Teodor Stoichev

Extraction and preconcentration techniques for chromatographic determination of chlorophenols in environmental and food samples

Methods for chlorophenols (CPs) determination (with low limits of detection) that can be applied to real environmental samples (waters, sediments, soils, biological tissues) and food are reviewed. Special emphasis is given to sampling, storage conditions and the application of preconcentration techniques for the determination of CPs using chromatographic methods. Solid phase extraction, solid phase microextraction, stir bar sorptive extraction, liquid phase microextraction, dispersive liquid-liquid microextraction, liquid-liquid-liquid microextraction and purge and trap methods are considered. Methods for microwave and ultrasonic extraction of CPs from solid matrices are also focused.

Speciation Analysis of Mercury in Aquatic Environment

Abstract This review considers methods for mercury speciation with low limits of detection that can be applied to real aquatic environmental samples (waters, sediments, biological tissues). Special attention is given to the necessity of clean sampling procedures and the proper storage of the samples. In this review, different extraction techniques for sediments and biological tissues are considered. The performance of different separation techniques, like liquid chromatography and off‐line and on‐line gas chromatography, are compared for their environmental applications.

Interferences during mercury speciation determination by volatilization, cryofocusing, gas chromatography and atomic absorption spectroscopy: comparative study between hydride generation and ethylation techniques

The interfering effects of sodium chloride and a mixture of metal ions on the speciation determination of mercury by derivatization (hydride generation or ethylation), preconcentration by cryotrapping, gas chromatographic separation and detection by quartz furnace atomic absorption spectroscopy were investigated. The potential of the masking agent EDTA to overcome the interference was also studied. The experiments were arranged according to a 2n+1 factorial experimental design, so the possibility of synergistic effects among the variables considered was also taken into account. NaCl interferes in the determination of methylmercury (MeHg+) by ethylation, but causes fewer problems in the case of inorganic mercury (Hg2+) or if the analysis is carried out by hydride generation. The presence of metal ions strongly decreases the sensitivity in the determination of both compounds by hydride generation, but has no effect if ethylation is used as the derivatization technique. EDTA only partially eliminates the interfering effect of metals in the determination of MeHg+ by hydride generation. It also avoids decomposition of MeHg+ to Hg0 , promoted by NaCl, after derivatization of the compounds by hydride generation. The results obtained are discussed in terms of a comparison between the two derivatization techniques used, i.e., hydride generation and ethylation. Potential chemical pathways and reaction mechanisms for the observed interferences are also given.

Effects of minocycline and its degradation products on the growth of Microcystis aeruginosa.

This work aimed to investigate the influence of Microcystis aeruginosa on the rate of minocycline (MNC) removal (abiotic degradation, physical binding or chemical transformation by cells) and the toxicity of MNC and its degradation products to the cyanobacterium. Most of the work was carried out in culture media in the presence or in the absence of M. aeruginosa. The rate of the MNC abiotic degradation in culture media strongly decreased with the increase of the MNC initial concentration. The exudates did not influence the rate of MNC degradation in the media. For concentrations ≥0.48 μM, the rate of the MNC removal from the media was faster in the presence of M. aeruginosa. Biotic MNC removal occurs by both physical binding by the cells (10%) and chemical transformations. EC(50) and EC(20) for MNC on the growth of M. aeruginosa were 0.92 and 0.13 μM, respectively. Interestingly, MNC degradation products might promote M. aeruginosa growth.

Fate and effects of octylphenol in a Microcystis aeruginosa culture medium.

Octylphenol (OP) is a xenobiotic with endocrine disrupting properties found in freshwaters worldwide. Its effects have been studied in organisms with nuclear receptors but effects on phytoplankton communities are poorly characterized, despite the fact that these organisms are constantly exposed to this compound. For this reason fate and effects of OP in the cyanobacterium Microcystis aeruginosa were assessed from 10 nM to 5 microM OP concentration. Up to a test concentration of 250 nM, OP removal increased significantly in the presence of cyanobacteria, the compound half-life in the absence of cells being 15 days against 9 days in the presence of the cells. Only 4% of the total OP removed was found bound to the cells, indicating an active metabolization of the compound. Moreover, the role of the exudates produced by M. aeruginosa, in the OP removal from culture medium, was assessed. Culture medium with exudates, resulting from a 7-day growth of M. aeruginosa, spiked with 50 nM OP, showed a higher half-life (22 days). Compared to culture medium without exudates, it can be hypothesized that higher organic matter concentrations make the hydrolysis or photolysis of OP more difficult. In culture media, the cells of M. aeruginosa could compensate and even counteract this, as OP half-life was shortened. At higher OP levels (1.25 and 5 microM) M. aeruginosa growth was impaired, indicating toxic effects. This shortage of biomass prevented the M. aeruginosa-assisted OP withdrawal from the culture media.

Spatial distribution of some trace and major elements in sediments of the Cávado estuary (Esposende, Portugal).

For the first time, the occurrence and spatial distribution of several elements, including some toxic metals, have been investigated in sediments of the estuary of the Cávado River (Esposende, Portugal). The pseudo total concentrations of Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, V and Zn in sediments collected at 24 sites covering the tidal part of the estuary were determined. According to the concentrations measured, the Cávado estuary can be considered as non-contaminated. For most of the elements, the concentrations tended to be higher upstream. Only a moderate enrichment in Cr and Ni was detected in a few sites. An important decrease in concentration was observed for the most toxic metals compared to historical data reported in the literature. Several hotspots were identified, but even in those cases the amount of metals stored in the sediments does not represent a toxicological threat to living organisms.

Pentachlorophenol toxicity to a mixture of Microcystis aeruginosa and Chlorella vulgaris cultures

Pentachlorophenol (PCP) is a priority pollutant due to its persistence and high toxicity. For the first time, PCP effects were investigated at laboratory scale on co-cultures of two ubiquitous freshwater phytoplankton species: the cyanobacterium Microcystis aeruginosa and the microalgae Chlorella vulgaris. The cells were exposed to environmental levels of PCP for 10 days in Fraquil culture medium, at nominal concentrations from 0.1 to 10,000 μg L(-1). Growth was assessed by area under growth curve (cell count vs. time). The phytoplankton community structure can be changed as a consequence of a PCP contamination. Low μg L(-1) levels of PCP are advantageous to M. aeruginosa. This is the first report of the promoting effect of PCP on the growth of aquatic cyanobacteria, using mixtures with microalgae. As a result of the direct toxic effects of high PCP concentrations on M. aeruginosa, C. vulgaris cell count increased given that in biological controls M. aeruginosa inhibited the C. vulgaris growth. At 16.7 mg L(-1), PCP already had direct toxic effects also on the microalga. The pH of culture medium tended to decrease with increasing PCP concentrations, which was mostly related to the growth inhibition of cyanobacterium caused by PCP. The PCP concentration was stable in the co-cultures, which differed from what has been observed in monocultures of the same two species. Short-term laboratory assays with two phytoplankton species gives important information on the species interactions, namely possible direct and indirect effects of a toxicant, and must be considered in ecotoxicity studies regarding environmental extrapolations.

Fate and effects of nonylphenol in the presence of the cyanobacterium Microcystis aeruginosa

Interactions of nonylphenol (NP), a toxic and oestrogenic degradation product of widely used non-ionic surfactants, with the cyanobacterium Microcystis aeruginosa were studied. Batch cultures were incubated for 10 days with NP concentrations between 10 and 570 nM. NP was removed more quickly in the presence of M. aeruginosa (half-life 2.7–5.2 days) than in its absence (half-life 6.7–10.2 days) at all concentrations tested. At the end of the experiment, NP could not be found in the biomass, so the biotic removal is due to uptake and chemical transformation, and not to physical binding on the cells. The observed effective concentrations, EC50 and EC20, were 0.45 and 0.25 μ M, respectively. Therefore, NP is expected to have toxic effects on M. aeruginosa only in very contaminated surface waters. However, for concentrations that go far beyond environmental levels, cyanobacteria are able to cope with NP toxicity by internalising the compound in a less toxic form. Therefore, the presence of cyanobacteria may increase the rate of NP removal from the aquatic environment.

Simple statistical models for relating river discharge with precipitation and air temperature—Case study of River Vouga (Portugal)

Simple statistical models were developed to relate available meteorological data with daily river discharge (RD) for rivers not influenced by melting of ice and snow. In a case study of the Vouga River (Portugal), the RD could be determined by a linear combination of the recent (PR) and non-recent (PNR) atmospheric precipitation history. It was found that a simple linear model including only PR and PNR cannot account for low RD. The model was improved by including non-linear terms of precipitation that accounted for the water loss. Additional improvement of the models was possible by including average monthly air temperature (T). The best model was robust when up to 60% of the original data were randomly removed. The advantage is the simplicity of the models, which take into account only PR, PNR and T. These models can provide a useful tool for RD estimation from current meteorological data.

Chromatographic Methods for Determination of Chlorophenols as Biomarkers of Exposure to Pesticides and Organochlorine Substances

Chromatographic methods for chlorophenols (CPs) determination that can be applied to clinical (blood, urine) and breast milk samples are reviewed. Special emphasis is given to sample storage conditions and to the application of preconcentration techniques. Solid phase extraction, solid phase microextraction, stir-bar sorptive extraction, liquid phase microextraction and steam distillation methods are considered in view of the potential use of CPs as biomarkers of exposure to different pesticides.