herbicides can also pose risks to non-target organisms.
iv)Surface water contamination: Pesticides can reach surface water through run-off from treated plants and soil. Contamination of water by pesticides is widespread.
v)Groundwater contamination: Groundwater pollution due to pesticides is a world -wide problem. According to USGS, at least 143 different pesticides and 21 transformation products have been found in ground water, including pesticides from every major chemical class. Once ground water is polluted with toxic chemicals, it may take many years for the contamination to dissipate or be cleaned up. Cleanup may also be very costly and complex, if not impossible.
vi)soil contamination
vii)Effects on soil fertility(beneficial soil microorganisms):Heavy element of soil with pesticides can cause populations of beneficial microorganisms to decline. Overuse of chemical fertilizers and pesticides have effects on the soil organisms that are similar to human overuse of antibiotics.
viii)Contamination of air ,soil and non-target vegetation: Pesticides effect can directly hit  non –target vegetation or can drift or volatilize from the treated area and contaminate  air ,soil and non –target plants.
viii)Non –target organisms: Pesticides are found as common contaminants in soil , air water and on non -target organisms in our urban landscapes. Once there, they can harm plants and animals ranging from beneficial soil organisms and insects , non-target plants ,fish ,birds and other wildlife. Exposure of eggs to  2,4 D reduced successful hatching of chicken eggs and caused feminization or sterility in pheasant chicks. Chlorpyrifos, a common contaminant of urban streams is highly toxic to fish, and has caused fish kills in waterways near treated fields or buildings .