Development of microbial communities in organochlorine pesticide contaminated soil: A post-reclamation perspective

In order to meet constantly increasing demands for land without damaging pristine environments like forests or grasslands, reclamation and re-purposing of historically contaminated areas should become a priority. Successful reclamation goes hand in hand with the soil functional recovery potential and with resilient microbial communities capable of performing the necessary ecosystem services. In this context, we designed a greenhouse pot experiment as a mock reclamation situation, where traces of lindane at hazard threshold and twice the concentration accepted for waste deposits are left in the soil after conventional clean-up by excavation and land filling. We assessed the effects of lindane at 50 and 100 mg kg⁻¹ regarding crop growth and nutrient turnover (with focus on the nitrogen cycle) as two key parameters for soil functions. The bulk and rhizosphere soil bacterial community composition were chosen as parameters for soil resilience in lindane contamination conditions. Lindane severely affected plant growth and development. The potential nitrogen fixation, quantified as nifH gene copy number, suffered direct negative effects of lindane contamination in bulk soil, which could represent an additional obstacle for phytoremediation. Changes in rhizosphere bacterial community composition were related to lindane toxic effects towards the plants, which might have supported the growth of opportunists and saprophytes. In bulk soil, the bacterial community shifted towards lindane tolerant taxa like Sphingomonas and Porphyrobacter that are interesting with regard to their applications in bioremediation. We concluded that lindane at hazard threshold concentration left in soil after clean-up has negative effects both soil functionality, and the recovery of the bacterial communities to their original composition when lindane resistant plant crops are not involved.