Etude du cycle biogéochimique du cuivre et du cadmium dans deux écosystèmes forestiers

The biogeochemical cycle of copper and cadmium has been studied in two forested ecosystems for two years. These two sites are: a) a Norway spruce forest (Picea abies) on an acid brown soil (FAQ: Dystric cambisol) and b) a mixed coniferous forest (Picea abies, Pinus cembra, Larix decidua and Abies alba) on a podzol. Both of them are located on low heavy metal polluted sites: the Swiss Plateau (850 m a.s.l.) for the first one and the oriental edge of the Mont-Blanc Massif (1650 m a.s.l.) for the second one. The Cu and Cd stocks in the vegetation and in the soil are evaluated. Heavy metal fluxes through the ecosystems are determined by analysis of concentrations and quantities of rain, throughfalls, stemflows, lysimetric soil solution and litterfall. In addition, the forms of Cu and Cd immobilization in soils are studied by means of sequential extraction, whereas immobilization forms in solution are studied by means of ion exchange chromatography and selective electrode. The results obtained allowed us to draw conclusions concerning the general pollution level in the experimental sites and the annual and/or detailed behaviour of Cu and Cd in the ecosystems. The conclusions are the following: As expected, the sites are not polluted since concentrations and fluxes are low. The chemical composition of solutions is modified during transition through the ecosystem, especially the copper concentrations. The acid brown soil humic layer is more efficient than the podzol humic layer in modifying this composition. There is no significant seasonal variation of concentrations and fluxes. However, the metal diffusion through the ecosystem is almost immediate. The soil plays an essential role in the immobilization of the heavy metals. The organic and organo-mineral layers are particularly active in this process. Exportations out of the ecosystems are limited. They are relatively more important for the podzol than for the acid brown soil and higher for Cd than for Cu. Transfer and stocking forms, and the ways of input to the soil depend on the metal considered: Copper input to the soil is mainly due to litterfall. In the soil, the metal has a preference to be associated with organic matter. In solution, it forms complexes with dissolved organic matter (mainly fulvic acid of MW < 1000 dalton). So, it is strongly retained within the soil and it cannot be easily drained out of the soil profile. At the opposite, cadmium is mostly transported by liquid means (throughfalls). In solution, it is present as free cadmium ions. In the soil, it is less strongly fixed than Cu since Cd is mostly associated with Fe and Mn oxides. For both of the metals, the free ion concentration in solution depends on pH and the saturation rate of organic matter. The latter has a heterogenous and polyfunctional character which explains a similar complexing capacity for all the samples studied. The differences observed in copper and cadmium behaviour can explain the variable diffusion of a polluting Cu and Cd flux through a given ecosystem and to the aquifer. The soil intervenes as a discriminating factor when the two experimental sites are compared.

Analysis of carbon and nitrogen dynamics in riparian soils: Model development

David Andrew Barry, Jordi Batlle-Aguilar, Alessandro Brovelli

The quality of riparian soils and their ability to buffer contaminant releases to aquifers and streams are connected intimately to moisture content and nutrient dynamics, in particular of carbon (C) and nitrogen (N). A multi-compartment model – named the Riparian Soil Model (RSM) – was developed to help investigate the influence and importance of environmental parameters, climatic factors and management practices on soil ecosystem functioning in riparian areas. The model includes numerous improvements compared to many similar tools, in particular regarding the capability to simulate a wide range of temporal scales, from daily to centuries, along with the ability to predict the concentration and vertical distribution of dissolved organic matter (DOM). The ecological importance of DOM has been highlighted on numerous occasions, and it was found that its concentration controls the amount of soil organic matter (SOM) stored in the soil as well as the respiration rate. The moisture content was computed using a detailed water budget approach, assuming that within each time step all the water above field capacity drains to the layer underneath, until it becomes fully saturated. A mass balance approach was also used for nutrient transport, whereas the biogeochemical reaction network was developed as an extension of an existing C and N turnover model. Temperature changes across the soil profile were simulated using an existing analytical solution of the heat transport equation, assuming periodic temperature changes in the topsoil. To verify the consistency of model predictions and illustrate its capabilities, a synthetic but realistic soil profile in a deciduous forest was simulated. Model parameters were taken from the literature, and model predictions were consistent with experimental observations for a similar scenario. Modelling results stressed the importance of environmental conditions on SOM cycling in soils. The mineral and organic C and N stocks fluctuate at different time scales in response to oscillations in climatic conditions and vegetation inputs/uptake. Low frequency fluctuations with a period larger than 10 y were observed also, which were not connected to any single environmental process.

Elsevier2012

Assessing toxic impacts on aquatic ecosystems in life cycle assessment (LCA)

Jérôme Payet

In the last decade, several Life Cycle Assessment (LCA) methods for assessing impact of products on living resources have been developed. Beyond the quantified assessments of impacts on living systems, it also checked the feasibility of the impact assessment on human health and ecosystems quality and helps to identify the limits of such methods. Among the different impact categories, that of toxic substances on ecosystems occupies an important place. The extent of these impacts has been stressed on many occasions and the necessity of preserving ecological areas and biodiversity has become a major issue on an international level. By focusing on aquatic ecosystems, this thesis aims at identifying constraints connected with assessment of the impact of chemical substances on ecosystems in LCA and setting up a method for assessing impacts of toxic substances on aquatic ecosystems which meets the requirements of a comparative approach like Life Cycle Assessment. The overall purpose of the thesis is to propose a comparative method for the Life Cycle Impact Assessment of toxics on aquatic ecosystems. With that aim, the dissertation is going throughout 6 major issues: The feasibility of the comparative impact assessment on ecosystems and the identification of associated constraints. The development of a statistical method for comparing impact on ecosystems; The review of the data availability for calculation of Effect Factors. The choice of the most relevant ecotoxicity measure (ECxs1, NOECs2 and LOECs3) for a comparative purpose. The development of best-estimate extrapolation factors for assessing chronic effects based on acute data. The analysis of the ecological realism of the comparative assessment method. These points are analysed throughout the 7 chapters of the thesis. Chapter 1 aims at introducing the thesis. A general presentation of Life Cycle Assessment is proposed, following by a detailed description of the Life Cycle Impact Assessment on ecosystems. This description covers the state of the art of researches and identifies the development needed. Therefore the scope of the thesis and the main points that must be addressed by this research are presented. Chapter 2 starts with a review of existing methods for Life Cycle Impact Assessment on ecosystems (LCIA), the chapter presents the parametric version of the AMI method (Assessment of the Mean Impact), which has been developed during the PhD for the assessment of impact on aquatic ecosystems. For this purpose, a framework and the main requirements for the development of this method are presented. For a comparative assessment, the Hazardous Concentration of a toxic affecting 50% of the species over their chronic EC50 (Effect Concentration affecting 50% of tested individuals), also called HC50EC50, is selected for the calculation of Effect Factors to be implemented in current LCIA methods. The Confidence Interval on the HC50EC50 is provided, enabling comparison between the impact values obtained as results of a Life Cycle Assessment study. The choice of EC50s is based on review of the main ecotoxicological databases, and analysis of the availability and reliability of test results. Moreover, bearing in mind that mostly acute data are available, while LCA deals mainly with chronic exposure, best-estimate extrapolation factors for the HC50EC50 and the associated uncertainty are provided for inorganics, nonpesticide organics, and pesticide organics. Concerning the method itself, in order to find the best methods for calculation of a toxicity indicator, several statistical estimators, parametric and non-parametric approaches are compared, identifying their properties and respective strengths for a comparative method. The analysis relates to both the reliability of the estimator and its Confidence Interval, especially in terms of statistical robustness and Effect Factor stability. Based on these findings, the AMI method is described in detail, and an example of application comparing two wheat crop scenarios differing by the pesticides used is presented. Chapter 3 presents in detail the four methods currently used for the development of Effect Factors for the Life Cycle Impact Assessment (LCIA) on Ecosystems: the parametric version of AMI (Assessment of the Mean Impact) based on HC50EC50s; the Eco-Indicator based on HC50NOECs; USES-LCA based on both HC5NOECs and the Most sensitive species, and the PNEC (Predicted No- Effect Concentration) based on the Most sensitive species. After presentation of the LCIA framework and its main divergences from Environmental Risk Assessment for chemical regulation, the four methods are detailed and applied for the calculation of Effect Factors for 83 substances, covering inorganics, non-pesticide organics, and pesticide organics. Each method is therefore analysed concerning three key points: applicability in the LCA framework, environmental relevance, and statistical reliability. Particular attention is paid to possible bias and the uncertainty, highlighting the following findings: (1) HC5NOECs are on average 50 times higher than the most sensitive species, and this difference in conservatism introduces a bias in the analyses for the method mixing HC5NOECs and most sensitive species. (2) Effect Factors based on the most sensitive species increase the relative weight of the most toxic chemicals by two orders of magnitude, depending on whether the study is based on US or European ecotoxicity databases. (3) the methods based on HC50EC50s and HC5NOECs are the only ones able to provide a Confidence Interval on the Effect Factor, but the Confidence Interval on the HC5NOECs can be more than 10 orders of magnitude greater than that of the HC50EC50s. (4) compared with the Confidence Interval on the HC50EC50s, the most sensitive species cannot be distinguished from HC50EC50s for chemicals characterised by fewer than 5 species, and the HC5NOECs cannot be distinguished from the HC50EC50s for chemicals characterised by fewer than 8 species. Chapter 4 compares two statistical estimators, aiming at calculate the average toxicity of substances on biological species. The two methods provide an estimation of the HC50EC50 and the associated Confidence Interval. On the one hand, parametric method using the geometric mean and a calculation of the confidence interval with Student is considered. On the other hand, a distribution-free method calculates the HC50EC50 based on the median response of species and the confidence interval based on bootstrap. In order to facilitate the use of the non-parametric method, a table linking the number of species tested and the size of the confidence interval is provided for samples from 5 to 500 species. The comparison is based on actual data concerning 191 substances covering inorganics, non-Pesticide organics, and Pesticide organics. The mean and width of the chronic EC50s samples for all the substances are presented. The Shapiro-Wilk test is performed for the 191 EC50s samples and the assumption of log-normality of the distribution failed in more than 20% of the cases. Two causes of this non Log-normality are identified; (1) the skewness, which is shown to be an important issue for the assessment of the average toxicity of chemicals while (2) the multi-modal distributions, which are not likely to influence considerably the final result. A detailed application of the two methods is done with the comparison of two herbicides, the Sulfosulfuron and the Prosulfuron, where the distribution-free method appears to be more powerful than the parametric for a substance-to-substance comparison. Nevertheless, the distribution-free method requires a minimum of 5 chronic EC50s, that cannot be satisfied in most cases. Chapter 5 aims at illustrating the previous chapter in using the nonparametric version of the AMI method for the comparative assessment of the impacts of metals on aquatic ecosystems. This chapter briefly describes the method, then it focuses on the comparative analysis of 9 metals sometimes tested with different salts and speciations. Two interesting results can be highlighted: (1) the toxicity of metals covers the whole range of toxicity of chemicals; (2) the confidence interval of the HC50EC50 for metals is on average twice as great for metals compared with other chemicals. This increase in the variability of ecotoxicological responses from species is likely to be due to the change in bioavailability of metals associated with a change of test conditions (e.g. pH, or Organic Matter). Chapter 6 reviews and analyses the reliability of existing aquatic toxicity databases which can be used for the calculation of Effect Factors for Life Cycle Impact Assessment (LCIA). For that purpose, the main LCIA methods are presented focusing on their data requirement. It concerns: EDIP4 (based on the PNEC); AMI5 (based on parametric HC50EC50); Eco-Indicator (based on the HC50NOEC); USES-LCA (based on the HC5NOEC). Moreover 6 ecotoxicity databases available in an electronic format are analysed: Aquire; Pesticide Ecotoxicity Database (PED); IUCLID; Acute Toxicity Database (ATD); Fathead Minnow database (FMD); and ECETOC Aquatic Toxicity Database (EAT). The analysis especially focuses on the identification of the substances and organisms, the definition of the tests conditions, and the control procedure of the database. A selection of tests is done, retaining a dataset of 128,864 tests results, acute, sub-chronic and chronic. A description of the data availability on the basis of the selected test is performed, considering the available EC50s (Effect Concentration affecting 50% of the individuals tested), LOECs and NOECs (Lowest or No Observed Effect Concentration). The number of covered substances is also analysed regarding the number of species or phyla considered. On that basis, an estimation of the maximum number of possible Effect Factors is performed. The results highlight the discrepancy between the large number of test results available (128,864), and the relatively restricted number of Effect Factors (betweeen 34 and 4959 depending on the method)) that can be calculated for a comparative purpose like LCIA. Chapter 7 provides a conclusion to the work, answering the points underlined in introduction. Then, the fey features of the AMI method are restated and the perspectives and output of the work are presented. In the last part of the thesis, the AMI HC50EC50 database is presented. It provides acute and chronic HC50EC50 data calculated with the parametric version of AMI (geometric mean of the EC50s and confidence interval based on Student) for 522 susbtances. ------------------------------ 1 ECx: concentration of susbtance that affects 50% of the individuals tested for a given effect. 2 NOEC: No Observable Effect Concentration 3 LOEC: Lowest Observable Effect Concentration 4 EDIP: Environmental Design for Industrial Product 5 AMI : Assessment of the Mean Impact

EPFL2004

Non-GMO approach for the improvement of heavy metal accumulation and extraction of high yielding crop species for efficient phytoextraction of contaminated soil

Erika Nehnevajova

Some plants able to take up heavy metals from contaminated soils offer a possibility to clean up sites contaminated with heavy metals. Plants thus act as a solar driven pump, which can extract and concentrate heavy metals from the environment. Since most of the metal hyperaccumulating wild plants only produce very low biomass and most of plants producing high biomass accumulate only moderate amounts of metals, the current research is mainly focused on the overcoming of this deficiency to optimise metal phytoextraction. The main goal of this EC financed study was aimed at improvement of phytoextraction through improved metal extraction of high yielding oil crops, such as Helianthus annuus L. and Brassica juncea L. producing a high biomass. The use of their oil and biomass for technical purpose (lubricants, biogas and energy) allows to produce an additional value from this in situ decontamination technique and to improve the economical balance of phytoextraction. The enhancement of metal accumulation properties of sunflower and Indian mustard by non-GMO approach and of stimulated metal bioavailability in the soil were the main milestones of the present study. Classical fertilisers were used to lower soil pH, increasing metal availability from the soil and conventional biotechnological approaches were used as an alternative to genetic engineering to enhance both metal accumulation and extraction efficiency of oil crops. The first field experimentation (2002) was mainly focused on the screening of 15 commercial sunflower cultivars growing on a contaminated field in Rafz (Switzerland) to select the cultivar with the naturally highest potential to accumulate and extract metals from contaminated soil, and to assess the effect of classical fertilisers on metal accumulation/extraction of the sunflower cultivars. Highly significant differences of heavy metal accumulation and extraction were found between cultivars. Cadmium extraction varied by a factor of 4, Zn extraction by factor of 3 and Pb extraction by a factor of 14 between the cultivars with the highest and lowest metal extraction treated with the same fertiliser. Sulphate fertilisation significantly enhanced Zn and Pb extraction, whereas ammonium nitrate enhanced Cd extraction by most of the sunflower cultivars. Cultivar Salut showed the highest Cd, Zn and Pb extraction and was chosen for the next mutation breeding. Classical mutation breeding techniques were assumed to be efficient to improve the efficiency of metal accumulation of high yielding crops. Therefore, in vitro breeding was used to improve metal uptake of Indian mustard and chemical mutagenesis using ethyl methanesulphonate (EMS) was additionally applied for sunflowers, hybrid cultivar Salut and genetically homogenous inbred lines. Somaclonal variation of tissue culture was used as a source of genetic variability to increase the potential of metal accumulation in Indian mustard. After the selection of B. juncea callus cultures on a medium spiked with 10-200 μM of Cd or Pb, new somaclonal variants were regenerated from metal tolerant callus cells. A subsequent screening of 30 new B. juncea regenerants growing on a hydroponic medium spiked with toxic metals showed that 7 new somaclones (23 %) possessed a significantly higher shoot metal extraction than the control plants. The best regenerant showed a 6 times higher Cd, a 3 times higher Zn and a 4 times higher Pb extraction in the shoots than the control. Prior to the mutation breeding of sunflower, the effects of toxic metals on the growth, metal accumulation in shoot and root, metal translocation of control sunflower cultivars were investigated on a hydroponic medium spiked with toxic metal. Based on phytotoxic effects of roots and shoots the assessed sunflowers showed the following tolerance towards toxic metals: Pb >> Zn > Cd. The effect of the chemical mutagenesis on the efficiency of metal accumulation and extraction was first assessed on a hydroponic system, spiked with Cd, Zn and Pb. The results show that the EMS mutagenesis affected metal uptake, root and shoot metal accumulation and root to shoot metal translocation in mutant variants. We obtained M1 sunflower mutants with an enhanced metal accumulation, mutants with a lower metal accumulation and mutants without changed metal accumulation characteristics compared to the control plants. The next two field experiments in 2003 and 2004 were focused on the screening of 500 sunflower mutants of M1 generation and 300 sunflower mutants of M2 generation on the metal contaminated Rafz site to assess the effect of mutagenesis on yield, metal accumulation and extraction. The M1 sunflower mutants showed a 2-3 times higher Cd, Zn and Pb concentration in shoots, but a considerably reduced growth, as compared to control cultivars due to the phytotoxic effect of the mutagen. The sunflower mutants of M2 generation also showed a 2-3 times higher metal shoot accumulation than the control plants, and even more the metal extraction of the best M2 sunflower mutants "Giant Mutant 14/190/04" was increased 7.5 times for Cd, 8.2 times for Zn and 9.2 times for Pb extraction compared to the control plants. Theoretical calculations of phytoextraction potential of sunflower point out that the best sunflower mutant can produce up to 26 t dry matter yield per ha and remove 13.3 kg Zn per ha and year at the metal contaminated site in Rafz (Switzerland), that is a gain of factor 9 compared to Zn removal of control sunflowers. From a practical point of view this improvement looks very promising for boosting future phytoextraction research.

EPFL2005