Topsoil pollution and the tolerance of its bacteria to heavy metals in Hamadan municipal waste burial sites

The biological pollution of landfill sites for urban waste is a crucial concern. This study aims to investigate the resistance of bacteria in contaminated soils at waste burial sites against heavy metals in Hamadan.

The physical and chemical characteristics of soils were examined, and the total amounts of metals such as copper, lead, zinc, and cadmium were measured. Additionally, pollution load index (PLI), average pollution index (PIavg), and pollution degree (Cdeg) were estimated and analyzed. Furthermore, the percentage of stable bacteria resistant to copper, lead, cadmium, and zinc in the NA culture medium was studied by measuring the logarithm of microorganism abundance

Among the mentioned sites, the soil surrounding the leachate lagoon exhibited the highest levels of organic carbon, available phosphorus, and potassium. The PLI and PIavg indices for virgin soil were below one, indicating that this soil was not polluted. However, these indices were above one for the other five sites, indicating pollution. The intensity of soil pollution in these sites exceeded the permissible limit. The logarithm of population for fungi, actinomycetes, pseudomonas, and enterobacters was highest in the new rubbish landfill, with values of 5.35, 5.28, 6.13, and 5.98, respectively. The percentage of bacteria resistant to lead was 100% in all sampled soils, but in the leachate, it was lower than 64%.

Overall, the percentages of bacteria resistant to copper, zinc, and cadmium in the new rubbish landfill site were higher compared to other sites, which may be attributed to the landfilling of urban waste in the soil.