Microbiological, biochemical and ecotoxicological evaluation of soils in the area of biochar production in relation to polycyclic aromatic hydrocarbon content

The objective of the study was the estimation of the effect of polycyclic aromatic hydrocarbons (PAH) on the biological properties of soils in the vicinity of biochar production sites. Assays performed in the soils included the content of PAHs, as well as the microbiological (counts of bacteria and fungi), biochemical (enzymatic activity: dehydrogenases, acidic and alkalic phosphatase, protease and urease) and ecotoxicological properties of the soils (phytotoxicity to Lepidium sativum, Microtox®—Vibrio fischeri, MARA—11 different microorganisms, Daphtoxkit F™—Daphnia magna). In spite of the low level of industrialisation of the area studied, the content of PAHs in the soils was very high. Depending on the soil sampling site, the content of total PAHs varied from 1796.8 to 101,282.7μg/kg. The highest levels in the soils studied were characteristic of fluoranthene and pyrene. The counts of bacteria and fungi, as well as the enzymatic activity, were clearly related with the sampling sites. In most of the objects studied those parameters had high values, which indicated correct runs of the biological processes in most of the soils studied. Depending on the ecotoxicological assay applied, and on the sampling sites, the toxicity of the soils was varied, but only in a few cases the phytotoxicity was correlated with the content of PAHs. •Soils in the area of biochar production were characterised by high content of PAHs.•No impact of PAHs was observed in relation to microbial parameters.•Microbial parameters (bacteria and fungi, enzymatic activity) had high values.•Ecotoxicological tests showed low sensitivity to investigated soils.