Pesticides play a critical role in maintaining agricultural productivity, but intensive practice, repeated use and run off into the surface and ground water can pose a threat to the human and his domesticated animals. The study was carried out to identify the level of organochlorine pesticides and polychlorinated biphenyl residues in water wells using Limnatis nilotica leeches as bioindicators during summer and spring of the year 2013 at some localities of Al-Jabel Al-Akhdar, Libya. The chlorinated organic pesticide residues were ranged from 0.001 to 11.449 ng/g extracted from the whole homogenate body of leeches collected from five investigated wells. The obtained results showed that 100% of the analyzed samples contained detectable level of the monitored insecticides (HCH, aldrin, dieldrin, endrin, o،p-DDE, p،p-DDE, o،p-DDD, p،p-DDD and o،p-DDT). It is found
that 100% of the samples gave results with levels below the MRL for HCH, aldrin, dieldrin, endrin concentration residues. Among all samples, 60% of the samples gave results with levels of total DDT concentration residues below the MRL, while 40% of the samples contained levels of insecticide residues above the MRL. On the other hand, there were occurrence of several polychlorinated biphenyl derivatives and 100% of the samples gave results above the level of the maximum contamination level for total PCB. The existence of total PCB at the highest levels were detected in Michael and El-Wasita wells at the summer season reaching 29 and 27 ng/g, respectively. However, the lowest detected level of total PCB reached (1.00) ng/g in leach tissues collected from Tiba well during summer season. The high levels of PCB derivatives detection in all leech samples is a health hazard reflected the continue uses of this materials source until this date and may be cause various diseases in Al-Jabel Al-Akhdar areas. Generally, the attained results emphasized that leeches are useful tools in biomonitoring of both organochlorine pesticides and polychlorinated biphenyl residues.