Distribution of trace elements in the tissues of benthic and pelagic fish from the Kerguelen Islands

New information on the concentrations of Cd, Cu, Hg and Zn in the liver, kidney and muscles of eight marine benthic and pelagic sub-Antarctic fish species are presented to determine the importance of these metals in the marine systems of the Kerguelen Islands. Compared to the reported metal concentrations in other Antarctic fish species, the present results are globally within the same range of concentrations, although Cd displayed a very high interspecific variability in liver and kidney. Indeed, the highest Cd concentrations in liver, ranging from 10.0 to 52.1 microg x g(-1) dry wt. but also the lowest Cd concentrations in muscles (<0.030 microg x g(-1) dry wt.) have been displayed by the pelagic Myctophidae Gymnoscopelus piabilis. Metal concentrations differences might be related to diet and feeding habits of benthic and pelagic fish species. However, Cd and Hg concentrations in the edible muscle are lower than the French limit values (相似文献   

Mercury transport and bioaccumulation in riverbank communities of the Alvarado Lagoon System, Veracruz State, Mexico

The Alvarado Lagoon System (ALS) is located within the Papaloapan River Basin in southern Veracruz, Mexico. The ALS is a shallow system (2 m) connected to the Gulf of Mexico through a narrow sea channel. There are a large number of riverbank communities within the ALS that are dependent upon its biological productivity for comestible and economic subsistence. The purpose of this project was to determine the levels of mercury in water, sediment, fish, and hair samples from within the Papaloapan River Basin and to characterize the risk of Hg exposure to the individuals that reside in these communities. Water and fish samples were collected during the wet (September 2005) and dry (March 2003 and 2005) seasons. Hair samples, dietary surveys, and sediment samples were obtained during the wet and dry seasons of 2005. Total Hg in the water column ranged from 1.0 to 12.7 ng/L. A strong correlation (R(2)=0.82; p<0.001) between total Hg and total suspended solids in the water column suggests that particulate matter is a transport mechanism for Hg within the lagoon system. Total Hg in the sediments ranged from 27.5 to 90.5 ng Hg/g dry weight with no significant difference between the 2005 wet and dry seasons. There was a mild, but significant, correlation between total Hg and % carbon for the March 2005 sediment samples (R(2)=0.435; p=0.020), suggesting that Hg is associated with organic matter on the solid phase. Concentrations of total Hg in fish and shellfish harvested from the ALS ranged from 0.01 to 0.35 microg Hg/g wet. The levels of total Hg in hair ranged from 0.10 to 3.36 microg Hg/g (n=47) and 58% of the samples were above 1.00 microg Hg/g. The findings from this study suggest that individuals who frequently consume fish and shell fish containing low levels of Hg (<0.3 microg/g) can accumulate low to moderate body burdens of Hg, as indicated by hair Hg concentrations>1.0 microg/g, and may be at risk for experiencing low dose mercury toxicity.     

Fish bile used to detect estrogenic substances in treated sewage water

Endocrine disrupting effects on fish associated with sewage treatment effluents have been demonstrated in several studies. To investigate if the effluents from two modern Swedish sewage treatment plants contained estrogenic substances, juvenile rainbow trout were exposed to sewage water before and after the last treatment step which is a sand filter. As a biomarker for estrogenic effect, vitellogenin was analysed in the blood plasma of the exposed fish. To identify substances possibly responsible for the effect, bile fluid from the exposed fish were analysed with GC/MS. Elevated levels of vitellogenin were only seen in the fish exposed at one of the sewage treatment plants, the one with shorter residence time in the biological treatment steps, which suggests that the residence time is of importance for the ability to reduce the amount of estrogenic substances in the sewage water. The highest elevation of vitellogenin was seen in the fish exposed to water before the sand filter, which indicates that the sand filter contributes to further reduction of estrogenic substances in the sewage water. In bile from the same group of fish, considerably higher concentrations of estrone, bisphenol A and 4-nonylphenol (4.0 microg/g bile, 23 microg/g bile and 24 microg/g bile, respectively) were observed compared to bile from control fish (<0.04 microg/g bile, 0.21 microg/g bile, and 3.5 microg/g bile, respectively). The more potent steroidal estrogens were suggested to be major contributors to the observed estrogenic effect, although xenoestrogens were detected at higher concentrations in the bile fluid.     

Mercury contamination in fish from gold mining areas in Indonesia and human health risk assessment

This study investigates the effects on fish and assesses human health hazards from mercury released in two gold mining areas in Indonesia: Tatelu (North Sulawesi Province) and Galangan (Katingan District, Central Kalimatan Province). In Tatelu, 154 fish specimens of 10 freshwater species were collected, as well as five marine species from the fish market. The mean concentration of total mercury in muscles of freshwater fish from this area was 0.58+/-0.44 microg/g, with more than 45% of fish having Hg levels above the WHO guideline for human consumption of 0.5 microg/g. In Galangan, where 263 fish specimens of 25 species were collected, the total mercury in muscles averaged 0.25+/-0.69 microg/g. Excluding data from flooded open pits in sub-area P4, mean Hg levels in fish from Galangan were 2 to 4 times lower than 0.5 microg/g, while fewer than 10% of fish from Galangan exceeded WHO guidelines. The Hazard Quotient (HQ) was applied to both areas to determine the threat of MeHg exposure for communities in both areas. The HQ is a risk assessment indicator which defines the ratio of exposure level to a single substance in relation to a reference dose. Samples from Tatelu (excluding marine species) had an HQ above one, while those from Galangan resulted in values of 2.4 for the whole area and 9.9 for sub-area P4, pointing to potentially harmful fish consumption for the local population. By using the single-compartment model to estimate mercury levels in blood and hair from daily intake dose, sub-area P4 showed the highest levels, higher than the upper limit guideline for pregnant women, but still lower than threshold levels associated with observed clinical effects.     

Maximum likelihood mixture estimation to determine metal background values in estuarine and coastal sediments within the European Water Framework Directive

Some of the recently derived European Directives, such as the Water Framework and Marine Strategy, have, as ultimate aims, to achieve concentrations of hazardous substances in the marine environment near background values. Hence, the determination of natural background levels, in marine sediments, is highly relevant. The present study proposes the use of the maximum likelihood mixture estimation (MLME) to determine regional background levels and upper threshold of metal concentration, with the Basque Country as a case study (with a data set of 575 samples, from estuarine and littoral areas, including both intertidal and subtidal sediments). The heuristic procedure is applied with unimodal data distributions (Cd, Cr, Fe and Ni) and the mixture density estimations, based upon maximum likelihood, are carried out with polypopulational data distributions (As, Cu, Mn, Hg, Pb and Zn). The upper limits of the distribution are proposed, as the limits between 'High Status' and 'Good Status' (according to the Water Framework Directive terminology). The regional upper limits were 0.45 microg g(-1) for Cd, 71 microg g(-1) for Cr, 53,542 microg g(-1) for Fe, 57 microg g(-1) for Ni, 24 microg g(-1) for As, 64 microg g(-1) for Cu, 447 microg g(-1) for Mn, 0.27 microg g(-1) for Hg, 66 microg g(-1) for Pb, and 248 microg g(-1) for Zn. The results from this study can assist further in the determination of sediment reference conditions, to assess chemical status, within the above-mentioned directives; likewise, it will be studied as a useful methodology in determining regional metal backgrounds in other European countries.     

Physico-chemical controls on phosphorus cycling in two lowland streams. Part 2--the sediment phase

This article investigates the temporal and spatial controls on sediment-phosphorus (P) dynamics in two contrasting sub-catchments of the River Kennet, England. Suspended sediment (collected under representative flow conditions) and size-fractionated bedload (collected weekly for one year) from the Rivers Lambourn and Enborne was analysed for a range of physico-chemical determinands. Total P concentrations were highest in the most mobile fractions of sediment: suspended sediment, fine silt and clay and organic matter (mean concentrations of 1758, 1548 and 1440 microg P g(-1) dry sediment, respectively). Correlation analysis showed significant relationships between total P and total iron (n= 110), total manganese (n= 110), organic matter (n= 110) and specific surface area (n= 28) in the Lambourn (r2 0.71, 0.68, 0.62 and 0.52, respectively) and between total P and total iron (n= 110), total manganese (n= 110) and organic matter (n= 110) in the Enborne (r2 0.74, 0.85 and 0.68, respectively). These data highlight the importance of metal oxyhydroxide adsorption of P on fine particulates and organic matter. However, high total P concentrations in the granule gravel and coarse sand size fraction during the summer period (mean concentration 228 microg P g(-1) dry sediment) also highlight the role of calcite co-precipitation on P dynamics in the Lambourn. P to cation ratios in Lambourn sediment indicated that fine silt and clay and granule gravel and coarse sand size fractions were potential sources of P release to the water column during specific periods of the summer and autumn. In the Enborne, however, only the granule gravel and coarse sand size fraction had high ratios and a slow, constant release of P was observed. In addition, scanning electron microscopy work confirmed the association of P with calcite in the Lambourn and P with iron on clay particles in the Enborne. The study highlighted the importance of the chemical and physical properties of the sediment in influencing the mechanisms controlling P storage and release within river channels.     

Distribution and behavior of trace metals in the sediment and porewater of a tropical coastal wetland

Vertical profiles (0-30 cm below surface) of four trace metals-Cadmium (Cd), Chromium (Cr), Lead (Pb) and Zinc (Zn)-in the sediment and sediment porewater of an ecologically important intertidal mudflat in the Mai Po and Inner Deep Bay Ramsar Site were thoroughly studied over a period of 10 months (from March 1999 to January 2000). Two surveys, one in summer and another in winter, involving a total of eight sampling stations were conducted to study the seasonal variation of the remobilization characteristics of these trace metals in the mudflat sediment. The range of depth averaged concentration of these trace metals in the mudflat sediment was: 0.3-0.8 microg/g (Cd); 9.8-91.0 microg/g (Cr); 7.3-69.1 microg/g (Pb); and 39.5-192.0 microg/g (Zn), while that in the sediment porewater was: 0.3-121.1 microg/l (Cd); 3.0-2704.1 microg/l (Cr); 2.6-105.6 microg/l (Pb); and 32.6-4238.3 microg/l (Zn). In general, levels of dissolved trace metals in the sediment porewater were much higher in the summer than in the winter while their concentrations in the sediment were more or less the same throughout the year. Enrichment of Cd, Pb and Zn in the sediment porewater of the upper oxic layer and that of Cr in the oxic-sub-oxic boundary was generally observed. Regions in the vicinity of the Mai Po mangroves and the river mouths of Shenzhen River and Shan Pui River were found to be hotspots of trace metal pollution. Benthic diffusive fluxes of trace metals from the mudflat sediment were also estimated. Of the four trace metals, cadmium showed the greatest tendency toward remobilization from the sediment phase to the more bio-available porewater phase.     

Trace metal concentrations in water,sediments and fish tissue from Lake Tanganyika

Trace metal (Cu, Pb, Fe, Mn, Zn, Cd) concentrations were determined in water, sediments, various fin fish species and a bivalve (Mutela spekei) from Lake Tanganyika using an atomic absorption spectrophotometer. Integrated water samples to depths of 10 m were collected using a pre-rinsed flexible plastic pipe. Sediment samples were collected using a ponar mud sampler. Fish samples were obtained using a variety of fishing techniques. No differences in trace metal concentrations were observed in both inshore and offshore waters. Levels in inshore sediments were much higher than for the offshore ones. Sediment input through run-off may have been the cause for the differences. However, the levels were much lower than those reported for Lake Malawi sediments. The concentrations in the fish tissue were within ranges reported elsewhere for Lake Tanganyika fish species. The centrapomid Lates stappersii and the clupeids Limnothrissa miodon and Stolothrissa tanganicae are the most important commercial species in the lake followed by Lates marie. Lead and cadmium are of concern to human health. The mean concentrations of the two metals in the commercial fish species were as follows: L. stappersii (5.03 microg Pb/g, 0.28 microg Cd/g); L. marie (4.96 microg Pb/g, 0.25 microg Cd/g); L. miodon (4.64 microg Pb, 0.38 microg Cd); and S. tanganicae (4.96 microg Pb/g, 0.39 microg Cd/g). Levels of lead and iron in the bivalve species were exceptionally very high, being 11.08 and 6.54 mg/g, respectively.     

Silver contamination on abiotic and biotic compartments of Nahuel Huapi National Park lakes, Patagonia, Argentina

The Ag contents of abiotic and biotic compartments of different lakes of Nahuel Huapi National Park, Patagonia, Argentina were analyzed. The water bodies studied were lakes Nahuel Huapi, Moreno, Escondido, Espejo Chico and Traful, the latter chosen as a reference lake. The Ag concentration profiles of short sediment cores, dated by (210)Pb and (137)Cs techniques, were analyzed, as well as suspended load collected from three sites of lake Nahuel Huapi. The biota studied were the native mussel Diplodon chilensis (digestive gland and total soft tissues pooled samples) and five species of fish, two native and three introduced (liver and muscle pooled samples). Ag contents were determined by Instrumental Neutron Activation Analysis (INAA). The upper layers of the sediment cores sampled in lake Nahuel Huapi were enriched in Ag contents compared to deep layers in accumulation periods corresponding to the second half of the 20th century, but this enrichment was neither observed in the reference lake Traful, nor in lakes Espejo Chico and Escondido. Ag was enriched over background level (0.1 microg g(-1)) also in suspended load collected in lake Nahuel Huapi. Ag fluxes to sediments were computed for suspended load and enriched sediment core layers. Highest Ag fluxes, from 350 to 470 microg m(-2) year(-1), were measured in Nahuel Huapi near the site where the liquid effluents of the Bariloche city sewage treatment plant are released to the lake. The spatial distribution of the other Ag fluxes suggests that this is the main source of Ag to lake Nahuel Huapi and lateral transport occurs within the water body. Ag concentrations on biota samples were consistent with these conclusions. Mussels collected in lake Nahuel Huapi showed higher Ag concentrations than in the other lakes, especially when compared to lake Traful. Ag contents in mussels were strongly associated with sediment intake, but enriched probably due to sediment grain size sorting during the intake processes. Evidence of food chain biomagnification of Ag in fish liver was observed. Ag contents in fish liver were higher at lake Nahuel Huapi even considering the high intra-specific variability, with highest values ranging from 10 to 29 microg g(-1) dry weight for brown trout and rainbow trout.     

Fate and microbiological effects of furazolidone in a marine aquaculture sediment.

Furazolidone is used in the treatment of bacterial diseases in farmed fish. During application a large proportion of the administered drug reaches the environment directly or via feces. The persistence and metabolism of furazolidone in sediment from a Norwegian salmon farm is described. Furazolidone, in contrast to oxytetracycline and oxolinic acid, is actively metabolized by microorganisms in the sediment. The main metabolite is 3-(4-cyano-2-oxobutylidene-amino)-2-oxazolidone. This is a well known metabolite of the degradation of furazolidone in mammals, fish and Escherichia coli. 3-(4-Cyano-2-oxobutylideneamino)-2- oxazolidone had no detectable antibacterial activity. The half-life of furazolidone in the sediment at 4 degrees C was calculated to be 18 h.     

Multiple Pb sources in marine sediments near the Australian Antarctic Station, Casey

An extensive Pb isotope ratio survey of approximately 100 marine sediment samples from near Casey Station, East Antarctica has been undertaken. Sediment surface grabs and cores were collected over nine years between 1997-2006 and, following HF total digestion, were analysed by magnetic sector ICP-MS. Fifty-two reference samples ([Pb] range 5-26 mg kg(-1)) from 6 non-impacted locations displayed a broad range of Pb isotope ratios representative of the natural background geology of the region ((208)Pb/(204)Pb ratios of 37.5-40; (206)Pb/(204)Pb ratios of 17-19). Potentially impacted sediments from Brown Bay (n=27, [Pb] range 18-215 mg kg(-1)), adjacent to the current and former Australian Stations at Casey (and the associated Thala Valley tip site) showed contamination by Pb characteristic of Broken Hill and Mt Isa Australian deposits ((208)Pb/(204)Pb and (206)Pb/(204)Pb values of 35.5-36 and 16.0-16.1, respectively). The nearby abandoned Wilkes Station was previously manned by both US (1957-59) and Australian (1959-69) expeditioners. Adjacent marine sediment samples (n=24, [Pb] range 13-40 mg kg(-1)) displayed Pb isotopic signatures suggesting anthropogenic input from multiple sources. On a three-isotope diagram Wilkes sediments were found to display Pb ratios lying intermediate between Missouri (US), Broken Hill/Mt Isa (Australia)/Idaho (US), and natural geogenic Pb end members. Discarded Pb batteries, paint samples and fuel spills were all considered in this work as possible point sources of Pb contamination to the local environment. Batteries are thought to be the dominant source.     

Pilot study of intrauterine exposure to methylmercury in Eastern Aegean islands, Greece

A group of islands with a total population of about 200,000 was identified in the Eastern Aegean, where there was evidence to suggest possible increased exposure to methylmercury (MeHg) through consumption of fresh local fish and other seafood from seas bordered by mercury-bearing rock. A feasibility study was conducted to explore the possibility of defining a local population of mother-child pairs in whom to investigate the intrauterine exposure effect. Analysis of 246 hair samples collected from pregnant women and mothers of newborn babies and children under 5 years showed levels of total Hg from 0.046 microg/g to 17.5 microg/g, geometric mean 1.36 microg/g, and of MeHg from 0.031 microg/g to 16.2 microg/g, geometric mean 1.07 microg/g. About 5% of the mothers had hair total Hg levels in excess of 6.00 microg/g. Investigation of dietary habits showed that one-third of the mothers eat fresh local fish at least 3 times weekly, one-third once a week and 10% rarely or never. There was a close association between weekly rates of local fish consumption and hair levels of both total Hg and MeHg. A power calculation determined that a cohort of 3000 mother-child pairs would enable comparison of a high-exposure group (those with the upper 5% of hair MeHg) with a low exposure group (5%, selected from those with the lower 30% of hair MeHg, matched for confounding factors), in order to detect an effect size of 0.35 to 0.45 at a power of 85-95%. It is concluded that the mothers and children in the Eastern Aegean islands studied comprise a population suitable for an epidemiological study of the effects of intrauterine exposure to MeHg via maternal fresh local fish consumption.     

Some results on Hg content in hair in different populations in Albania

The mercury content in hair, for exposed dental workers and unexposed groups of people living in Albania was studied. The influence of factors such as age, sex, body weight, fish consumption in the diet, number of dental amalgam fillings and time exposed to mercury, was determined. The mean value of mercury content in hair for the subjects under study (0.705 microg/g) was found to be lower than the value referred from the World Health Organization (WHO) for people who do not consume fish with a high methylmercury content (1-2 microg/g). A significant positive correlation of Hg content with the number of dental amalgam fillings, time under exposure and frequency of fish consumption in the diet was found. These correlations became stronger when exposed and unexposed groups of people were evaluated separately.     

Total mercury and methylmercury levels in fish from hydroelectric reservoirs in Tanzania

Total mercury (THg) and methylmercury (MeHg) levels have been determined in fish species representing various tropic levels in four major hydroelectric reservoirs (Mtera, Kidatu, Hale-Pangani, Nyumba ya Mungu) located in two distinct geographical areas in Tanzania. The Mtera and Kidatu reservoirs are located along the Great Ruaha River drainage basin in the southern central part of the country while the other reservoirs are located within the Pangani River basin in the north eastern part of Tanzania. Fish mercury levels ranged from 5 to 143 microg/kg (mean 40 microg/kg wet weight) in the Mtera Reservoir, and from 7 to 119 microg/kg (mean 21 microg/kg) in the Kidatu Reservoir downstream of the Great Ruaha River. The lowest THg levels, in the range 1-10 microg/kg (mean 5 microg/kg), were found in fish from the Nyumba ya Mungu (NyM) Reservoir, which is one of the oldest reservoirs in the country. Fish mercury levels in the Pangani and Hale mini-reservoirs, downstream of the NyM Reservoir, were in the order of 3-263 microg/kg, with an average level of 21 microg/kg. These THg levels are among the lowest to be reported in freshwater fish from hydroelectric reservoirs. Approximately 56-100% of the total mercury in the fish was methylmercury. Herbivorous fish species contained lower THg levels than the piscivorous species; this was consistent with similar findings in other fish studies. In general the fish from the Tanzanian reservoirs contained very low mercury concentrations, and differed markedly from fish in hydroelectric reservoirs of similar age in temperate and other regions, which are reported to contain elevated mercury concentrations. The low levels of mercury in the fish correlated with low background concentrations of THg in sediment and flooded soil (mean 2-8 microg/kg dry weight) in the reservoir surroundings. This suggested a relatively clean reservoir environment that has not been significantly impacted by mercury contamination from natural or anthropogenic sources.     

Transfer of metals to plants and red deer in an old lead mining area in Spain

Lead mining in the Sierra Madrona mountains and the valley of Alcudia in Southern Spain began in the 1st millennium B.C., and the area was intermittently exploited up until the end of the 20th century. The degree of contamination by Pb, Zn, Cd, Cu, As and Se of soil, water and sediment, and the transfer to 13 species of plants, and then to red deer (Cervus elaphus) have been studied. Mined areas had higher concentrations in stream sediments than control areas. The highest concentrations were observed for Pb (1481 microg g(-1) d.w.) and As (1880 microg g(-1)) in the sediment of a stream flowing beside the spoil dump at Mina de Horcajo. Plants from mining sites contained consistently higher levels of Pb and As, and their concentrations in plants were correlated. The highest concentrations of Pb were in Gramineae (Pb: 97.5, As: 2.4 microg g(-1) d.w.), and the lowest in elmleaf blackberry (Rubus ulmifolius). The highest mean liver concentrations were found in red deer from the mining sites for Pb (0.805 microg g(-1) d. w.), Cd (0.554 microg g(-1)), Se (0.327 microg g(-1)), and As (0.061 microg g(-1)), although these were well below the levels associated with clinical poisoning.     

Health assessment for mercury exposure among schoolchildren residing near a gold processing and refining plant in Apokon, Tagum, Davao del Norte, Philippines

Artisanal gold-mining activities in the Philippines have proliferated since the early 1980s. Presently, environmental and health monitoring conducted by several governmental agencies is limited to the determination of total mercury only. Previous studies undertaken focused mainly on the exposure of adults and workers to mercury during mining/processing operations. However, in one area in Mindanao, mined ores are brought down and processed in the lowlands where residential communities are exposed to environmental pollutants resulting from gold processing/refining operations. The area of study is Apokon, Tagum, Davao del Norte, which has 29 gold processing and refining plants. Health complaints among schoolchildren in Apokon Elementary School were received by the Department of Health and were attributed to the mercury pollution in the environment. As part of a collaboration with the Health Department, UP-National Poisons Control and Information Service, the National Institute for Minamata Disease (NIMD), Japan, provided technical assistance in the analytical determination of mercury in biological and environmental samples. Elevated mercury concentrations were noted in some of the river systems up to 15 km from the mining areas. Environmental quality monitoring showed T-Hg sediment levels ranged from 0.553 to 66.471 microg/g dry wt. while water samples from river systems exhibited mercury levels from 72.8 to 78.4 ng/ml. Twenty-seven sediment samples from river systems near mining operations and seven water samples were also brought to the Institute for analysis. Fish samples collected showed levels ranging from 1.07 to 438.8 ng/g for total mercury and 0.71-377.18 ng/g for methylmercury. Methylmercury content in fish is predominant. All water and sediment samples collected from three sampling sites have elevated T-Hg level while three fish species have elevated T-Hg and methylmercury levels (WHO/CDC, 1994). Blood and hair samples from 162 schoolchildren aged 5-17 years were collected and analyzed at the NIMD for mercury analysis. Analytical procedures used in the NIMD for mercury testing were applied. Laboratory results showed that total mercury hair samples ranged from 0.278 to 20.393 microg/g while methylmercury hair results were from 0.191 to 18.469 microg/g. Methylmercury in hair showed levels from 45.96 to 99.81%. Total blood mercury levels ranged from 0.757 to 56.88 microg/l while Me-Hg blood levels ranged from 1.36 to 46.73 microg/l. It was determined that 10 children had elevated T-Hg blood levels while one child had high total and methylmercury levels in hair. A summary of physical examination results showed that the predominant findings include under-height, gingival discoloration, adenopathy, underweight and dermatologic abnormalities among children examined.     

Selenium depuration: residual effects of dietary selenium on Sacramento splittail (Pogonichthys macrolepidotus)

We examined the growth performance, tissue selenium (Se) concentration, and histopathology of Sacramento splittail (Pogonichthys macrolepidotus) fed a control diet (0.4 microg Se/g) for 1, 3, 7, 13, 21 wk after a 9-month dietary exposure to 0.4, 12.6, 26.0, and 57.6 microg Se/g dry diet. Splittail previously fed 57.6 microg Se/g showed a significantly (P<0.05) lower final body weight but had higher weight gain than fish fed 0.4 microg Se/g diet at the end of the 21-wk depuration study. There were no significant differences in body weight in fish previously fed diets with or less than 26.0 microg Se/g. Liver and muscle Se concentrations decreased significantly in fish previously fed 26.0 and 57.6 microg Se/g diet but did not change significantly in fish fed 12.6 or less mug Se/g diet at the end of 21 wk. Liver Se concentrations dropped to the same concentration as fish fed 0.4 microg Se/g diet after a 13-wk depuration in all treatments. Muscle Se concentrations remained significantly higher in fish previously fed 12.6 or higher microg Se/g diets when compared to fish fed control diet at the end of a 21-wk depuration. Except for the presence of preneoplastic basophilic foci in two fish previously fed 57.6 microg Se/g diet, normal liver morphology was observed in splittail in all treatments at the end of 21-wk depuration. Prevalences of kidney lesions were increased in fish previously fed 26.0 and 57.6 microg Se/g diets at 3 and 7 wk, and decreased at 13 and 21 wk of depuration. No kidney lesions were observed in fish previously fed 12.6 microg Se/g diet or less. In conclusion, growth of splittail previously fed a diet containing 57.6 microg Se/g was still affected at the end of 21-wk depuration. The 21-wk depuration was not long enough for muscle Se concentrations to return to basal levels in fish previously fed 12.6 or more microg Se/g diet. Deleterious health effects of Se persisted in fish previously fed diets with 26.0 or more microg Se/g diet. Current results suggest that splittail that survived the 9-month exposure to 12.6 or less microg Se/g diet under current laboratory conditions is likely to thrive if Se in diet was reduced to control concentration.     

Filtering activity of Spongia officinalis var. adriatica (Schmidt) (Porifera, Demospongiae) on bacterioplankton: implications for bioremediation of polluted seawater

A study on the filtering activity has been carried out on reared specimens of the demosponge Spongia officinalis var. adriatica coming from an off-shore farm displaced off the Apulian coast (Ionian Sea). The experience was carried out under laboratory conditions, by using natural seawater collected from the sponge environment. The study demonstrates a high efficiency of the sponge in removing bacteria. Bacterial concentration significantly decreases in presence of the sponge, with a marked drop after 2 h from the start of the experience. The maximum clearance rate was 210 ml h(-1) g(-1) DW at 60 min. Retention efficiency reached the highest value of 61% at 120 min. The bacterial density removed by the S. officinalis filtering activity was 12.3 +/- 1.8 x 10(4) cells ml(-1) corresponding to a biomass of about 11.7 +/- 1.4 microg Cl(-1). The sponge fed preferentially large- and medium-size bacteria, whereas the small ones are fed after the removal of the largest size categories. The results obtained suggest that S. offcinalis is a suitable species for marine environmental bioremediation.     

Role of dissolved and particulate cadmium in the accumulation of cadmium in cultured oysters (Crassostrea gigas)

Pacific oysters (Crassostrea gigas) collected on the coast of British Columbia, Canada have occasionally shown cadmium (Cd) concentrations at or above 2 microg g(-1) (wet weight), which has resulted in the loss of some international markets. This study investigated the source and transfer of Cd to oysters by focusing on the role of dissolved and particulate Cd in seawater. Parameters monitored for 1 year at two oyster farm sites on Vancouver Island included: oyster tissue mass and shell length, Cd in oysters, dissolved Cd, particulate Cd, temperature and salinity. Results show that dissolved Cd was the main source of Cd to the oysters and that Cd was mainly concentrated in the gut tissues. A seasonal trend was observed in Cd in oysters, in which levels were lowest during periods of higher temperatures. Results also indicate that the local oceanographic inputs and sediment diagenesis directly affect dissolved Cd and thereby influence the Cd levels in oysters. Particulate matter was not found to be a source of Cd in oysters, and was actually negatively correlated. This was likely due to the uptake of dissolved Cd by phytoplankton and the effect of phytoplankton on oyster tissue mass.     

泥浆护壁钻孔灌注桩施工及监理

针对施工过程中钻孔灌注桩存在的问题,从孔径、泥浆、孔的垂直度、孔深、沉渣与沉淤等方面对钻孔灌注桩施工中影响承载力的施工及监理要点进行了分析,并对钢筋笼加工与吊装、混凝土灌注等工序作了阐述。