Bioaccumulative and conchological assessment of heavy metal transfer in a soil-plant-snail food chain

Background

Alendronate (ALD) is a member of the bisphosphonate family which is used for the treatment of osteoporosis, bone metastasis, Paget's disease, hypocalcaemia associated with malignancy and other conditions that feature bone fragility. ALD is a non-chromophoric compound so its determination by conventional spectrophotometric methods is not possible. So two derivatization reactions were proposed for determination of ALD through the reaction with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) and 2,4-dinitrofluorobenzene (DNFB) as chromogenic derivatizing reagents.

Results

Three simple and sensitive spectrophotometric methods are described for the determination of ALD. Method I is based on the reaction of ALD with NBD-Cl. Method II involved heat-catalyzed derivatization of ALD with DNFB, while, Method III is based on micellar-catalyzed reaction of the studied drug with DNFB at room temperature. The reactions products were measured at 472, 378 and 374 nm, for methods I, II and III, respectively. Beer's law was obeyed over the concentration ranges of 1.0-20.0, 4.0-40.0 and 1.5-30.0 ??g/mL with lower limits of detection of 0.09, 1.06 and 0.06 ??g/mL for Methods I, II and III, respectively. The proposed methods were applied for quantitation of the studied drug in its pure form with mean percentage recoveries of 100.47 ± 1.12, 100.17 ± 1.21 and 99.23 ± 1.26 for Methods I, II and III, respectively. Moreover the proposed methods were successfully applied for determination of ALD in different tablets. Proposals of the reactions pathways have been postulated.

Conclusion

The proposed spectrophotometric methods provided sensitive, specific and inexpensive analytical procedures for determination of the non-chromophoric drug alendronate either per se or in its tablet dosage forms without interference from common excipients.

Graphical abstract

     

Environmental assessment of heavy metal and natural radioactivity in soil around a coal-fired power plant in China

Concentrations of heavy metals and natural radionuclides in soil around a major coal-fired power plant of Xi’an, China were determined by using XRF and gamma ray spectrometry, respectively. The measured results of heavy metals show that the mean concentrations of Cu, Pb, Zn, Co and Cr in the studied soil samples are higher than their corresponding background values in Shaanxi soil, while the mean concentrations of Mn, Ni and V are close to the corresponding background values. The calculated results of pollution load index of heavy metals indicate that the studied soils presented heavy metal contamination. The concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the studied soil samples range from 27.6 to 48.8, 44.4 to 61.4 and 640.2 to 992.2 Bq kg^?1 with an average of 36.1, 51.1 and 733.9 Bq kg^?1, respectively, which are slightly higher than the average of Shaanxi soil. The air absorbed dose rate and the annual effective dose equivalent received by the local residents due to the natural radionuclides in soil are slightly higher than the mean values of Shaanxi. Coal combustion for energy production has affected the natural radioactivity level and heavy metals (Cu, Pb, Zn, Co and Cr) concentrations of soil around the coal-fired power plant.     

Arsenic compounds in a marine food chain

A three-organism food chain within a rock pool at Rosedale, NSW, Australia, was investigated with respect to arsenic compounds by high performance liquid chromatography – hydraulic high pressure nebulization – inductively coupled plasma mass spectrometry (HPLC-HHPN-ICP-MS). Total arsenic concentration was determined in the seaweed Hormosira banksii (27.2 μg/g dry mass), in the gastropod Austrocochlea constricta (74.4 μg/g dry mass), which consumes the seaweed, and in the gastropod Morula marginalba (233 μg/g dry mass), which eats Austrocochlea constricta. The major arsenic compounds in the seaweed were (2′R)-dimethyl[1-O-(2′,3′-dihydroxypropyl)-5-deoxy-β-d-ribofuranos-5-yl]arsine oxide and an unidentified compound. The herbivorous gastropod Austrocochlea constricta transformed most of the arsenic taken up with the seaweed to arsenobetaine. Traces of arsenite, arsenate, dimethylarsinic acid, arsenocholine, the tetramethylarsonium cation, and several unknown arsenic compounds were detected. Arsenobetaine accounted for 95% of the arsenic in the carnivorous gastropod Morula marginalba. In Morula marginalba the concentration of arsenocholine was higher, and the concentrations of the minor arsenic compounds lower than in the herbivorous gastropod Austrocochlea constricta.     

Iron catalyzed polyethylene chain growth on zinc: a study of the factors delineating chain transfer versus catalyzed chain growth in zinc and related metal alkyl systems

The bis(imino)pyridine iron complex, [[2,6-(MeC=N-2,6-iPr2C6H3)2C5H)N]FeCl2] (1), in combination with MAO and ZnEt2 (> 500 equiv.), is shown to catalyze polyethylene chain growth on zinc. The catalyzed chain growth process is characterized by an exceptionally fast and reversible exchange of the growing polymer chains between the iron and zinc centers. Upon hydrolysis of the resultant ZnR2 product, a Poisson distribution of linear alkanes is obtained; linear alpha-olefins with a Poisson distribution can be generated via a nickel-catalyzed displacement reaction. Other dialkylzinc reagents such as ZnMe2 and ZniPr2 also show catalyzed chain growth; in the case of ZnMe2 a slight broadening of the product distribution is observed. The products obtained from Zn(CH2Ph)2 show evidence for chain transfer but not catalyzed chain growth, whereas ZnPh2 shows no evidence for chain transfer. The Group 13 metal alkyl reagents AlR3 (R = Me, Et, octyl, IBu) and GaR3 (R = Et, nBu) act as highly efficient chain transfer agents, whereas GaMe3 exhibits behavior close to catalyzed chain growth. LinBu, MgnBu2 and BEt3 result in very low activity catalyst systems. SnMe4 and PbEt4 give active catalysts, but with very little chain transfer to Sn or Pb. The remarkably efficient iron catalyzed chain growth reaction for ZnEt2 compared to other metal alkyls can be rationalized on the basis of: (1) relatively low steric hindrance around the zinc center, (2) their monomeric nature in solution, (3) the relatively weak Zn-C bond, and (4) a reasonably close match in Zn-C and Fe-C bond strengths.     

Soil-modified carbon paste electrode: a useful tool in environmental assessment of heavy metal ion binding interactions

Carbon paste electrodes (CPEs) modified with different soils in their native form were prepared to create a soil-like solid phase suitable for application in studies of heavy metal ion uptake and binding interactions. The preparation of CPEs modified with five different soils was examined and their heavy metal ion uptake behavior investigated using a model Cu(II) aqueous solution. Metal ions were accumulated under open circuit conditions and were determined after a medium exchange using differential pulse anodic stripping voltammetry, applying pre-electrolysis at –0.7 V. The soil-modified CPE accumulation behavior, including the linearity of the current response versus Cu(II) concentration, the influence of the pH on the solution, and the uptake kinetics, was thoroughly investigated. The correlation between the soil-modified CPE uptake capability and the standard soil parameters, such as ion exchange capacity, soil pH, organic matter and clay content, were evaluated for all five examined soils. The influence of selected endogenous cations (K(I), Ca(II), Fe(III)) on the transfer of Cu(II) ions from a solution to the simulated soil solid phase was examined and is discussed. Preliminary examinations of the soil-modified CPE uptake behavior with some exogenous heavy metal ions of strong environmental interest (Pb(II), Hg(II), Cd(II) and Ag(I)) are also presented. This work demonstrates some attractive possibilities for the application of a soil-modified CPE in studying soil-heavy metal ion binding interactions, with a further potential use as a new environmental sensor appropriate for fast on-site testing of polluted soils.     

Soil-modified carbon paste electrode: a useful tool in environmental assessment of heavy metal ion binding interactions

Carbon paste electrodes (CPEs) modified with different soils in their native form were prepared to create a soil-like solid phase suitable for application in studies of heavy metal ion uptake and binding interactions. The preparation of CPEs modified with five different soils was examined and their heavy metal ion uptake behavior investigated using a model Cu(II) aqueous solution. Metal ions were accumulated under open circuit conditions and were determined after a medium exchange using differential pulse anodic stripping voltammetry, applying preelectrolysis at -0.7 V. The soil-modified CPE accumulation behavior, including the linearity of the current response versus Cu(II) concentration, the influence of the pH on the solution, and the uptake kinetics, was thoroughly investigated. The correlation between the soil-modified CPE uptake capability and the standard soil parameters, such as ion exchange capacity, soil pH, organic matter and clay content, were evaluated for all five examined soils. The influence of selected endogenous cations (K(I), Ca(II), Fe(III)) on the transfer of Cu(II) ions from a solution to the simulated soil solid phase was examined and is discussed. Preliminary examinations of the soil-modified CPE uptake behavior with some exogenous heavy metal ions of strong environmental interest (Pb(II), Hg(II), Cd(II) and Ag(I)) are also presented. This work demonstrates some attractive possibilities for the application of a soil-modified CPE in studying soil-heavy metal ion binding interactions, with a further potential use as a new environmental sensor appropriate for fist on-site testing of polluted soils.     

Contamination assessment of heavy metal in surface sediments of the Wuding River, northern China

The heavy metal contents and the contamination levels of the surface sediments of the Wuding River, northern China, were investigated. Heavy metal concentration ranged in μg g⁻¹: 50.15–71.91 for Cr, 408.1–442.9 for Mn, 20.11–43.59 for Ni, 17.51–20.1 for Cu, 68.32–89.57 for Zn, 0.2–0.38 for Cd and 15.08–16.14 for Pb in the Wuding River sediments. The enrichment factor (EF) and the geo-accumulation index (Igeo) demonstrated that the sediments of the Wuding River had been polluted by Cd, Cr and Ni, which mainly originated from anthropogenic sources, whereas the sediments had not been polluted by Zn, Pb, Cu and Mn, which were derived from the crust. In addition, the assessment results of EF and Igeo suggested that the sediments of the Wuding River was “moderately” polluted by Cd and “unpolluted to moderately” polluted by Cr and Ni. The elevated urban sewage discharges and agriculture fertilizers usage in river basin are the anthropogenic sources of these heavy metals in river.     

Bioaccumulation of arsenic and its fate in a freshwater food chain

Accumulation, biomethylation and excretion of arsenic by an autotrophic freshwater alga, and the transport and transformation of the arsenic in the freshwater food chain [alga (autotroph)-moina (planktonic grazer) or shrimp (herbivore)-guppy (carnivore)] were investigated. These experimental results lead to the conclusion that total arsenic concentrations in organisms after accumulation from foods decreased one order of magnitude per elevation of the trophic level and biomethylation of the arsenic increased successively with an elevation in the trophic level. Predominant methylated arsenic species in moina and guppy were dimethyl- and trimethyl-arsenic compounds, respectively. Shrimp accumulated dimethyl- and trimethyl-arsenic compounds in nearly equivalent quantities. No or little monomethylarsenic compound was detected either in herbivores or carnivores.     

Rubidium in the food chain

In spite of its abundant occurrence in the earth's crust (310 mg Rb/kg) and its composition of a stable (72.2%) and a radioactive (27.8%) isotope, rubidium (Rb) belongs to the forgotten ultratrace elements. The interest in this ultratrace element grew considerably after Rb deficiency experiments with goats had shown that their growth was depressed, that >80% of them aborted their kids. The geological origin of the site takes significant effect on the Rb content of the flora. Granite and gneiss weathering soils produce the by far Rb-richest plant populations, and drinking water. The water of the gneiss sites contained 18 g Rb/l, that of diluvial sands 3 g/l. Herbivores store most Rb whereas carnivores and omnivores accumulate significantly less Rb. The analysis of 137 foodstuffs and beverages in 15-fold repetition showed that the starch-and sugar-rich cereals, pasta, bread and confectionary are poor in Rb (1 mg/kg dry mater (DM)). Fruit and vegetables accumulate between 5 and >60 mg Rb/kg (asparagus). Boiling drastically reduces the Rb content of vegetables. Animal foodstuffs are relatively poor in Rb. Poultry meat as well as freshwater fish are relatively rich in Rb. Coffee (40 mg/kg DM) and black tea (100 mg Rb/kg DM) store much Rb, 85% of which pass into the beverage.     

Rubidium in the food chain

In spite of its abundant occurrence in the earth's crust (310 mg Rb/kg) and its composition of a stable (72.2%) and a radioactive (27.8%) isotope, rubidium (Rb) belongs to the forgotten ultratrace elements. The interest in this ultratrace element grew considerably after Rb deficiency experiments with goats had shown that their growth was depressed, that >80% of them aborted their kids. The geological origin of the site takes significant effect on the Rb content of the flora. Granite and gneiss weathering soils produce the by far Rb-richest plant populations, and drinking water. The water of the gneiss sites contained 18 μg Rb/l, that of diluvial sands 3 μg/l. Herbivores store most Rb whereas carnivores and omnivores accumulate significantly less Rb. The analysis of 137 foodstuffs and beverages in 15-fold repetition showed that the starch-and sugar-rich cereals, pasta, bread and confectionary are poor in Rb (1 mg/kg dry mater (DM)). Fruit and vegetables accumulate between 5 and >60 mg Rb/kg (asparagus). Boiling drastically reduces the Rb content of vegetables. Animal foodstuffs are relatively poor in Rb. Poultry meat as well as freshwater fish are relatively rich in Rb. Coffee (40 mg/kg DM) and black tea (100 mg Rb/kg DM) store much Rb, 85% of which pass into the beverage.     

Toxic metal species and food regulations--making a healthy choice

As a safeguard for human health, guidelines and regulations stipulating maximum permissible concentrations (MPCs) of metals in foods have been set to limit our dietary exposure to toxic metals. It is now well accepted, however, that the chemical form of the metal must be considered when assessing the possible human health consequences of exposure, and this in turn has led to discussion on the incorporation of speciation data in the setting of MPCs for metals in foods. Some practical aspects and implications of framing food legislation in terms of metal species are presented.     

Cobaloxime as a catalytic chain transfer agent

Cobaloxime, synthesized from Co^II acetate and dimethylglyoxime, was used as a chain transfer agent in the free radical polymerization of methyl methacrylate. It proved to be a catalytic chain transfer agent analogous to work recently reported on cobalt porphyrins. Chain transfer constants ranged from 10³–10⁴ and were chain length dependent. Catalytic behavior was demonstrated by calculating turnover numbers which showed that each cobaloxime molecule participated in many hundreds of chain transfer reactions.     

Shining a light on catalytic chain transfer

The catalytic chain transfer polymerization of styrene is only truly effective when the reaction mixture is exposed to (UV-)light. The apparent chain transfer constant depends inversely on radical concentration and can be increased up to 8000. These results can be explained by combining aspects of both catalytic chain transfer and the formation of cobalt-carbon bonds. For the catalytic chain transfer polymerization of n-butyl acrylate a chain transfer constant of 650 was found. The resulting transfer coefficient has the same order of magnitude as the one for n-butyl methacrylate. This means that the absence of an α-methyl group hardly influences the transfer step itself. Furthermore, the effect of possible impurities on the catalytic chain transfer polymerization of methyl methacrylate is investigated.     

Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents

This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl‐B‐9‐borabicyclononane (Me‐B‐9‐BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]‐catalyzed ethylene (Cp₂ZrCl₂ and rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂ as a catalyst) and styrene (Cp*Ti(OMe)₃ as catalyst) polymerizations. The two trialkylboranes were found—in most cases—able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)‐terminated PE and s‐PS polymers after an oxidative workup process, suggesting the formation of the B‐polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp₂ZrCl₂/MAO, whereas it became less effective when the catalyst changed to rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂. Both TEB and Me‐B‐9‐BBN caused an efficient chain transfer in the Cp₂ZrCl₂/MAO‐catalyzed ethylene polymerization; nevertheless, Me‐B‐9‐BBN failed in vain with rac‐Me₂Si(2‐Me‐4‐Ph)₂ZrCl₂/MAO. In the case of styrene polymerization with Cp*Ti(OMe)₃/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as B? H‐bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane‐terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534–3541, 2010     

Ligand exchange of metal carbonyls by chain mechanisms. Electrochemical kinetics of electron transfer catalysis

The metal carbonyl derivatives LM(CO)_n of manganese, rhenium, molybdenum and tungsten undergo facile ligand substitution by an electrode-mediated process. Phosphine, pyridine and isocyanaide substitutions are shown to be chain reactions by coulometric analysis and by cyclic voltammetry of the metal carbonyl solutions containing the added nucleophiles L. Reversible electrochemical parameters can be obtained for both LM(CO)_n and the substitution product LM(CO)_n. These allow the digital simulation of the cyclic voltammograms by Feldberg's method, which provides a detailed analysis of the kinetics of the electrocatalytic mechanism for ligand substitution. Generally, the radical cation LM(CO)_n⁺ produced initially at the anode undergoes rapid exchange with L to afford the cationic substituted species LM(CO)_n⁺. This step is followed by electron transfer with the reactant LM(CO)_n to yield the substitution product LM(CO)_n and regenerate the radical cation LM(CO)_n⁺, which completes the chain propagation sequence. Multiple repetition of this cycle is indicated by the high current efficiencies which are obtainable. The second order rate constants for the ligand exchange of the 17-electron radical cations LM(CO)_n⁺ with added L are evaluated, and found to be more than 10⁶ times larger than that for the neutral, diamagnetic precursor LM(CO)_n. The radical cations LM(CO)_n⁺ also react readily with phosphine and alkyl isocyanide nucleophiles, leading to a characteristic distortion of the CV waves. Digital simulation of such cyclic voltammograms allows the kinetics of these processes, particularly the redox catalysis in the oxidation of phosphines by LM(CO)_n⁺, to be evaluated quantitatively. The enhanced reactivity of the 17-electron radical cations LM(CO)_n⁺ is discussed in relationship to recent reports of the substitution lability in other 17- and 19-electron metal carbonyls.     

Molecularly imprinted polymers by reversible addition-fragmentation chain transfer precipitation polymerization for preconcentration of atrazine in food matrices

Controlled/living free radical polymerization (CLRP) has been accepted as an effective technique in preparation of polymers because of its inherent advantages over traditional free radical polymerization. In this work, reversible addition-fragmentation chain transfer (RAFT) polymerization, the ideal candidate for CLRP, was applied to prepare atrazine molecularly imprinted polymers (MIPs) by precipitation polymerization. The resultant RAFT-MIPs demonstrated uniform spherical shape with rough surface containing significant amounts of micropores, leading to an improvement in imprinting efficiency compared with that of the MIPs prepared by traditional precipitation polymerization (TR-MIPs). The maximum binding capacities of the RAFT-MIPs and TR-MIPs were 2.89 mg g⁻¹ and 1.53 mg g⁻¹, respectively. The recoveries ranging from 81.5% to 100.9% were achieved by one-step extraction by using RAFT-MIPs for preconcentration and selective separation of atrazine in spiked lettuce and corn samples. These results provided the possibility for the separation and enrichment of atrazine from complicated matrices by RAFT-MIPs.     

Radiological hazard assessment of natural radionuclides and heavy metal pollution in deep mud samples of Van Lake,Turkey

Journal of Radioanalytical and Nuclear Chemistry - In the present investigation, thin layer activation technique has been employed to study the effectiveness of an amine derivative compound, namely...     

A single-site model for divalent transition and heavy metal adsorption over a range of metal concentrations

Metal adsorption data over a range of surface coverages typically are characterized by curvilinear metal adsorption isotherms. These isotherms generally have a slope of 1 at low surface coverage and a shallower slope at higher surface coverages. The curvature of metal adsorption isotherms with increasing surface coverage is frequently interpreted in terms of sequential adsorption onto different types of surface sites, multinuclear surface complexation, or nonideality of metal adsorption. We demonstrate that the curvature of metal adsorption isotherms can also be attributed to changes in surface charge and potential that depend on the predominant type of metal surface complex. A single-site extended triple-layer model is used to reinterpret previously studied metal adsorption isotherms and pH edges for a wide variety of metals (Cd2+, Co2+, Cu2+, Pb2+, and Zn2+) and solids (goethite, hydrous ferric oxide, corundum, and magnetite) in different electrolyte solutions (NaNO3 and NaClO4). Only metal adsorption on ferrihydrite at very low surface coverages is not consistent with the single-site triple-layer model. This discrepancy might be explained if ferrihydrite is in fact not a single phase but a mixture of two or more phases. Metal surface coverages ranging from 10(-4) to 10.2 mmol/m2 on the other minerals can be accounted for with a single-site extended triple-layer model if appropriate metal adsorption reactions are chosen. In addition, several examples suggest that, within the context of the model, surface complexation schemes can be established that describe metal adsorption over both a wide range of surface coverage and a wide range of ionic strength.     

Interaction of a carbonate-containing reagent with heavy metal ions in aqueous solutions

Results of interaction of a carbonate-containing water-treatment waste with ions of copper(II), zinc(II), nickel(II), iron(III), and chromium(III) in aqueous solutions are compared.