Mercury levels in muscle of two fish species and sediments from the Cartagena Bay and the Ciénaga Grande de Santa Marta, Colombia

Mercury (Hg) content in sediments and muscle from two fish species were determined in Cartagena Bay and Ciénaga Grande de Santa Marta, an industrialized bay and an unpolluted estuary in the Caribbean coast of Colombia. Sampling was conducted four times during March-November 1996, including both the dry and rainy seasons. Significant differences in Hg concentration were detected both for fish and sediments between the two waterbodies. Hg values ranged from 94 to 10,293 microg/kg dry weight (dw) in sediments from Cartagena Bay and between 20 and 109 microg/kg dw in Ciénaga Grande de Santa Marta. Highest Hg concentrations were observed for the omnivorous species Eugerres plumieri, and lowest concentrations were found in the detritivorous Mugil incilis. High Hg concentrations in sediments of Cartagena Bay were detected in front of the sewage discharge of an extinct chlor-alkali plant, with decreasing concentrations in stations far from the source. Our results suggest that Hg can be persistent in the sediments of previously exposed ecosystems and that the use of their biological resources should be avoided until decontamination programs guarantee safe levels of the metal in the environment.     

In situ sequential treatment of a mixed contaminant plume

Groundwater plumes often contain a mixture of contaminants that cannot easily be remediated in situ using a single technology. The purpose of this research was to evaluate an in situ treatment sequence for the control of a mixed organic plume (chlorinated ethenes and petroleum hydrocarbons) within a Funnel-and-Gate. A shallow plume located in the unconfined aquifer at Alameda Point, CA, was found to contain up to 218,000 μg/l of cis-1,2 dichloroethene (cDCE), 16,000 μg/l of vinyl chloride (VC) and <1000 μg/l of 1,1 dichloroethene (1,1 DCE), trans-1,2 dichloroethene (trans-1,2 DCE) and trichloroethene (TCE). Total benzene, toluene, ethylbenzene and xylenes (BTEX) concentrations were <10,000 μg/l. Contaminated groundwater was funneled into a gate, 3.0 m wide, 4.5 m long and 6.0 m deep (keyed into the underlying aquitard) where treatment occurred. The initial gate segment consisted of granular iron, for the reductive dechlorination of the higher chlorinated ethenes. The second segment, the biosparge zone, promoted aerobic biodegradation of petroleum hydrocarbons and any remaining lesser-chlorinated compounds, stimulated by dissolved oxygen (DO) and carbon dioxide (CO₂) additions via an in situ sparge system (CO₂ was used to neutralize the high pH produced from reactions in the iron wall). Groundwater was drawn through the gate by pumping two wells located at the sealed, downgradient, end. Over a 4-month period an estimated 1350 g of cDCE flowed into the treatment gate and the iron wall removed 1230 g, or 91% of the mass. The influent mass of VC was 572 g and the iron wall removed 535 g, corresponding to 94% mass removal. The other chlorinated ethenes had significantly lower influent masses (3 to 108 g) and the iron wall removed the majority of the mass resulting in >96% mass removal for any of the compounds. In spite of these high removal percentages, laboratory column tests indicated that at these levels of chlorinated contaminants, surface saturation of the iron grains likely contributed to lower than expected reaction rates. In the biosparge zone, mass removal of cDCE appeared to occur predominantly by biodegradation (65%) with volatilization (35%) being an important secondary process. The dominant removal process for VC was volatilization (70%) although significant biodegradation was also indicated (30%). Laboratory microcosm results confirmed the potential for aerobic biodegradation of cDCE and VC. When average influent field concentrations for cDCE and VC were 220,000 and 46,000 μg/l, respectively, the sequential treatment unit removed 99.6% of the total mass and when the influent concentrations decreased to 26,000 and 19,000 μg/l for cDCE and VC, respectively, >99.9% removal within the treatment gate was attained. BTEX compounds were found to be significantly retarded in the iron treatment zone. Although they did eventually break through the granular iron, and into the gravel transition zone, none of these compounds was detected in the biosparge zone. No noticeable interferences between the anaerobic (reductive) and aerobic parts of the system occurred during testing. The results of this experiment show that in situ treatment sequences are viable, although further work is needed to optimize performance.     

A study of the atmospheric reaction of CH3S with O3 as a function of temperature

The atmospheric reaction of the methylthiyl radical (CH₃S) with O₃ was investigated as a function of temperature (259–381 K), in the pressure range of 25–300 Torr, using the technique of laser photolysis/laser-induced fluorescence. The resulting Arrhenius expression, with an uncertainty of ±2σ, was k₁(T=259–381 K)=(1.02±0.30)×10⁻¹² exp[(432±77) K/T] cm³ molecule⁻¹ s⁻¹. The obtained rate constant k₁ was independent of pressure over the limited range employed. Our results are compared with the previous studies carried out, at single temperature and as a function of temperature, by different techniques.     

Biospheric influence on carbon dioxide measurements in Italy

The study concerning carbon dioxide measurements taken during the 1997, 1998 and 1999 summer campaigns at two different altitude stations and biospheric conditions are presented. The higher station (Mt. Cimone, 2165 m a.s.l.) is characterised by 360° free horizon and is located on a rocky mountain while the lower (Ninfa lake, 1550 m a.s.l.) is located inside the red spruce and beech forest. The different behaviour of CO₂ at the two mountain stations has been registered. It shows the strong effect of nighttime soil emission and vegetation respiration on CO₂ mixing ratio increases and of diurnal vegetative activity on CO₂ concentration decreases at the lower measurement site. The baseline character of the higher measurement site has been confirmed by comparison of CO₂ diurnal amplitudes recorded at the two stations.     

Comparison of the degradation of p-hydroxybenzoic acid in aqueous solution by several oxidation processes

A comparative study is made of 12 methods of chemical oxidation applied to degrading p-hydroxybenzoic acid in aqueous solution. The oxidation processes tested were: UV, O3, UV/TiO2, O3/Fe2+, O3/H2O2, O3/UV, UV/H2O2, H2O2/Fe2+, H2O2/Fe2+/O3, UV/H2O2/O3, H2O2/Fe2+/UV and O3/UV/H2O2/Fe2+. The 12 processes were ranked by reactivity. In a kinetic study, the overall kinetic rate constant was split up into three components: direct oxidation by UV irradiation (photolysis), direct oxidation by ozone (ozonation), and oxidation by free radicals (mainly OH*).     

Flotation of metal-loaded clay anion exchangers. Part I: the case of chromates

Synthetic hydrotalcite-like layered materials are known for their ability to remove anions, like the chromates. These sorbents usually exist in powder form, thereby exhibiting high surface area and rapid kinetics for adsorption, but presenting appreciable problems in the subsequent solid/liquid separation process. Almost complete removals were obtained in this paper, from batchwork dispersed-air flotation in presence of a flocculant. Due to the experienced difficulty of flotation of thermally activated (at 500 degrees C) hydrotalcite metal-loaded particles, the application of various surfactants was studied. Continuous-flow laboratory runs certified also the effectiveness of this combined process of sorptive flotation, a promising innovative treatment technology.     

Kinetics of oxidation of chlorobenzenes and phenyl-ureas by Fe(II)/H2O2 and Fe(III)/H2O2. Evidence of reduction and oxidation reactions of intermediates by Fe(II) or Fe(III)

The rates of degradation of 1,2,4-trichlorobenzene (TCB), 2,5-dichloronitrobenzene (DCNB), diuron and isoproturon by Fe(II)/H2O2 and Fe(III)/H2O2 have been investigated in dilute aqueous solution ([Organic compound]0 approximately 1 microM, at 25.0 +/- 0.2 degrees C and pH < or = 3). Using the relative rate method with atrazine as the reference compound, and the Fe(II)/H2O2 (with an excess of Fe(II)) and Fe(III)/H2O2 systems as sources of OH radicals, the rate constants for the reaction of OH* with TCB and DCNB were determined as (6.0 +/- 0.3)10(9) and (1.1 +/- 0.2)10(9) M(-1) s(-1). Relative rates of degradation of diuron and isoproturon by Fe(II)/H2O2 were about two times smaller in the absence of dissolved oxygen than in the presence of oxygen. These data indicate that radical intermediates are reduced back to the parent compound by Fe(II) in the absence of oxygen. Oxidation experiments with Fe(III)/H2O2 showed that the rate of decomposition of atrazine markedly increased in the presence of TCB and this increase has been attributed to a regeneration of Fe(II) by oxidation reactions of intermediates (radical species and dihydroxybenzenes) by Fe(III).     

Dynamics of radionuclide concentrations in calcified tissues of reindeer in the western Russian Arctic

The specific activities of artificial and natural nuclides were determined in bone and teeth of reindeer that had lived before, during, and after nuclear tests on the Archipelago Novaya Zemlya and of reindeer from the nearby mainland region. In bone of reindeer from Novaya Zemlya, 90Sr and 210Pb are the main source of beta-activity, the 210Po is the main source of the alpha activity. In bone of reindeer that lived on Novaya Zemlya during underground tests, the 90Sr activity was relatively high (0.75 +/- 0.20 Bq/g dry weight). In animals that lived after the tests were banned, the level was significantly lower (0.44 +/- 0.17 Bq/g) and did not differ from the level of the 90Sr activity found in the mainland reindeer bone. On Novaya Zemlya, the concentrations of the natural 210Pb in bone of the recent reindeer (0.57 +/- 0.19 Bq/g) is similar to that which was in the teeth of reindeer a hundred years ago (0.65-0.75 Bq/g) and significantly higher than in the recent mainland reindeer from different regions (0.18-0.17 Bq/g).