Alnus glutinosa and soil microbial community response to HCH contamination
While the pesticide hexachlorocyclohexane (HCH) and its isomers have long been banned, their presence in the environment is still reported worldwide, despite being prohibited for decades. In this exterior study, our objective was to determine the bioaccumulation potential of alpha, beta and delta HCH isomers by Alder saplings (Alnus glutinosa). Each HCH isomer was mixed separately with soil to achieve a final concentration of 50 mg/kg. All variants, including a control without HCH, were set in triplicate and had instant access to water for three months. Subsequently, HCH levels were assessed in soil and seedling sections (root, trunk, branches, leaves) by gas chromatography-mass spectrometry, while amplicon 16S rRNA sequencing was used to study the rhizosphere and soil microbial community. Highest HCH isomer concentrations were detected in roots, with a decreasing trend toward branches and leaves. The delta-HCH isomer was taken up in highest quantities, with alpha-HCH and beta-HCH recorded at much lower concentrations. Interestingly, high concentrations of alpha-HCH were also detected in the beta-HCH polluted soil. Phytohormone analysis indicated that A. glutinosa reacted to HCH contamination through changes in cytokinin, jasmonate, abscisate and gibberellin content. With some exceptions, rhizosphere microbial population abundance was similar in all HCH isomer samples, e.g. the common soil bacterium Pseudomonas spp. decreased in all HCH-amended samples, while Tomentella was dominant in beta-HCH and control rhizosphere samples and lowest in delta-HCH samples. Further studies will be undertaken to elucidate why delta-HCH was most easily bioaccumulated.