Effect of molecular weight of dissolved organic matter on toxicity and bioavailability of copper to lettuce

doi:10.1016/S1001-0742(09)60346-6

Journal of Environmental Sciences

Volume 22, Issue 12, December 2010, Pages 1960-1965

https://doi.org/10.1016/S1001-0742(09)60346-6 Get rights and content

Abstract

To clarify the effects of molecular weight of dissolved organic matter (DOM) on the toxicity and bioavailability of copper (Cu) to plants, DOM extracted from chicken manure was ultra-filtered into four fractions according to their molecular weights by means of sequential-stage ultrafiltration technique. Lettuce seeds were germinated by being exposed to the solutions containing Cu²⁺ with or without different fractions of DOM. The concentration of copper in roots, leaves, sprouts and the length of roots were investigated. The results showed that not all fractions of DOM could improve copper availability or toxicity. The fraction of DOM with larger molecular weight more than 1 kDa had higher complexation stability with Cu²⁺ and caused lower concentration of free Cu²⁺ ion in the solution of copper plus the fraction, resulting in lower availability and toxicity of copper to lettuce, but the fraction with molecular weight less than 1 kDa had the opposite function. Therefore, the molecular weight of 1 kDa may be the division point to determine DOM to increase or decrease copper availability and toxicity.

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Dissolved (<0.45 µm) trace elements (TEs) represent the sum of free ions, simple complexes and colloid-associated forms which have different mobility and bioavailability in soils. The distribution of TEs amongst these chemical forms was directly quantified in soil extracts using asymmetric flow field-flow fractionation (AF4) coupled to ultraviolet–visible absorbance spectrophotometry (UV) and inductively coupled plasma mass spectrometry (ICP-MS). The soil extracts were obtained using single extraction method with water and 0.01 M CaCl₂, respectively. The yields of dissolved TEs extracted from the soils were profoundly impacted by extractants. Using AF4-UV-ICPMS, we show that dissolved species of Ba, Cr, Li, Mn and Mo were primarily present as “truly dissolved”/mainly ionic species (<1 kDa), e.g., hydrated cations, simple complexes or oxyanions, and therefore, likely represented the most bioavailable fraction. The distribution of these TEs amongst dissolved forms was unaffected by the different extractants. However, their dissolved concentrations were profoundly affected. Distributions of Al, As, Co, Cu, Fe, Ni, Pb, Th, Tl, U, V and Zn among the various chemical forms significantly differed with water and CaCl₂ extractants. In water extracts, a greater proportion of these elements was associated with colloidal forms having sizes from 1 kDa to 0.45 µm, i.e., dissolved organic matter (DOM) or/and inorganic colloids. Water not only released greater colloid-complexed concentrations of TEs, like Al, As, Fe, Pb, Th, Tl, U and V, but also liberated greater amounts associated with ionic and small forms. Extractants like water and CaCl₂ are useful for recovering bioavailable TEs from soils. However, the dissolved TEs extracted using water or CaCl₂ represented TE concentrations and forms with different bioavailability. The AF4-UV-ICPMS technique is useful for directly quantifying TEs existing as mainly ionic species and those bound with DOM and inorganic colloids, and thus offers clear insight into their bioavailability in soils. This method also facilitates a better understanding of the effects of extractants on estimating TE bioavailability.
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Dissolved organic matter (DOM) is a kind of substance with complex compositions and wide molecular weight distribution, which can strongly combine with various pollutants. Therefore, the binding characteristics of DOM and heavy metal pollutants can be studied specifically according to the binding characteristics of DOM and pollutants. In this study, DOM in surface water bodies was divided into three levels (MW < 1 kDa, 1 kDa < MW < 5 kDa, MW > 5 kDa) according to different molecular weights (MW). The binding properties were investigated by fluorescence spectrum analysis and complex model. Four components (C1–C4) were identified by PARAFAC. Among them, the contribution rate of protein-like components C1, C2 and C4 to the total fluorescence intensity reached more than 78%, and the log K_a values of low molecular weight components were the highest, which were 3.28, 3.14 and 3.47, respectively, indicating higher binding ability with Cu²⁺.With the decrease of molecular weight, the log K_b value increases, indicating that the complexation is more stable. The humic component C3 in high molecular weight has stronger binding stability with Cu²⁺, but the number of binding sites for C3 is 0.36, while that for C2 is 1.51, indicating that its binding sites and binding ability are relatively low. The results showed that the DOM ligand of Cu²⁺ in surface water showed a certain molecular weight dependence. In addition, different MW DOM lead to different pollution forms. Different properties of DOM ligand combined with Cu²⁺ were studied in order to control the migration, transformation, bioavailability, morphology and stability of heavy metal pollutants, and to provide theoretical support for the practical application management of surface water pollution control.
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Effect of molecular weight of dissolved organic matter on toxicity and bioavailability of copper to lettuce

Abstract

Talanta

Science of the Total Environment

Analytica Chimica Acta

Environment International

Ecotoxicity and Environmental Safety

Analytica Chimica Acta

Bioresource Technology

Thermal stability of some azo-derivatives and their complexes

Journal of Thermal Analysis and Calorimetry

Trace element chemistry in residual treated soil: key concepts and metal bioavailability

Journal of Environment Quality

Heavy metal species, mobility and availability in soils

Journal of Plant Nutrition and Soil Science

Metal-humic complexes and plant micronutrients uptake

Plant and Soil

Micronutrient cation complexes in soil solution: IV. The chemical state of manganese in soil solution

Soil Science Society of America Proceedings