The effect of landfill leachate and Pyrene on sorghum bicolor growth parameters and soil bacterial communities

Pyrene is one of the polycyclic aromatic hydrocarbons that has carcinogenic, mutagenic and teratogenic effects for living organisms. Landfill leachate is another environmental pollutant that covers a wide range of pollutants, especially heavy metals. The simultaneous presence of two types of pollutants with organic and inorganic structures can increase their toxicity.  In this experimental study, the single and simultaneous effect of Landfill leachate and pyrene on plant growth parameters and the number of heterotrophic soil bacteria was investigated. The study was conducted for 90 days at concentrations of 150, 300, 500, 750 and 1000 mg/kg-1 of pyrene and percentages 0, 30, 50, 70 and 100% of landfill leachate. The results showed that after 90 days, the highest dry stem and root biomass were obtained in irrigation treatment with pyrene and Landfill leachate (Blank)-non-contaminated municipal water with quantities of 8.2 and 3.5 g, respectively; moreover, the lowest stem and root biomass related to the treatment were observed in the simultaneous presence of 30% leachate and pyrene with a concentration of 300 mg/kg-1 with quantities of 5 and 1.8 g, respectively. Leachate did not produce any biological toxicity at any of the surfaces used, but the use of pyrene at concentrations of 1500 mg/kg-1 and above reduced the number of heterotrophic bacteria. According to the  results, the simultaneous presence of the two pollutants, pyrene and leachate, exacerbates the phytotoxicity due to possible interactions between them. Pyrene as a carbon source is decomposed by bacteria at low concentrations, but it inhibits metabolism and growth at high concentrations.