Assessing the fractionation and bioavailability of heavy metals in soil–rice system and the associated health risk

Environmental Geochemistry and Health - This study developed a method to build relationships between chemical fractionations of heavy metals in soils and their accumulations in rice and estimate...     

Speciation of heavy metals in suspended particulates in urban air†

An anayltical procedure based on a sequential extraction scheme is applied to samples of suspended particulates from an urban area of Barcelona. This area presents high levels of air pollution owing to automotive emissions and industrial activity.

The procedure allows the partitioning of particulate trace metals into four fractions: soluble and exchangeable, bound to carbonates and iron‐manganese oxides, bound to organic matter and residual. In this work, the chemical associations of Fe, Pb, Cu, Mn, Cr and Cd have been investigated.

In the analysed samples, only the cadmium is predominantly in the first fraction whereas the other metals are largely associated to carbonates and Fe‐Mn oxides.     

Effects of a lead- and cadmium-resistant fungal strain on the absorption of heavy metals by Vetiveria zizanioides北大核心CSCD

A two-factor randomized complete block experiment was used to explore the remediation by a plant-microorganism combination on soils contaminated by lead (Pb) and cadmium (Cd). Factor A was the amount of fungi, for which four values were considered, namely, 0, 1, 3, and 5 g. Factor B was the level of contamination by lead and cadmium, for which six values were considered, namely, Cd0Pb0, Cd10Pb400, Cd20Pb600, Cd30Pb800, Cd50Pb1200, and Cd80Pb1800 (data in units of mg/ kg). The results showed that the resistant fungi promoted the growth of vetiver (Vetiveria zizanioides). At weights of 1, 3, and 5 g, the resistant fungi increased the biomass of vetiver by 41.9%, 74.9%, and 71.7% respectively. The resistant fungi stimulated the absorption of lead and cadmium by both the aerial and underground parts of vetiver. In the presence of 80 mg/kg of Cd2+ and 1 800 mg/kg of Pb2+, the contents of lead in the aerial parts of vetiver were increased by 120.6%, 265.4%, and 242.9%, while the lead content in the underground parts were increased by 110.3%, 278.2%, and 266.2%, after the addition of 1 g, 3 g, and 5 g of fungi, respectively. The content of cadmium in the aerial parts increased by 113.2%, 238.3%, and 217.3%, while the content of cadmium in the underground parts increased by 103.1%, 298.8%, and 274.4%, after the addition of 1 g, 3 g, and 5 g of fungi, respectively. The addition of fungi strengthened the effect of V. zizanioides to remediate soils contaminated by lead and cadmium, and the remediation after the addition of 3 g of fungi was better than that after treatment with 1 g and 5 g of fungi. The combination of resistant fungi and the heavy metal enrichment plant, vetiver, under different concentrations of lead and cadmium showed that the fungi had a significant effect on the remediation of soils contaminated by lead and cadmium. © 2018 Science Press. All rights reserved.     

A study on the effects of four heavy metals on five species of chironomous larvae present on Mahé Island of Seychelles

A study was conducted on the island of Mahé, Seychelles, on five species of chironomous larvae endemic to the island. The chironomous larvae were exposed to four heavy metals – copper (Cu), cadmium (Cd), mercury (Hg), and zinc (Zn), for a 96-hr period, and the LC₅₀ values were calculated. It was observed that the most sensitive species of chironomous larvae was Gymnometriocnemus mahensis. The least sensitive form of chironomous larvae examined was Paramerina minima. The 96-hr LC₅₀ values obtained for Tanypus complanatus for Cu, Cd, Hg, and Zn were 1.9 (1.73–2.09), 1.35 (1.17–1.57), 0.33 (0.26–0.43), and 28.96 (27.03–31.03) ppm, respectively. Similar results were obtained for other species studied.     

Chromosome damage in individuals exposed to heavy metals†

Testing the mutagenic activity of environmental pollutants has become an important area of modern environmental science and prophylactic medicine. The most suitable method for short‐term mutagenicity testing on man, at present, are chromosome studies on somatic cells of exposed individuals. Mutation types analyzed by such studies are of high practical relevance as indicator system of genetic damage induced in man under in vivo conditions. A rather large series of such studies has been dedicated to the action of heavy metals on individuals contacted with these metals under therapeutic, ecological or occupational conditions or by intoxication. Lead, cadmium, chromium, nickel, mercury, zinc and other metals as well as their compounds have been under study. Analyses of that kind, of course, are hampered by difficulties with the distinct estimation of the actual load as well as unclear conditions of exposition, e.g. simultaneous exposition to different metals.

Results obtained till now arouse some suspicion of a direct or indirect mutagenic activity in man by certain chromium and platinum compounds, arsenic, mercury, and combinations of lead with other heavy metals (cadmium, zinc, arsenic, antimony, etc.). Life style, above all smoking habits, well may act comutagenic. In most cases, however, mutagenic activity of metals and metal compounds apparently is clearly superposed by their toxic activity. In specific cases, chromosome studies also may contribute to discover sources of ecological exposition and to monitor occupational load by heavy metals.     

Alkylation of metals and the activity of metal‐alkyls†

The biochemical basis for resistance to metal ion toxicity is emerging though it is complicated by the different resistance mechanisms. Several strategies for resistance to toxic metal ions have been identified:

1. The development of energy driven efflux pumps which keep toxic element levels low in the interior of the cell. Such mechanisms have been described for Cd(II) and As(V).

2. Oxidation (e.g. AsO^2‐ to AsO₄ ^3‐) or reduction (e.g. Hg²⁺ to Hg⁰) can enzymatically and intracellularly convert a more toxic form of an element to a less toxic form.

3. The biosynthesis of intracellular polymers which serve as traps for the removal of metal ions from solution such as traps have been described for cadmium, calcium, nickel and copper.

4. The binding of metal ions to cell surfaces.

5. The precipitation of insoluble metal complexes (e.g. metal sulfides and metal oxides) at cell surfaces.

6. Biomethylation and transport through cell‐membranes by diffusion controlled processes.

In this short review I shall discuss the implications of biomethylation as a detoxification mechanism for microorganisms as well as for certain higher organisms.     

Voltammetric study on the interaction of the heavy metals Cd(II) and Mn(II) with transfer‐RNA,DNA and other polynucleotides

Small amounts of bivalent cations, usually provided by Mg²⁺, are in the living cell necessary for the biological activity of t‐RNA as these bivalent cations influence the tertiary and secondary structure of this globular polynucleotide.

In context with the discussed possibility of carcinogenic actions of ingested Cd it is of particular interest to check whether there exist specific strong interactions of this toxic heavy metal with nucleic acids.

Therefore, the binding of the toxic heavy metal ion Cd²⁺ and the essential heavy metal ion Mn²⁺ to t‐RNA and for comparison to DNA and the polynucleotides poly‐U, poly‐A and poly‐A‐poly‐U has been studied. Free metal ion concentrations have been determined by differential pulse polararography. Association constants and the number of binding sites have been evaluated by the Scatchard method and alternatively according to a simple electrostatic model of the polyelectrolytes. With the Scatchard method for t‐RNA and all polynucleotides with helical structure two different binding sites of different strength are observed. Those with higher association constants are assigned to the helical parts of t‐RNA. Interaction sites with low association constants correspond to the parts with no ordered tertiary structure, as their exclusive occurrence for poly‐U, having a completely stochastic coil structure, reflects. The values of the association constants for the stronger and weaker association sites are in the respective polynucleotides for both investigated bivalent metal ions of comparable magnitude. This emphasizes that the interaction is essentially of electrostatic nature and depends primarily on the charge of the interacting species.

Thus the specific strong interaction of Cd by the intercalation into the tertiary structure of nucleic acids or by chelation of their base units can be ruled out as one possibility for carcinogenity of Cd.

Moreover, under physiological conditions the high excess of competitive Mg²⁺ will suppress the interaction of Cd based on electrostatic forces.     

The use of the embryo‐culture techniques in the research on the Teratogenic and Mutagenic properties of metals†

Actually, embryos can be cultured from the one‐cell stage up to the blastocyst stage, and their development can be easily monitored at any time: severe effects caused by toxic compounds are traduced by rapid embryonic death, less pronounced effects can be expressed by a lowered cleavage activity or by an arrest of the development from a particular stage. The system can be improved by transferring the embryos at the blastocyst stage in another more complete medium where they can “implant”; and form an inner cell mass with differentiated ectoderm and endoderm. Since last years, it has also become possible to culture postimplantation rodent embryos for short periods involving a number of particularly critical stages of organogenesis, such as the formation and closure of the anterior neuropore. Embryo‐culture also represents a useful system to study cytogenetic effects of chemicals which are often linked to lethal or teratogenic effects. These different possibilities are illustrated by examples of studies already performed with metals, and dealing with their teratogenic and/or cytogenetic effects on pre‐ and postimplantation rodents.     

Large plasmids governing multiple resistances to heavy metals: A genetic approach∗

Gram negative bacteria classified as Alcaligenes eutrophus and carrying large resistance plasmids (generally two) were found in various industrial sites highly contaminated by heavy metals (Zn⁺⁺, Cu⁺⁺, Co⁺⁺,...). These strains were detected by DNA hybridization with a probe made with a 9kb fragment (ccz⁺ fragment) encoding for resistances to Cd⁺⁺, Co⁺⁺ and Zn⁺⁺, and cloned from plasmid pMOL30. This plasmid was isolated from the representative strain A. eutrophus CH34 which harbours the plasmids pMOL30 (240 kb) and pMOL28 (165 kb). Phenotypes related to pMOL28 and pMOL30 include the tolerance to Cd⁺⁺, Co⁺⁺, Cr0₄ ⁼, Cu⁺⁺, Hg⁺⁺, Ni⁺⁺, Pb⁺⁺ and Zn⁺⁺. The described genetic properties of these plasmids refer to some cloned or mapped functions and to some plasmid rearrangements. Plasmid pMOL85 (250 kb) which is related to pMOL30 was also described. Its host (A. eutrophus DS185) was isolated from a zinc desert. pMOL85 can efficiently self transfer in plasmidfree derivatives.     

Evaluation and remediation of organics,nutrients and heavy metals in landfill leachate – a case study in Beijing

Leachate pollution in landfill sites is a major source of environmental concern. This study evaluates organics, nutrients and heavy metals in a landfill site in Beijing, and introduces a method combining coagulation–flocculation with filtration for the advanced treatment of leachate. The results confirm that COD_Cr, TN, NH₄⁺ ? N, TP, Mn and As in leachate treated by an anaeobic–oxic biological method are unable to meet discharge or surface water quality standards. When treated with coagulation–flocculation combined with filtration under optimal conditions (cationic polyacrylamide dosage of 8.0 mg/L; polyaluminium chloride dosage of 350 mg/L; 0.4–0.6 mm ceramsite media in the filtration process), the residual NH₄⁺? N, TN, Mn and As in the leachate meet the maximum allowed values for landfill leachate discharge or surface water quality standards in China; the exceptions are chemical oxygen demand and total phosphorus. Leachate treatment processes could be further strengthened or improved.     

Comments on the Carcinogenicity and Mutagenicity of metals and their compounds†

The carcinogenicity of metals has received extensive study, both epidemiologically and in the laboratory. These have included case reports of occasional human occurrence or clusters of cancer cases as well as extensive epidemiologic studies; in addition, there has been significant laboratory research on the whole animals and in vitro systems. This body of information will be examined selectively.

I will not in this paper attempt a comprehensive review of the mutagenicity and carcinogenicity of metals and their compounds. Rather, I will attempt to set forth some historical perspectives, and to comment on some current gaps and needs.

Other papers in this workshop have presented thorough and very current reviews of most of the topics briefly noted in this presentation and do not require repetition here.

The cancer issue has been studied and reported on far more extensively than that relating to heritable mutations. There has been in recent years increasing interest in the use of short term tests for mutagenicity and cell transformation. These, however, are primarily with respect to their relationship to cancer production rather than to germ cell injury. Interest in cancer from metal compounds goes back a long time; in fact, one of the earliest reports was on the carcinogenicity of arsenic not many decades after the pioneering report of Sir Perceval Pott on cancer in chimney sweeps. Since then cancer has been definitely associated in humans with chromium compounds, nickel, and with less assurance but probably definitely with beryllium and cadmium. The confirmation of these findings in laboratory animals has been uneven. In the case of arsenic, for example, there has been only limited success in the production of cancer in laboratory animals with arsenic.

Many other metals have been found in laboratory studies to produce cancer, although with most of these, evidence of production of cancer in humans is either absent or extremely uncertain.

The extensive body of recent information relating to the testing of metals with a variety of short term tests will be briefly reviewed.     

Bioaccumulation and adverse effects of trace metals and polycyclic aromatic hydrocarbons in the common onion Allium cepa as a model in ecotoxicological bioassays

The common onion Allium cepa can be easily used in ecotoxicological bioassays to evaluate the bioavailability and adverse effects of pollutants and complex mixtures like waste, industrial effluent or coal-mining drainage that contain elevated levels of trace metals and polycyclic aromatic hydrocarbons (PAHs). In this study, onions were exposed for 7 days to individual metals (1?µg?mL^?1), i.e., aluminium, copper, iron and manganese, or PAHs (1.5?ng?mL^?1), i.e., benzo[a]antracene and benzo[a]pirene. Biological effects, measured as growth inhibition of roots and leaves, were integrated with analysis of bioaccumulation in roots, bulbs and leaves. Copper, iron and benzo[a]pirene caused a significant inhibition in root development of newly formed tissues, whereas only slight variations were caused by other chemicals; the number of new root filaments and the length of the leaves did not show significant variations, thus not representing sensitive parameters to evaluate adverse effects of pollutants in A. cepa. Chemicals bioaccumulation was always significant in roots, whereas levels in bulbs and leaves exhibited increased levels only for manganese, and a decrease for aluminium. The overall results confirmed the sensitivity of the bioassays with A. cepa, suggesting their utility for future applications to evaluate the adverse effects of complex mixtures containing metals or PAHs.     

Evaluation and sensitivity of cyanobacteria,Nostoc muscorum and Synechococcus PCC 7942 for heavy metals stress – a step toward biosensor

This study attempted to determine the effects of heavy metals on the photosynthetic blue-green algae for their potential to use as a biosensor. The bioaccumulation of metals and its effects on pigments of Nostoc muscorum and Synechococcus PCC 7942 were assessed. The culture was grown in BG 11 liquid medium supplied with different metals like mercury (Hg), lead (Pb), and cadmium (Cd) and incubated (µM 20 concentrations) for 10 days under optimal conditions. The accumulated amounts of metals were determined by atomic absorption spectroscopy (AAS). The stress effects on photosynthetic pigment chlorophyll a (Chl a) were monitored by laser-induced fluorescence (LIF). Bio-concentration factor (BCF) reached a peak in cells on the 2nd day of incubation followed by a gradual reduction. The highest reduction in the pigment concentrations (Chl a and β carotene) was observed at 20?µM?L^?1 Hg treatment. The results indicate that, cyanobacteria may serve as both potential species to be used as a biosensor and used to clean up heavy metals from contaminated water. These changes were analyzed with the long-term goal of exploiting cyanobacterial cells as biosensors.     

Toxicity,degradation and analysis of the herbicide atrazine

Excessive use of pesticides and herbicides is a major environmental and health concern worldwide. Atrazine, a synthetic triazine herbicide commonly used to control grassy and broadleaf weeds in crops, is a major pollutant of soil and water ecosystems. Atrazine modifies the growth, enzymatic processes and photosynthesis in plants. Atrazine exerts mutagenicity, genotoxicity, defective cell division, erroneous lipid synthesis and hormonal imbalance in aquatic fauna and nontarget animals. It has threatened the sustainability of agricultural soils due to detrimental effects on resident soil microbial communities. The detection of atrazine in soil and reservoir sites is usually made by IR spectroscopy, ELISA, HPLC, UPLC, LC–MS and GC–MS techniques. HPLC/LC–MS and GC–MS techniques are considered the most effective tools, having detection limits up to ppb levels in different matrices. Biodegradation of atrazine by microbial species is increasingly being recognized as an eco-friendly, economically feasible and sustainable bioremediation strategy. This review presents the toxicity, analytical techniques, abiotic degradation and microbial metabolism of atrazine.     

Trace metals in the western Mediterranean Sea∗

Data on Cd, Pb and Cu concentrations in seawater referring to five years of field studies on the western Mediterranean Sea are reported in order to present a space and time integrated situation on the levels of these metals. Surface total metal concentrations present rather homogeneous distributions between the different areas considered, including the Tyrrhenian Sea. The metal concentrations in three areas affected by natural and industrial wastes are also discussed. The vertical distribution of the dissolved Cd, Pb and Cu in the Alboran Sea seems to be rather homogeneous, both vertically and among the stations chosen between the Strait of Gibraltar and the Island of Alboran.     

Spatial distribution and controlling factors of heavy metals contents in paddy soil and crop grains of rice–wheat cropping system along highway in East China

There is consensus concerning the heavy metal pollution from traffic emission on roadside agricultural land. However, few efforts have been paid on examining the contamination characteristics of heavy metals in roadside paddy-upland rotation field, and especially in combination with detailed quantitative analysis. In this study, we investigated the concentrations of heavy metals (Pb, Cd, Cr and Zn) in soil and crop grains of the rice-wheat cropping system along a major highway in East China in 2008 and analyzed the spatial distribution characteristics of heavy metals and their influencing factors with GIS and Classification and Regression Trees (CART). Significantly elevated levels of heavy metals in soil, rice and wheat grains indicated the heavy metals contamination of traffic emission in roadside rice-wheat rotation field. The contamination levels of Cd, Cr and Zn in wheat grain were higher than rice grain, while that of Pb showed an opposite trend. Obvious dissimilarities in the spatial distributions of heavy metals contents were found between in the soil, rice and wheat grains, indicating that the heavy metals contents in the roadside crop grains were not only determined by the concentrations of heavy metals in the paddy soil. Results of CART analysis showed that the spatial variation of the heavy metals contents in crop grains was mainly affected by the soil organic matter or soil pH, followed by the distance from highway and wind direction. Our findings have important implications for the environmental assessment and crop planning for food security along the highway.     

Speciation of particulate trace metals in sediments of Anarbe reservoir∗

Total concentration and chemical forms of heavy metals in samples of sediment from a drinking water reservoir have been analysed. The result of total metal contest shows Fe and Mn concentration increase along the reservoir, from 4.4% in Fe and 0.07% in Mn in the end part to 6.4% Fe and 0.22% Mn at the dam. However, a decrease in organic matter along the reservoir is observed. In order to test the accuracy of the digestion methods used, a standard reference material was also analysed.

Trace metal concentrations, with exception of Cadmium, Pb and Mn, found in fraction 5 are higher than those observed in the others extractions, Fe, Ni, Zn, Cr and Cu content in non‐residual fraction is found mainly in moderately reducible fraction, but the percentage of this fraction in each metal is very different.     

Assessment of the in vivo genotoxicity of a new formulation of Bacillus thuringiensis var israelensis SH-14

Biological control agents have become a useful alternative for the reduction of the use of chemical insecticides. LABIOFAM (Cuba) is developing a new formulation of a biolarvicide that possesses as active biological agent Bacillus thuringiensis var israelensis serotype H14. In order to evaluate the genotoxicity of this new formulation, an in vivo battery test was used: micronucleus (MN), chromosome aberrations (CAs), and sperm morphology (SM) assays. A dose of 6.45?×?10⁸ spores was administered per animal via oral administration. Bone marrow cells were collected 24?h after a two day treatment for the MN assay, and 24?h after a unique treatment for the CA assay, using cyclophosphamide as the positive control. Sperm cells were collected at 5 weeks from the first of five administrations for the SM test, using acrylamide as positive control. Bacillus thuringiensis var israelensis serotype H14 failed to show either a significative increase of micronucleated polychromatic erythrocytes, chromosomal aberrations, or sperm abnormalities. Acute oral administration of a high dose of Bacillus thuringiensis var israelensis serotype H14 did not produce mutagenic effects in bone marrow or sperm cells.     

High mercury bioaccumulation in Pacific salmons from the Sea of Okhotsk and the Bering Sea

Mercury (Hg) accumulation in fishes is a serious threat for food security because mercury induces dieseases. Here we studied the total mercury content in four species of Pacific salmon (pink, chum, sockeye and chinook), caught in the Sea of Okhotsk, the Bering Sea, and the Kuril oceanic waters. Results show that the lowest concentration of mercury was found in the pink salmon, and the highest was 5–6 times higher in sockeye. Hg concentrations exceed several times those in other species of Pacific salmon from the North Pacific