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.     

Occurrence of spruce bark beetles in forest stands at different levels of air pollution stress

The spruce bark beetle, Ips typographus (L.) is the most serious pest of mature spruce stands, mainly Norway spruce, Picea abies (L.) Karst. throughout Eurasia. A complex of weather-related events and other environmental stresses are reported to predispose spruce stands to bark beetle attack and subsequent tree mortality; however the possible role of industrial pollution as a predisposing factor to attack by this species is poorly understood. The abundance and dynamics of I. typographus populations was evaluated in 60-80 year old Norway spruce stands occurring on 10 x 50 ha sites in five countries within the Carpathian range that were selected in proximity to established ozone measurement sites. Data were recorded on several parameters including the volume of infested trees, captures of adult beetles in pheromone traps, number of attacks, and the presence and relative abundance of associated bark beetle species. In several cases, stands adjacent to sites with higher ozone values were associated with higher bark beetle populations. The volume of sanitary cuttings, a reflection of tree mortality, and the mean daily capture of beetles in pheromone traps were significantly higher at sites where the O(3) level was higher. However, the mean infestation density on trees was higher in plots associated with lower O(3) levels. Captures of beetles in pheromone traps and infestation densities were higher in the zone above 800 m. However, none of the relationships was conclusive, suggesting that spruce bark beetle dynamics are driven by a complex interaction of biotic and abiotic factors and not by a single parameter such as air pollution.     

Variability of catechin and 4-hydroxyacetophenone distribution in Norway spruce needles in relation to their position, age, and growing conditions

The amount of catechin and 4-hydroxyacetophenone in the methanolic extract of the Norway spruce needles at the locality Bíly Kríz (Moravian-Silesian Beskydy Mts.) was found in the range 2.8-12.1 mg g(-1) (dry weight) and 0.2-17.7 mg g(-1) (dry weight), respectively. Total amount of catechin (sum of the last three needle year-classes) is statistically higher (p<0.01) in the sparse areas compared to the dense ones and similar trends were recorded for catechin content in current and one-year-old needles. These results may support an idea about primary control of phenolic production by the incident solar radiation, which depends on the social position of the tree and canopy closure degree.     

Irrigation runoff insecticide pollution of rivers in the Imperial Valley, California (USA)

The Alamo and New Rivers located in the Imperial Valley, California receive large volumes of irrigation runoff and discharge into the ecologically sensitive Salton Sea. Between 1993 and 2002 we conducted a series of studies to assess water quality using three aquatic species: a cladoceran (Ceriodaphnia dubia), a mysid (Neomysis mercedis), and a larval fish (Pimephales promelas). Although no mortality was observed with the P. promelas, high-level toxicity to the invertebrate species was documented in samples from both rivers during many months of each year. Toxicity identifications and chemical analyses identified the organophosphorus insecticides (OP), chlorpyrifos and diazinon, as the cause of C. dubia toxicity. The extent of the C. dubia mortality was highly correlated with quantities of these OPs applied in the river watersheds. C. dubia mortality occurred during more months of our 2001/2002 study than in the 1990s investigations. During 2001/2002, the extensive C. dubia mortality observed in New River samples was caused by OP insecticide pollution that originated from Mexico. Mortality to N. mercedis in New River samples was likely caused by contaminants other than OP insecticides. Our studies document OP insecticide-caused pollution of the Alamo River over a 10-year period and provide the necessary information for remediation efforts.     

Sorption of lead in soil as a function of pH: a study case in México

Reactions of lead sorption onto soil are largely affected by properties and composition of soil and its solution. In this study, the lead sorption onto regosol eutric soil from Francisco I. Madero, Zacatecas, Mexico is evaluated at different pH values. Soil samples were suspended in lead solutions of 10, 25, 50, 100, 150, 200, 300, and 400 mg/l (as Pb(NO3)2). The pH was adjusted at 2, 3, 4, and 5.5 with nitric acid for each of the lead solution concentrations. In all the cases the ionic strength was I=0.09 M with calcium nitrate. The solid-liquid-ratios were fixed in 1:100 and 1:200 g/ml. The results show that lead sorption increases when pH increases. Experimental isotherms were adjusted by both Langmuir and Freundlich models. The Langmuir affinity parameter, K, indicates that the lead sorption capacity of Francisco I. Madero soils is largely perceptible to pH changes.     

A combination of ion exchange and electrochemical reduction for nitrate removal from drinking water. Part I: nitrate removal using a selective anion exchanger in the bicarbonate form with reuse of the regenerant solution.

The process of selective nitrate removal from drinking water by means of ion exchange was studied. A commercial strong base anion exchanger with triethylammonium (-N+Et3) functional groups was used in the bicarbonate (HCO3-) and carbonate (CO3(2-)) form. The aim of this study was to optimize ion-exchanger regeneration in view of the subsequent electrochemical reduction of nitrates in the spent regenerant solution. The effects of ion-exchanger form, concentration of regenerant solution, and presence of nitrates, chlorides, and sulphates in the regenerant solution were studied. The strong base anion exchanger in HCO3- form that was investigated was able to treat 270 bed volumes of model water solution containing 124 mg dm(-3) nitrates. To achieve adequate regeneration of the saturated anion exchanger, it is necessary to use approximately 30 bed volumes of fresh 1-M sodium bicarbonate (NaHCO3) regenerant solution. The presence of residual 50-mg dm(-3) nitrates in the regenerant solution, treated by electrolysis, resulted in an increase in the dose of regenerant solution to 35 bed volumes and a decrease in the subsequent sorption run of approximately 13%. The volume of applied regenerant solution was high, but the consumption of NaHCO3 for regeneration was low.     

Significance of platinum group metals emitted from automobile exhaust gas converters for the biosphere

Intention, Goal, Scope, Background  Following the introduction of automobile catalytic converters the platinum group metals (PGM) platinum (Pt), palladium (Pd) and rhodium (Rh) gain on increasing interest in environmental research as these metals are emitted with exhaust fumes into the environment. Consequently, elevated PGM levels were found in different environmental matrices uch as road dusts, soils along heavily frequented roads, sediments of urban rivers etc. Accordingly, the effects of increasing PGM emissions on the biosphere are controversially discussed. Objective  This paper summarizes the present knowledge on the biological availability of PGM to plants and animals. As biological availability is one of the most decisive factors determining the toxicologi-cal potential of xenobiotics, this information is very important to evaluate the possible threat of the noble metals to ecosystems. Results and Discussion  The availability of soluble as well as particle bound PGM to terrestrial plants was demonstrated in several studies. Experimental investigations revealed uptake of Pt, Pd and Rh also by aquatic plants. Additionally, the biological availability of the noble metals for animals has been verified in experimental studies using soluble metal salts, catalytic converter model substances, sediments of urban rivers, road dust or tunnel dust as metal sources. These studies refer mainly to aquatic animals. Beside of free living organisms, in particular worms parasitizing fish demonstrated a high potential to accumulate PGM. This could be of great interest in respect of biomonitoring purposes. Generally, for plants as well as for animals Pd turns out to be the best available metal among the PGM. Compared to other heavy metals, the biological availability of PGM from road dust to zebra mussels(Dreissena polymorpha) ranged between that of Cd and Pb. Conclusion  Especially chronic effects of PGM on the biosphere can not be excluded due to (1) their cumulative increase in the environment, (2) their unexpected high biological availability and bioaccumulation and (3) their unknown toxicological and ecotoxicological potential. However, it appears that acute effects on ecosystems due to anthropogenic PGM emission are not likely. Recommendation and Outlook  Research on environmental PGM contamination of the biosphere, especially the fauna, and on long-term toxiciry of low PGM concentrations is highly appreciated. These studies require very sensitive analytical techniques to determine PGM even in low sample amounts. Research has to be done in particular on reliable determination of (ultra) trace levels of Pd and Rh as the lack of data on these two metals is mainly due to analytical problems.     

Ligand exchange rate of metal-nom complexes by EDTA

Metal complexation by natural ligands is important for metal transport and distribution in surface and ground water. The goal of the work was to study the ligand exchange rate for two important metal ions in natural aquatic systems (Al, Fe) was determined using EDTA and natural organic matter (NOM) of humic type as ligands. After adding EDTA to a solution containing metal-NOM complexes, these complexes dissociated and metal-EDTA complexes were formed. Metal-NOM complexes were separated from metal-EDTA complexes with the help of size-exclusion chromatography and detected by on-line inductively coupled plasma-mass spectrometry (ICP-MS). Injecting the samples into the system over time after addition of EDTA allowed us to measure the rate of the exchange of NOM by EDTA. The experiments could be well described with a first-order rate law assuming that the dissociation of the metal-NOM complexes is the rate-determining step. The exchange rate of Fe was found to be faster than that of Al. This corresponds well with the exchange rate of water molecules from the coordination sphere of the metal ions, which is also faster for Fe than for Al. Furthermore, the UV and the fluorescence signal of the chromatograms were measured. The results indicate that no disaggregation of NOM molecules took place, although about 75-85% of the aggregate-forming metal ions exchanged NOM by EDTA in their coordination sphere. This suggests clearly the fundamental role of NOM in colloidal transport of metals and in their bioavailability.     

Environmental impact and recovery at two dumping sites for dredged material in the North Sea

The environmental impact and recovery associated with the long and uninterrupted disposal of large volumes of moderately contaminated dredged material from the port of Rotterdam was studied at nearby dumping sites in the North Sea. Observations were made on sediment contamination, ecotoxicity, biomarker responses and benthic community changes shortly after dumping at the 'North' site had ceased and at the start of disposal at the new dumping site 'Northwest'. During the period of dumping, very few benthic invertebrates were found at the North site. Concentrations of cadmium, mercury, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs) and tributyltin (TBT) in the fine sediment fraction (<63 microm) from this site were 2-3 times higher than at the reference site. In four different bioassays with marine invertebrates the sediments showed no acute toxic effects. In tissue (pyloric caeca) of resident starfish Asterias rubens, residual levels of mercury, zinc, PCBs and dioxin-like activity were never more than twice those at the reference site. Four different biomarkers (DNA integrity, cytochrome P450 content, benzo[a]pyrene hydroxylase activity and acetylcholinesterase inhibition) were used on the starfish tissues, but no significant differences were found between North and the reference site. Minor pathological effects were observed in resident dab Limanda limanda. One year after dumping had ceased at the North site, a significant increase in the species richness and abundance of benthic invertebrates and a concomitant decrease in the fine sediment fraction of the seabed were observed. After 8.2 million m3 of moderately contaminated dredged material had been dumped at the new dumping site Northwest, the species richness and abundance of benthic invertebrates declined over an area extending about 1-2 km eastwards. This correlated with a shift in sediment texture from sand to silt. The contamination of the fine sediment fraction at the Northwest location doubled. It is concluded that marine benthic resources at and around the dumping sites have been adversely affected by physical disturbance (burial, smothering). However, no causal link could be established with sediment-associated contaminants from the dredged spoils.     

Twentieth century overview of heavy metals in the Galician Rias (NW Iberian Peninsula)

The 18 Galician Rias, comprising 25% of the Iberian Peninsula coastline, form a unique system within the European continental Atlantic coast and provide a useful reference area for studies of metals. These rias are sensitive to anthropogenic influence due to the socioeconomic importance generated in these areas by industry, aquaculture, port activities, fishing, tourism and, accordingly, several islands lying within close proximity to the rias have recently been declared natural parks. Aquaculture in the Galician Rias is a growth industry and in 2000 the rias supported 3386 mussel rafts producing 2.5 x 10(8) kg year(-1), i.e. 40% of European Union total seafood production. The Galician Rias are partially stratified estuaries with positive residual circulation with fresh (runoff lower than 100 m3 s(-1) and salt water mixing inside the basins. This behaviour has direct consequences on metal fluxes whereby the rias behave as a barrier and accumulate metals in the sediments. Metals tend to deposit close to point sources and remobilization occurs inside the ria, leading to a seaward decrease in metal concentration. With the exception of the Ulla (Arosa Ria) and Eume (Ares-Betanzos Ria) head rivers and the Lagares river (Vigo Ria) the available data suggest that riverine freshwater inputs are not the main source of contamination. Metal studies reported in the literature mainly relate to Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn, and to a lesser extent Hg and Sn. Studies of other harmful metals such as Ag, Se and As are notably lacking. In addition, the studies have been localized and mainly restricted to the surface sediment. Data of heavy metals in the dissolved phase, suspended particulate matter and biota is scarce in the mainstream literature and should be considered in the future research. From the entire Galician coast, data from seven rias of socio-economic importance form the bulk of the published work. There is an urgent need to standardize procedures, employ 'clean' procedures to avoid contamination of samples and regular assessment of analytical accuracy with CRMs in order that results can be compared among the scientific community and produce reliable results. The continuation of coastal environmental studies requires an enlargement of the sampling locations as well as systematic and periodic analysis of known pollution sources in order to decide whether coastal regeneration action is needed. Studies dedicated to metals in the water column are lacking and need more attention in future research. The majority of the available data correspond to the fluvial front (30%) at ria head and, to a lesser extent, to the oceanic front (3%), under summer upwelling events. Current awareness of the rias suggests that they are not contaminated although there is some evidence of important localized anthropogenically induced enrichments at the outflow of the Lagares River (Pb, Zn), the San Simón inlet (Pb) and near to the harbor (Pb, Zn, Cu) in the Vigo Ria, the inner part (Cu, Zn, Hg, Pb) of the Pontevedra Ria, the Ulla River estuary (Cu, Cr, Mn, Ni; Zn) in the Arosa Ria, the inner zone (Cu, Pb, Zn) of the Coru?a Ria, the Ferrol Ria (Zn) and the Eume Estuary (Zn, Mn, Ni, Co) in the Ares-Betanzos Ria. In addition, TBT enrichment has been found along the Galician coast, being highest in the industrial bays (Vigo, Coru?a and Ferrol). Nevertheless, it is important to point out the lack of information concerning the relationship between metal concentrations in different fractions of sediments and/or water and their bioavailability and toxicity on biota in order to confirm metal contamination dangers. The present paper reviews all the information published on metals in the rias up to the year 2000 and takes a biogeochemical standpoint, i.e. metal presence in the ria reservoirs: water column, suspended particulate matter, sediments and biota, as well as the fluvial and oceanic frontiers.