Soil bacteria and protists show different sensitivity to polycyclic aromatic hydrocarbons at controlled chemical activity

Abstract

This study linked growth inhibition of soil bacteria and protists to the chemical activity (a) of polycyclic aromatic hydrocarbons (PAHs) and compared the sensitivities of bacteria and protists. Passive dosing from pre-loaded silicone provided well-defined and constant a of PAHs in independent tests. Single-species growth inhibition with two bacterial (Pseuodomonas fluorescens DR54 and Sinorhizobium meliloti) and two protist (Cercomonas longicauda and Acanthamoeba castellanii) strains at maximum a (amax) of nine and four PAHs, respectively, showed no inhibition of PAHs with amax below 0.1 (pyrene and anthracene), while growth inhibition was observed for PAHs with amax above 0.1 (e.g. fluorene, fluoranthene and naphthalene). The bacteria were less sensitive than the protists. Soil bacterial community-level growth inhibition by naphthalene was in good agreement with single-species data, but also indicated the presence of sensitive bacteria that were inhibited by a below 0.05 and increasing pre-exposure time giving higher inhibition. The a of 50% inhibition (Ea50) was 0.434 and 0.329 for 0.5 and 4 h pre-exposure time, respectively. Invertebrates tended to be more sensitive than single-celled organisms tested here. This suggests that PAH exposure leads to differential toxicity in soil biota, which may affect soil food web structure and cycling of organic matter.

Biodegradation of an essential oil UVCB - Whole substance testing and constituent specific analytics yield biodegradation kinetics of mixture constituents

“…Particularly the general absence of significant lag-phases suggests that the test concentration was below an inhibitory level (Hammershøj et al, 2019). Reduced sensitivity to baseline toxicity in degrader microorganisms compared to larger organisms have been reported earlier (Winding et al, 2019).…”

Biodegradation Kinetics of Fragrances, Plasticizers, UV Filters, and PAHs in a Mixture─Changing Test Concentrations over 5 Orders of Magnitude

“…For phenanthrene, this was 21% of its subcooled liquid solubility 47 and thus near the concentrations range for baseline toxicity. 48,49 The other test chemicals had level 1 concentrations 1 to 4 orders of magnitude below the literature data for their water solubility. WWTP effluent concentrations interfered with the lower test concentrations for some of the chemicals (Figure 1), most distinctly for tonalide and homosalate (Figure 1B), where biodegradation was not evaluated for the lower three concentration levels.…”

Biodegradation kinetics testing of two hydrophobic UVCBs – potential for substrate toxicity supports testing at low concentrations

“…This pattern, with a decoupling of growth and biodegradation, has also been observed for microorganisms in soil, where an exposure to gasoline vapors at toxic levels led to a decoupling between microbial growth and respiration. 26 The near absence of a concentration effect for the diesel oil constituents might be explained by the surface water inoculum containing degrading microorganisms that were not very sensitive to the diesel oil, 40 which is not unlikely given that hydrocarbons are ubiquitous in the aquatic environment due to their many diffuse sources. 41…”