Alfredo Pérez-de-Mora

Phytostabilization of semiarid soils residually contaminated with trace elements using by-products: Sustainability and risks

We investigated the efficiency of various by-products (sugarbeet lime, biosolid compost and leonardite), based on single or repeated applications to field plots, on the establishment of a vegetation cover compatible with a stabilization strategy on a multi-element (As, Cd, Cu, Pb and Zn) contaminated soil 4-6 years after initial amendment applications. Results indicate that the need for re-treatment is amendment- and element-dependent; in some cases, a single application may reduce trace element concentrations in above-ground biomass and enhance the establishment of a healthy vegetation cover. Amendment performance as evaluated by % cover, biomass and number of colonizing taxa differs; however, changes in plant community composition are not necessarily amendment-specific. Although the translocation of trace elements to the plant biotic compartment is greater in re-vegetated areas, overall loss of trace elements due to soil erosion and plant uptake is usually smaller compared to that in bare soil.

Long-term impact of acid resin waste deposits on soil quality of forest areas II. Biological indicators

In this study, we evaluated the effects of two acid resin deposits on the soil microbiota of forest areas by means of biomass, microbial activity-related estimations and simple biological ratios. The determinations carried out included: total DNA yield, basal respiration, intracellular enzyme activities (dehydrogenase and catalase) and extracellular enzyme activities involved in the cycles of C (beta-glucosidase and chitinase), N (protease) and P (acid-phosphatase). The calculated ratios were: total DNA/total N; basal respiration/total DNA; dehydrogenase/total DNA and catalase/total DNA. Total DNA yield was used to estimate soil microbial biomass. Results showed that microbial biomass and activity were severely inhibited in the deposits, whilst resin effects on contaminated zones were variable and site-dependant. Correlation analysis showed no clear effect of contaminants on biomass and activities outside the deposits, but a strong interdependence with natural organic matter related parameters such as total N. In contrast, by using simple ratios we could detect more stressful conditions in terms of organic matter turnover and basal metabolism in contaminated areas compared to their uncontaminated counterparts. These results stress that developed ecosystems such as forests can buffer the effects of pollutants and preserve high functionality via natural attenuation mechanisms, but also that acid resins can be toxic to biological targets negatively affecting soil dynamics. Acid resin deposits can therefore act as contaminant sources adversely altering soil processes and reducing the environmental quality of affected areas despite the solid nature of these wastes.

Long-term impact of acid resin waste deposits on soil quality of forest areas I. Contaminants and abiotic properties.

Acid resins are residues characterised by elevated concentrations of hydrocarbons and trace elements, which were produced by mineral oil industries in Central Europe during the first half of the last century. Due to the lack of environmental legislation at that time, these wastes were dumped into excavated ponds in public areas without further protection. In this work, the long-term effects of such resin deposits on soil quality of two forest areas (Bayern, Germany) were assessed. We evaluated the distribution and accumulation of contaminants in the surroundings of the deposits, where the waste was disposed of about 60 years ago. General soil chemical properties such as pH, C, N and P content were also investigated. Chemical analysis of resin waste from the deposits revealed large amounts of potential contaminants such as hydrocarbons (93 g kg(-1)), As (63 mg kg(-1)), Cd (24 mg kg(-1)), Cu (1835 mg kg(-1)), Pb (8100 mg kg(-1)) and Zn (873 mg kg(-1)). Due to the location of the deposits on a hillside and the lack of adequate isolation, contaminants have been released downhill despite the solid nature of the waste. Five zones were investigated in each site: the deposit, three affected zones along the plume of contamination and a control zone. In affected zones, contaminants were 2 to 350 times higher than background levels depending on the site. In many cases, contaminants exceeded the German environmental guidelines for the soil-groundwater path and action levels based on extractable concentrations. Resin contamination yielded larger total C/total N ratios in affected zones, but no clear effect was observed on absolute C, N and P concentrations. In general, no major acidification effect was reported in affected zones.

MPN- and Real-Time-Based PCR Methods for the Quantification of Alkane Monooxygenase Homologous Genes ( alkB ) in Environmental Samples

Hydrocarbons are major contaminants of soil ecosystems as a result of uncontrolled oil spills and wastes disposal into the environment. Ecological risk assessment and remediation of affected sites is often constrained due to lack of suitable prognostic and diagnostic tools that provide information of abiotic-biotic interactions occurring between contaminants and biological targets. Therefore, the identification and quantification of genes involved in the degradation of hydrocarbons may play a crucial role for evaluating the natural attenuation potential of contaminated sites and the development of successful bioremediation strategies. Besides other gene clusters, the alk operon has been identified as a major player for alkane degradation in different soils. An oxygenase gene (alkB) codes for the initial step of the degradation of aliphatic alkanes under aerobic conditions. In this work, we present an MPN- and a real-time PCR method for the quantification of the bacterial gene alkB (coding for rubredoxin-dependent alkane monooxygenase) in environmental samples. Both approaches enable a rapid culture-independent screening of the alkB gene in the environment, which can be used to assess the intrinsic natural attenuation potential of a site or to follow up the on-going progress of bioremediation assays.

Progress in Microbial Activity and Chemical Properties of a Trace Element Polluted Soil Under Assisted Natural Remediation

In this work, we studied the temporal dynamics of several microbiological properties in a trace element polluted soil under the influence of various amendments and/or a plant cover during a 30 month-period. The experiment was carried out in containers filled with ca. 150 kg of contaminated soil. Seven treatments were established: four organic (leonardite LEO, litter LIT, municipal waste compost MWC and biosolid compost BC) and one inorganic (sugarbeet lime SL), where the grass Agrostis stolonifera L. was sown, and two control treatments (with plant CTRP or without plant CTR). Soil was sampled four times during the experimental period. The microbiological properties studied were: microbial biomass C, microbial biomass C/total organic C, dehydrogenase, aryl-sulphatase, β-glucosidase, acid-phosphatase and protease enzyme activities. Dynamics of microbiological properties differed between treatments being results not only affected by soil pH or trace element concentrations, but also by changes derived from the different treatments in organic matter quality and quantity, as well as nutrient content in soil. While microbial biomass C, dehydrogenase, aryl-sulphatase and protease activities were highly correlated with soil pH and soluble trace element contents, changes in β-glucosidase activity were mainly influenced by water soluble C concentrations. It was also observed that enzymatic activities generally decreased over time after no more amendment additions occurred. Nonetheless, during the experiment microbial biomass and activities were generally higher in all treatments compared to the untreated control and thus remediation practices had a positive and significant effect on trace element stabilization and microbial activity in the contaminated soil.