RESIDUE STUDIES: Use of pesticides is steadily rising in Pakistan' agriculture. Rice is the second highest export of Pakistan earning sizeable foreign exchange. With a view to aver possibility of contamination of this commodity with undesirable quantities of pesticide residues which may adversely affect country's foreign trade. studies were undertaken with there pesticides popularly used on this crop; viz., diazinon (an organophosphate). Lindane (an organochlorine) and carbaryl (a carbamate) . Results obtained indicated that residues of all the three insecticides do fall to negligible levels (Nil to 0.6, Ni to 0.46 and Nil to 0.5 ppm respectively) within a month 0 application on the crop.
Gamma BHC is commonly used for pest control in the region. Studies on behaviour of the insecticide from folia surfaces was studied in the laboratory and it was found that under summer conditions the insecticide is readily volatilize, from the leaves within few hours. Similar studies were undertake on DDT's fate from fallow agricultural area around Karachi Sindh. sprayed with the insecticide. In this case also it was: found that the insecticide is dissipated comparatively much slowly from plots covered with polythene sheet than from plot: left uncovered under local harsh summer conditions. Result: obtained on both these products/aspects have been incorporated in this dissertation.
Rice is cultivated in Pakistan initially as a nursery wherefrom plants are transplanted to grow to maturity to yield the grain. Early-season pest attack from insects cause callous damage to the crop. To protect the crop from ravages of pests, preventive spraying with insecticide(s)is administered. Investigation were undertaken to see if the consumers are exposed to any health hazards if they feed on rice which had beer treated with DDT and fenitrothion in the nursery stage. It was found that DDT residues fell to 2.0 3.2 ppm level by the end of one week when 3 nursery treatments were made. With fenitrothion zero level of residues was reached in a week when three applications here made to rice nursery.
Environmental pollution is caused by non-target crop spraying with persistent insecticides like DDT. An ,assessmen1 made in the agricultural areas of Punjab and NWFP had revealed, that residues of DDT were present upto 5 ppm in soil samples collected from sugarcane, tobacco, cotton and vegetable growing areas of the enumerated provirces. Subsequently, an experimen1 was conducted to investigate as to how contamination of soil in agricultural fields occurs. A paddy growing area in Baluchistan which had aerially been sprayed with a DDT formulation was selected for the study. Results obtained revealed that though DD' residues, ten days after spraying, fell by 39.11 and 84.66%n from paddy straw and pannicles respectively, they increased by 18.36% in the adjacent soil , revealing the fashion in which non-target fall-out does pollute the environment.
Though known as a non-systemic insecticide, some results included in the present dissertation reveal in-ward movement of the DDT. Firstly it has been proved that application of the insecticide to cotton by ground spraying as well as b) aerial application. DDT and its metabolites are translocated to the seed-oil. Which is an item of human diet in Pakistan. Secondly an investigation conducted on mustard plant with radio-labelled DDT revealed that residue did get absorbed from the foliar surfaces.
Success achieved in developing a cheap and authentic vapour-phase separation technique to be used in conjunction with as chromatography for determination of sub-nanogram levels of residues of a few OP pesticides in certain fruits 1ind vegetables has also been described in the present thesis.
A trend has been established in Pakistan to use combinations of expensive synthetic pyrethroids (SPs) with comparatively cheaper organophosphate (OP) insecticides. An investigation conducted by the present researcher established that this practice does not have much positive edge over conventional combinations of OC's (organochlorines) and OP's. Results obtained have been included in the present document. In another study it has been proved that residues of monocrotophos, fenitrothion fell to non-detectable level within a week while none were pres'3nt after a fortnight in case of endosulfan in the cotton crop which receives foliar application with these products.
Granular application of systemic OP's are made to cotton crop in its early stage to save the crop against early season pest attack. An investigation conducted with phorate and disulfoton proved that this practice does provide enough residue of these products to save it effectively against pest attack. It has been found that one-third residues of these pesticides were present in the crop even six weeks after their application.
A number of investigations were conducted fruit and vegetable plants to study behaviour of residues of certain OP and OC's and also to evolve techniques to provide effective protection against pest attack without an occupational risk t(workers and also to end users of the produce, averting, simultaneously, any environmental hazards. Results0: development of such novel techniques have also found a place in this presentation.
STABILITY OF PESTICIDES: Very little printed information is available regarding stability of pesticides from tropical and sub-tropical regions o. the world where their formulations are exposed to extremes o. climate. An effort was. therefore. made to investigate shelf-life. of twelve selected OC and 01' pesticides under accelerated storage conditions recommended by FAO and also by subjecting them for 2. months storage under field conditions prevailing in four different ecological conditions of Pakistan. Results obtained. have also been included in this dissertation.