Bacterial diversity on an abandoned, industrial wasteland contaminated by polychlorinated biphenyls, dioxins, furans and trace metals

Most former industrial sites are contaminated by mixtures of trace elements and organic pollutants. Levels of pollutants do not provide information regarding their biological impact, bioavailability and possible interactions between substances. There is genuine interest in combining chemical analyses with biological investigations. We studied a brownfield where several industrial activities were carried out starting in the 1970s, (incineration of pyralene transformers, recovery of copper by burning cables in the open air). Four representative plots showing different levels of polychlorobiphenyls were selected. Organic and trace metal levels were measured together with soil pedological characteristics. The bacterial community structure and functional diversity were assessed by 16S metagenomics with deep sequencing and community-level physiological profiling. Additionally, a vegetation survey was performed. Polychlorobiphenyls (8 mg.kg(-1) to 1500 mg.kg(-1)) were from 2.4 x 10(3)-fold to 6 x 10(5)-fold higher than the European background level of 2.5 mu g.kg(-1). Polychlorinated dibenzo-p-dioxins and dibenzofurans ranged from 0.5 to 8.0 mu g.kg(-3). The soil was also contaminated with trace metals, i.e., Cu > 187, Zn > 217 and Pb > 372 mg.kg(-1). Location within the study area, trace metal content and soil humidity were stronger determinants than organic pollutants of bacterial community structures and activities. Thus, the highest biological activity and the greatest bacteriological richness were observed in the plot that was less contaminated with trace metals, despite the high level of organic pollutants in the plot. Moreover, trace element pollution was associated with a relatively low presence of Actinobacteria and Rhizobia. The plot with the highest metal contamination was rich in metal-resistant bacteria such as Sphingomonadales, Geodermatophilaceae and KD4-96 (Chloroflexi phylum). Acidobacteria and Sphingomonadales, capable of resisting trace metals and degrading persistent organic pollutants, were dominant in the plots that had accumulated metal and organic contamination, but bacterial activity was lower in these plots than in the other plots. (C) 2020 Elsevier B.V. All rights reserved.