Biological parameters of the restoration of soils polluted by crude oil

The purpose of this study was to identify parameters of rhizospheric microflora, soil fauna and radish plants in order to measure the effectiveness of the decontamination of a Fluvisol affected by crude oil. Bioassays were established with radish plants (Raphanus sativus L.) in 0,85 ha of restored soil and 0,377 ha of adjacent control soil in Cunduacan, state of Tabasco, Mexico, in the three climatic seasons of the year: northers (November to February), southers or dry season (March to May) and rainy season (June to October). A completely randomised design with a factorial arrangement (soil type and season of the year) was applied four replicates. Five microflora variables, the diversity of the soil fauna and seven plant variables were evaluated. The data were analysed using orthogonal contrasts, an ANOVA and multiple correlations. Ecotoxicological impact indices (EII) were also calculated. The restored topsoil still has from 6 480 to 11 210 mg kg(-1) of total petroleum hydrocarbons (TPH), which caused necrosis and up to a 92 % mortality in plants. The bulb (-0.658**) did not form leading to a reduction in plant biomass (-0.691**), these were the most sensitive parameters in the dry season. The most affected variable (p <= 0.01) in the dry and rainy seasons was the soil fauna density (-0.729**). The EII proposed provided values that make it possible to identify sensitive parameters of bioindicators used to evaluate the restoration quality of Fluvisols polluted by crude oil.