Melamine-based organoclay to sequester atrazine

Sequestration of aqueous atrazine by organoclays prepared from the surfactant 6-piperazin-1-yl-N,N'-bis-(1,1,3,3-tetramethyl-butyl)-(1,3,5)triazine-2,4-diamine and Gonzales bentonite was assessed using 14C-labeled atrazine. Organoclays with varying ratios of surfactant to clay were evaluated with respect to their ability to sequester atrazine from an aqueous solution. Organoclays containing 100-200 g kg-1 surfactant on a total weight basis provided the most efficient adsorption of atrazine, with apparent KOC values exceeding 5000 l kg-1 at these loading fractions. Less than 12% of sequestered atrazine was released during four sequential day long washings, supporting our expectation that the majority of the reaction of atrazine with the surfactant lead to irreversible chemical bond formation through nucleophilic aromatic substitution.     

Prediction of ozone concentrations in Oporto city with statistical approaches

The performance of three statistical methods: time-series, multiple linear regression and feedforward artificial neural networks models were compared to predict the daily mean ozone concentrations. The study here reported was based on data from one urban site with traffic influences and one rural background site. The studies were performed for the year 2002 and the respective four trimesters separately. In the multiple linear regression and feedforward artificial neural network models, the concentrations of ozone, the concentrations of its precursors (nitrogen oxides) and some meteorological variables for one and two days before the prediction day were used as predictors. For the application of these models in the validation step, the inputs of ozone concentration for one and two days before were replaced by the ozone concentrations predicted by the models. The results showed that time-series modelling was not profitable. In the development step, similar performances were obtained with multiple linear regression and feedforward artificial neural network. Better performance indexes were achieved with feedforward artificial neural network models in validation step. Concluding, feedforward artificial neural network models were more efficient to predict ozone concentrations.     

Organochlorine contaminants in complete clutches of Morelet's crocodile (Crocodylus moreletii) eggs from Belize

Seven complete clutches of Morelet's crocodile (Crocodylus moreletii) eggs were collected in northern Belize and examined for organochlorine (OC) pesticide residues. The primary OC detected, p,p-DDE, was found in every egg analyzed (n=175). Other OCs detected included p,p-DDT, p,p-DDD, methoxychlor, aldrin, and endosulfan I. Concentrations of individual OCs ranged from 4 ppb (ng chemical/g egg wet weight) to greater than 500 ppb. A statistical evaluation of p,p-DDE levels in three complete clutches was used to derive the minimum number of eggs needed from a clutch to precisely determine the mean p,p-DDE concentration representative of that clutch. Sample sizes of 8 (80% confidence level) and 11 (90% confidence level) were determined to yield an accurate estimate of contaminant levels in a full clutch of eggs. The statistically recommended sample size of 11 eggs (at 90% confidence level) was successfully tested on the four additional clutches.     

Effects of medetomidine, a novel antifouling agent, on the burrowing bivalve Abra nitida (Müller)

The effects of medetomidine, a novel antifouling candidate, on the burrowing bivalve Abra nitida were studied. The burrowing behaviour, sediment reworking activity and faeces production were assessed after 24 h exposure of A. nitida to sublethal concentrations of medetomidine. Medetomidine caused a significant decrease in the burrowing response and in the sediment reworking activity. The median effective concentrations (EC50) were 430 nM (86 microg/l) and 4.4 nM (0.9 microg/l), respectively. No effects on the faeces production were detected. Although significant effects of medetomidine on A. nitida were registered, a reversibility of the effects was observed when 24 h-exposed animals were incubated in clean seawater and sediment for 24 h. Considerations relating to the future commercialisation of medetomidine for antifouling purposes are discussed.     

Seasonal and spatial patterns of metals at a restored copper mine site II. Copper in riparian soils and Bromus carinatus shoots

Soil and plants were sampled throughout winter and spring near a perennial stream traversing a restored mine site in a winter-rainy climate. Within 1m of an acidic reach of the stream, soil had pH 3-5 and 50-100 microg/g "bioavailable" copper (extractable with 0.01 M CaCl2). Soil 2-3 m from the stream had pH 5-8 and lower (less than 3 microg/g) bioavailable copper. "Oxide-bound" copper (extractable with 2N HCl) was 50-100 microg/g at most locations. Copper concentrations in the shoots of field-collected Bromus carinatus declined from 20 microg/g in winter to 2 microg/g in spring at all sampling sites. A similar temporal pattern was found in plants grown under controlled conditions. Thus B. carinatus has a developmental program for control of shoot copper concentration, causing a seasonally-varying pattern of copper phytoaccumulation over a large range of copper availability in the soil.     

Occurrence and accumulation of organochlorine contaminants in swordfish from Mediterranean Sea: a case study

Polychlorinated biphenyls including coplanar congeners and DDT compounds were measured in the liver of a teleost species: namely, Xiphias gladius. PCB concentrations (median: 1121 ng/g lipid wt) were comparable with DDT levels (median: 1236 ng/g lipid wt). PCBs revealed a profile dominated by hexa-, penta- and heptachlorinated congeners. Among DDTs, the compound in the greatest concentration was p,p'-DDE, representing 70% of the total DDT burden, followed by o,p'-DDT>p,p'-DDT>p,p'-DDD=o,p'-DDD. Mean total 2,3,7,8-TCDD equivalent of five coplanar PCBs was 8.83 pg/g lipid weight. The isomers with higher TEQs values were non-ortho congeners than mono-ortho ones.     

Degradation of the pharmaceutical metronidazole via UV, Fenton and photo-Fenton processes

Degradation rates and removal efficiencies of Metronidazole using UV, UV/H2O2, H2O2/Fe2+, and UV/H2O2/Fe2+ were studied in de-ionized water. The four different oxidation processes were compared for the removal kinetics of the antimicrobial pharmaceutical Metronidazole. It was found that the degradation of Metronidazole by UV and UV/H2O2 exhibited pseudo-first order reaction kinetics. By applying H2O2/Fe2+, and UV/H2O2/Fe2+ the degradation kinetics followed a second order behavior. The quantum yields for direct photolysis, measured at 254 nm and 200-400 nm, were 0.0033 and 0.0080 mol E(-1), respectively. Increasing the concentrations of hydrogen peroxide promoted the oxidation rate by UV/ H2O2. Adding more ferrous ions enhanced the oxidation rate for the H2O2/Fe2+ and UV/H2O2/Fe2+ processes. The major advantages and disadvantages of each process and the complexity of comparing the various advanced oxidation processes on an equal basis are discussed.     

Contribution of anthropogenic pollutants to the increase of tropospheric ozone levels in the Oporto Metropolitan Area, Portugal since the 19th century

The main purpose of this study was to evaluate the contribution of anthropogenic pollutants to the increase of tropospheric ozone levels in the Oporto Metropolitan Area (Portugal) since the 19th century. The study was based on pre-industrial and recent data series, the results being analyzed according to the atmospheric chemistry. The treatment of ozone and meteorological data was performed by classical statistics and by time-series analysis. It was concluded that in the 19th century the ozone present in the troposphere was not of photochemical origin, being possible to consider the respective concentrations as reference values. For recent data a cycle of 8h for ozone concentrations could be related to traffic. Compared to the 19th century, the current concentrations were 147% higher (252% higher in May) due to the increased photochemical production associated with the increased anthropogenic emissions.     

Calcite-seeded crystallization of calcium phosphate for phosphorus recovery

For phosphorus recovery from wastewater, the present paper aims at understanding the crystallization of calcium phosphate by using calcites (Juraperle and Coccolith) as seeds from hard water. Synthetic hard water with 60 mgCl(-1) carbonate and 10 mgPl(-1) phosphate was prepared and used in the batch experiments of calcite-seeded crystallization. The solution composition was measured throughout the batch crystallization process, and the corresponding saturation indices with respect to the minerals were calculated with PHREEQC Program. The surface of the calcite seeds was observed and measured with environmental scanning electron microscopy (ESEM), Fourier transform infrared (FTIR) and BET method. The studies show that both calcites are effective seeds for the crystallization of calcium phosphate from hard water; the used calcites are more efficient than the original ones because newly formed crystals with calcium phosphate have covered their surfaces. The studies show that the calcite seeds can be used for phosphorus recovery from hard waters.     

Mobility of heavy metals from tailings to stream waters in a mining activity contaminated site

In this paper the results of a recent characterization of Rio Piscinas (SW of Sardinia, Italy) hydrological basin are reported. In such area (about 50 km2), previous mining activities caused a serious heavy metal contamination of surface waters, groundwater, soils and biota. Acid mine drainage phenomena were observed in the area. The main sources of contamination are the tailings stored in mine tunnels and abandoned along fluvial banks. A methodological approach was adopted in order to identify relations between tailings and water contamination. Representative samples of tailings and stream sediments samples were collected. XRD analyses were performed for mineralogical characterization, while acid digestion was carried out for determining metal contents. Batch sequential leaching tests were performed in order to assess metal mobility. Also groundwater and stream water were sampled in specific locations and suitably characterized. All information collected allowed the understanding of the effect of tailings on water contamination, thus contributing to the qualitative prediction of pollution evolution on the basis of metal mobility. Finally, a potential remediation strategy of stream water is proposed.