Toxicity level of hydrocarbons depends on the type of hydrocarbon as well as the microorganisms. In my opinion, we need to be more specific in the term of what type of H.C and What kind of microorganisms. We also need to consider soil texture and structure when comes into contact with oil pollution. For example, aromatic HCs are more toxic than alkanes while low molecular alkanes are more toxic than high molecular alkanes. Even among bacteria, gram negative bacteria are more tolerant than gram positive ones. Clay soils  have more potentiality to create a toxic environment for bacteria than sandy soils.  

Bacterial diversity changes when soil is polluted with oil. At this point, it is important for us to differentiate between bacteria count and diversity. And at the end, the answer for "if toxicity impacts biodegradation process" is yes; although the severity of impact from oil pollution in soil depends on different factors and environmental conditions.  

 Dear Hermann,

Thanks for you sending the reference. Would it be possible for you to send an author's copy to me please? 

Thanks again for your response

Best regards

Toxicity of hydrocarbon to biodegraders depends on the type of hydrocarbon being degraded(aliphatic hyrocarbon or aromatic hydrocarbon). In most case low solubility and high hydrophobic nature of  hydrocarbon make them highly unavailable to biodegraders .  In  such case microorganism release various metabolites such as  biosurfactant for degrading the hydrocarbons.

Dear Dr. Heipieper

Same as Dr. Nnadi, I´m interested in this topic and I don´t have access to the reference you cited. In case it is possible for you, could you send an author´s copy to me?

Thank you, and regards.