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1.
Some vascular plants are known to concentrate trace metals and are regarded to be suitable indicators of atmospheric metal deposition. Among plant species used for biogeochemical studies dandelion ( Taraxacum officinale.) is convenient for monitoring air/soil pollution. The plant commonly occurs in different ecosystems with relatively parallel stages of ontogenesis over a broad area of geographical regions. Its leaves and roots are easily accessible for sampling. Leaf to root ratios of metal concentrations in dandelion may indicate the source of metals during the growing season. Trace metals in leaves and roots of dandelion from 132 sites in Poland showed higher concentrations in the plants from the SW region compared to those from the NE region of the country. However, the differences were only statistically significant ( = 0.05) for Cd, Ni, and Pb. Geometric means of metal concentrations (mg kg –1, air dried weight) in dandelion leaves of the SW and NE regions were: Cd 0.85, 0.52; Cr 0.99, 0.81; Cu 11.2, 11.1; Fe 184.4, 100.0; Mn 59.7, 51.4; Ni 2.1, 1.5; Pb 4.4, 3.0; and Zn 49.6, 41.3, respectively. Markedly higher concentrations of Cd, Pb, and Zn were found in the leaves of the dandelion over roots in the SW region. These metals are the most serious aerial pollutants in that part of the country. 相似文献
2.
Carbon, nitrogen, oxygen and sulfide budgets are derived for the Black Sea water column from a coupled physical-biogeochemical model. The model is applied in the deep part of the sea and simulates processes over the whole water column including the anoxic layer that extends from ?115 m to the bottom (?2000 m). The biogeochemical model involves a refined representation of the Black Sea foodweb from bacteria to gelatinous carnivores. It includes notably a series of biogeochemical processes typical for oxygen deficient conditions with, for instance, bacterial respiration using different types of oxidants (i.e denitrification, sulfate reduction), the lower efficiency of detritus degradation, the ANAMMOX (ANaerobic AMMonium OXidation) process and the occurrence of particular redox reactions. The model has been calibrated and validated against all available data gathered in the Black Sea TU Ocean Base and this exercise is described in Gregoire et al. (2008). In the present paper, we focus on the biogeochemical flows produced by the model and we compare model estimations with the measurements performed during the R.V. KNORR expedition conducted in the Black Sea from April to July 1988 (Murray and the Black Sea Knorr Expedition, 1991). Model estimations of hydrogen sulfide oxidation, metal sulfide precipitation, hydrogen sulfide formation in the sediments and water column, export flux to the anoxic layer and to the sediments, denitrification, primary and bacterial production are in the range of field observations.With a simulated Gross Primary Production (GPP) of 7.9 mol C m −2 year −1 and a Community Respiration (CR) of 6.3 mol C m −2 year −1, the system is net autotrophic with a Net Community Production (NCP) of 1.6 mol C m −2 year −1. This NCP corresponds to 20% of the GPP and is exported to the anoxic layer. In order to model Particulate Organic Matter (POM) fluxes to the bottom and hydrogen sulfide profiles in agreement with in situ observations, we have to consider that the degradation of POM in anoxic conditions is less efficient that in oxygenated waters as it has often been observed (see discussion in Hedges et al., 1999). The vertical POM profile produced by the model can be fitted to the classic power function describing the oceanic carbon rate ( CR= Z−α) using an attenuation coefficient α of 0.36 which is the value proposed for another anoxic environment (i.e. the Mexico Margin) by Devol and Hartnett (2001). Due to the lower efficiency of detritus degradation in anoxic conditions and to the aggregation of particles that enhanced the sinking, an important part of the export to the anoxic layer (i.e. 33%, 0.52 mol C m −2 year −1) escapes remineralization in the water column and reaches the sediments. Therefore, sediments are active sites of sulfide production contributing to 26% of the total sulfide production.In the upper layer, the oxygen dynamics is mainly governed by photosynthesis and respiration processes as well as by air-sea exchanges. ?71% of the oxygen produced by phytoplankton (photosynthesis+nitrate reduction) is lost through respiration, ?21% by outgasing to the atmosphere, ?5% through nitrification and only ?2% in the oxidation of reduced components (e.g. Mn 2+, Fe 2+, H 2S).The model estimates the amount of nitrogen lost through denitrification at 307 mmol N m −2 year −1 that can be partitioned into a loss of ?55% through the use of nitrate for the oxidation of detritus in low oxygen conditions, ?40% in the ANAMMOX process and the remaining ?5% in the oxidation of reduced substances by nitrate.In agreement with data analysis performed on long time series collected since the 1960s (Konovalov and Murray, 2001), the sulfide and nitrogen budgets established for the anoxic layer are not balanced in response to the enhanced particle fluxes induced by eutrophication: the NH 4 and H 2S concentrations increase. 相似文献
3.
White lupin is an annual crop that has been used for phytostabilization of acidified multicontaminated (heavy metals and As)
soils from the Aznalcóllar spill-affected area, Southern Spain. One of the most important factors for successful phytostabilization
is monitoring the pollutant bioavailability in the soil. The aim of this work was to determine the best-suited method for
assessing the bioavailability of heavy metals together with As in the Aznalcóllar spill-affected area, by means of a systematic
comparison between different extraction methods (Ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA), CaCl 2, NaNO 3, BCR, (NH 4) 2SO 4 and rhizo). Both AB-DTPA and the first step of the BCR method were found to be unsuitable for assessing the bioavailability of heavy
metals and As to plants growing in acidic soils. However, CaCl 2-extractable As, Cu, and Zn and NaNO 3-extractable As and Zn were well correlated with their concentrations in plant organs. Rhizo and (NH 4) 2SO 4, with the highest determination coefficients, were the most recommended simple extraction methods to assess the bioavailability
of As, Cu, Fe, Mn, and Zn in acidified multicontaminated soils using white lupin as an excluder model plant. 相似文献
4.
Microbial oxidation of organic compounds (including methane), in freshwater sediments, may result in precipitation of carbonates,
which may become an important geochemical archive of paleoenvironmental variations. Most probably low δ 13C value in calcite in eutrophic systems results from an advanced oxidation of organic compounds in turbulent or/and sulphate-rich
conditions. Likewise, high δ 13C value in calcite from organic-rich sediments may evidence low redox potential of the freshwater system. Oxidation of methane
and organic matter results in significant isotope effects in sulphates dissolved in water. Therefore, to better understand
the origin of carbon isotope signal in carbonates, concentration and stable isotope measurements in dissolved sulphate (water
column), bubble methane and calcite (freshwater sediments) have been carried out in 24 lakes, 2 ponds and 4 rivers in Poland.
The highest concentration of sulphate has been detected in rivers (85.47 SO 4
2− mg/l) and an artificial lake (70.30 SO 4
2− mg/l) located in the extremely SO 4
2−-polluted region called the “Black Triangle”. The lowest concentration of sulphate is found in dystrophic and mountain lakes
(from 0.5 SO 4
2− to about 3 mg/l). The lowest δ 34S(SO 4
2−) and δ 18O(SO 4
2−) values occur in unpolluted lakes in eastern Poland (−0.94 and 1.38‰, respectively). The highest S and O isotopic ratios
are found in a polluted lake in western Poland (δ 14S(SO 4
2)=12.95‰) and in a dystrophic lake in eastern Poland (δ 18O(SO 4
2) = 16.15‰) respectively. It is proposed that δ 34SO 4
2− and ( 18O(SO 4
2−) values in lakes represent a good tool to assess and quantify anthropogenic impact by acid precipitation and to monitor variations
in the trophic state and redox processes controlled by biodegradation of organic compounds in sediments and water column.
In general, increasing depth (up to 12 m) of the water column is associated with decreasing trend the δ 13C(CH 4) value from about –35 to about –78‰. However, δ 13C value in sedimentary calcite (δ 13C vary from –10 to 0.5‰) shows opposite trends as compared to the corresponding methane. This is probably due to redox processes
and distribution of heavy isotopes between methane and calcite. Likewise, turbulent water (river) show high δ 13C value in methane and low δ 13C value in calcite—this is probably due to an enhanced oxidation of methane producing 13C-depleted CO 2. In contrast to clean lakes, it is observed that an increase of the δ 13C(CH 4) value occurs with increasing depth of the water column in a strongly SO 4
2−-contaminated lake. This is probably due to a loss of biological buffering potential of the lake accompanied by an active
oxidation of methane precursors. 相似文献
6.
The occurrence of bioactive trace pollutants such as pharmaceuticals in natural waters is an emerging issue. Numerous pharmaceuticals
are not completely removed in conventional wastewater treatment plants. Advanced oxidation processes may represent an interesting
alternative to completely mineralize organic trace pollutants. In this article, we show that sulfate radicals generated from
peroxymonosulfate/Co II are more efficient than hydroxyl radicals generated from the Fenton’s reagent (H 2O 2/Fe II) for the degradation of the pharmaceutical compound, carbamazepine. The second-order rate constant for the reaction of SO 4
·− with carbamazepine is 1.92·10 9 M −1 s −1. In laboratory grade water and in real urban wastewater, SO 4
·− yielded a faster degradation of carbamazepine compared to HO · . Under strongly oxidizing conditions, a nearly complete mineralization of carbamazepine was achieved, while under mildly
oxidizing conditions, several intermediates were identified by LC–MS. These results show for the first time in real urban
wastewater that sulfate radicals are more selective than hydroxyl radicals for the oxidation of an organic pollutant and may
represent an interesting alternative in advanced oxidation processes. 相似文献
7.
Zea mays was grown in nutrient solution with different concentrations of sulphite and sulphate (0, 5, and 10 mM) at pH 5 or 7, with or without aeration, for five days. Sulphite injured the plants, especially at low pH. Lack of aeration increased the sulphite injury of the plants at the high pH. in the aerated solutions, sulphite concentrations approached zero after five hours, while the unaerated solutions still contained sulphite after four days. Very little sulphite was found in the plants. The results indicate that the toxicity to the plants of the different chemical species of the sulphite in the solution decreases in the following order: SO 2 (aq) > HSO 3
– > SO 3
2–. 相似文献
8.
In anoxic sediments, as those found in estuaries, the mobility of metals can be controlled by the formation of stable sulfide
complexes. The potential bioavailability of a metal can then be predicted on the basis of the acid volatile sulfide (AVS)
and simultaneously extracted metals (SEM) criterion. Distributions of AVS and SEM (Hg, Cu, Pb, Cd, Zn, and Ni) along the sediment
profiles were determined seasonally for three rivers that constitute the Santos-Cubat?o estuarine system (SE Brazil), which
is located in one of the most industrialized areas of Latin America. AVS and SEM concentrations varied significantly, from
0.04 to 31.9 μmol g −1 and 0.086–6.659 μmol g −1, respectively. The highest AVS levels in sediments were detected in the winter, whereas high SEM values predominated in the
summer. Considering SEM–AVS molar differences as a parameter to evaluate potential bioavailability, sediments nearest to the
industrial area represent higher risk to biota, especially during the summer. It is due to relatively low AVS values and not
necessarily high concentrations of metals. 相似文献
9.
Water pollution by antibiotics is an increasing concern, which may be addressed by advanced oxidation processes using sulfites as precursors of sulfate radicals (SO4·–), yet the efficiency of sulfite activation is limited. Here, we tested copper cobalt sulfide (CuCo2S4) to activate sulfite, based on the synergy among transition metals and the facilitation of transition metal redox circulation by reductive sulfur species. We analyzed CuCo2S4 structure by X-Ray photoelectron spectroscopy, and we studied the effect of pH and radical scavengers. Results show 90–100% abatement of tetracycline concentration at pH 8.0–10.0, with SO4·– and HO· as the main reactive radicals. This finding is explained by the accelerated redox recycling of copper and cobalt by sulfur, and by the synergetic effect between active cobalt and copper sites. 相似文献
10.
Leachates from the El Fraile tailings impoundment (Taxco, Mexico) were monitored every 2 months from October 2001 to August 2002 to assess the geochemical characteristics. These leachates are of interest because they are sometimes used as alternative sources of domestic water. Alternatively, they drain into the Cacalotenango creek and may represent a major source of metal contamination of surface water and sediments. Most El Fraile leachates show characteristics of Ca–SO 4, (Ca+Mg)–SO 4, Mg–SO 4 and Ca–(SO 4+HCO 3) water types and are near-neutral (pH=6.3–7.7). Some acid leachates are generated by the interaction of meteoric water with tailings during rainfall events (pH=2.4–2.5). These contain variable levels of SO 4
2− (280–29,500 mg l −1) and As (<0.01–12.0 mg l −1) as well as Fe (0.025–2352 mg l −1), Mn (0.1–732 mg l −1), Zn (<0.025–1465 mg l −1) and Pb (<0.01–0.351 mg l −1). Most samples show the highest metal enrichment during the dry seasons. Leachates used as domestic water typically exceed the Mexican Drinking Water Guidelines for sulfate, hardness, Fe, Mn, Pb and As, while acidic leachates exceed the Mexican Guidelines for Industrial Discharge Waters for pH, Cu, Cd and As. Speciation shows that in near-neutral solutions, metals exist mainly as free ions, sulfates and bicarbonates, while in acidic leachates they are present as sulfates and free ions. Arsenic appears as As (V) in all samples. Thermodynamic and mineralogical evidence indicates that precipitation of Fe oxides and oxyhydroxides, clay minerals and jarosite as well as sorption by these minerals are the main processes controlling leachate chemistry. These processes occur mainly after neutralization by interaction with bedrock and equilibration with atmospheric oxygen. 相似文献
11.
Numerous studies had focused on the association between air pollution and health outcomes in recent years. However, little evidence is available on associations between air pollutants and premature rupture of membranes (PROM). Therefore, we performed time-series analysis to evaluate the association between PROM and air pollution. The daily average concentrations of PM2.5, SO2 and NO2 were 54.58 μg/m3, 13.06 μg/m3 and 46.09 μg/m3, respectively, and daily maximum 8-h average O3 concentration was 95.67 μg/m3. The strongest effects of SO2, NO2 and O3 were found in lag4, lag06 and lag09, and an increase of 10 μg/m3 in SO2, NO2 and O3 was corresponding to increase in incidence of PROM of 8.74% (95% CI 2.12–15.79%), 3.09% (95% CI 0.64–5.59%) and 1.68% (95% CI 0.28–3.09%), respectively. There were no significant effects of PM2.5 on PROM. Season-specific analyses found that the effects of PM2.5, SO2 and O3 on PROM were more obvious in cold season, but the statistically significant effect of NO2 was observed in warm season. We also found the modifying effects by maternal age on PROM, and we found that the effects of SO2 and NO2 on PROM were higher among younger mothers (<?35 years) than advanced age mothers (≥?35 years); however,?≥?35 years group were more vulnerable to O3 than?<?35 years group. This study indicates that air pollution exposure is an important risk factor for PROM and we wish this study could provide evidence to local government to take rigid approaches to control emissions of air pollutants. 相似文献
12.
There is increased concern over the effects of elevated concentrations of Al in the environment. Unfortunately, studies of the environmental chemistry and toxicity of Al have been limited by our understanding of the processes regulating the aqueous concentration, speciation and bioavailability of this element.Although Al is the most abundant metallic element in the Earth's crust, it is highly insoluble and generally unavailable to participate in biogeochemical reactions. However, under highly acidic or alkaline conditions, or in the presence of complexing ligands, elevated concentrations may be mobilized to the aquatic environment. Ecologically significant concentrations of Al have been reported in surface waters draining acid-sensitive regions that are receiving elevated inputs of acidic deposition. Acid- sensitive watersheds are characterized by limited release of basic cations (Ca 2+, Mg 2+, Na +, K +) and/or retention of strong acid anions (SO 4
2–, NO 3
–, Cl –). Under these conditions inputs of strong acids are not completely neutralized, but rather acidic water is exported from the terrestrial environment. It has been hypothesized that acidic deposition to acid-sensitive watersheds mobilizes Al within the mineral soil, causing elevated concentrations in soil solutions and surface waters. As a result of mineral phase solubility constraints, concentrations of aqueous Al increase exponentially with decreases in pH below 6.0.Monomeric Al occurs as a series of complexes in the aqueous environment, including aquo, OH –, F –, SO 4
2–, HCO 3
– and organic species. Of these aquo, OH –, F – and organic complexes are the most significant in natural waters.Elevated concentrations of Al are ecologically significant because: 1) Al is an important pH buffer in acidic waters, regulating the lower limit of pH values following acidification by strong acids; 2) through adsorption and coagulation reactions, Al may alter the cycling and availability of important elements like phosphorus, organic carbon and certain trace metals; 3) Al may serve as a coagulant facilitating the removal of light attenuating materials, thereby increasing the clarity and decreasing the thermal stability of lakes; and 4) Al is potentially toxic to organisms. Better understanding of the chemistry and speciation of Al is essential to assess these effects. 相似文献
13.
This study evaluated variations in heavy metal contamination of stream waters and groundwaters affected by an abandoned lead–zinc mine, where a rockfill dam for water storage will be built 11 km downstream. For these purposes, a total of 10 rounds of stream and groundwater samplings and subsequent chemical analyses were performed during 2002–2003. Results of an exploratory investigation of stream waters in 2000 indicated substantial contamination with heavy metals including zinc (Zn), iron (Fe) and arsenic (As) for at least 6 km downstream from the mine. Stream waters near the mine showed metal contamination as high as arsenic (As) 8,923 μg L −1, copper (Cu) 616 μg L −1, cadmium (Cd) 223 μg L −1 and lead (Pb) 10,590 μg L −1, which greatly exceeded the Korean stream water guidelines. Remediation focused on the mine tailing piles largely improved the stream water qualities. However, there have still been quality problems for the waters containing relatively high concentrations of As (6–174 μg L −1), Cd (1–46 μg L −1) and Pb (2–26 μg L −1). Rainfall infiltration into the mine tailing piles resulted in an increase of heavy metals in the stream waters due to direct discharge of waste effluent, while dilution of the contaminated stream waters improved the water quality due to mixing with metal free rain waters. Levels of As, Cu and chromium (Cr) largely decreased after heavy rain but that of Pb was rather elevated. The stream waters were characterized by high concentrations of calcium (Ca) and sulfate (SO 4), which were derived from dissolution and leaching of carbonate and sulfide minerals. It was observed that the proportions of Ca and SO 4 increased while those of bicarbonate (HCO 3) and sodium and potassium (Na+K) decreased after a light rainfall event. Most interestingly, the reverse was generally detected for the groundwaters. The zinc, being the metal mined, was the most dominant heavy metal in the groundwaters (1758–10,550 μg L −1) near the mine, which far exceeded the Korean standard of 1000 μg L −1 for drinking water. The decreases in the heavy metals contents in the groundwaters associated with reduced rainfall were quite different from the increases observed for the stream waters, which is not clearly understood at this time and warrants further investigation. 相似文献
14.
Eelgrass ( Zostera marina L.) has access to nutrient pools in both the water column and sediments. We investigated the potential for eelgrass to utilize nitrate nitrogen by measuring nitrate reductase (NR) activity with an in vivo tissue assay. Optimal incubation media contained 60 m M nitrate, 100 m M phosphate, and 0.5% 1-propanol at pH 7.0. Leaves had significantly higher NR activity than roots (350 vs 50 nmoles NO
2
–
produced g FW –1 h –1). The effects of growing depth (0.8 m MLW, 1.2 m, 3.0 m, 5.0 m) and location within the eelgrass meadow (patch edge vs middle) on NR activity were examined using plants collected from three locations in the Woods Hole area, Massachusetts, USA, in July 1987. Neither depth nor position within the meadow appear to affect NR activity. Nitrate enrichment experiments (200 M NO
3
–
for 6 d) were conducted in the laboratory to determine if NR activity could be induced. Certain plants from shallow depth (1.2 m) showed a significant response to enrichment, with NR activity increasing from >100 up to 950 nmoles NO
2
–
g FW –1 h –1 over 6 d. It appears that Z. marina growing in very shallow water (0.8 m) near a shoreline may be affected by ground water or surface run-off enrichments, since plants from this area exhibited rates up to 1 600 nmol NO
2
–
g FW –1 h –1. Water samples from this location consistently had slightly higher NO
3
–
concentrations (1.4 M) than all other collection sites (0.7 M). Thus, it is possible that chronic run-off or localized groundwater inputs can create sufficient NO
3
–
enrichment in the water column to induce nitrate reductase activity in Zostera leaves. 相似文献
15.
Trace metal concentrations were determined in particulate matter (PM 10) in ambient air of four purposively selected residential areas in Ibadan, Nigeria namely Bodija market (BM), Ojo Park (OP), Oluyole Estate (OE) and University of Ibadan (UI). PM 10 was determined in the morning (7–10 a.m.) and afternoon (2–5 p.m.) for 12 weeks in the dry season months of January–March using a volumetric sampler following standard procedures and levels compared with WHO guideline limits. Glass-fibre filter papers exposed to the particulate matter were digested using appropriate acid mixtures, and the digest analysed for trace metals including Ni, Cr, Mn, Zn, and Pb using ICPMS method and levels compared with WHO limits. Data was analysed using ANOVA and Pearson correlation test at 5 % level of significance. The highest mean PM 10 concentrations 502.3 ± 39.9 μg/m 3 were recorded in the afternoon period at BM, while the lowest concentration 220.6 ± 69.9 μg/m 3 was observed in the morning hours at UI. There was a significant difference between the PM 10 levels across the various locations ( p < 0.05), and all the levels were higher than WHO limit of 50 μg/m 3. The highest levels of Ni, Zn and Pb were recorded at BM, which also had the highest PM 10 burden. The trend in Pb levels across the locations was BM > UI > OP > OE with the highest level 5.70 μg/m 3 in BM nearly fourfolds WHO limits of 1.5 μg/m 3. There was a significant correlation between PM 10 and Ni ( p < 0.05).Urban communities with increased human activities especially motor traffic recorded both higher levels of PM 10 and toxic trace metals. There is need to carry out source apportionment to establish the origin of these trace metals in future studies. 相似文献
16.
The aim of this study was to evaluate the effects of copper (Cu) stress on accumulation and transport of trace elements, nitrogen assimilation, and growth parameters of Verbascum olympicum. Eight-week-old seedlings were grown in Hoagland's solution and exposed to 0, 50, 250, or 500?µM CuSO 4 for seven days in laboratory conditions. Bioaccumulation of trace elements (boron, bismuth, cobalt, Cu, iron, lithium, manganese, molybdenum, nickel, lead, zinc) in the roots and leaves was determined by inductively coupled plasma–mass spectrometry after one, three, and seven days. Chlorophyll content, nitrate reductase, and glutamine synthetase activities, soluble protein content, and biomass were determined. Copper accumulated in the roots and leaves (up to 19609.8 and 256.2?mg?kg ?1 dry weight, respectively). Other trace elements accumulated to higher levels in the roots of Cu-treated plants compared with those of control plants. High Cu concentrations decreased nitrogen-assimilatory enzyme activities. Compared with control plants, those treated with high Cu concentrations showed lower chlorophyll contents, total protein contents, and biomass. Nitrogen assimilation and growth parameters of V. olympicum were negatively affected by Cu treatment but mineral nutrition was not severely disrupted. The results support the suitability of V. olympicum as a candidate for phytoremediation of Cu-contaminated soils. 相似文献
17.
Rates of sulfate reduction were measured during the spring dry and summer wet seasons of 1992 in shallow coastal sediments of the central Great Barrier Reef lagoon. In the dry season, sulfate reduction rates, integrated to 18–20 cm depth, ranged from 23.8 to 30.8 mmol S m -2 d -1. In the wet season, heavy monsoonal rains and wind-induced waves caused severe disturbance of sediments leading to less anoxic conditions, and to a 2- to 3-fold decline in rates of sulfate reduction (10.2 to 12.8 mmol S m -2 d -1). The percentage of reduced 35S recovered as acid-volatile sulfide (% AVS red) ranged from 15.8 to 44.9% in spring, and was significantly reduced at each station in summer (range 14.5 to 31.4%). An analysis of variance indicated that seasonality accounted for 31.5% of the total variance in total rates of sulfate reduction, with only 7.5% of the variance accounted for by depth into the sediment; there were no station differences. In both seasons, there were no clear patterns in the proportion of radiolabel incorporated into the AVS and chromium-reducible sulfur (CRS) pools with depth into the sediment. These results are contrary to the seasonal patterns and pathways of sulfate reduction in temperate coastal sediments. 相似文献
18.
A laboratory modelling for the assessment of damage to marble by the SO 2-acidity in the vicinity of stacks has been devised. The modelling is based on the role of metal oxide particulates (also emitted by smoke-stacks) which catalytically convert SO 2 to SO 3 forming H 2SO 4 (in presence of water), which has an excessively high selectivity, compared with HNO 3, for corroding marble. The requisites of the modelling are: (1) determination of composition of the marble, (2) immersion of samples of marble blocks (after measurement of surface areas) in H 2SO 4 solutions of known concentrations, maintaining pH and temperature at their initial values, (3) determination of concentrations of Ca and Mg (major components of marble) in the leachate, and thereby evaluating the mass loss of the marble, in terms of mg marble cm –2 day –1, for each level of H 2S0 4 concentration, (4) application of derived data for evaluation of duration (in years) for the decay of 1 cm thickness of marble block by the process of surface corrosion. From the modelling, it was found that the duration for the damage of 1 cm thickness of the marble sample used here by SO 2 acidities of 1, 5, 10, 50 and 100 ppm are 83.01, 69.02, 31.24, 8.19 and 4.31 years respectively. 相似文献
19.
The temperate seagrass Zostera marina L. typically grows in highly reducing sediments. Photosynthesis-mediated O 2 supplied to below-ground tissues sustains aerobic respiration during photosynthetic periods. Roots, however, experience daily periods of anoxia and/or hypoxia at night and under conditions that reduce photosynthesis. Rhizosphere cores of Z. marina were collected in August 1984 from Great Harbor, Massachusetts, USA. We examined short-term anaerobic metabolism of [U- 14C]sucrose in excised roots and roots of intact plants. Under anaerobic conditions roots showed appreciable labeling of CO 2, ethanol and lactate, and slight labeling of alanine and other metabolites. Over 95% of the 14C-ethanol was recovered in the root exudate. Release of other metabolites from the roots was minimal. Ethanol was also released from hypoxic/anoxic roots of intact plants and none of this ethanol was transported to the shoot under any experimental conditions. Loss of ethanol from roots prevented tissue levels of this phytotoxin from increasing during anaerobiosis despite increased synthesis of ethanol. Anaerobic metabolism of [U- 14C]glutamate in excised roots led to appreciable labelling of -aminobutyrate, which was known to accumulate in eelgrass roots. Roots recovered to fully aerobic metabolism within 4 h after re-establishment of aerobic conditions. The contributions of these root metabolic responses to the ability of Z. marina to grow in reducing marine sediments are related to light-regulated interactions of shoots and roots that likely dictate depth penetration, distribution and ecological success of eelgrass. 相似文献
20.
In risk assessment of aquatic sediments, much attention is paid to the difference between acid volatile sulfide (AVS) and simultaneously extracted metals (SEM) as indicators of metal bioavailability. Distribution of AVS and SEM (Cd, Cu, Ni, Pb and Zn) were determined in 20 representative sampling sites collected along the Egyptian Mediterranean coast. Total SEM concentration [ΣSEM] ranged from 0.012 to 0.241 μmoleg ?1. AVS concentrations were much more variable, showing significant spatial variations. The values ranged from 0.015 to 31.326 μmoleg ?1. The different relationships between AVS and SEM to establish mechanical models such as the ratio of ΣSEM and AVS [ΣSEM/AVS], the difference between the ΣSEM and AVS [ΣSEM–AVS], or the organic carbon normalised difference between SEM and AVS [ΣSEM-AVS]/ foc models were used as parameters to evaluate potential bioavailability. Considering SEM/AVS model, sediments at the Western Harbour, Eastern Harbour, Ras El-Burr, El-Gamil East, and Port Said stations are occasionally toxic, while according to SEM-AVS model, no indication of associated adverse toxic effect would occur at any of the sampling sites. Calculated [ΣSEM-AVS]/ foc was<130 μmoleg ?1 in the sediments indicating that sediments should pose a low risk of adverse biological effects owing to cadmium, copper, lead, nickel and zinc. Association of adverse effects to aquatic organisms was determined, using the classification of the sediments according to the Sediment Quality Guidelines (SQGs). The marine Threshold Effect Levels (TEL) and Probable Effect Levels (PEL) were used in this work and in order to obtain a more realistic measure of predicted toxicity, mean PEL quotients (PELq) were calculated. The mean PELq calculated for the sampling sites was (0.11–1.5) and categorised as slightly toxic at all stations except Baghoush, Nobarreya and western harbour, which had PELq<0.1 and categorised as non-toxic. The obtained data concluded that the remobility and bioavailability of trace metals contained in surfacial sediments of the Egyptian Mediterranean coastal area are low. 相似文献
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