Ann Ruttens

Phytoremediation of contaminated soils and groundwater: lessons from the field.

Background, aim, and scopeThe use of plants and associated microorganisms to remove, contain, inactivate, or degrade harmful environmental contaminants (generally termed phytoremediation) and to revitalize contaminated sites is gaining more and more attention. In this review, prerequisites for a successful remediation will be discussed. The performance of phytoremediation as an environmental remediation technology indeed depends on several factors including the extent of soil contamination, the availability and accessibility of contaminants for rhizosphere microorganisms and uptake into roots (bioavailability), and the ability of the plant and its associated microorganisms to intercept, absorb, accumulate, and/or degrade the contaminants. The main aim is to provide an overview of existing field experience in Europe concerning the use of plants and their associated microorganisms whether or not combined with amendments for the revitalization or remediation of contaminated soils and undeep groundwater. Contaminations with trace elements (except radionuclides) and organics will be considered. Because remediation with transgenic organisms is largely untested in the field, this topic is not covered in this review. Brief attention will be paid to the economical aspects, use, and processing of the biomass.Conclusions and perspectivesIt is clear that in spite of a growing public and commercial interest and the success of several pilot studies and field scale applications more fundamental research still is needed to better exploit the metabolic diversity of the plants themselves, but also to better understand the complex interactions between contaminants, soil, plant roots, and microorganisms (bacteria and mycorrhiza) in the rhizosphere. Further, more data are still needed to quantify the underlying economics, as a support for public acceptance and last but not least to convince policy makers and stakeholders (who are not very familiar with such techniques).

Progress in remediation and revegetation of the barren Jales gold mine spoil after in situ treatments

A series of single extractions and short-term plant tests were performed in order to test a variety of inexpensive mineral amendments for the in situ inactivation of trace elements on the fine-grained spoil of the former gold mine of Jales, Portugal. Based on the results of these tests, mesocosms (lysimeters) were constructed and a small-scale semi-field trial was carried out since 1998. The long-term effect of steelshots (SS, iron grit), beringite (B), and municipal compost (C) as spoil amendments was investigated. Vegetation establishment on the treated spoils was successful with Holcus lanatus L. in year 1 and Pinus pinaster Ait. in year 2. Therefore, a detailed monitoring program was implemented for determining the sustainability of trace elements in situ inactivation by C (5%), CB (5% compost combined with 5% beringite), CSS (5% compost combined with 1% steelshots), and CBSS (5% compost combined with 5% beringite and 1% steelshots) treatments (all amendments are expressed by soil dry weight) and of the revegetation. After 3 years, revegetation was excellent in the CSS treatment, and successful for the CBSS. Volunteer plant species became established in treated spoils during year 2. In contrast, the trees planted on the C treated spoil declined from year 2 and some died. In year 3, the trees on the CB treatment started to decline. Arsenic and zinc exposure are suggested to explain the negative effects on pine growth. In agreement with results of single extractions, compost addition in the spoil increased long-term arsenic percolation. Lead leaching was also enhanced. The CBSS and CSS treatments were the most effective for limiting water-soluble As and decreasing long-term metal leaching.

Immobilization of trace metals and arsenic by different soil additives: Evaluation by means of chemical extractions

INRA, Bordeaux Aquitaine Res Ctr, Agron Unit, F-33883 Villenave Dornon, France. Limburgs Univ Ctr, Dept SBG, B-3590 Diepenbeek, Belgium. Univ Kuopio, Dept Ecol & Environm Sci, FIN-70211 Kuopio, Finland. Univ Tras os Montes & Alto Douro, P-5001 Villa Real, Portugal.Boisson, J, INRA, Bordeaux Aquitaine Res Ctr, Agron Unit, BP 81, F-33883 Villenave Dornon, France.

Phytoremediation for heavy metal-contaminated soils combined with bioenergy production

Abstract In June 2007, a project started in Flanders (Belgium) in which we will apply phytoremediation to clean soils that are diffusely polluted with heavy metals. Uptake ranges of heavy metals by rape seed, maize and wheat will be enhanced by increasing the bioavailability of these heavy metals by the addition of biodegradable physico‐chemical agents and by stimulating the heavy‐metal uptake capacity of the microbial community in and around the plant. In addition, the harvested biomass crops will be converted into bioenergy by using different energy‐recovery‐techniques. The energy and heavy metal mass balances will be compared for four different energy‐recovery techniques (anaerobic digestion, incineration, gasification and production of biodiesel). The overall information obtained will result in an economic evaluation of the use of phytoremediation combined with bioenergy production for the remediation of sites which are diffusely polluted with heavy metals. In the present review we will first explain ...

Agronomic Practices for Improving Gentle Remediation of Trace Element-Contaminated Soils

The last few decades have seen the rise of Gentle soil Remediation Options (GRO), which notably include in situ contaminant stabilization (“inactivation”) and plant-based (generally termed “phytoremediation”) options. For trace element (TE)-contaminated sites, GRO aim to either decrease their labile pool and/or total content in the soil, thereby reducing related pollutant linkages. Much research has been dedicated to the screening and selection of TE-tolerant plant species and genotypes for application in GRO. However, the number of field trials demonstrating successful GRO remains well below the number of studies carried out at a greenhouse level. The move from greenhouse to field conditions requires incorporating agronomical knowledge into the remediation process and the ecological restoration of ecosystem services. This review summarizes agronomic practices against their demonstrated or potential positive effect on GRO performance, including plant selection, soil management practices, crop rotation, short rotation coppice, intercropping/row cropping, planting methods and plant densities, harvest and fertilization management, pest and weed control and irrigation management. Potentially negative effects of GRO, e.g., the introduction of potentially invasive species, are also discussed. Lessons learnt from long-term European field case sites are given for aiding the choice of appropriate management practices and plant species.

Chemically Assisted Phytoextraction: A Review of Potential Soil Amendments for Increasing Plant Uptake of Heavy Metals

The contamination of soils by trace metals has been an unfortunate sideeffect of industrialization. Some of these contaminants can interfere with vulnerable enduses of soil, such as agriculture or nature, already at relatively low levels of contamination. Reversely, conventional civil–technical soil-remediation techniques are too expensive to remediate extended areas of moderately contaminated soil. Phytoextraction has been proposed as a more economic complementary approach to deal with this specific niche of soil contamination. However, phytoextraction has been shown to be a slow-working process due to the low amounts of metals that can be annually removed from the soil under normal agronomic conditions. Therefore, extensive research has been conducted on process optimization by means of chemically improving plant availability and the uptake of heavy metals. A wide range of potential amendments has been proposed in the literature, with considerable attention being spent on aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA). However, these compounds have received increasing criticism due to their environmental persistence and associated risks for leaching. This review presents an overview of potential soil amendments that can be employed for enhancing metal uptake by phytoextraction crops, with a distinct focus on more degradable alternatives to persistent compounds such as EDTA.

Short Rotation Coppice Culture of Willows and Poplars as Energy Crops on Metal Contaminated Agricultural Soils

Phytoremediation, more precisely phytoextraction, has been placed forward as an environmental friendly remediation technique, that can gradually reduce increased soil metal concentrations, in particular the bioavailable fractions. The aim of this study was to investigate the possibilities of growing willows and poplars under short rotation coppice (SRC) on an acid, poor, sandy metal contaminated soil, to combine in this way soil remediation by phytoextraction on one hand, and production of biomass for energy purposes on the other. Above ground biomass productivities were low for poplars to moderate for willows, which was not surprising, taking into account the soil conditions that are not very favorable for growth of these trees. Calculated phytoextraction efficiency was much longer for poplars than these for willows. We calculated that for phytoextraction in this particular case it would take at least 36 years to reach the legal threshold values for cadmium, but in combination with production of feedstock for bioenergy processes, this type of land use can offer an alternative income for local farmers. Based on the data of the first growing cycle, for this particular case, SRC of willows should be recommended.

Short-Rotation Coppice of Willow for Phytoremediation of a Metal-Contaminated Agricultural Area: A Sustainability Assessment

Large areas of land contaminated with cadmium (Cd), lead (Pb), and zinc (Zn) are currently in agricultural production in the Campine region in Belgium. Cadmium contents in food and fodder crops frequently exceed legal threshold values, resulting in crop confiscation. This imposes a burden on agriculture and regional policy and, therefore, encourages proper soil management. One way to increase agricultural income and improve soil quality is by growing alternative nonfood crops such as willows in short-rotation coppice (SRC) systems that remediate the soil. This paper compares SRC of willow with rapeseed and energy maize regarding four attributes: metal accumulation capacity, gross agricultural income per hectare, CO2 emission avoidance potential, and agricultural acceptance. Based on multicriteria decision analysis, we conclude that, although SRC of willow has a high potential as an energy and remediating crop, it is unlikely to be implemented on the short term in Flanders unless the economic incentives for the farmers are improved.

Long-term sustainability of metal immobilization by soil amendments: cyclonic ashes versus lime addition.

A soil column leaching experiment was used to gain insight into the long-term metal immobilization capacity of cyclonic ashes (CAH) compared to lime (LIME). Twenty six years of rainfall were simulated. Initially, all amended soils were brought to an equal soil pH. This was done to obtain optimal conditions for the detection of metal immobilization mechanisms different from just a pH effect. During the simulation period, soil pH in all treatments decreased in parallel. However, the evolution of metal mobility and phytoavailability showed a clearly distinct pattern. The strong reduction in metal immobilizing efficiency observed in the lime treatment at the end of the simulation period was much less pronounced, or even absent, in the CAH treatments. Moreover, metal accumulation in plants grown on the CAH amended soil was significantly lower compared to the untreated and the lime treated soil. CAH + SS treatment delivered the strongest reductions in metal mobility and bioavailability.

Soil‐solution speciation of CD as affected by soil characteristics in unpolluted and polluted soils

Total metal content by itself is insufficient as a measure to indicate actual environmental risk. Understanding the mobility of heavy metals in the soil and their speciation in the soil solution is of great importance for accurately assessing environmental risks posed by these metals. In a first explorative study, the effects of general soil characteristics on Cd mobility were evaluated and expressed in the form of empirical formulations. The most important factors influencing mobility of Cd proved to be pH and total soil content. This may indicate that current legislation expressing the requirement for soil sanitation in Flanders (Belgium) as a function of total soil content, organic matter, and clay does not successfully reflect actual risks. Current legal frameworks focusing on total content, therefore, should be amended with criteria that are indicative of metal mobility and availability and are based on physicochemical soil properties. In addition, soil-solution speciation was performed using two independent software packages (Visual Minteq 2.23 and Windermere Humic Aqueous model VI [WHAM VI]). Both programs largely were in agreement in concern to Cd speciation in all 29 soils under study. Depending on soil type, free ion and the organically complexed forms were the most abundant species. Additional inorganic soluble species were sulfates and chlorides. Minor species in solution were in the form of nitrates, hydroxides, and carbonates, the relative importance of which was deemed insignificant in comparison to the four major species.