Seasonal changes of metal accumulation and distribution in shining pondweed (Potamogeton lucens)

In this study, submerged aquatic plant Potamogeton lucens, corresponding sediment and water samples were seasonally collected from Lake Sapanca (Turkey) and analysed for their heavy metal contents (Pb, Cr, Cu, Mn, Ni, Zn and Cd). While heavy metals concentrations in the water samples were decreased as Zn > Cr > Ni > Pb > Mn > Cu > Cd, in sediment samples were Mn > Zn > Ni > Cu > Cr > Pb > Cd, respectively. Generally, heavy metals concentrations in the plant tissues were decreased in sequence of Mn > Zn > Cu > Ni > Cr > Pb > Cd. It was determined that Cu, Mn and Zn were actively transported to the root, where they were accumulated especially in autumn. Lower accumulation factor ratios were seen in spring than other seasons. Cd exhibited a relatively clear pattern of increasing accumulation in P. lucens with increasing sediment metal concentrations. Significant positive correlations were observed between Cr, Cu, Ni and Cd contents in sediment and Cd contents in root of P. lucens. The investigations suggested that Ni and Mn have a tendency to be accumulated in leaf especially in autumn and Cr and Cd to be accumulated in shoot especially in summer.     

Isolation and characterization of a heavy metal-resistant Burkholderia sp. from heavy metal-contaminated paddy field soil and its potential in promoting plant growth and heavy metal accumulation in metal-polluted soil

A heavy metal-resistant bacterial strain was isolated from heavy metal-contaminated soils and identified as Burkholderia sp. J62 based on the 16S rDNA gene sequence analysis. The heavy metal- and antibiotic resistance, heavy metal solubilization of the isolate were investigated. The isolate was also evaluated for promoting plant growth and Pb and Cd uptakes of the plants from heavy metal-contaminated soils in pot experiments. The isolate was found to exhibit different multiple heavy metal and antibiotic resistance characteristics. Atomic absorption spectrometer analysis showed increased bacterial solubilization of lead and cadmium in solution culture and in soils. The isolate produced indole acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase. The isolate also solubilized inorganic phosphate. Inoculation with the isolate was found to significantly (p < 0.05) increase the biomass of maize and tomato plants. Increase in tissue Pb and Cd contents varied from 38% to 192% and from 5% to 191% in inoculated plants growing in heavy metal-contaminated soils compared to the uninoculated control, respectively. These results show that heavy metal-solubilizing and plant growth promoting bacteria are important for plant growth and heavy metal uptake which may provide a new microbial enhanced-phytoremediation of metal-polluted soils.     

Comparison of trace element concentrations in livers of diseased, emaciated and non-diseased southern sea otters from the California coast

Infectious diseases have been implicated as a cause of high rates of adult mortality in southern sea otters. Exposure to environmental contaminants can compromise the immuno-competence of animals, predisposing them to infectious diseases. In addition to organic pollutants, certain trace elements can modulate the immune system in marine mammals. Nevertheless, reports of occurrence of trace elements, including toxic heavy metals, in sea otters are not available. In this study, concentrations of 20 trace elements (V, Cr, Mn, Co, Cu, Zn, Rb, Sr, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, Hg, Tl, Pb, and Bi) were measured in livers of southern sea otters found dead along the central California coast (n = 80) from 1992 to 2002. Hepatic concentrations of trace elements were compared among sea otters that died from infectious diseases (n = 27), those that died from non-infectious causes (n = 26), and otters that died in emaciated condition with no evidence of another cause of death (n = 27). Concentrations of essential elements in sea otters varied within an order of magnitude, whereas concentrations of non-essential elements varied by two to five orders of magnitude. Hepatic concentrations of Cu and Cd were 10- to 100-fold higher in the sea otters in this study than concentrations reported for any other marine mammal species. Concentrations of Mn, Co, Zn, and Cd were elevated in the diseased and emaciated sea otters relative to the non-diseased sea otters. Elevated concentrations of essential elements such as Mn, Zn, and Co in the diseased/emaciated sea otters suggest that induction of synthesis of metallothionein and superoxide dismutase (SOD) enzyme is occurring in these animals, as a means of protecting the cells from oxidative stress-related injuries. Trace element profiles in diseased and emaciated sea otters suggest that oxidative stress mediates the perturbation of essential-element concentrations. Elevated concentrations of toxic metals such as Cd, in addition to several other organic pollutants, may contribute to oxidative stress-meditated effects in sea otters.     

Mercury bioaccumulation and phytotoxicity in two wild plant species of Almadén area

Mercury is a widely distributed environmental pollutant, able to induce toxicity in living organisms, including higher plants. Some plant species are able to grow in mine sites, like the Almadén zone in Spain. Our study focus on two of these plant species, Rumex induratus and Marrubium vulgare and their responses to natural Hg exposure. Total Hg concentration in the soil below the plants could be classified as toxic, although the available fraction was low. Hg availability was higher for the M. vulgare than for the R. induratus plot. Hg concentrations in field plants of R. induratus and M. vulgare grown on these soils can be considered as phytotoxic, although no symptoms of Hg toxicity were observed in any of them. According to the BAF ([Hg]_tissue/[Hg]_avail), R. induratus showed a higher ability in Hg uptake and translocation to shoots, as well as higher concentrations of MDA and –SH:Hg ratios, so that this plant is more sensitive to Hg than M. vulgare. The resistance to Hg and the capability to extract Hg from the soil make both M. vulgare and R. induratus good candidates for Hg phytoremediation of contaminated soils.     

Levels of organochlorine pesticides in human milk from central Taiwan

The present study determined the residues of organochlorine pesticides (OCPs) in human milk collected in central Taiwan between December 2000 and November 2001. The OCPs were analyzed by GC/MS for 36 human milk samples from healthy women ranging between 20 and 36 years of age. The predominant OCPs were p,p′-DDE, p,p′-DDT, -CHL, heptachlor epoxide, heptachlor, β-HCH, and γ-HCH, with median levels of 228, 19, 7.4, 4.0, 2.3, 1.2, and 0.8 ng/g lipid, respectively. The residues of OCPs in human milk from central Taiwan were comparable to those described in results from Sweden, the United Kingdom, and Japan, and were significantly lower than those from investigations in Asian countries, including China, Thailand, Indonesia, and Vietnam. Low DDE/DDT ratio (mean = 13.6, SD = 6.54) indicated that residual OCPs in human milk mainly originate from past exposure. A notable decrease in DDT levels (∑ DDT = 333 ng/g lipid) in human milk was found in this study compared to results from the previous two decades (∑ DDT = 3595 ng/g lipid). Hypothetically, the level of -CHL was significantly associated with total TEQ levels in Taiwanese human milk because of the sources of food contaminant, i.e. animal fat. Based on low OCP levels in Taiwanese human milk and low estimated median daily intake of total DDTs for a breastfed infant (1358 ng/kg/day) with the assumption of an infant weighting 4 kg and consuming 699 g milk per day in the first month after birth, the Taiwanese policy of breast-feeding promotion was supported.     

Sorption-desorption of cadmium in aqueous palygorskite, sepiolite, and calcite suspensions: isotherm hysteresis

Sorption isotherms have been widely used to assess the heavy metal retention characteristics of soil particles. Desorption behavior of the retained metals, however, usually differ from that of sorption, leading to a lack of coincidence in the experimentally obtained sorption and desorption isotherms. In this study, we examine the nonsingularity of cadmium (Cd) sorption–desorption isotherms, to check the possible hysteresis and reversibility phenomena, in aqueous palygorskite, sepiolite and calcite systems. Sorption of Cd was carried out using a 24-h batch equilibration experiment with eight different Cd solution concentrations, equivalent to 20–100% of maximum sorption capacity of each mineral. Immediately after sorption, desorption took place using successive dilution method with five consecutive desorption steps. Both Cd sorption and desorption data were adequately described by Freundlich equation (0.81 < r² < 0.99). The sorption and desorption reactions, however, did not provide the same isotherms, indicating that hysteresis occurred in Cd sorption–desorption processes. The extent of hysteresis was quantified based on the differences obtained from sorption and desorption isotherms regarding the amount of Cd sorbed, the Freundlich exponent, and the Cd distribution coefficient. The results revealed that, sepiolite possessed the most hysteretic behavior among the minerals studied. Calcite showed much smaller hysteresis compared to the other two silicate clays at low Cd surface load, but its hysteresis indices significantly increased, and exceeded that of palygorskite, as the amount of Cd in the systems increased. The average amount of Cd released after five desorption steps, was 13.8%, 2.2% and 3.6% for the palygorskite, sepiolite and calcite, respectively, indicating that a large portion of Cd was irreversibly retained by the minerals.     

Cold season CH4, CO2 and N2O fluxes from freshwater marshes in northeast China

Cold season (winter and thaw) CH₄, CO₂ and N₂O fluxes from freshwater marshes (47°35′N, 133°31′E, Northeast China) were measured, using the static chamber method. The mean CH₄ and CO₂ fluxes from Carex lasiocarpa (Cl) were 0.5 ± 0.19 and 6.23 ± 1.36 mg C m⁻² h⁻¹, respectively, and those from Deyeuxia angustifoli (Da) were 0.18 ± 0.15 and 5.22 ± 2.48 mg C m⁻² h⁻¹, respectively in winter. There was no significant difference between Cl and Da (p > 0.05). The contributions of winter CH₄ fluxes were about 5.5% and 3% in the Cl and Da, respectively. Marshes are an important potential N₂O sink in winter season in northeast China. During thaw, the CH₄ and CO₂ emissions rapidly increased, 4.5–6 times of winter emissions. Wetland became a source of N₂O. Cold season gases flux from northern wetlands play an important role in the seasonal gas exchange.     

Screening 31 endocrine-disrupting pesticides in water and surface sediment samples from Beijing Guanting reservoir

For screening 31 potential or suspected endocrine-disrupting pesticides in water and surface sediments, a multiresidue analysis method based on gas chromatography with electron capture detection (GC/ECD) was developed. Solid phase extraction (SPE) technology with Oasis^® HLB cartridge was also applied in sample extraction. The relevant mean recoveries were 70–103% and 71–103% for water and sediment, respectively. Relative standard deviations (RSD) are 2.0–7.0%, 4.0–8.0% for water and sediment, respectively. Thirty one pesticides (-HCH, β-HCH, γ-HCH, δ-HCH, hexachlorobenzene (HCB), aldrin, heptachlor, endosulfan I & II, p,p′-DDD, o,p′-DDT, p,p′-DDT, p,p′-DDE, endrin aldehyde, endosulfan sulphate, methoxychlor, hepachlor epoxide, -chlordane, γ-chlordane, dieldrin, endrin, dicofol, acetochlor, alachlor, metolachlor, chlorpyriphos, nitrofen, trifluralin, cypermethrin, fenvalerate, deltamethrin) in water and surface sediment samples from Beijing Guanting reservoir were analyzed. Concentrations of pesticides ranged from 7.59 to 36.0 ng g⁻¹ on a dry wt. basis for sediment samples, from 279.3 to 2740 ng l⁻¹ for pore waters and from 48.8 to 890 ng l⁻¹ for water samples, respectively, with a mean concentration of 10.7 ng g⁻¹ in sediment, 735 ng l⁻¹ in pore water and 295 ng l⁻¹ in water, respectively. The data obtained provides information on the levels and sources of endocrine-disrupting pesticides in Guanting reservoir. These results underscore the need to improved environmental protection measures in order to reduce the exposure of the population and aquatic biota to these endocrine-disrupting compounds.     

Multi-generation studies with Chironomus riparius--effects of low tributyltin concentrations on life history parameters and genetic diversity

While toxicological data are available for numerous chemicals from standard tests, little is known on effects of pollutants over several generations or regarding chronic effects of chemicals on genetic diversity. Within the experiments, effects of the model pollutant tributyltin (TBT) were investigated over eleven generations at a sublethal TBT concentration of 4.46 μg as Sn kg⁻¹ sediment dw on life-cycle parameters and genetic variability of Chironomus riparius. Moreover, the adaptation potential towards TBT was determined. This experimental design enables the identification of TBT effects on life-cycle parameters and the determination of a potential extinction risk caused by chronic exposure. Furthermore, effects on the genetic structure can be determined, which are not predictable based solely on knowledge of the toxic mode of action of the chemical.

Genetic variety was determined via microsatellite analysis, measuring individual length differences of highly variable satellite DNA fragments. For the identification of changes in tolerances towards the stressor, acute and chronic toxicity experiments were conducted.

During the multi-generation study, significant effects on development and reproduction were determined. For some generations, the emergence was significantly (p < 0.05) delayed under TBT exposure. Reproduction seems to be a sensitive parameter as well, whereby females laid significantly larger egg masses (p < 0.05) in the latter generations. TBT did not affect the population growth rate nor the genetic variability, while clear deviations from the Hardy–Weinberg equilibrium appeared. The study also provides strong evidence for the acquirement of a higher tolerance towards the stressor in the TBT-exposed group.     

Cadmium accumulation and Cd-binding proteins in marine invertebrates--a radiotracer study

Tissue and subcellular accumulation of cadmium were studied in different tissues of three marine invertebrates (blue mussel Mytilus edulis, the tunicate Ciona intestinalis and the sea star Asterias rubens) using radioactive ¹⁰⁹Cd as a tracer. The organisms were exposed to 0.05, 2 and 50 μg Cd l⁻¹ for 21 days. Quantitative data were obtained by dissecting, weighing and subsequently measuring radioactivity in organs and tissues. Differences between each exposure and each tissue with regard to the amount of radioactivity and metallothionein (MT) content were evaluated. Obvious interspecies differences in Cd accumulation were observed, as well as differences between tissues of the three species. The highest concentrations of Cd in all exposure treatments were found in the hepatopancreas of M. edulis and body wall of A. rubens. Taking all treatments into account, Cd accumulation in the tunic of C. intestinalis was high compared to other tissues from this species. Over 60% of Cd was present in the S50 fraction in all treatments in all three species. Metallothionein levels were increased at the highest Cd-exposure in all species and tissues, except in branchial pharynx of C. intestinalis where the highest MT level was reached following exposure to 2 μg Cd l⁻¹. The most surprising finding was that even the lowest Cd exposure concentration (0.05 μg Cd l⁻¹) caused MT induction in pyloric caeca of A. rubens, but there was no dose-dependent increase in MT at higher exposure levels.     

Determination of dithiocarbamate fungicide propineb and its main metabolite propylenethiourea in airborne samples

A simple, rapid and sensitive GC–MS method for the determination of dithiocarbamate fungicide propineb [polymeric zinc propylenebis (dithiocarbamate)] and an improved HPLC procedure for the simultaneous determination of its main metabolite, propylenethiourea, and ethylenethiourea, the main metabolite of all ethylenedithiocarbamates, in airborne samples are described. The method for the analysis of propineb involves the evolution of carbon disulfide (CS₂), under acidic conditions in the presence of stannous chloride, extraction of the generated CS₂ into a layer of isooctane which is then analyzed for CS₂ content by GC–MS in SIM mode. Under the optimum conditions, the retention time of CS₂ was 1.89 min and the total time of chromatographic analysis was 5 min. Recoveries from spiking glass microfibre filters (GF/A) and silica gel filters were 86 ± 7 (n = 9) and 89 ± 4 (n = 9), respectively. The limit of detection is 0.7 ng per filter, which is equivalent to about 0.8–1.0 ng m⁻³ in air. In parallel, an HPLC method with ultraviolet detection is presented for the simultaneous analysis of the metabolites. Separation of the two metabolites was attained in less than 5 min. Recoveries from spiking GF/A and silica gel filters for ethylenethiourea were 100 ± 1 (n = 3) and 98 ± 2 (n = 3), respectively, while for propylenethiourea were 102 ± 1 (n = 3) and 98 ± 1 (n = 3), respectively. The detection limits are about 36–43 and 40–49 ng m⁻³ in air for ethylenethiourea and propylenethiourea, respectively. All the analytes spiked in the filters are proven to be stable for more than one month, at −4 °C.     

Influences of salinity on the biokinetics of Cd, Se, and Zn in the intertidal mudskipper Periophthalmus cantonensis

The biokinetics (aqueous uptake, dietary assimilation, and elimination) of Cd, Se, and Zn in the intertidal mudskipper, Periophthalmus cantonensis, were examined at different acclimated salinities using the radiotracer technique. The dietary assimilation efficiency from ingested radiolabeled polychaetes was the highest for Se (32–40%), followed by Zn (5–7%) and Cd (2–3%), and was not influenced by salinity within a range of 10–30 psu. Uptake from the dissolved phase typically exhibited a linear pattern within the first 12 h of exposure, followed by a second slower uptake. The highest concentration factor (CF) was found for Zn, followed by Cd and Se. Differences in salinity did not significantly affect the CF of the three metals within the first 12 h, but the CFs were significantly higher at lower salinities (10–20 psu) than at the highest salinity (30 psu) by the end of 48 h exposure. Because the degrees to which the uptake of Se (a metalloid) and Cd/Zn were affected by salinity were comparable, we concluded that metal speciation as a result of salinity change was not important in leading to a change in metal CF. Physiological changes may be responsible for the increasing uptake at lowered salinity. The elimination rates of the three metals (0.01–0.06 d⁻¹) were not significantly affected by salinity, but Se was eliminated at a faster rate following aqueous uptake than following dietary ingestion. There was no consistent influence of exposure routes on Cd and Zn elimination. The accumulated Cd was mainly associated with the gut, whereas the muscle was the dominant target site for Se and Zn accumulation.     

Assessment of toxicity of a glyphosate-based formulation using bacterial systems in lake water

A new Aeromonas bioassay is described to assess the potential harmful effects of the glyphosate-based herbicide, Roundup^®, in the Albufera lake, a protected area near Valencia. Viability markers as membrane integrity, culturability and β-galactosidase production of Aeromonas caviae were studied to determine the influence of the herbicide in the bacterial cells. Data from the multifactor analysis of variance test showed no significant differences (P > 0.05) between A. caviae counts of viability markers at the studied concentrations (0, 50 and 100 mg l⁻¹ of glyphosate).

The effects of Roundup^® on microbial biota present in the lake were assessed by measuring the number of indigenous mesophilic Aeromonas in presence of different amounts of the herbicide at 0, 50 and 100 mg l⁻¹ of glyphosate. In samples containing 50 and 100 mg l⁻¹ of glyphosate a significant (P < 0.05) increase in Aeromonas spp. counts and accompanying flora was observed.

The acute toxicity of Roundup^® and of Roundup^® diluted with Albufera lake water to Microtox^® luminescent bacterium (Vibrio fischeri) also was determined. The EC₅₀ values obtained were 36.4 mg l⁻¹ and 64.0 mg l⁻¹ of glyphosate respectively. The acidity (pH 4.5) of the herbicide formulation was the responsible of the observed toxicity.     

Seasonal variation of the distribution of PCBs in sediments and biota in a PCB-contaminated estuary

To elucidate the effects of seasonal variation of precipitation on the distribution of polychlorinated biphenyls (PCBs) in estuarine sediments and benthic feeders, PCB concentrations of river surface sediments and mullet fish (Liza macrolepis) were investigated in the estuary of Er-Jen River near former PCB contamination sites before and after each wet season from 2002 to 2004. Analyses of grain size distribution and organic matter revealed that the pre-existing surface sediments were covered by and mixed with the soil particulates brought by surface runoff after each wet season. Obvious increment of PCB content and significantly elevated fraction (p < 0.005) of light PCBs of the river mouth’s sediments after each wet season indicated that the invading particles were rich in unweathered PCBs. PCBs previously buried in the surface soil of heavily contaminated sites were flushed into this estuary through surface runoff. The precipitation altered the PCB patterns in sediment organic matter, the dietary source of mullet, and consequently changed that of mullets accordingly, which all possessed significant greater fraction of light PCBs. In this study, it was demonstrated that seasonal summer precipitation affected the distribution of PCBs on surface sediments and the mullets of this estuary. PCB residuals retained in this region still pose potential threats to biota resided here.     

Characterizing As(III,V) adsorption by soils surrounding ash disposal facilities

Leachate derived from unlined coal ash disposal facilities is a potential anthropogenic source of arsenic to the environment. To establish a theoretical framework for predicting attenuation of arsenic by soils subject to ash landfill leachate, which is typically enriched in calcium and sulfate, the adsorption of As(V) and As(III) was characterized from 1 mM CaSO₄ for 18 soils obtained down-gradient from three ash landfill sites and representing a wide range in soil properties. As(V) consistently exhibited an order of magnitude greater adsorption than As(III). As(V) adsorption was best described by coupling pH with 15 s DCB-Fe (R² = 0.851,  = 0.001), although pH coupled to clay, DCB-Fe, or DCB-Al also generated strong correlations. For As(III), pH coupled to Ox–Fe (R² = 0.725,  = 0.001) or Ox–Fe/Al (R² = 0.771,  = 0.001) provided the best predictive relationships. Ca²⁺ induced increases in As(V) adsorption whereas sulfate suppressed both As(V) and As(III) adsorption. Attenuation of arsenic from ash leachate agreed well with adsorption measured from 1 mM CaSO₄ suggesting that the use of 1 mM CaSO₄ in laboratory adsorption tests is a reasonable approach for estimating arsenic behavior in soils surrounding ash landfills. We also showed that the impact of leachate-induced changes in soil pH over time may not be significant for As(V) adsorption at pH < 7; however, As(III) adsorption may be impacted over a wider pH range especially if phyllosilicate clays contribute significantly to adsorption. The benefits and limitations of predicting arsenic mobility using linearized adsorption coefficients estimated from nonlinear adsorption isotherms or from the relationships generated in this study are also discussed.     

Sorption of As, Cd and Tl as influenced by industrial by-products applied to an acidic soil: equilibrium and kinetic experiments

In situ stabilization of toxic elements in contaminated soils by the addition of amendments is being considered as an effective technique for remediation. In this paper, we performed both kinetics and equilibrium-based sorption experiments of three toxic elements (As, Cd and Tl) in soils amended with two by-products (phosphogypsum and sugar foam, rich in gypsum and calcium carbonate, respectively) to ascertain the feasibility of their application for improving the sorption capacity of As, Cd and Tl from the soil at 25, 35 and 50 °C. Kinetic studies indicated that the sorption follows a pseudo-second-order (PSO) kinetics and the sorption is a two-step diffusion process where both film and intraparticle diffusion played important roles in the sorption mechanisms of the elements. The Langmuir isotherms applied for sorption studies showed that the estimated maximum sorption capacity of the elements in control and amended soils decreased in the order of Cd > As > Tl. Using the thermodynamic equilibrium parameters obtained at different temperatures, the thermodynamic constants of sorption (ΔG, ΔH and ΔS) were also evaluated, indicating spontaneous and endothermic nature of the process, except Tl which was exothermic. An optimal scaling procedure was undertaken to determine the relationships between the kinetic and equilibrium sorption parameters. By means of statistical analysis it was seen that these inter-parametric relationships are dependent on the element nature.     

Trace elements in atmospheric particulate matter over a coal burning power production area of western Macedonia, Greece

Total suspended particle (TSP) concentrations were determined in the Eordea basin (western Macedonia, Greece), an area with intensive lignite burning for power generation. The study was conducted over a one-year period (November 2000–November 2001) at 10 sites located at variable distances from the power plants. Ambient TSP samples were analyzed for 27 major, minor and trace elements. Annual means of TSP concentrations ranged between 47 ± 33 μg m⁻³ and 110 ± 50 μg m⁻³ at 9 out of the 10 sites. Only the site closest to the power stations and the lignite conveyor belts exhibited annual TSP levels (210 ± 97 μg m⁻³) exceeding the European standard (150 μg m⁻³, 80/779/EEC). Concentrations of TSP and almost all elemental components exhibited significant spatial variations; however, the elemental profiles of TSP were quite similar among all sites suggesting that they are affected by similar source types. At all sites, statistical analysis indicated insignificant (P < 0.05) seasonal variation for TSP concentrations. Some elements (Cl, As, Pb, Br, Se, S, Cd) exhibited significantly higher concentrations at certain sites during the cold period suggesting more intense emissions from traffic, domestic heating and other combustion sources. On the contrary, concentrations significantly higher in the warm period were found at other sites mainly for crustal elements (Ti, Mn, K, P, Cr, etc.) suggesting stronger influence from soil resuspension and/or fly ash in the warm months. The most enriched elements against local soil or road dust were S, Cl, Cu, As, Se, Br, Cd and Pb, whereas negligible enrichment was found for Ti, Mn, Mg, Al, Si, P, Cr. At most sites, highest concentrations of TSP and elemental components were associated with low- to moderate-speed winds favoring accumulation of emissions from local sources. Influences from the power generation were likely at those sites located closest to the power plants and mining activities.     

Experimental Zn(II) retention in a sandy loam soil by very small columns

The use of column experiments, usually performed to better approximate field conditions, may provide information that is not available from batch experiments. In such experiments heavy metals are often adsorbed until saturation followed by desorption experiments. When the affinity of the metal to soil is high, the retention factor (R) could be greater than thousands and the duration of experiments can become impractically long. In order to use reasonable laboratory time, the flow rate should be increased or the column size decreased. The increase in flow rate produces undesirable kinetic and dispersion effects, so we used very small soil columns (pore volume = 0.31–0.70 ml) and relatively high flow rates (0.03–0.12 ml min⁻¹) in studies of Zn(II) adsorption and retention in soils. Conservative tracer flow column experiments under saturation conditions were carried out to determine flow parameters for different flow rates. Column pore volume (V_p), Peclet numbers (Pe) and longitudinal dispersion coefficients (D_L) were determined from breakthrough curves. The effect of type of electrolyte and ionic strength on the Zn(II) retention onto soil was determined. The influence of flow rate and bed height on the retention coefficient and on the mass transfer zone was also studied. The effect of different influent Zn(II) concentrations on the R values obtained was analyzed. Freundlich parameters from column experiments were compared with batch ones. The leaching efficiency of different electrolytes, salts of weak organic acids and EDTA was also studied.     

The enhancement of photodegradation efficiency using Pt-TiO2 catalyst

The residues from the extraction of lead/zinc (Pb/Zn) ores of most Pb/Zn mines are permanently stored in tailings ponds, which require revegetation to reduce their environmental impact. This can only be done if the main constraints on plant establishment are evaluated. This can readily be done by field and greenhouse studies.

To test this, the properties of different tailings from Lechang Pb/Zn mine located at the north of Guangdong Province in southern China have been studied. Physical and chemical properties including concentrations of metals (Pb, Zn, Cd and Cu) in the tailings and soils collected from different sites have been measured. The results showed that tailings contain low nitrogen (0.016–0.075%), low-organic matter (0.58–1.78%), high salt (3.55–13.85 dS/m), and high total and diethylene–tetramine–pentaacetic acid (DTPA)-extractable metal concentrations (total: 1019–1642 μg g⁻¹ Pb, 3078–6773 μg g⁻¹ Zn, 8–23 μg g⁻¹ Cd, and 85–192 μg g⁻¹ Cu; DTPA-extractable: 59–178 μg g⁻¹ Pb, 21–200 μg g⁻¹ Zn, 0.30–1.5 μg g⁻¹ Cd, and 4.3–12 μg g⁻¹ Cu). Aqueous extracts of tailings/soils (10%, 20% and 30%, w/v) from different sites were prepared for testing their effects on seed germination and root elongation of a vegetable crop Brassica chinensis and a grass species Cynodon dactylon. It was found that root elongation provided a better evaluation of toxicity than seed germination. The ranking of toxicity using root elongation was: high-sulfur tailings>tailingdam>sparsely vegetated tailings>densely vegetated tailings>mountain soil for both plants. This order was consistent with DTPA-extractable Pb contents in the tailings and soils. B. chinensis seedlings were then grown in the mixtures of different proportions of tailings and farm soil for 4 weeks, and the results (dry weights of seedlings) were in line with the root elongation test. All these demonstrated that heavy metal toxicity, especially available Pb, low content of nutrient, and poor physical structure were major constraints on plant establishment and colonization on the Pb/Zn mine tailings.     

Distribution of mercury in adult penaeid shrimps from Altata-Ensenada del Pabellón lagoon (SE Gulf of California)

The Altata-Ensenada del Pabellón lagoon system is located in the central part of Sinaloa state, NW Mexico. The major sources of pollution are represented by the waste effluents from the intensive agriculture and the urban sewage from the cities of Culiacán (population of 750 000) and Navolato (population of 50 000). In this lagoon system diverse penaeid shrimps occur; the crystal shrimp Farfantepenaeus brevirostris, the brown shrimp F. californiensis, the blue shrimp Litopenaeus stylirostris, the white shrimp L. vannamei and the Pacific seabob Xiphopenaeus kroyeri. With the purpose of knowing distribution and relative concentrations of Hg in the main tissues of penaeid shrimps, levels of Hg in five species from Altata-Enesenada del Pabellón lagoon on the SE Gulf of California were determined. Analysis were carried out by reducing mercury compounds after acid digestion reduction with SnCl₂ and detection by cold vapour atomic absorption. In general, hepatopancreas was the tissue where Hg was mostly accumulated, followed by muscle and exoskeleton. The sequence of Hg concentrations in the five species studied here for every tissue was: hepatopancreas L. vannamei > F. californiensis > L. stylirostris > F. brevirostris > X. kroyeri; muscle L. stylirostris > F. brevirostris > L. vannamei > F. CALIFORNIENSIS=X. kroyeri and exoskeleton F. brevirostris > F. californiensis > L. vannamei > L. stylirostris > X. kroyeri.