Ecotoxicological effects of heavy metal bioaccumulation in two trophic levels

The pollution generated by the heavy metals (HM) contained in mining wastes (tailings) is a worldwide recognized environmental concern. Due to the persistence, toxicity, bioaccumulation, and biomagnification capacity through the food chains, the release of HM into the environment causes negative effects on human health and the ecosystems. Wigandia urens Kunth (Boraginaceae) is a plant species that naturally establishes and grows in tailings and is consumed by the grasshopper Sphenarium purpurascens Charpentier (Orthoptera: Pyrgomorphidae). HM accumulation in this plant and their subsequent consumption by defoliating insects allow these contaminants to enter the food webs and favor their biomagnification. This study evaluated the effect of HM bioaccumulation in the leaf tissue of W. urens on the characteristics associated with its physical defense against herbivores and the effect of HM exposure on population parameters of grasshoppers through their ontogeny under controlled conditions. The results showed a significant increase in leaf hardness and in the number of simple and glandular trichomes in the leaves of W. urens growing on mine tailing substrate compared to those grown on the control substrate without HM. W. urens individuals growing on mine tailing substrate presented the following heavy metal foliar bioaccumulation pattern: Fe > Zn > Pb > Cu. These metals were also bioaccumulated in individuals of S. purpurascens fed with leaves of the plants exposed to mine tailings, observing differences in their concentration pattern through ontogeny. Grasshoppers fed on leaf tissue containing HM showed higher mortality in the first two developmental instars and lower body biomass throughout their ontogeny in comparison to the individuals fed on leaf tissue of plants growing on the control treatment without HM. In conclusion, W. urens is a species with phytoremediation potential for soils contaminated with HM, since it is naturally established in contaminated sites, has a wide geographic distribution, and bioaccumulates significant amounts of different HM. Furthermore, as was observed in this report, the W. urens physical and chemical defense against herbivores was enhanced by HM exposure, compromising the fitness and development of the herbivore S. purpurascens through its ontogeny and thus interrupting the entry and transfer of heavy metal through the food chain.

Aspergillus luchuensis, an Endophyte Fungus from the Metal Hyperaccumulator Plant Prosopis laevigata, Promotes Its Growth and Increases Metal Translocation

Heavy metal pollution is a worldwide environmental and human health problem. Prosopis laevigata is a hyperaccumulator legume that bioaccumulates Pb, Cu and Zn. With interest in designing phytoremediation strategies for sites contaminated with heavy metals, we isolated and characterized endophytic fungi from the roots of P. laevigata growing on mine tailings located in Morelos, Mexico. Ten endophytic isolates were selected by morphological discrimination and a preliminary minimum inhibitory concentration was determined for zinc, lead and copper. A novel strain of Aspergillus closest to Aspergillus luchuensis was determined to be a metallophile and presented a marked tolerance to high concentrations of Cu, Zn and Pb, so it was further investigated for removal of metals and promotion of plant growth under greenhouse conditions. The control substrate with fungi promoted larger size characters in P. laevigata individuals in comparison with the other treatments, demonstrating that A. luchuensis strain C7 is a growth-promoting agent for P. laevigata individuals. The fungus favors the translocation of metals from roots to leaves in P. laevigata, promoting an increased Cu translocation. This new A. luchuensis strain showed endophytic character and plant growth-promotion activity, high metal tolerance, and an ability to increase copper translocation. We propose it as a novel, effective and sustainable bioremediation strategy for copper-polluted soils.

The bioaccumulation potential of heavy metals by Gliricidia sepium (Fabaceae) in mine tailings

As a result of mining activities, waste of different types is generated. One example is mine tailings that contain potentially toxic elements such as heavy metals that negatively impact the environment and human health. Hence, developing treatments to guarantee its efficient elimination from the environment is necessary. Among these treatments, phytoremediation takes advantage of the potential of different plant species, to remove heavy metals from polluted sites. Gliricidia sepium is a tree that grows up to 15 m high and distributed from southern Mexico to Central America. This study evaluates the heavy metal bioaccumulation capacity in roots and leaves, and the effect of such bioaccumulation on fifteen macro- and one micro-morphological characters of G. sepium growing during 360 days in control, and in mine tailing substrates. G. sepium individuals growing on the exposed substrate registered the following average heavy metal bioaccumulation pattern in the roots: Fe > Pb > Zn > Cu, while in the leaf tissue, the bioaccumulation pattern was Cu > Fe > Pb > Zn. Macro- and micro-morphological characters evaluated in G. sepium decreased in plants exposed to metals. The translocation factor showed that Cu and Pb registered average values greater than 1. In conclusion, G. sepium is a species with potential for the phytoremediation of soils contaminated with Fe, Cu, and Pb, and for phytostabilizing soils polluted with Fe, Pb, Zn, and Cu, along with its ability to establish itself and turn into an abundant plant species in polluted sites, its capacity to bioaccumulate heavy metals in roots and leaves, and its high rate of HM translocation.

Dodonaea viscosa (Sapindaceae) as a phytoremediator for soils contaminated by heavy metals in abandoned mines

Dodonaea viscosa (L.) Jacq. is a plant with a wide distribution that expands throughout almost all Mexican territory and is used in traditional medicine to treat many ailments. This species has been found associated with polluted areas, including mine tailings. Huautla, Morelos, Mexico, was a metallurgic district where mining activities generated 780,000 tons of waste rich in metals, deposited at 500 m from the town without any treatment; this situation has been related to different environmental threats and human health risks. The study was carried out for 18 months on seedlings developed under greenhouse conditions in two treatments: control substrate and mine tailings substrate. The concentration of six metals (Cd, Cr, Cu, Fe, Pb, and Zn) was measured through atomic absorption spectrophotometry in plant tissues, roots, and leaves. Effects of metal exposure were analyzed by size, micro-morphological character changes, and genetic damage in foliar tissue using the comet assay. The results showed significantly higher metal concentrations in the roots and leaves of individuals growing on the mine tailing substrate in comparison to the same plants tissues growing on control substrate. Positive and significant relationships between exposure time and metal concentration in roots and leaves, and between metal bioaccumulation in leaves and genetic damage were registered. Four out of six micro-morphological and size characters evaluated decreased significantly in exposed plants, except for stomatic index and root biomass. The most important metals in terms of the number of significantly affected micro-morphological and size characters showed the next pattern: Fe > Cd = Cr = Pb > Cu > Zn. D. viscosa is an efficient accumulator of Cu, Cd, Fe, Pb, and Zn in its root and leaf tissues. Overall, metal translocation factors in exposed D. viscosa plants showed the following pattern: Zn > Cu > Cd. We conclude that D. viscosa has the potential to phytoextract (Zn, Cu, and Cd), and phytostabilize (Cu, Cd, Fe, Pb, and Zn) metals from polluted soils, and along with its abundance, natural establishment in mine tailings, high levels of metal translocation, and bioconcentration factors, without affecting plant development, it can be an ideal candidate for phytoremediation of metal polluted soils.

Assisted Phytostabilization of Mine-Tailings with Prosopis laevigata (Fabaceae) and Biochar

Phytoremediation is a cost-effective technique to remediate heavy metal (HM) polluted sites. However, the toxic effects of HM can limit plant establishment and development, reducing phytoremediation effectiveness. Therefore, the addition of organic amendments to mine wastes, such as biochar, improves the establishment of plants and reduces the bioavailability of toxic HM and its subsequent absorption by plants. Prosopis laevigata can establish naturally in mine tailings and accumulate different HM; however, these individuals show morphological and genetic damage. In this study, the effect of biochar on HM bioaccumulation in roots and aerial tissues, HM translocation, morphological characters and plant growth were evaluated, after three and six months of exposure. Plants grown on mine tailings with biochar presented significantly higher values for most of the evaluated characters, in respect to plants that grew on mine tailing substrate. Biochar addition reduced the bioaccumulation and translocation of Cu, Pb, and Cd, while it favored the translocation of essential metals such as Fe and Mn. The addition of biochar from agro-industrial residues to mine tailings improves the establishment of plants with potential to phytoextract and phytostabilize metals from polluted soils. Using biochar and heavy metal accumulating plants constitutes an assisted phytostabilization strategy with great potential for HM polluted sites such as Cd and Pb.

Proteomic analysis of Burkholderia zhejiangensis CEIB S4-3 during the methyl parathion degradation process

Methyl parathion is an organophosphorus pesticide widely employed worldwide to control pests in agricultural and domestic environments. However, due to its intensive use, high toxicity, and environmental persistence, methyl parathion is recognized as an important ecosystem and human health threat, causing severe environmental pollution events and numerous human poisoning and deaths each year. Therefore, identifying and characterizing microorganisms capable of fully degrading methyl parathion and its degradation metabolites is a crucial environmental task for the bioremediation of pesticide-polluted sites. Burkholderia zhejiangensis CEIB S4-3 is a bacterial strain isolated from agricultural soils capable of immediately hydrolyzing methyl parathion at a concentration of 50 mg/L and degrading the 100% of the released p-nitrophenol in a 12-hour lapse when cultured in minimal salt medium. In this study, a comparative proteomic analysis was conducted in the presence and absence of methyl parathion to evaluate the biological mechanisms implicated in the methyl parathion biodegradation and resistance by the strain B. zhejiangensis CEIB S4-3. In each treatment, the changes in the protein expression patterns were evaluated at three sampling times, zero, three, and nine hours through the use of two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), and the differentially expressed proteins were identified by mass spectrometry (MALDI-TOF). The proteomic analysis allowed the identification of 72 proteins with differential expression, 35 proteins in the absence of the pesticide, and 37 proteins in the experimental condition in the presence of methyl parathion. The identified proteins are involved in different metabolic processes such as the carbohydrate and amino acids metabolism, carbon metabolism and energy production, fatty acids β-oxidation, and the aromatic compounds catabolism, including enzymes of the both p-nitrophenol degradation pathways (Hydroquinone dioxygenase and Hydroxyquinol 1,2 dioxygenase), as well as the overexpression of proteins implicated in cellular damage defense mechanisms such as the response and protection of the oxidative stress, reactive oxygen species defense, detoxification of xenobiotics, and DNA repair processes. According to these data, B. zhejiangensis CEIB S4-3 overexpress different proteins related to aromatic compounds catabolism and with the p-nitrophenol  degradation pathways, the higher expression levels observed in the two subunits of the enzyme Hydroquinone dioxygenase, suggest a preferential use of the Hydroquinone metabolic pathway in the p-nitrophenol degradation process. Moreover the overexpression of several proteins implicated in the oxidative stress response, xenobiotics detoxification, and DNA damage repair reveals the mechanisms employed by B. zhejiangensis CEIB S4-3 to counteract the adverse effects caused by the methyl parathion and p-nitrophenol exposure.

Glyphosate Pollution Treatment and Microbial Degradation Alternatives, a Review

Glyphosate is a broad-spectrum herbicide extensively used worldwide to eliminate weeds in agricultural areas. Since its market introduction in the 70's, the levels of glyphosate agricultural use have increased, mainly due to the introduction of glyphosate-resistant transgenic crops in the 90's. Glyphosate presence in the environment causes pollution, and recent findings have proposed that glyphosate exposure causes adverse effects in different organisms, including humans. In 2015, glyphosate was classified as a probable carcinogen chemical, and several other human health effects have been documented since. Environmental pollution and human health threats derived from glyphosate intensive use require the development of alternatives for its elimination and proper treatment. Bioremediation has been proposed as a suitable alternative for the treatment of glyphosate-related pollution, and several microorganisms have great potential for the biodegradation of this herbicide. The present review highlights the environmental and human health impacts related to glyphosate pollution, the proposed alternatives for its elimination through physicochemical and biological approaches, and recent studies related to glyphosate biodegradation by bacteria and fungi are also reviewed. Microbial remediation strategies have great potential for glyphosate elimination, however, additional studies are needed to characterize the mechanisms employed by the microorganisms to counteract the adverse effects generated by the glyphosate exposure.

Assessing effects of chronic heavy metal exposure through a multibiomarker approach: the case of Liomys irroratus (Rodentia: Heteromyidae)

Wild animals that inhabit inside mine tailings which contain heavy metals are an excellent study model to conduct ecotoxicological studies that analyze chronic metal exposures at low doses (realistic exposures). This study was conducted in Huautla, Morelos, Mexico, in a mining district where 780,000 tons of wastes were deposited in open air. Liomys irroratus is a small mammal species that lives inside these mine tailings. A multibiomarker approach study was performed to analyze metal bioaccumulation levels (biomarker of exposure) by inductively coupled plasma mass spectrometry, DNA damage levels (biomarker of early effects) through the alkaline comet assay, and population genetic structure and diversity (biomarker of permanent effects), using seven microsatellite loci, in 75 L. irroratus individuals, from two mine tailings and one reference site. Concentrations of aluminum, copper, iron, nickel, lead, and zinc were statistically higher in the liver of exposed individuals. Significant DNA damage levels were registered in the mine tailings groups. Aluminum, lead, and nickel had the highest contribution to the genetic damage levels observed, while aluminum and nickel had the highest contribution to genetic diversity effects. A positive and significant relationship was detected between individual genetic diversity (internal relatedness) and genetic damage (DNA single-strand breaks). Genetic structure of L. irroratus populations revealed that the main source of genetic variation was located within populations. We consider that multibiomarker studies in environmental settings using sentinel species are valuable for environmental risk assessment and ecological responses in chronic exposed populations.

Transcriptomic analysis of Burkholderia cenocepacia CEIB S5-2 during methyl parathion degradation

Methyl parathion (MP) is a highly toxic organophosphorus pesticide associated with water, soil, and air pollution events. The identification and characterization of microorganisms capable of biodegrading pollutants are an important environmental task for bioremediation of pesticide impacted sites. The strain Burkholderia cenocepacia CEIB S5-2 is a bacterium capable of efficiently hydrolyzing MP and biodegrade p-nitrophenol (PNP), the main MP hydrolysis product. Due to the high PNP toxicity over microbial living forms, the reports on bacterial PNP biodegradation are scarce. According to the genomic data, the MP- and PNP-degrading ability observed in B. cenocepacia CEIB S5-2 is related to the presence of the methyl parathion-degrading gene (mpd) and the gene cluster pnpABA'E1E2FDC, which include the genes implicated in the PNP degradation. In this work, the transcriptomic analysis of the strain in the presence of MP revealed the differential expression of 257 genes, including all genes implicated in the PNP degradation, as well as a set of genes related to the sensing of environmental changes, the response to stress, and the degradation of aromatic compounds, such as translational regulators, membrane transporters, efflux pumps, and oxidative stress response genes. These findings suggest that these genes play an important role in the defense against toxic effects derived from the MP and PNP exposure. Therefore, B. cenocepacia CEIB S5-2 has a great potential for application in pesticide bioremediation approaches due to its biodegradation capabilities and the differential expression of genes for resistance to MP and PNP.

Morphological, physiological, and genotoxic effects of heavy metal bioaccumulation in Prosopis laevigata reveal its potential for phytoremediation

Mining industry generates large volumes of waste known as mine tailings, which contain heavy metals (HMs) that generate a risk to environmental health. Thus, remediation of HM pollution requires attention. In this study, HM bioaccumulation, genotoxic damage, and morphological and physiological changes in the tree species Prosopis laevigata were evaluated in order to assess its potential for remediation of mine tailings. P. laevigata plants were established in two treatments (reference substrate and tailing substrate) under greenhouse conditions. Every 2 months, six individuals were selected per treatment for 1 year. From each individual, macromorphological (height, stem diameter, and number of leaves), micromorphological (stomatal coverage and stomatal index), and physiological parameters (chlorophyll content) were evaluated, as well as the concentration of Pb, Cu, Cd, Cr, Fe, and Zn in root and foliar tissue. Genetic damage was assessed by the comet assay in foliar tissue. These parameters were evaluated in adult individuals established in mine tailings. Roots bioaccumulated significantly more HM compared to foliar tissue. However, the bioaccumulation pattern in both tissues was Fe > Pb > Zn > Cu. The plants in tailing substrate reduced significantly the morphological and physiological characters throughout the experiment. Only the bioaccumulation of Pb affected significantly the levels of genetic damage and the number of leaves, while Zn reduced plant height. The percentage of plants that have translocation factor values greater than 1 are Cu (92.9) > Fe (85.7) > Pb (75.0) > Zn (64.3). P. laevigata has potential to phytoremediate environments contaminated with metals, due to its dominance and establishment in abandoned mine tailings, and its ability to bioaccumulate HM unaffecting plant development, as well as their high levels of HM translocation.

Metal brain bioaccumulation and neurobehavioral effects on the wild rodent Liomys irroratus inhabiting mine tailing areas

Ecotoxicological studies are necessary in order to evaluate the effects of environmental exposure of chemicals on wild animals and their ecological consequences. Particularly, neurobehavioral effects of heavy metal elements on wild rodents have been scarcely investigated. In the present study, we analyzed the effect of metal bioaccumulation (Pb, As, Mg, Ni, and Zn) in the brain and in the liver on exploratory activity, learning, memory, and on some dopaminergic markers in the wild rodent Liomys irroratus living inside mine tailings, at Huautla, Morelos, Mexico. We found higher Pb concentration but lower Zn in striatum, nucleus accumbens, midbrain, and hippocampus in exposed animals in comparison to rodents from the reference site. Exposed rodents exhibited anxious behavior evaluated in the open field, while no alterations in learning were found. However, they displayed slight changes in the memory test in comparison to reference group. The neurochemical evaluation showed higher levels of dopamine and 5-hydroxyindolacetic acid in midbrain, while lower levels of metabolites dihydroxyphenyl acetic acid and homovanillic acid in striatum of exposed rodents. In addition, mRNA expression levels of dopaminergic D2 receptors in nucleus accumbens were lower in animals from the mining zone than in animals from the reference zone. This is the first study that shows that chronic environmental exposure to metals results in behavioral and neurochemical alterations in the wild rodent L. irroratus, a fact that may comprise the survival of the individuals resulting in long-term effects at the population level. Finally, we suggest the use of L. irroratus as a sentinel species for environmental biomonitoring of mining sites.

Functional Analysis of a Polluted River Microbiome Reveals a Metabolic Potential for Bioremediation

The objective of this study is to understand the functional and metabolic potential of the microbial communities along the Apatlaco River and highlight activities related to bioremediation and its relationship with the Apatlaco’s pollutants, to enhance future design of more accurate bioremediation processes. Water samples were collected at four sampling sites along the Apatlaco River (S1–S4) and a whole metagenome shotgun sequencing was performed to survey and understand the microbial metabolic functions with potential for bioremediation. A HMMER search was used to detect sequence homologs related to polyethylene terephthalate (PET) and polystyrene biodegradation, along with bacterial metal tolerance in Apatlaco River metagenomes. Our results suggest that pollution is a selective pressure which enriches microorganisms at polluted sites, displaying metabolic capacities to tolerate and transform the contamination. According to KEGG annotation, all sites along the river have bacteria with genes related to xenobiotic biodegradation. In particular, functions such as environmental processing, xenobiotic biodegradation and glycan biosynthesis are over-represented in polluted samples, in comparison to those in the clean water site. This suggests a functional specialization in the communities that inhabit each perturbated point. Our results can contribute to the determination of the partition in a metabolic niche among different Apatlaco River prokaryotic communities, that help to contend with and understand the effect of anthropogenic contamination.

Heavy metal bioaccumulation and morphological changes in Vachellia campechiana (Fabaceae) reveal its potential for phytoextraction of Cr, Cu, and Pb in mine tailings

Vachellia campechiana (Mill Seigler & Ebinger) is widely distributed in Mexico and is a dominant species of tailings in Huautla, in the state of Morelos, Mexico. Mining activities carried out in this region generated about 780 thousand tons of bioavailable heavy metal waste (HMs) that were deposited in the environment without any treatment. This study evaluates the bioaccumulation capacity and morphological changes of V. campechiana growing during 1 year in control or tailing substrates (treatments) under greenhouse conditions. The concentration of six HMs was also measured in roots, leaves, and seeds by atomic absorption spectrophotometry. Five metals showed a similar bioaccumulation pattern in the roots and leaves of V. campechiana grown in both substrates: Pb > Fe > Cr > Cu > Zn. The concentrations of Cr, Cu, and Pb were significantly higher in the roots and leaves of individuals growing on the exposed substrate. The presence of essential metals (Cu, Fe, Zn) was only recorded in the seeds, with similar concentrations in both treatments. Seventeen of 18 morphological characters evaluated in V. campechiana decreased in plants exposed to metals. Pb, Cu, and Fe showed a bioconcentration factor greater than one in roots and leaves. The translocation factor showed the following pattern: Cr > Cu = Pb. In conclusion, V. campechiana is a candidate species to phytoremediate environments contaminated with Pb, Cr, and Cu due to its ability to establish itself and turn into the dominant plant species in polluted sites, its ability to bioaccumulate non-essential metals in roots and leaves, and its high rate of HMs translocation.

Transcriptional analysis reveals the metabolic state of Burkholderia zhejiangensis CEIB S4-3 during methyl parathion degradation

Burkholderia zhejiangensis CEIB S4-3 has the ability to degrade methyl parathion (MP) and its main hydrolysis byproduct p-nitrophenol (PNP). According to genomic data, several genes related with metabolism of MP and PNP were identified in this strain. However, the metabolic state of the strain during the MP degradation has not been evaluated. In the present study, we analyzed gene expression changes during MP hydrolysis and PNP degradation through a transcriptomic approach. The transcriptional analysis revealed differential changes in the expression of genes involved in important cellular processes, such as energy production and conversion, transcription, amino acid transport and metabolism, translation, ribosomal structure and biogenesis, among others. Transcriptomic data also exhibited the overexpression of both PNP-catabolic gene clusters (pnpABA′E1E2FDC and pnpE1E2FDC) present in the strain. We found and validated by quantitative reverse transcription polymerase chain reaction the expression of the methyl parathion degrading gene, as well as the genes responsible for PNP degradation contained in two clusters. This proves the MP degradation pathway by the strain tested in this work. The exposure to PNP activates, in the first instance, the expression of the transcriptional regulators multiple antibiotic resistance regulator and Isocitrate Lyase Regulator (IclR), which are important in the regulation of genes from aromatic compound catabolism, as well as the expression of genes that encode transporters, permeases, efflux pumps, and porins related to the resistance to multidrugs and other xenobiotics. In the presence of the pesticide, 997 differentially expressed genes grouped in 104 metabolic pathways were observed. This report is the first to describe the transcriptomic analysis of a strain of B. zhejiangensis during the biodegradation of PNP.

Species distribution modelling and cpSSR reveal population history of the Neotropical annual herb Tithonia rotundifolia (Asteraceae)

The impacts of the historical geologic and climatic events on the diversity and genetic structure of Neotropical taxa have recently become a subject of study. However, annual plants associated with tropical dry forests remain under-studied. The exploration of additional taxa in contrasting environments will improve the current understanding of responses of the Neotropical biota to these events. Here, we explore the species distribution and geographic structure of the annual herb Tithonia rotundifolia. We sampled 175 individuals from 19 populations of T. rotundifolia. Species distribution modelling and six microsatellite chloroplast loci were used to infer its population history. We identified areas of historical climate suitability and then tested if there is genetic structuring among these areas. Haplotypes showed strong phylogeographic structure. Historical climatic suitability areas were found along the Pacific coast; however, a gap was found at the Isthmus of Tehuantepec (IT). Although Bayesian analysis showed population structuring, amova revealed that the IT is not its main driver. Instead, a subdivision into a higher number of regions had higher F_CT values. Also, populations to the east of the IT showed evidence of recent population expansion and migration in a south-north direction. Pleistocene climate fluctuations partially explain the geographic structure of T. rotundifolia. However, life-history characteristics such as limited seed dispersal and the patchy distribution of suitable habitats explain the high haplotype diversity and population sub-structuring and diversity. Lastly, the absence of geographic structure of some haplotypes may indicate long-distance dispersal, or hybridisation with the closely related T. tubaeformis.

Response of Zea mays to multimetal contaminated soils: a multibiomarker approach

Heavy metals present in mine tailings pollute agroecosystems, put the integrity of the environment at risk and become a major route of exposure to humans. The present study was carried out in Taxco, Guerrero, Mexico, where millions of tons of mine tailings have been deposited. Soils from this region are used for agricultural activities. Maize (Zea mays) was selected as a test plant, because it is one of the most common and important cereal crops in Mexico and worldwide. Thirteen metals were selected and their bioaccumulation in roots, leaves and fruits were measured in plants cultivated in soils contaminated with mine tailings and those cultivated in non-contaminated soils. The effect of metal bioaccumulation on: macro and micromorphology, size, biomass, coloration leaf patterns and on DNA damage levels in different structures were determined. The bioaccumulation pattern was: root > leaf > fruit, being only Mn and Cr bioaccumulated in all three structures and V in the roots and leaves. A significant effect of metal bioaccumulation on 50% of the size and leaf shape and 55% of the biomass characters in Z. mays exposed plants was detected. Regarding micromorphological characters, a significant effect of metal bioaccumulation on 67% of the leaf characters and on 100% of the color basal leaf characters was noted. The effect of metal bioaccumulation on the induction of DNA damage (leaf > fruit > root) was detected employing single cell gel electrophoresis analysis. An approach, in which multi endpoints are used is necessary to estimate the extent of the detrimental effects of metal pollution on agroecosystem integrity contaminated with mine tailings.

Genetic variation in foundation species governs the dynamics of trophic interactions

Various studies have demonstrated that the foundation species genetic diversity can have direct effects that extend beyond the individual or population level, affecting the dependent communities. Additionally, these effects may be indirectly extended to higher trophic levels throughout the entire community. Quercus castanea is an oak species with characteristics of foundation species beyond presenting a wide geographical distribution and being a dominant element of Mexican temperate forests. In this study, we analyzed the influence of population (He) and individual (HL) genetic diversity of Q. castanea on its canopy endophagous insect community and associated parasitoids. Specifically, we studied the composition, richness (S) and density of leaf-mining moths (Lepidoptera: Tischeridae, Citheraniidae), gall-forming wasps (Hymenoptera: Cynipidae), and canopy parasitoids of Q. castanea. We sampled 120 trees belonging to six populations (20/site) through the previously recognized gradient of genetic diversity. In total, 22 endophagous insect species belonging to three orders (Hymenoptera, Lepidoptera, and Diptera) and 20 parasitoid species belonging to 13 families were identified. In general, we observed that the individual genetic diversity of the host plant (HL) has a significant positive effect on the S and density of the canopy endophagous insect communities. In contrast, He has a significant negative effect on the S of endophagous insects. Additionally, indirect effects of HL were observed, affecting the S and density of parasitoid insects. Our results suggest that genetic variation in foundation species can be one of the most important factors governing the dynamics of tritrophic interactions that involve oaks, herbivores, and parasitoids.

Inhaled vanadium pentoxide decrease gamma-tubulin of mouse testes at different exposure times

Vanadium is an important environmental and industrial pollutant whose concentrations have increased in the last decades. Due to its status as reproductive toxicant and a microtubule damaging agent, the present study investigated by immunohistochemistry the effect of the inhalation of vanadium pentoxide on gamma-tubulin within somatic and testicular germ cells. Male mice inhaled vanadium pentoxide (V2O5) (0.02 M) 1 h/twice a week for 12 weeks. Our results demonstrated that vanadium accumulates in the testes starting with the initial inhalation (24 h), and this pattern remained until the last week of treatment. In general, vanadium was capable of significantly decreasing the percentage of gamma-tubulin in all analyzed testicular cells (Sertoli, Leydig and germ cells) starting with the first week of treatment. For all cell types studied, regression analysis revealed a negative and significant relationship between the percentage of immunopositive cells to gamma-tubulin and exposure time, showing a time dependent response in all cases. Our findings suggest that alterations on this protein might imply changes in microtubule-involved function such as cell division, which in the testes might lead to damage in the spermatogenesis, leading probably to infertility.

Metal mixture inhalation (Cd-Pb) and its effects on the bronchiolar epithelium. An ultrastructural approach

The current study explores the effects of the inhalation of lead (Pb), Cd and its mixture (Pb-Cd) in a mice model, analysing metal concentrations in the lung, and the morphological modifications in the bronchiolar epithelium identified by scanning electron microscopy after eight weeks of inhalation. Our results indicate that metal concentrations in lung were higher compared to controls; however, Pb concentrations drastically decrease in the mixture. This reduction was also observed in the inhalation chamber. The main changes observed in the bronchiole were mostly in the mixture. The modifications were mainly given by Cd alone and in the mixture, with a decreased number of nonciliated bronchiolar cells and an increased number of bundles of dividing cells. The additive effect of Pb-Cd is suggested, as the extensive damage observed was more evident when mice were exposed to the mixture, and the results endured more research in the area of inhaled mixtures.

Thrombocytosis induced in mice after subacute and subchronic V2O5 inhalation

Reports about vanadium (V) inhalation toxicity on the hematopoietic system, specifically about coagulation are limited. Therefore, we decided to evaluate the effects of V with a complete blood count and morphologic analysis of platelets on blood smears. CD-1 male mice inhaled V2O5 0.02 M 1 h twice weekly over 12 weeks. Blood samples were obtained by direct heart puncture; Wright stained smears were used for platelet quantification. An increase in platelet count from the third week of exposure was observed, as well as the presence of megaplatelets. Our results demonstrate, for the first time, that V induces thrombocytosis and it might correlate with some thromboembolic diseases. Further analysis is needed to evaluate the functionality of these platelets as well as the cause of its increase.

Penicillium sp. as an organism that degrades endosulfan and reduces its genotoxic effects

Endosulfan is an organochloride and persistent pesticide that has caused concern because of its impact in the environment and its toxicity to and bioaccumulation in living organisms. In this study, we isolated an endosulfan-degrading fungus from the activated sludge from an industrial wastewater treatment plant. Through repetitive enrichment and successive subculture in media containing endosulfan as the sole carbon source, a fungus designated CHE 23 was isolated. Based on a phylogenetic analysis, strain CHE 23 was assigned to the genus Penicillium sp. In a mineral salt medium with 50 mg/l endosulfan as the sole source carbon, CHE 23 removed the added endosulfan in a period of six days. To verify the decrease in endosulfan toxicity due to the activity of the fungus, we performed genotoxicity tests trough the single cell gel electrophoresis assay or comet assay, with Eisenia fetida as the bioindicator species. This organism was exposed to the supernatants of the culture of the fungus and endosulfan. Our results indicated that the genotoxicity of endosulfan was completely reduced due the activity of this fungus. These results suggest that the Penicillium sp. CHE 23 strain can be used to degrade endosulfan residues and/or for water and soil bioremediation processes without causing toxicity problems, which are probably due to the generation of no-toxic metabolites during biodegradation.

Genetic structure and diversity of animal populations exposed to metal pollution

Studying the genetic diversity of wild populations that are affected by pollution provides a basis for estimating the risks of environmental contamination to both wildlife, and indirectly to humans. Such research strives to produce both a better understanding of the underlying mechanisms by which genetic diversity is affected,and the long-term effects of the pollutants involved.In this review, we summarize key aspects of the field of genetic ecotoxicology that encompasses using genetic patterns to examine metal pollutants as environmental stressors of natural animal populations. We address genetic changes that result from xenobiotic exposure versus genetic alterations that result from natural ecological processes. We also describe the relationship between metal exposure and changes in the genetic diversity of chronically exposed populations, and how the affected populations respond to environmental stress. Further, we assess the genetic diversity of animal populations that were exposed to metals, focusing on the literature that has been published since the year 2000.Our review disclosed that the most common metals found in aquatic and terrestrial ecosystems were Cd, Zn, Cu and Pb; however, differences in the occurrence between aquatic (Cd=Zn>Cu>Pb>Hg) and terrestrial (Cu>Cd>Pb>Zn>Ni)environments were observed. Several molecular markers were used to assess genetic diversity in impacted populations, the order of the most common ones of which were SSR's > allozyme > RAPD's > mtDNA sequencing> other molecular markers.Genetic diversity was reduced for nearly all animal populations that were exposed to a single metal, or a mixture of metals in aquatic ecosystems (except in Hyalella azteca, Littorina littorea, Salmo trutta, and Gobio gobio); however, the pattern was less clear when terrestrial ecosystems were analyzed.We propose that future research in the topic area of this paper emphasizes seven key areas of activity that pertain to the methodological design of genetic ecotoxicological studies. Collectively, these points are designed to provide more accurate data and a deeper understanding of the relationship between alterations in genetic diversity of impacted populations and metal exposures. In particular, we believe that the exact nature of all tested chemical pollutants be clearly described, biomarkers be included, sentinel organisms be used, testing be performed at multiple experimental sites, reference populations be sampled in close geographical proximity to where pollution occurs, and genetic structure parameters and high-throughput technology be more actively employed. Furthermore, we propose a new class of biomarkers,termed "biomarkers of permanent effect," which may include measures of genetic variability in impacted populations.

Evidence of population genetic effects in Peromyscus melanophrys chronically exposed to mine tailings in Morelos, Mexico

Effects of environmental chemical pollution can be observed at all levels of biological organization. At the population level, genetic structure and diversity may be affected by exposure to metal contamination. This study was conducted in Huautla, Morelos, Mexico in a mining district where the main contaminants are lead and arsenic. Peromyscus melanophrys is a small mammal species that inhabits Huautla mine tailings and has been considered as a sentinel species. Metal bioaccumulation levels were examined by inductively coupled plasma mass spectrometry and genetic analyses were performed using eight microsatellite loci in 100 P. melanophrys individuals from 3 mine tailings and 2 control sites. The effect of metal bioaccumulation levels on genetic parameters (population and individual genetic diversity, genetic structure) was analyzed. We found a tissue concentration gradient for each metal and for the bioaccumulation index. The highest values of genetic differentiation (Fst and Rst) and the lowest number of migrants per generation (Nm) were registered among the exposed populations. Genetic distance analyses showed that the most polluted population was the most genetically distant among the five populations examined. Moreover, a negative and significant relationship was detected between genetic diversity (expected heterozygosity and internal relatedness) and each metal concentration and for the bioaccumulation index in P. melanophrys. This study highlights that metal stress is a major factor affecting the distribution and genetic diversity levels of P. melanophrys populations living inside mine tailings. We suggest the use of genetic population changes at micro-geographical scales as a population level biomarker.

Comparison of two wild rodent species as sentinels of environmental contamination by mine tailings

BACKGROUND

Contamination with heavy metals is among the most hazardous environmental concerns caused by mining activity. A valuable tool for monitoring these effects is the use of sentinel organisms. Particularly, small mammals living inside mine tailings are an excellent study system because their analysis represents a realistic approach of mixtures and concentrations of metal exposure.

PURPOSE

We analyzed metal tissue concentrations and DNA damage levels for comparison between genders of a sentinel (Peromyscus melanophrys) and a nonsentinel (Baiomys musculus) species. Also, the relationship between DNA damage and the distance from the contamination source was evaluated.

METHODS

This study was conducted in an abandoned mine tailing at Morelos, Mexico. Thirty-six individuals from both species at the exposed and reference sites were sampled. Metal concentrations in bone and liver of both species were analyzed by atomic absorption spectrophotometry, and DNA damage levels were assayed using the alkaline comet assay.

RESULTS

In general, concentrations of zinc, nickel, iron, and manganese were statistically higher in exposed individuals. A significant effect of the organ and the site on all metal tissue concentrations was detected. Significant DNA damage levels were registered in the exposed group, being higher in B. musculus. Females registered higher DNA damage levels than males. A negative relationship between distance from the mine tailing and DNA damage in B. musculus was observed.

CONCLUSIONS

We consider that B. musculus is a suitable species to assess environmental quality, especially for bioaccumulable pollutants--such as metals--and recommend that it may be considered as a sentinel species.

Bromocriptine treatment in a murine parkinson's model: Ultrastructural evaluation after dopaminergic deafferentation

The objective of this article was to identify the effects of bromocriptine on the ultrastructure of the caudate nucleus in rats with a 6-hydroxidopamine (6-OHDA) unilateral lesion of the substantia nigra pars compacta. Eighteen Wistar male rats were stereotactically lesioned with 6-OHDA (n=12), or sham lesioned (n=6). Two days after rotational behavior was tested, and 2 days later, 6 rats were treated with 0.3 mg/Kg bromocriptine orally for a month and 6 rats were kept for the same time without treatment. The neuropile of the sham operated and bromocriptine-treated rats was well preserved contrary to the non-bromocriptine-treated rats. Also, it was found that there was a significant difference in the number of synaptic endings with edema in caudate of bromocriptine-treated rats compared with non-treated rats; however, the size of the synaptic endings were different to those found in the sham lesioned rats. Also, as in the sham lesioned group, the bromocriptines showed more synaptic contacts with dendritic spines contrasting to the non-treated group. The results suggest that bromocriptine possesses antioxidant properties because it decreased the ultrastructural alterations after 6-OHDA lesion.

Spleen and bone marrow megakaryocytes as targets for inhaled vanadium

An increased incidence in ischemic and thromboembolic events in the population of cities with rising air suspended particle pollution has suggested the interaction of some of the components of these particles in the coagulation system. A previous report from our laboratory identified thrombocytosis as a consequence of the subacute and chronic inhalation of vanadium. With this preceding information we decided to evaluate the effects of this element in the spleen and bone marrow in a mouse experimental model. CD-1 male mice inhaled V2O5 0.02 M for one hour twice a week for twelve weeks. The spleen and bone marrow were processed for light microscopy. The increase in quantity and size of megakaryocytes (MKs) in the exposed group in both organs was striking. Also, modifications in the cytoplasm, granule content and nuclear ultrastructure were evident. Our results indicate the influence of vanadium on megakaryopoyesis, an effect which could be the onset of the thrombocytosis previously reported by our group. The modifications in MKs described here suggest that inhaled vanadium could induce megakaryocytic proliferation, which may result in increased production of platelets and increased risk for thromboembolic events.

Ultrastructural findings in murine seminiferous tubules as a consequence of subchronic vanadium pentoxide inhalation

Vanadium (V) is a transition metal emitted to the atmosphere during the combustion of fossil fuels. Its current status as an atmospheric pollutant increases the need for information about the effects that this element might have on the reproductive health of exposed populations. The present study investigated changes in testicular ultrastructure following inhalation exposure of male mice to V (as vanadium pentoxide). Tissue V level was constant during the 12-week time period. We observed necrosis of spermatogonium, spermatocytes and Sertoli cells, as well as pseudo-nuclear inclusion and disruption of cellular junctions. Our findings stressed the importance of the hemato-testicular barrier in supporting the function of Sertoli cells and suggest as a possible target of V, tight junction proteins. Further analysis is needed in order to identify the role that reactive oxidative species (ROS) might have on these cellular junctions, and if a specific protein is the target of its toxic effects. The relevance of this report concerns the impact that metal air pollution could have on male fertility in dense cities with vehicular traffic problems.

Hippocampal cell alterations induced by the inhalation of vanadium pentoxide (V(2)O(5)) promote memory deterioration

Spatial memory may be severely impaired as a consequence of ageing and neurodegenerative diseases, conditions that include neuronal damage. Vanadium (V) is a metalloid widely distributed in the environment and exerts severe toxic effects on a wide variety of biological systems. Reports about V inhalation toxicity on the CNS are limited, thus the purpose of this study is to determine the effects of Vanadium pentoxide (V(2)O(5)) inhalation (0.02M) on the memory and its correlation with the cytology of the hippocampus CA1. Forty eight CD-1 male mice were trained in spatial memory tasks and inhaled 1h twice a week; after each inhalation animals were evaluated and sacrificed from 1 to 4 weeks, perfused and processed for Golgi method and for ultrastructure evaluation. The cytological analysis consisted in counting the number of dendritic spines of 20 pyramidal neurons of hippocampus CA1, as well as ultrastructural characteristics. Results show that V inhalation produces a time dependent loss of dendritic spines, necrotic-like cell death, and notorious alterations of the hippocampus CA1 neuropile, which correlate with spatial memory impairment. Our data suggest that V induces important cellular and functional alterations, fact that deserves special attention since the concentration's trend of this element in the atmosphere is increasing.

DNA damage as an early biomarker of effect in human health

In the last few decades the need for new approaches to assess DNA damage has been increasing due to the implications that different insults on genetic material may have on human health. In this context, the identification of how chemical agents with different mechanisms of action (i.e., antineoplastic drugs) damage DNA provides a good model to investigate some cellular and molecular mechanisms underlying the basis of genetic toxicology. The nasal epithelium is the first barrier with which environmental pollutants interact, and for this reason this epithelium can be useful as a sentinel in order to assess the interactions between the environment and the living organisms. Taking these phenomena into account and using a simple, sensitive and rapid method such as the single cell gel electrophoresis, we could obtain information and an initial approach on the DNA status. This assay in combination with other techniques that provide more information about other molecular parameters could give us a better view of the biological status of the living cell.

Sex differences in bronchiolar epithelium response after the inhalation of lead acetate (Pb)

In order to identify if there were sex differences in lead (Pb) lung concentrations and in bronchiolar response after its inhalation, a mice inhalation model was conducted. Sixty CD-1 adult mice from each sex inhaled separately, lead acetate 0.1 M for 1 h, thrice weekly during 15 days. Animals were evaluated for Pb-lung concentrations by atomic absorption spectrometry and for morphological evaluation by scanning electron microscopy (SEM). Higher Pb-lung concentrations were determined in females, however, more cell damage was found in males, finding that correlated with an increased loss of the nonciliated bronchiolar cells (NCBC) more sloughing and necrosis. Differences in particle clearance, oxidative stress handling, cytokines pathway activation and cytochrome P450 enzymes activity, all influenced by sex hormones, might be a possible explanation for our findings. The relevance of further studies in this field is stressed, as well as its relation to the different development expected for each sex in disease evolution, possible complications and treatment response.

Ependymal epithelium disruption after vanadium pentoxide inhalation. A mice experimental model

The blood-brain barrier (BBB) protects the CNS against chemical insults. Regulation of blood-brain tissue exchange is accomplished by ependymal cells, which possess intercellular tight junctions. Loss of BBB function is an etiologic component of many neurological disorders. Vanadium (V) is a metalloid widely distributed in the environment and exerts potent toxic effects on a wide variety of biological systems. The current study examines the effects of Vanadium pentoxide (V2O5) inhalation in mice ependymal epithelium, through the analysis of the brain metal concentrations and the morphological modifications in the ependymal cells identified by scanning and transmission electron microscopy after 8 weeks of inhalation, in order to obtain a possible explanation about the mechanisms that V uses to enter and alter the CNS. Our results showed that V2O5 concentrations increase from the first week of study, stabilizing its values during the rest of the experiment. The morphological effects included cilia loss, cell sloughing and ependymal cell layer detachment. This damage can allow toxicants to modify the permeability of the epithelium and promote access of inflammatory mediators to the underlying neuronal tissue causing injury and neuronal death. Thus, understanding the mechanisms of BBB disruption would allow planning strategies to protect the brain from toxicants such as metals, which have increased in the atmosphere during the last decades and constitute an important health problem.

Inhalation of cadmium, lead or its mixture Effects on the bronchiolar structure and its relation with metal tissue concentrations

The human population in the industrialized world is constantly exposed to chemical mixtures of pollutants such as metals; information about the consequences of the interactions of these compounds on health is scarce. The current study examines the effects of the inhalation of lead (Pb), cadmium (Cd) and Pb-Cd mixture in mice models analyzing the metal concentrations in lung, and the morphological modifications in the bronchiolar epithelium identified by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) after 4 weeks of inhalation. Our results showed that metal concentrations in lung were higher compared to controls; however, Pb concentrations drastically decrease with the mixture. This reduction was also observed in the inhalation chamber. These data correlate with the morphological alterations observed, which consisted of flattened and decreased number of nonciliated bronchiolar cells (NCBC), bald ciliated cells and bundles of NCBC. These modifications were mainly given by Cd, alone or in combination with Pb. The clusters formed by NCBC cells suggest cell proliferation which probably means that after metal inhalation, the cells enhance their proliferative capacity in order to repopulate the bronchiolar wall.

Pulmonary lymphoid lesions in an experimental model of collapsing glomerulopathy in rats

The characterization of lung damage in an experimental model of collapsing glomerulopathy (CG) in rats is described.

METHODS

12 rats were divided into two groups and injected intravenously (iv) with 1 mg/saline in a final volume of 1 ml/ day in the tail vein for 5 days, with fractionated serum from control and CG subjects. Proteinuria was quantified, and the Glomerular filtration rate was calculated based on creatinine clearance (CC). Rats were sacrificed by perfusion fixation at day 5.

RESULTS

Rats injected with serum from CG patients developed proteinuria (p<0.001). A decrease in CC (0.68+/-0.19) in these rats was also observed. Glomerular tuft retraction and mesangial proliferation was observed in all rats receiving serum from the CG patients. Peribronchiolar infiltrate integrated mainly by lymphocytes, was identified in all CG rats. In some areas this infiltration disrupted the basement membrane and damaged the epithelium. No histopathological abnormalities in the kidney or lungs were found in rats receiving control serum.

CONCLUSION

Patchy pulmonary lymphoid infiltrates were found in the CG model. Up to now there was no information about pulmonary lymphoid infiltration in CG patients. Besides fluid overload due to renal insufficiency or a nephrotic syndrome, other causes of pulmonary involvement in CG patients should be explored.

Nigrostriatal modifications after vanadium inhalation: an immunocytochemical and cytological approach

Vanadium (V) has increased in the air as a component of suspended particles originated from fuel combustion. In this report, a model of inhaled V in mice was implemented to identify the effect that V has in the corpus striatum and substantia nigra, structures with high concentrations of dopamine and scarce antioxidants burden. Mice inhaled 0.02 M V2O5 1 h twice a week and were sacrificed at points from 1 to 8 weeks after inhalation, perfused, and processed for Golgi method and for tyroxine hidroxylase (TH) inmunocytochemistry. Cytological analysis consisted in counting the number of dendritic spines in 20 medium-size spiny neurons and the number of TH immunoreactive neurons in the substatia nigra pars compacta. Dendritic spine density decreased drastically after V exposure; the same was observed with the TH-positive neurons, which decreased in a time-dependent mode. No previous morphological studies about V and nervous system have been reported. The decrease in spine density and in TH-positive neurons might have functional repercussions that should be studied because the trend of this element in the atmosphere is to increase.

Ultrastructural modifications in the mitochondrion of mouse Sertoli cells after inhalation of lead, cadmium or lead-cadmium mixture

CD-1 mice inhaled 0.01 M lead acetate, 0.006 M cadmium chloride or Pb-Cd mixture during 1h twice a week during 4 weeks. Testes were processed for transmission electron microscopic analysis. The percentage of damaged mitochondria was related to exposure time and the type of metal inhaled, noticing more damage when the mixture was administered. A dose-time relationship was found. Cadmium chloride caused the most severe mitochondrial alteration compared to lead acetate, whereas the mixture was more aggressive compared with each metal alone. Our results suggest that the changes in Sertoli cell could lead to a transformation process that may interfere with spermatogenesis.

Genotoxic differences by sex in nasal epithelium and blood leukocytes in subjects residing in a highly polluted area

We describe differences by sex in genotoxic damage found in a population of medical students exposed to a highly oxidative atmosphere, compared with a control group, measured by the single-cell gel electrophoresis assay and histological changes in nasal epithelium smears. Cells were obtained from the nasal epithelium and blood leukocytes. Higher DNA damage in nasal cells and leukocytes was found in males compared to females and control subjects. The percentage of squamous metaplastic changes in the nasal epithelium was also higher in males compared with females and controls. The co-mutation of normal nasal epithelium by squamous cells might modify its protective function in the nose, increasing the risk of damage to the lower respiratory tract. Although, as medical students, males and females were exposed to the same environment and activity patterns, male genotoxicity damage was higher in control and exposed subjects. More research should be done in order to identify direct or indirect sexual hormone intervention.

Nasal cytology and genotoxic damage in nasal epithelium and leukocytes: asthmatics versus nonasthmatics

BACKGROUND

The best example of a chronic inflammatory respiratory disease is asthma, a disease which has an increasing prevalence worldwide. This chronic inflammation is also related to the generation of oxidative stress since the cells involved in the allergic reaction are capable of producing reactive oxygen species (ROS), and this might predispose asthmatics to increased genotoxic damage.

METHODS

A respiratory symptomatology questionnaire was self-applied by asthmatic and nonasthmatic students. A single cell gel electrophoresis assay in two different cell types (nasal epithelial cells and leukocytes) was performed, and the cytology of the nasal smears stained with HE was evaluated.

RESULTS

Both groups reported having a runny nose. Asthmatics had greater DNA damage in the nasal epithelial cells in contrast to nonasthmatics. In leukocytes no statistical significance in DNA damage was identified. Metaplasia was evident in asthmatics that also showed eosinophils and neutrophils as well as goblet cells and mucus at a higher frequency compared with nonasthmatics.

CONCLUSIONS

Nasal symptoms did not correlate with genotoxic damage, since they were reported in both groups. Nasal epithelial cells of asthmatics are more sensitive to genotoxic damage, and chronic inflammatory response. Also the activity of eosinophils might mediate the DNA damage through the generation of ROS.