DDT residues in Lebanese soils.

The present study was conducted to evaluate the levels of residual DDT in Lebanese soils. A total of 113 surface soil samples were collected for analysis from three major agricultural regions in the country: Mount Lebanon, Beqa'a valley and the coastal plain. The values of residual DDT in soils ranged between 0 and 1190 ng g(-1). The majority of the analyzed soil samples were free or contained very low concentrations of DDE. Only two surface soil samples, which were collected from urban areas with high human activities, contained relatively high concentrations of residual DDT. The levels of residual DDT in all of the analyzed soil samples were within the permissible limits for agricultural soils.

Comparison of gas chromatography and immunoassay methods for analysis of total DDT in calcareous soils.

Three different calcareous soil samples from Lebanon were analyzed for total DDT pesticide residue using GC and ELISA methods. Two experiments were conducted on three different calcareous soil samples. In each experiment, triplicates of 5 gm soil samples were each fortified with standard solutions of DDE to reach concentrations of 0, 5, 25, 50, 100 and 200 ng g(-1) and allowed to equilibrate at room temperature for 6 hours. Each sample was then extracted with 25 mL of 90% methanol by shaking in glass bottles on a mechanical shaker for 16 hours. The bottles were allowed to stand for 30 minutes and aliquots were taken from the clear supernatant for analyses without further cleanup. The total DDT in the extract was measured in triplicate by GC and ELISA. The results indicated that the two methods were highly correlated (R = 0.955-0.994). Differences in soil properties did not affect the accuracy of the detection limits of ELISA. Immunoassay technique can be used for rapid and accurate measurement of total DDT residues in mineral calcareous soils in Lebanon.

Antifungal Activity of the Essential Oil of Origanum syriacum L.

The volatile oil of the Lebanese Za'atar ( Origanum syriacum L.) was characterized for its thymol and carvacrol content using gas-liquid chromatography. These two compounds constituted the major components of the oil and were present in equal proportions of 30% in the volatile oil extracted from the leaves and shoot tips of the Origanum plant during the preflowering stage. The percentage of carvacrol in the essential oil increased to 62% after flowering and maturation, while the concentration of thymol decreased to 14%. Origanum oil extracted from plants collected during midseason was evaluated for its antifungal activity against Aspergillus niger , Fusarium oxysporum , and Penicillium species. The oil exhibited strong inhibitory action against the three fungi tested. The minimum inhibitory concentration (MIC) of the oil was found to be 0.1 µl/ml of yeast extract sucrose broth for the fungi tested.