تاثير مقادير مختلف سرب و روي بر فعاليت جمعيت باكتريايي خاك

Background: Heavy metals such as lead and zinc are introduced to different ecosystems through industrial human activities and have inhibitory and toxic effects on microorganisms. This study was carried out to identify the effects of lead and zinc on soil microbial community through IC50 determination in 2003. Materials and Methods: In the first step of this study, 28 soil samples containing microbial community were exposed to 3 different concentrations of lead and zinc for 8 months. One flask was prepared in the same conditions without the addition of the above mentioned metals as a control sample. After 8 months the bacterial community was isolated from the soils. Each extracted bacterial community was contaminated with 10 different concentrations of zinc and lead in separate tubes (0.5 to 45 mmole/Kg soil). After 6 weeks, the number of bacteria was determined by plate count method and dehydrogenase activity was measured. The dose - response curves were drawn by non-linear regression method. 1C50s of treatments were determined upon drawn curves. Results: The Logistic model was used to plot dose- response curves. In all treatments, 1C50 increased with the increment of the concentration of heavy metals in the adaptation period. In control treatments IC50 of lead in CFU and dehydrogenase activity tests were 18.4 and 14.3 (mmollKg) respectively and IC50 of zinc was 8.85 and 8.06 (mmol/Kg) respectively. Conclusion: From this study it is concluded that the adaptation period increases the IC50 of lead and zinc in soil bacterial communities that were contaminated with lead and zinc. Zinc is more poisonous than lead and has adverse inhibitory effects on soil microbial community. Approximate concentration of 1 and 0.5 mmollKg for lead and zinc respectively as threshold tolerance concentrations should be considered in compilation of standard drafts.