Final Master's Exam Presentation 071615

Embed Size (px)

Text of Final Master's Exam Presentation 071615

Predicting Metal(loid) Phytoaccumulation/Phytoavailability from Soil Property and Chemical Extraction Method

Zhenfei Liang, M.S.Advisor: Nick BastaEnvironmental Science Graduate ProgramPredicting Metal(loid) Phytoaccumulation from Soil Property and Chemical Extraction

Good afternoon everyone. My name is Zhenfei Liang. I am a graduate student in the Environmental Science Graduate Program and working with my advisor Dr. Basta in the School of Environment and Natural Resources.The topic I will talk about today is Predicting metal(loid) phytoaccumulation from soil property and chemical extraction.1

ContentsINTRODUCTION

TRANSFER FROM SOIL TO PLANT

METAL(LOID) BIOAVAILABILITY

METHODS FOR PREDICTING PHYTOACCUMULATION

SOIL PROPERTY METHOD

CHEMICAL EXTRACTION METHOD

Conclusion

Perspectives

Here are the contents of my presentation.2

IntroductionConcern over metal contaminated soilIntroduction of metals into the food chainLoss of vegetation cover induces through phytotoxicityCycling of metals to surface soil horizons by tolerant plants to induce toxic effects on plants(McLaughlin, 2001)

WHY BOTHER?

First and foremost, lets look at the importance of this study. So why should we care the prediction of phytoaccumulation?As a matter of fact, there has always been concern over metal(loid) contaminanted soils. For instance,The metal(loid) contaminated soils can introduce metals into the food chain.And the vegetation cover grown on the soil may lose as a result of phytotoxicity.Lastly, the cycling of metals to surface soil horizons can induce toxic effects on plants.3

IntroductionPredicting plant uptake in contaminated soil important, with regard to plant nutrition, crop contamination, environmental qualityMeasuring total metal content in soil may not predict phytoaccumulation

Therefore, predicting plant uptake in metal(loid) contaminated soils is important, especially with regard to plant nutrition, crop contamination, and environmental quality.Analysis of total content may provide information on the accumulation of contaminants. However, measuring total content may not predict phytoaccumulation, since not all the forms of contaminants present are available to plants. Actually, there is consensus in literature that the determination of only total content does not provide enough information in contaminant environmental behavior, risk assessment practices and site-specific remediation. 4

Transfer FROM soil TO plantControlling factors: geochemical, climatic, biological, anthropogenicPhytoaccumulation depends upon abundance, speciation and binding characteristics on soil surfaces, governed by sorption, complexation and redox processes(Marschner, 1995; McBride, 1995; Sauv et al., 2000; Kabata-Pendias, 2004; Patra et al., 2004; Moreno et al., 2005; Sterckeman et al., 2005; Rieuwerts et al., 2006; Kalis et al., 2007; Anawar et al., 2008; Rmkens et al., 2009a; Rodrigues et al., 2010)

So why is that? Lets look at the transfer process of metal(loid)s from soil to plant:The transfer of metal(loid)s from soil to plant is an element flow from abiotic to biotic compartments of the biosphere, controlled by geochemical, climatic, biological and anthropogenic factors. Phytoaccumulation of contaminants depends upon their abundance, chemical forms and binding characteristics on soil surfaces, which is governed by soil chemical processes including sorption, complexation and redox. As shown in the right picture, metal uptake and accumulation in plants can be divided into five steps:First: A metal fraction is sorbed at root surface;Second: Bioavailable metal moves across cellular membrane into root cells;Third: A fraction of the metal absorbed into roots is immobilized in the vacuole;Fourth: Intracellular mobile metal crosses cellular membranes into root vascular tissue (xylem);Fifth: Metal is translocated from the root to aerial tissues (stems and leaves).5

Metal(loid) BioavailabilityAvailable fraction fraction of total amount of contaminant present in a specific environmental compartment, within a given time span, either available or can be made available for uptake by organisms from either direct surrounding of the organism or by ingestion of foodBioavailability contaminant absorbed into the organism and may cause an adverse or beneficial effect in the exposed organism

In contrast to total content, the bioavailability concept is more widely used.Before moving forward, lets first look at availability. The available fraction is the fraction of total amount of contaminant present in a specific environmental compartment, within a given time span, either available or can be made available for uptake by organisms from either direct surrounding of the organism or by ingestion of food.While bioavailability is the amount of contaminant absorbed into the organism and cause an adverse or beneficial effect in the exposed organism.6

Metal(loid) Bioavailability

Different researchers try to explain the bioavailability process involved in the soil-plant system from different perspectives. For instance, Dr. McBride at Cornell University, Drs. Wang and Han at Chinese Academy of Sciences, Dr. Kabata-Pendias at the Institute of Soil Science and Plant Cultivation in Pulawy, Poland. Noteworthily, my advisor Dr. Basta in his excellent review paper Trace element chemistry in residual-treated soil: Key concepts and metal bioavailability, assumes that the bioavailability process is a complex process affected by a variety of abiotic and biotic processes, including adsorption onto and desorption from mineral surfaces, precipitation, release through the dissolution of minerals, and interactions with soil, plants, and microbes. 7

Metal(loid) BioavailabilityBioavailability reduces uncertainty in exposure estimates and improves risk assessment from contaminated plantsAccurate prediction of bioavailability improve risk assessment in terrestrial ecosystems(Peijnenburg et al., 1997; Sauv et al., 1998; McLaughlin et al., 2000a; McLaughlin et al., 2000b; Peijnenburg et al., 2000; Weng et al., 2004; Dayton et al., 2006; Menzies et al., 2007; USEPA, 2007; Zhang et al., 2010)

Bioavailability could reduce uncertainty in exposure estimates and improve risk assessment from contaminated plants.And accurate prediction of bioavailability improves risk assessment in terrestrial ecosystems.Here we are talking about the bioavailability of metal(loid)s to plants, also called phytoavailability or phytoaccumulation.8

Methods For Predicting PhytoaccumulationPlant bioassay takes a long timePrediction is hot topic, great progress, but still difficult, no single one reliable method existsMechanistic models & empirical models Soil contaminant measurement methods: Single Chemical Extraction Chemical Speciation (sequential extraction or spectroscopy) Diffusive Gradients in Thin Films (DGT) (Zhang and Davison, 1995) Pore Water (PW) (McBride et al., 1997) Windermere Humic Aqueous Model (WHAM) (Tipping, 1998) Free Ion Activity Model (FIAM) (Sauv et al., 1998) Donnan Membrane Technique (DMT) (Temminghoff et al., 2000) terrestrial Biotic Ligand Model (tBLM) (Di Toro et al., 2001)

HOW TO MEASURE?

So how can we measure phytoaccumulation? Direct plant bioassy usually takes a long time, which is not a desirable way.The prediction of phytoaccumulation has been a hot topic for years in both agricultural and environmental studies. There has been a great progress made. However, prediction is still very difficult and no single one reliable method exists.The current existing prediction methods can be classified into two groups: methanistically based and empirically based. Mechanistic models, describing such rhizosphere-plant interactions, are rather difficult to develop due to the complexity of processes involved both at the soil-root interface as well as those regulating the internal translocation of contaminants to aboveground tissues. As an alternative, empirical models are used to link the chemical availability of contaminants in soil to internal levels in plants correcting for common soil properties.The current existing soil contaminant measurement methods include:Single Chemical ExtractionChemical Speciation (sequential extraction or spectroscopy)Diffusive Gradients in Thin Films (DGT)Pore Water (PW)Windermere Humic Aqueous Model (WHAM)Free Ion Activity Model (FIAM)Donnan Membrane Technique (DMT)terrestrial Biotic Ligand Model (tBLM)9

Soil Property MethodModifying effect of soil property on correlation and multiple-regression techniques routinely used to examine the relationship between and among soil properties and biological endpointsDominant soil properties to affect phytoaccumulation: pH, OC, CEC, clay content, and reactive Fe, Al, Mn oxides(Basta et al., 2005; Fairbrother et al., 2007)

This study will focus on soil property and chemical extraction methods. First, lets look at the soil property method.The modifying effects of soil property on correlation and multiple-regression techniques have been routinely used to examine the relationship between and among soil properties and biological endpoints. Dominant soil chemical/physical properties known to affect the phytoaccumulation of contaminants are soil pH, organic carbon (OC), cation exchange capacity (CEC), clay content, and reactive Fe, Al, and Mn oxides.10

Here is a list of relevant key literatures using soil property method to predict phytoaccumulation/phytoavailability. These are the correlation results, to the left of the equation is plant concentration of contaminants, to the right of the equation are correlated soil properties.11

Continued.12

Soil Property MethodSoil samples: natural source (naturally uncontaminated or contaminated), anth