Variation of mercury (Hg) in sediments and biota from Coatzacoalcos estuary during the dry, rainy and windy seasons was estimated. In sediments, Hg concentrations ranged from 0.07 μg g⁻¹ in site 13 (Ixhuatepec) located upstream, to 1.06 μg g⁻¹ in site 3 (Coatzacoalcos river), located in the industrialized area. Highest enrichment factor (EF) and index of geoaccumulation (I geo) in surficial sediments were 53 and 5.1 respectively. From EF and I geo, it is considered that Coatzacoalcos estuary is from moderately contaminated to contaminated. In most fish species from Coatzacoalcos estuary, the sequence of Hg concentration was liver>muscle>gills. Average Hg concentrations in soft tissue of bivalves ranged from 0.09 μg g⁻¹ in Corbicula fluminea to 0.18 μg g⁻¹ in Polymesoda caroliniana. Biota-sediment accumulation factor (BSAF) ranged from 0.9 in P. caroliniana during the rainy season (site 4) to 3.8 in P. caroliniana from the same site during the windy season.

This work investigates the solar heterogeneous photocatalytic degradation of three commercial acid dyes: Blue 9 (C.I. 42090), Red 51 (C.I. 45430), and Yellow 23 (C.I. 19140). TiO₂ P25 from Degussa was used as the photocatalyst. The dyes were completely degraded within 120 min of treatment in the following increasing order of removal rate: Blue 9 < Yellow 23 < Red 51. The photocatalytic color removal process was well described by a two-first-order in-series reaction, followed by another first-order reaction. Photolytic experiments showed that this process is quite inefficient and highly selective towards Red 51 only. The dyes' solution was completely decolorized and organic matter removals up to 99% were achieved with photocatalysis. The lack of selectivity and the possibility of using solar light to excite the photocatalyst are promising results regarding the feasibility of this technology.

A factorial-design-based fuzzy-stochastic modeling system (FFSMS) was developed in this study to systematically investigate impacts of uncertainties associated with hydrocarbon contaminant transport in subsurface through integration of a compositional model, factorial design method, fuzzy modeling approach and Monte Carlo simulation technique. The goodness of fit of the numerical model was analyzed by means of a pilot-scale experimental system. Once the model was calibrated, it was used in order to predict the contaminant concentration depending on values of several parameters including intrinsic permeability, porosity, and longitudinal dispersivity. These parameters were imprecisely known, and such an imprecision was handled by means of both fuzzy sets and/or stochastic theory. The individual and joint effects of these uncertain parameters were analyzed by modeling the dependence between the prediction and the imprecise parameters (factors) through factorial design analysis. The study results indicated that the uncertainties associated with input parameters had significant impacts on modeling outputs; the degree of influence of each model input varied significantly with the level of its imprecision. The study results demonstrated that proposed FFSMS can efficiently analyze the impact of different uncertainty sources associated with different hydrogeological parameters on the prediction of the hydrocarbon concentrations in groundwater. Such studies would provide strong basis for performing successful risk assessment and efficient remediation design for the management of contaminated site.

The objective of this study was to investigate the changes in the chemical partitioning of Cu, Pb, Cr and Zn within a column of soil incubated with an anaerobic sewage sludge (ANSS) for 2.5 months. The soil was irrigated during the incubation period. A sequential extraction method was used to fractionate these metals into exchangeable, weakly adsorbed, organic, Al oxide, Fe-Mn oxide, and residual, respectively. ANSS was applied at a loading rate of 69 Mg ha⁻¹. The soil is a Dystric Cambisol with low pH (<3.8), low CEC [<10 cmol(+) kg⁻¹ below the first 4 cm depth], and low base saturation (<7%). The addition of the ANSS caused a decrease in concentrations of Cu, Pb, and Cr in the A1 horizon, and an increase in the concentrations with depth. Below the A1 horizon, concentrations of Cu increased uniformly (~1 mg cm⁻¹), and the greatest increases were observed in the residual, Fe-Mn oxides, and weakly adsorbed fractions. Maximum increases in Pb occurred at 4-9 cm of depth (1.6 mg cm⁻¹), and mainly affected the weakly adsorbed fraction. Chromium essentially accumulated at the limit between the A2 and the Bw horizons (1.1-1.5 mg cm⁻¹) as residual and organic bound forms, probably through particulate transport. Zinc mainly accumulated in the A1 horizon (2.9 mg cm⁻¹) as exchangeable Zn. At depth, Zn increments were predominantly observed in the residual fraction. The results of this study thus demonstrate the redistribution of contaminants into different chemical pools and soil layers after sludge amendment.

The removal of naphthalene from aqueous solutions by filtration using columns filled with sand and natural vermiculite and sand and hydrophobic vermiculite in different proportions of 2%, 5%, and 10% was evaluated. Batch experiments had shown that the removal was higher than 90% when the filled adsorbent was constituted by 10% of hydrophobic vermiculite. When vermiculite was in lower concentration, that is, 2% and 5%, the removal percentage was lower than 74%. The removal of the naphthalene by the column filled with sand and natural vermiculite did not exceed 25%. The capacity of the columns was tested passing four volumes of aqueous solution of 0.01 mol L⁻¹ naphthalene. After the third volume, the capacity dropped but still retained the major part of pollutant. However, the removal can be reached in higher levels (higher than 90%) when it is filled with 10% of modified vermiculite and increasing the length of the column. With 5% of vermiculite, it is possible to remove 94%, increasing the length of column by a factor of 1.1 times, that is, increasing the original length of 25 to 27.5 cm. The results had demonstrated that the columns are efficient in the removal of the naphthalene and bring speculations to remove other possible organic compounds.

The effect of nickel (Ni) excess on selected aspects of chamomile (Matricaria chamomilla L.) metabolism was studied. Water-soluble Ni represented 27%, 46%, and 47%, and the methanol-soluble fraction 54%, 70%, and 88% of total shoot Ni content after 10 days of treatments with 3, 60, and 120 μM Ni, respectively. “Intra-root” Ni content represented 72% (3 μM), 96% (60 μM), and 78% (120 μM) of total root Ni. Leaf rosettes treated with 120 μM contained 137 μg Ni g⁻¹ DW after 10 days of treatment. The highest Ni concentration particularly affected the content of mineral nutrients (e.g., decrease of K and increase of Fe) and activity of selected antioxidative enzymes (increase of ascorbate peroxidase and guaiacol peroxidase activities). Malondialdehyde accumulation was not influenced (measured in methanol extracts). Among 17 detected free amino acids, accumulation of histidine, proline, methionine, and cysteine was most distinct in the leaf rosettes and/or roots, indicating their involvement in Ni detoxification. Lower Ni toxicity in comparison to previously tested metals is also discussed.

In the present study, a comparative assessment of 2,4,6-T (2,4,6-Trichlorophenol) degradation by different AOPs (Advanced Oxidation Processes - UV, UV/ H₂O₂, Fenton, UV/Fenton and UV/TiO₂) in the laboratory scale is performed. The effects of different reactant concentrations and pH are assessed. 2,4,6-T removal, Total Organic Carbon mineralization (TOC) and dechlorination are monitored. Of all the AOPs, UV/Fenton process is more effective in degrading 2,4,6-T. The optimum conditions obtained for the best degradation with UV/Fenton are: pH = 3, Fe⁺² concentration of about 5 ppm, and peroxide concentration of 100 ppm for an initial 100 ppm of 2,4,6 T concentration at room temperature. In these conditions, a pseudo first-order rate constant is evaluated. The degradation rate of 2,4,6 T followed the order: {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{TiO}}_{\text{2}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}}}} \right. \kern-\nulldelimiterspace} {{\text{TiO}}_{\text{2}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}}} > {\text{UV}} $$]]>

The bracket-like polypore fungus, Ganoderma australe, was selected for its potential to degrade lindane in liquid agitated sterile cultures. An orthogonal central composite design based on response surface methodology was used to find the optimum biodegradation and biosorption conditions of this pesticide and the growth conditions of the fungus. The factors tested include nitrogen content, initial concentration of lindane, incubation time, and temperature. The optimization parameters investigated were fungus biomass, fungus growth rate, final pH, specific biodegradation, specific biosorption, specific biodegradation rate, biodegraded to biosorbed ratio. The results of the experiments were statistically analyzed and the significance and effect of each factor on responses was assessed. The optimum (maximum) lindane biodegradation (3.11 mg biodegraded lindane per gram biomass) was obtained with nitrogen content of 1.28 g/L, lindane concentration of 7.0 ppm, temperature of 18.0°C, and 5 days of cultivation time.

Batch experiments were performed to denitrify groundwater using sawdust as a carbon source at Marydale, South Africa. Alkalinity, pH, electrical conductivity, nitrate, nitrite, ammonia, SO ₄ ²⁻ , heterotrophic plate count (HPC), dissolved organic carbon (DOC), potassium and chloride were monitored. Two soil depths, 75 to 100 and 165 to 200 cm, respectively, from the Marydale area were used as matrix material during denitrification based on contrasting chemical composition with respect to major ion composition and moisture to consider different denitrification rates for varying soil depths. Different N to C ratios were used to evaluate the denitrification efficiency and the least undesirable products, e.g., elevated SO ₄ ²⁻ , H₂S and other reduced compounds. DOC is directly proportional to the N to C ratio used. Nitrite was produced for most of the treatments as incomplete denitrification occurred. The incubation periods were 28 and 43 days, respectively. N to C ratios were 12.6:1, 24:1, 34:1 and 54:1. Longer incubation period and higher N to C ratio resulted in total removal of both nitrate and nitrite. The reaction was carbon-limited for lower N to C ratios. The denitrification rate was proportional to the carbon availability at any time during the experiment. There was no significant difference in denitrification using heterogeneous and homogeneous particle sizes for sawdust. Soil depth of 75-100 cm displayed a greater denitrification rate than 165-200-cm soil depth due to higher initial soil nitrate concentration. The method showed some specificity, as DOC, nitrite, nitrate, alkalinity and HPC were the only parameters that showed a change in concentration over the duration of the denitrification experiment under constant temperature and nitrogen gas atmosphere. DOC and HPC were unacceptable for domestic use, but methods such as boiling or chlorinating water can rid it of bacteria.

In this study, the occurrence of toxic heavy metals (As, Cd, Cr, Cu, Pb, and Zn) and relative bioaccumulation in biota samples were investigated in a freshwater ecosystem, the Basento river, one of the main aquatic systems in the south of Italy, which over the last years has been transformed into a sink of urban and industrial wastes. Therefore, the levels of arsenic, cadmium, chromium, copper, lead, and zinc were determined in water, sediments, and tissues of some macroinvertebrate--which are natural assessment endpoints for the evaluation of ecological risk in aquatic systems. Accumulation factors, as a ratio between the concentration of a given contaminant in biota and the one in an abiotic medium, were considered in order to estimate heavy metal contamination loads in biota. Statistical analysis was performed for a comparative evaluation of bioaccumulation among various macroinvertebrates, according to different feeding guilds. The Tukey honestly significantly different test showed significant differences in the bioaccumulation of As, Cd, and Cr among the considered biological receptors (collector-gatherer, predator, and filterer), suggesting that the biological uptake from immediate contact with the sediment or solid substratum (collector-gatherer), instead of the bioconcentration from water (filterer) or biomagnification along the biotic food webs (predators), is the more effective biological sequestering pathway for these metals. Biota-sediment accumulation factors, commonly used for the evaluation of sediment's role in aquatic systems contamination, were determined for the considered metals. A linear correlation between the concentrations of As, Cd, Cr, and Zn in macroinvertebrates and those in the sediments suggested that the metal uptake data in macroinvertebrates can provide useful information for the estimation of heavy metal exposure risk or bioavailability when making assessments of sediment toxicity in freshwater ecosystems.