الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
The three organophosphorus insecticides malathion , profenofos , and chlorpyrifos were tested to determine their acute toxicity to the four larval instars of the mosquito, Culex pipiens L. , the adult stage of the water flea, Daphnia magna (Straus) and two ages of the Nile Bolti, Oreochromis niloticus (one –and seven -days – old ) . The holding period for all insecticides was 24 h . Residues of one of the three preceding insecticides, malathion , were analyzed on and in squash fruits chemically , using the colorimetric and gas chromatography methods , simultaneously with aquatic bioassay using the three tested organisms as biomarkers .
Regarding the acute toxicity, it was found that mosquito larvae exhibited the highest sensitivity to all insecticides tested ; 24h lc50 values of malathion were 0.078 , 0.230 ,0.026 , 0.0557 ug / l . for the first , second , third , and the fourth larval instars , respectively. The corresponding figures at the LC90 level were 2.210 ,8.791 , 0.775 , and 26.050 ug /L . These figures show that the third instar was the most susceptible one .
With profenofos , the LC50 and LC90 values ranged between 0.013 to 0.044 , 1.689 to 7.979 ug/L , respectively . The obtained figures of toxicity showed that the last larval instar (4th) was the most sensitive instar . The four larval instars tolerated much higher levels of the third insecticide chlorpyrifos. LC50 and LC90 values ranged between 0.047 to 0.086 and 0.880 to 3.494 ug/L , respectively . The second and the first instars exhibited the highest toxicity to chlorpyrifos , depending on the level of toxicity evaluation.