Effects of storage method and duration on the toxicity of marine sediments to embryos of Crassostrea gigas oysters

The objective of laboratory sediment bioassays is to estimate in situ toxicity. This goal is difficult to achieve, as one of the main limitations of sediment toxicity tests is disruption of sediment geochemistry during sampling, handling and preservation. The effects of storage on the estimation of marine sediment toxicity to Crassostrea gigas embryos and larvae were investigated. Three storage methods and four storage periods were compared with three different sediment types contaminated by heavy metals, polycyclic aromatic hydrocarbons (PAHs) and both contaminants. Freezing and freeze-drying considerably increased the toxicity of decanted sediments and their elutriates as compared to the toxicity obtained with fresh sediments. Concerning the elutriates, the toxicity found with frozen and freeze-dried sediments was correlated with DOC, ammonia and PAH contents. However, the toxicity of fresh sediments kept at 4 degrees C increased with increasing duration of storage and was also correlated with the amount of ammonia in the elutriates.     

Oxidation of MCPA and 2,4-D by UV radiation, ozone, and the combinations UV/H2O2 and O3/H2O2

The phenoxyalkyl acid derivative herbicides MCPA (4-chloro 2-methylphenoxyacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid) were oxidized in ultrapure water by means of a monochromatic UV irradiation and by ozone, as well as by the combinations UV/H2O2 and O3/H2O2. In the direct photolysis of MCPA, the quantum yield at 20 degrees C was directly evaluated and a value of 0.150 mol Eins(-1) was obtained in the pH range 5-9, while a lower value of 0.41 x 10(-2) mol Eins(-1) was determined at pH=3. Similarly, for 2,4-D a value of 0.81 x 10(-2) mol Eins(-1) was deduced, independent of the pH of work. The influence of the additional presence of hydrogen peroxide was established in the combined process UV/H2O2, and the specific contribution of the radical pathway to the global photo-degradation was evaluated. The oxidation by ozone and by the combination O3/H2O2 was also studied, with the determination of the rate constants for the reactions of both herbicides with ozone and hydroxyl radicals at 20 degrees C. These rate constants for the direct reactions with ozone were 47.7 and 21.9 M(-1) s(-1) for MCPA and 2,4-D respectively, while the found values for the rate constants corresponding to the radical reactions were 6.6 x 10(9) and 5.1 x 10(9) M(-1) s(-1).     

Role of alpha-tocopherol and beta-carotene in ameliorating the fenvalerate-induced changes in oxidative stress, hemato-biochemical parameters, and semen quality of male rats

Role of alpha-tocopherol (vitamin E), beta-carotene and/or their combination as antioxidants against the toxicity of fenvalerate on blood hematology, free radicals, biochemical parameters, and semen quality were studied in male rats. Fenvalerate (20 mg/kg BW), vitamin E (100 mg/kg BW), beta-carotene (10 mg/kg BW), and vitamin E plus beta-carotene (100 + 10 mg/kg BW, respectively) were given alone or in combination with fenvalerate. The tested doses were given to rats every other day for 30 days. Results obtained showed that fenvalerate significantly (P < 0.05) induced free radicals in plasma and brain and insignificantly in liver and testes. While, vitamin E, beta-carotene alone and/or in combination decreased the levels of free radicals in plasma, liver, testes, and brain. The activities of glutathione S-transferase (liver), alkaline phosphatase (plasma and liver), aspartate aminotransferase (plasma, liver, and testes) and alanine aminotransferase (plasma and liver) were significantly (P < 0.05) increased due to fenvalerate administration. The activity of acetylcholinesterase was significantly (P < 0.05) decreased in brain and plasma, while plasma glucose, urea, creatinine, and bilirubin concentrations were significantly (P < 0.05) increased in rats treated with fenvalerate. Also, results showed a significant (P < 0.05) alterations in plasma proteins, hematological parameters, body weight, and relative weights of organs. Sperm concentration and motility (%) were significantly (P < 0.05) decreased, while dead and abnormal sperm increased in rats exposed to fenvalerate. Vitamin E, beta-carotene alone and/or in combination did not cause any changes in the investigated parameters, but improved semen quality and minimized the toxic effect of fenvalerate. The obtained results demonstrated the beneficial influences of vitamin E, beta-carotene alone and/or in combination in reducing the harmful effects of fenvalerate.     

Calculating pesticide sorption coefficients (Kd) using selected soil properties

Pesticide soil/solution distribution coefficients ( Kd values), commonly referred to as pesticide soil sorption values, are utilized in computer and decision aid models to predict soil mobility of the compounds. The values are specific for a given chemical in a given soil sample, normally taken from surface soil, a selected soil horizon, or at a specific soil depth, and are normally related to selected soil properties. Pesticide databases provide Kd values for each chemical, but the values vary widely depending on the soil sample on which the chemicals were tested. We have correlated Kd values reported in the literature with the reported soil properties for an assortment of pesticides in an attempt to improve the accuracy of a Kd value for a specific chemical in a soil with known soil properties. Mathematical equations were developed from regression equations for the related properties. Soil properties that were correlated included organic matter content, clay mineral content, and/or soil pH, depending on the chemical properties of the pesticide. Pesticide families for which Kd equations were developed for 57 pesticides include the following: Carboxy acid, amino sulfonyl acid, hydroxy acid, weakly basic compounds and nonionizable amide/anilide, carbamate, dinitroaniline, organochlorine, organophosphate, and phenylurea compounds. Mean Kd values for 32 additional pesticides, many of which had Kd values that were correlated with specific soil properties but for which no significant Kd equations could be developed are also included.     

Evaluation of relative photonic efficiency in heterogeneous photocatalytic reactors

The evaluation of photonic efficiency in heterogeneous photocatalysis remains elusive because the number of absorbed photons is difficult to assess experimentally. The photonic efficiency of heterogeneous photocatalytic reactors depends on the reactor geometry, irradiation source, and photocatalyst properties. In this work, the relative photonic efficiency of heterogeneous photocatalytic reactors to degrade an azo dye was evaluated using phenol as the standard system. The experimental tests were carried out in a batch reactor under different conditions of pH, catalyst dosage, initial concentration, and ultraviolet (UV) lamps. The kinetics of disappearance of both phenol and azo dye were studied using the initial rate method and were described according to the Langmuir-Hinshelwood (L-H) kinetic model. It was observed that the relative photonic efficiency depends on the adsorption/desorption properties of the photocatalyst.     

Antioxidant enzyme activities as affected by trivalent and hexavalent chromium species in Fontinalis antipyretica Hedw

The detoxification mechanisms of the aquatic moss, Fontinalis antipyretica Hedw., exposed to Cr was analyzed. In addition, the influence of Cr salts (as Cr nitrate, chloride and potassium bichromate) on these mechanisms has also been studied. The activity of antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1.), catalase (EC 1.11.1.6.), ascorbate peroxidase (APX, EC 1.11.1.11.), guaiacol peroxidase (GPX, EC 1.11.1.7.) and glutathione reductase (GR, EC 1.6.4.2.) increased in plants treated with Cr concentrations ranging from 6.25x10(-5) to 6.25mM when given as Cr(NO(3))(3). Antioxidant enzymes responded to the other two salts CrCl(3) and K(2)Cr(2)O(7) only with Cr concentrations higher than 6.25x10(-2)mM. Glutathione level and GSSG/GSH ratio also responded to Cr exposure but no dose-effect relationship could be observed. Moreover, two unknown thiol compounds were observed in mosses exposed to the highest Cr concentrations. Effects on chlorophyll contents and chlorophyll a/b ratios were also shown even at low Cr concentrations. Our results indicated that environmentally realistic concentrations of Cr could lead to impairment of the cellular activity towards F. antipyretica and that Cr(III), when present as a nitrate salt, was as harmful as Cr(VI).     

The effect of organic and hydraulic shock loads on the production of soluble microbial products in anaerobic digesters.

Anaerobic chemostats were used to investigate the effects of organic and hydraulic shock loads on the production of soluble microbial products (SMP). Production of SMP was found to increase during glucose spikes, reaching up 15% of the influent chemical oxygen demand. These SMP appear to be utilization-associated products produced as a result of the temporarily high organic load, and chemical analysis and ultrafiltration experiments revealed that most of these compounds are difficult to identify and that the majority of them are present in the low molecular weight (MW) range. Production of SMP also increased when the hydraulic retention time was reduced from 15 to 3 days, and an increase in DNA concentration in the bulk solution suggested enhanced cell lysis. Although the cause of lysis was not clear, it is believed that most of the SMP produced under such conditions were biomass-associated products following cell death. While the majority of these compounds lay in the low MW range, as much as 35% were found to have MWs greater than 1 kDa. During the period when the anaerobic chemostat was fed no alkalinity and the pH remained lower than 6.5 for more than a week, a slightly higher production of SMP and a shift in the MW distribution towards the production of higher MW SMP was observed.     

DOC removal paradigms in highly humic aquatic ecosystems

Background, aim, and scope  Dissolved humic substances (HS) usually comprise 50–80% of the dissolved organic carbon (DOC) in aquatic ecosystems. From a trophic and biogeochemical perspective, HS has been considered to be highly refractory and is supposed to accumulate in the water. The upsurge of the microbial loop paradigm and the studies on HS photo-degradation into labile DOC gave rise to the belief that microbial processing of DOC should sustain aquatic food webs in humic waters. However, this has not been extensively supported by the literature, since most HS and their photo-products are often oxidized by microbes through respiration in most nutrient-poor humic waters. Here, we review basic concepts, classical studies, and recent data on bacterial and photo-degradation of DOC, comparing the rates of these processes in highly humic ecosystems and other aquatic ecosystems. Materials and methods  We based our review on classical and recent findings from the fields of biogeochemistry and microbial ecology, highlighting some odd results from highly humic Brazilian tropical lagoons, which can reach up to 160 mg C L⁻¹. Results and discussion  Highly humic tropical lagoons showed proportionally lower bacterial production rates and higher bacterial respiration rates (i.e., lower bacterial growth efficiency) than other lakes. Zooplankton showed similar δ¹³C to microalgae but not to humic DOC in these highly humic lagoons. Thus, the data reviewed here do not support the microbial loop as an efficient matter transfer pathway in highly humic ecosystems, where it is supposed to play its major role. In addition, we found that some tropical humic ecosystems presented the highest potential DOC photo-chemical mineralization (PM) rates reported in the literature, exceeding up to threefold the rates reported for temperate humic ecosystems. We propose that these atypically high PM rates are the result of a joint effect of the seasonal dynamics of allochthonous humic DOC input to these ecosystems and the high sunlight incidence throughout the year. The sunlight action on DOC is positive to microbial consumption in these highly humic lagoons, but little support is given to the enhancement of bacterial growth efficiency, since the labile photo-chemical products are mostly respired by microbes in the nutrient-poor humic waters. Conclusions  HS may be an important source of energy for aquatic bacteria in humic waters, but it is probably not as important as a substrate to bacterial growth and to aquatic food webs, since HS consumption is mostly channeled through microbial respiration. This especially seems to be the case of humic-rich, nutrient-poor ecosystems, where the microbial loop was supposed to play its major role. Highly humic ecosystems also present the highest PM rates reported in the literature. Finally, light and bacteria can cooperate in order to enhance total carbon degradation in highly humic aquatic ecosystems but with limited effects on aquatic food webs. Recommendations and perspectives  More detailed studies using C- and N-stable isotope techniques and modeling approaches are needed to better understand the actual importance of HS to carbon cycling in highly humic waters.     

Impact of initial and boundary conditions on preferential flow

Preferential flow in soil is approached by a water-content wave, WCW, that proceeds downward from the ground surface. WCWs were obtained from sprinkler experiments with infiltration rates varying from 5 to 40 mm h^− 1. TDR-probes and tensiometers measured volumetric water contents θ(z,t) at seven depths, and capillary heads, h(z,t) at six depths in a column of an undisturbed soil. The wave is characterized by the velocity of the wetting front, c_W, the amplitude, w_S, and the final water content, θ. We tested with uni-variate and bi-variate linear regressions the impacts of initial volumetric water contents, θ_ini, and input rates, q_S, on c_W, w_S and θ.The test showed that θ_ini influenced θ and w_S and q_S effected c_W. The expected proportionality of w_S ≈ qs^1/3 was weak and c_W ≈ qs^2/3 was strong.