Seasonal residue levels of certain pesticides in El-Manzala lake, Egypt

Seasonal levels of certain pesticide residues were evaluated in water samples collected from El-Manzala lake. The determination was carried out using multi residue method of gas liquid chromatography. The investigated pesticides included insecticides (organochlorine and pyrethroids), herbicides and fungicides. This survey was performed in April, August and December 1998. Thirteen organochlorine insecticides were detected at different tested monthly intervals. The majority of these compounds showed their highest residue levels in December, α-p-DDT, α-HCH, γ-HCH and hexachlorbenezene showed similar residue level of 0.1 μg/L. Also each of p,p'-DDE and heptachlor-epoxide showed 0.16 μg/L. However, the residue levels were found to be 0.18, 0.14 and 0.12 μg/L for p,p'-DDD didieldrin and endrin respectively. Four compounds namely β-HCH, p,p'-DDT, α-HCH and dicrofol showed the highest concentrations in August with residue levels of 0.07, 0.08, 0.32 and 0.5 μg/L for these compounds respectively. The highest levels of detected pyrethroids were also observed in December. With residue levels of 0.88, 0.86, 0.42 and 0.34 μg/L for deltamethrin, cypermethrin, permethrin and fenvalerate respectively. Similar trend of results was observed for the detected herbicides and fungicides since these compounds revealed the highest residue levels in December. Such residue levels of detected herbicides were 0.48, 0.38 and 0.23 μg/L for atrazine, trifluralin and simazine respectively, whereas the fungicide residues were 0.56, 0.42, 0.54, 0.5, 0.56 and 0.32 μg/L for chlorothalonil, dichlorfluazon, imazalil, iprodione, procymidone, triadimefon and vinelozolin respectively.