Binding interactions between suberin monomer components and pesticides

Understanding the role of biomacromolecules and their interactions with pollutants is a key for elucidating the sorption mechanisms and making an accurate assessment of the environmental fate of pollutants. The knowledge of the sorption properties of the different constituents of these biomacromolecules may furnish a significant contribution to this purpose. Suberin is a very abundant biopolymer in higher plants. In this study, suberin monomers isolated from cork were analyzed by thermally-assisted methylation with tetramethylammonium hydroxide (TMAH) in a pyrolysis unit coupled to gas chromatography-mass spectrometry (GC/MS). The isolated monomer mixture was used to study the sorption of three pesticides (isoproturon, methomyl and oxamyl). The modes of pesticide-sorbent interactions were analyzed by means of two modeling calculations, the first one representing only the mixture of suberin monomers used in the sorption study, and the second one including glycerol to the mixture of suberin monomers, as a building block of the suberin molecule. The results indicated that the highest sorption capacity exhibited by the sorbent was for isoproturon (33%) being methomyl and oxamyl sorbed by the main suberin components to a lesser extent (3% and<1%, respectively). In addition to van der Waals interactions with the apolar region of sorbent and isoproturon, modeling calculations evidenced the formation of a hydrogen bond between the isoproturon NH group and a carboxylic oxygen atom of a suberin monomer. In the case of methomyl and oxamyl only weak van der Waals interactions stabilize the pesticide-sorbent adducts. The presence of glycerol in the model provoked significant changes in the interactions with isoproturon and methomyl.

New insights into the interactions between cork chemical components and pesticides. The contribution of π-π interactions, hydrogen bonding and hydrophobic effect

The role of chemical components of cork in the sorption of several pesticides has been investigated. For this purpose raw cork and three cork extracted fractions (i.e. cork free of aliphatic extractives, cork free of all extractives and cork free of all extractives and suberin) were used as sorbent of three ionic pesticides (propazine, 2,4-dichlorophenoxy acetic acid (2,4-D) and alachlor) and five non-ionic pesticides (chlorpyrifos, isoproturon, metamitron, methomyl and oxamyl) with a logKow within the range -0.47 to 4.92. The effect of cations on the ionic pesticides, propazine and 2,4-D sorption was also analyzed. Results indicated that the highest yields were obtained for chlorpyrifos and alachlor sorption onto raw cork (>55%). After removal of aliphatic extractives sorption of all pesticides increased that ranged from 3% for propazine to 31% for alachlor. In contrast, removal of phenolic extractives caused a sorption decrease. Low sorption yields were obtained for hydrophobic pesticides such as metamitron, oxamyl and methomyl (<11%) by using all cork fractions and extremely low when using raw cork (<1%). FTIR analysis was useful to indicate that lignin moieties were the main components involved on the sorption process. Modelling calculations evidenced that π-stacking interactions with the aromatic groups of lignin play a major role in determining the adsorption properties of cork toward aromatic pesticides. Results presented in this paper gain insights into the cork affinities for pesticides and the interactions involved in the sorption process and also enables to envisage sorption affinity of cork for other organic pollutants.

Toxicity of metal-ethylenediaminetetraacetic acid solution as a function of chemical speciation: an approach for toxicity assessment

The influence of complexation by ethylenediaminetetraacetic acid (EDTA) on the toxicity of Cd(II), Cu(II), Cd(II), and Ni(II) was investigated. Result of the Microtox test, which is based on measuring the decrease of light emitted by Vibrio fischeri bacterium when exposed to a toxicant, was used as an indication of toxicity. The effect of pH and EDTA molar ratio that might potentially modify the percentage of chemical species in solution on toxicity was evaluated. In general, results indicate that toxicity decreases when increasing the pH value as well as the EDTA molar ratio. Chemical modeling was used to predict metal speciation and correlation analysis to relate chemical species with the obtained toxicity results. The species that most contribute to toxicity resulted to be MeCl(+) (Me = metal), which is formed as a consequence of the presence of the bioassay medium (2 % NaCl). A model that predicts metal-solution toxicity by using the chemical species, which most contribute to toxicity is proposed as a useful tool for toxicity assessment in waters containing metal ions and EDTA.

A comparison of low-cost biosorbents and commercial sorbents for the removal of copper from aqueous media

Three biosorbents, crab carapace, the macroalgae Fucus vesiculosus and peat were compared with two commercial materials, an activated-carbon and an ion-exchange resin for the removal of copper from aqueous media. Kinetic models of Lagergren first-order, pseudo-second order and intraparticular diffusion were used to model the data. The process for all materials is best represented by the pseudo-second order rate model. Langmuir and Freundlich isotherms were used to describe the sorption equilibrium data. Maximum uptake values were 79.4, 114.9 and 71.4 mg g(-1) for crab carapace, F. vesiculosus and ion-exchange resin, respectively. Langmuir and Freundlich isotherm models could not be fitted to the experimental data for peat and activated-carbon. Ion-exchange was calculated to contribute approximately 75%, 77% and 44% to the total biosorption by crab carapace, F. vesiculosus and peat, respectively. The removal efficiencies of crab carapace and F. vesiculosus were >95% and comparable with those achieved using ion-exchange resin. Results from this study suggest that both crab carapace and F. vesiculosus are efficient and effective biosorbent materials for the removal of copper from aqueous solutions and given that they are also low-cost, may be considered viable alternatives to activated-carbon and ion-exchange resin.

Effect of cadmium(II), chromium(VI), and arsenic(V) on long-term viability- and growth-inhibition assays using Vibrio fischeri marine bacteria

As a complement to previous results obtained using the standard Microtox acute-toxicity test, which is based on measuring the rapid decrease of bioluminescence (5 to 30 minutes of exposure) in Vibrio fischeri bacteria in the presence of toxicants, the long-term effects of Cd(II), Cr(VI), and As(V) were studied on growth rate and viability assays of the same bacteria adapted to longer-lasting cultures, i.e., 48 or 72 hours instead of 5 or 30 minutes. Effects on viability or growth, as studied by establishing dose- and time-response curves, confirmed that these poisonous chemicals were not particularly toxic to these bacteria. Nevertheless, in the case of Cr(VI), the viability-inhibition assay appeared to be more sensitive than the Microtox acute-toxicity test. Interestingly, it was possible to observe a clear hormesis phenomenon, especially for Cd(II), under the conditions of both viability- and growth-inhibition assays.

Stress proteins induced by exposure to sublethal levels of heavy metals in sea bream (Sparus sarba) blood cells

Blood cells freshly collected from silver sea bream (Sparus sarba) were exposed in vitro to different sublethal concentrations of cadmium(II), lead(II) or chromium(VI). HSP70 stress proteins were significantly overexpressed after exposure to metal concentration as low as 0.1 microM. Under our experimental conditions, no overexpression of metallothioneins in blood cells was evidenced. Our results show that fish blood cells may constitute an interesting biological model for experimental and applied toxicology, especially in the case of environmental pollution.

Patterns of metals and arsenic poisoning in Vibrio fischeri bacteria

The Microtox bioassay was used to establish dose-response curves for some toxic elements in aqueous solutions, namely, Zn(II), Pb(II), Cu(II), Hg(II), Ag(I), Co(II), Cd(II), Cr(VI), As(V) and As(III). Experiments were carried out at either pH 6.0 or pH 7.0 to indicate that pH may influence the measured toxicity of some elements due to pH-related changes of their chemical speciation. EC20 values, which represent a measurable threshold of toxicity, were determined for each element and were found to rank as Pb(II)>Ag(I)>Hg(II) approximately Cu(II)>Zn(II)>As(V)>Cd(II) approximately Co(II)>As(III)>Cr(VI). These values were compared to the limit concentrations allowed in industrial wastewater according to the official regulations in Catalonia (Spain). It appears that the Microtox test is sensitive enough for detecting some of the tested elements with respect to official regulations of Catalonia (Spain) dealing with pollution control, with the exception of cadmium, mercury, arsenate, arsenite and chromate.

Analysis of Translocations in Stable Cells and their Implications in Retrospective Biological Dosimetry

The aim of the present study was to evaluate the influence of the exclusion of cells with unstable aberrations in the elaboration of dose-effect curves for translocations and their implications in biological dosimetry of past exposures. To establish dose-effect curves, peripheral blood samples were irradiated with 60Co gamma rays at ten different doses and the yield of translocations analyzed by FISH was considered in all cells and in stable cells (those without dicentrics, acentrics or rings). To discriminate transmissible translocations, the dose- effect curve for total apparently simple translocations in stable cells was chosen as the reference. In stable cells, dose- effect curves for apparently simple translocations without pseudosimple and complex-derived one-way patterns, tAbtBa and total translocations were obtained. None of these curves differed from the reference curve. When all cells were considered, only the curve for total translocations was significantly different from the reference curve. From the results obtained it can be concluded that the use of dose-effect curves for apparently simple translocations in stable cells and in all cells will give similar dose estimates in retrospective biological dosimetry studies. However, the use of dose-effect curves for total translocations in all cells will lead to underestimations of the dose mainly at high doses.

Effect of pH on arsenate and arsenite toxicity to luminescent bacteria (Vibrio fischeri)

Arsenic is an abundant metalloid and a dangerous pollutant when in solution under the arsenate or arsenite forms-As(V) and As(III), respectively. Since its biological effects are expected to depend on the oxidation state and on speciation, effect of pH on either As(V) or As(III) speciation and resulting toxicity was investigated using the Microtox bioassay based on change in light emission by the luminescent bacteria Vibrio fischeri. Within a 5.0-8.0 pH range, EC50 values for As(V) were found to decrease as pH became basic, reflecting an increase in toxicity; whereas in the case of As(III), EC50 values were almost unchanged within a 6.0-8.0 pH range and lowered only at pH 9.0. HAsO42- and H2AsO3-were found to be the most toxic species. A statistical approach based on testing the null hypothesis of additive toxicity revealed an antagonistic effect between the arsenate chemical species. At low concentrations, As(V) was regularly found to be more toxic than As(III), independent of the pH value. Conversely, at high concentrations, the toxicity of both As(III) and As(V) was found to chiefly depend on pH, as a consequence of the strong influence of this parameter on the chemical speciation.

Cellular stress induced in cultured human cells by exposure to sludge extracts from water treatment plants

Sludge extracts from three water treatment plants, corresponding either to the readily water-soluble fraction or to the heavy metal content found in the solid fraction were tested separately or in combination on human cultured cells for their ability to affect the growth rate and/or to trigger a synthesis of the stress-related hsp72 and metallothionein proteins. When given separately, the soluble extract or the metal mixture corresponding to the solid fraction of sludge failed to exert significant effects on cell growth rate and expression level of the stress proteins. However, when given in combination, they were found to exert a strong synergistic effect, as they impaired cell growth and induced a significant overexpression of both hsp72 and metallothionein. This result points out the complex molecular interactions in actual environmental samples when acting on biological structures. It underscores the need for biological tests to complement chemical analyses in environment monitoring.

Comparative evaluation of the potential noxiousness in domestic sludge used in agriculture and in commercial fertilizers

The noxiousness of actual sludge collected in eight water treatment plants around the city of Toulouse, France, was evaluated using a biological test based on the growth rate of cultured human cells. Results were compared with those obtained from 18 fertilizers and culture supports that are commercially available in gardening shops. Surprisingly, it was found that sludge extracts, at low concentrations (below 5 g of dry material/liter), were improving the cell growth rate, which suggests the presence of useful oligoelements. At higher concentrations, a noxious effect, expressed as inhibition of cell growth, was observed. However, this negative effect was of the same order of magnitude as that obtained, under the same experimental conditions, with commercial garden fertilizers which are available and used without any restriction. It is concluded that discarding the sludge, after submission to the biological test, in controlled amount as an agricultural fertilizer should not be hazardous to the environment.

Cellular method for evaluation of noxiousness of inorganic pollutants in industrial wastes: calculation of a safety index for monitoring sludge discharge

This article deals with a biological test of safety applicable to industrial wastes. The test is based on the measurement of the growth rate of cultured human cells exposed to waste samples with different dilutions. As a first approach, 15 chemicals in which discharge concentrations are submitted to sanitary regulations were tested one by one. For Zn, Cu, Ni, Cd, Ag, Co, Mg, sulfates, and fluorides, it was possible to detect concentrations that are below the allowed limit. For Hg, Al, As(V), Cr(III), Fe, and Pb, the concentrations that affect cell growth are higher than the allowed limit. Tests were also performed using actual samples (liquid effluent from a laundry and sludge from waste-water treatment plants). Results indicate that, in contrast to chemical analyses, the current biological test has the advantage of providing an indication of global toxicity, integrating all substances and factors that can be harmful to life processes. From the sludge data and the observed threshold of concentration that does not affect cell growth, a numeric safety index has been calculated which indicates the amount of sludge that could be dispersed, as a fertilizer, per hectare of agricultural soil. Such an index could be conveniently used for designing sewage sludge disposal strategies.

Expression of stress proteins in cultured human cells as a sensitive indicator of metal toxicity

Human cell lines cultured under standardized conditions are found to react after a wide variety of aggressive but sub-lethal treatments by expressing stress proteins, mainly of the HSP68, HSP70 and HSP90 families. The stress reaction is a repair mechanism which rapidly takes place after minute damages caused to cell structures. It was therefore proposed to develop a sensitive biomarker to monitor environmental pollution, especially related to metals, based on the evaluation of stress protein production. This was achieved by computer-assisted densitometric analysis of autoradiographies of electrophoretically separated (35)S-labelled proteins. The results indicate that our biological models consisting in HT29 and HepG2 cell-lines react to low concentrations of cadmium or nickel by a clear-cut increase of stress proteins expression. In most cases, this effect is much more significant and much more rapid to observe than changes in growth curves. It may constitute a reliable index of cell susceptibility to environmental aggressions.

Toxicity of cadmium species on luminescent bacteria

The toxicity of cadmium compounds against luminescent bacteria has been measured using the Microtox(R) toxicity bioassay and has been related to the cadmium species. Since the Microtox(R) test is carried out in NaCl (2%) and cadmium forms stable chloro complexes, NaNO(3) and NaClO(4) have been tested successfully as alternative to sodium chloride to provide the adequate osmotic protection of the bacteria. The influence of medium and ionic strength as well as different exposure times on EC(50) values has been evaluated.