Irene Rosellini

The Bioavailability Processes as a Key to Evaluate Phytoremediation Efficiency

Bioavailability is the key to understanding the risks from pollution and to defining remediation strategies, since organisms only respond to the fraction that is biologically available. Plants are able to uptake the substances only if present in available forms in the soil environment; this means that bioavailability is the key to evaluating the feasibility of phytoextraction as a remediation technology.

Phytoremediation Towards the Future: Focus on Bioavailable Contaminants

The hypothesis that one of the possible future trends of phytoextraction should be the removal of the bioavailable contaminants has recently received renewed and increasing interest. This fraction is the most hazardous to the environment and human health. The evaluation of contaminant bioavailability is essential for the appropriate application of the technology. Before selecting a phytoextraction process, it is necessary to consider the specific characteristics of the soil at the contaminated site in order to evaluate how the soil properties will influence the final result of remediation in the field. With this approach based on the concept of bioavailable contaminant stripping (BCS), an evaluation of the hazards of the residual fraction not removed by plants is left to a risk assessment procedure. This approach can be safely applied, if the soil ability to replenish the bioavailable pools in the long term is considered. This problem can be overcome by enhanced bioavailable contaminant stripping (EBCS) which evaluates this amount through the combined use of chemical extraction with a mobilizing agent, specific for each metal, and pot experiments in which successive growing cycles must confirm the absence of the bioavailable fractions. Phytoextraction can be selected as “green remediation” to minimize the mobile and bioavailable fractions of contaminants, while improving soil quality.

Assisted phytoremediation of a multi-contaminated soil: Investigation on arsenic and lead combined mobilization and removal

The removal of contaminants from an earthy matrix by phytoremediation requires the selection of appropriate plant species and a suitable strategy to be effective. In order to set up an assisted phytoremediation intervention related to a disused industrial site affected by an arsenic and lead complex contamination, an extensive experimental investigation on micro and mesocosm scale has been conducted. Particular attention was given to the choice of plant species: using crop plants (Lupinus albus, Helianthus annuus and Brassica juncea) a series of parallel test campaigns have been realized to investigate different scenarios for the reclamation. With regard to the arsenic contamination, which is certainly the most worrying, the possibility of employing a hyper-accumulator species (Pteris vittata) has also been investigated, highlighting advantages and difficulties associated with such an approach. The application of various mobilizing agents in different concentrations was tested, in order to maximize the extraction efficiency of plants in respect of both contaminants, showing the necessity of a chemically assisted approach to promote their uptake and translocation in the shoots. Phosphate addition appears to produce the desired results, positively affecting As phyto-extraction for both hyper-accumulator and crop plants, while minimizing its toxic effects at the investigated concentrations. With regard to Pb, although tests with EDDS have been encouraging, EDTA should be preferred at present due to lower uncertainties about its effectiveness. The performed tests also improved the addition of mobilizing agents, allowing the simultaneous removal of the two metals despite their great diversity (which in general discourages such approach), with significant saving of time and an obvious improvement of the overall process.

Polycyclic Aromatic Hydrocarbons and Heavy Metal Contaminated Sites: Phytoremediation as a Strategy for Addressing the Complexity of Pollution

Since the industrial revolution, soil has been increasingly subjected to continuous negative pressure, largely determined by human activities, which have dispersed heavy metals and many persistent organic compounds causing severe soil contamination. Among pollutants, heavy metals and polycyclic aromatic hydrocarbons (PAHs), which are ubiquitous and generated also from natural resources, are of particular concern. The simultaneous presence of both kinds of pollutants is very common in brownfield sites, and the clean-up of these areas presents technical difficulties and requires appropriate solutions at a reasonable cost. Remediation technologies have often used invasive processes that greatly damage soil characteristics, causing the deterioration of this important resource. In this chapter, the objectives are to briefly examine the processes involved in heavy metal and PAH reactions in soil in order to evaluate the best possible cost-effective remediation strategies for maintaining a high quality of soil and surrounding environment.

Soil Quality Protection at Heavy Metal-Contaminated Manufactured Gas Plant Sites: Role of Biological Remediation

Soil contamination by metals has been a serious problem since the very beginning of the industrial revolution and nowadays causes widespread environmental concern. Most frequently, the results of soil pollution are due to phenomena of co-contamination (multi-metals or organic and inorganic pollutants) that have negative consequences for soil quality and require appropriate solutions for their reclamation. Remediation technologies have often used invasive processes that impact the characteristics of the soil substantially, causing the degradation of this important resource. The simultaneous presence of different metals is very common in MGP sites, and the remediation of these areas is technically demanding and requires suitable interventions at a reasonable cost. A case study is reported to evaluate both biological and nonbiological approaches used at a former MGP site. Two technologies have been compared in order to evaluate the best possible cost-effective strategies for the maintenance of high soil quality. Results suggest the applicability of biological strategies, in this case phytoremediation, thanks to the efficiency achieved with minimal disturbance of surrounding areas.