Metal(loid) contamination in seafood products

Seafood products are important sources of proteins, polyunsaturated lipids and phospholipids, and also of numerous micronutrients (vitamins and minerals). However, they may also present chemical contaminants that can constitute a health risk and that must be considered when evaluating the risk/benefit associated with consumption of this group of foods. Toxic metals and metalloids in seafood, such as mercury (Hg), cadmium (Cd), arsenic (As), and lead (Pb), are subjected to legislative control in order to provide the consumer with safe seafood. This review provides an exhaustive survey of the occurrence of these toxic metal(loid)s in seafood products, and of the risk resulting from their consumption. Consideration is given to aspects related to speciation, food processing, and bioavailability, which are key factors in evaluating the risk associated with the presence of these toxic trace elements in seafood products.     

Modeling of microbial dynamics and geochemical changes in a metal bioprecipitation experiment

A biogeochemical transport modeling study was carried out to analyze large-scale laboratory column experiments in which ethanol was used as an electron donor to create favorable conditions for the immobilization of selected trace metals (Zn and Cu) in groundwater. Microbial activity was explicitly simulated to capture the dynamic changes of the redox zonation within the column (i) in the early phase of the experiment (microbial lag) and (ii) in response to a significant decrease in the pH of the feed solution introduced after 188 days. The simulated redox dynamics agreed well with the observations after the pH-dependency of microbial growth was incorporated into the microbial model. The study showed that residual minerals may have buffered the pH for a period after the pH of the feed solution was decreased. Where the buffering capacity was exhausted, the pH decreased, leading to a successive downstream movement of the redox boundaries. The simulations reproduced the Zn immobilization within the sulfate-reducing zone as well as its partial remobilization after this zone moved further downstream. The immobilization of Cu within the denitrifying zone could also be well explained by incorporating malachite (Cu2(OH)2CO3) precipitation in the simulations.     

Metal(loid) diagenesis in mine-impacted sediments of Lake Coeur d'Alene, Idaho

Mining activity along the South Fork of the Coeur d' Alene River in northern Idaho has resulted in fluvial mine tailings enriched in Pb, As, Ag, Sb, Hg, Cd, and Zn deposited on the lakebed of Lake Coeur d'Alene, thus serving as a potential benthic source of inorganic contaminants. Our objective was to characterize the dominant solid phase materials and diagenetic processes controlling metal(loid) solubilities, and thus their potential release to the overlying water column. Aqueous and solid concentrations of metal(loid) contaminants were examined along with distinct species of Fe and S within sediments and interstitial water. A gradient from oxic conditions at the sediment-water interface to anoxic conditions below 15 cm exists at all sites, resulting in a dynamic redox environment that controls the partitioning of contaminants. Fluvial deposition from frequent seasonal flood events bury ferric oxides residing at the sediment-water interface leading to reductive dissolution as they transition to the anoxic zone, consequently releasing associated metal(loids) to the interstitial water. Insufficient sulfur limits the formation of sulfidic minerals, but high carbonate content of this mining region buffers pH and promotes formation of siderite. Diagenetic reactions create chemical gradients encouraging the diffusion of metal(loids) toward the sediment--water interface, thereby, increasing the potential for release into the overlying water.     

Effects of iron purity and groundwater characteristics on rates and products in the degradation of carbon tetrachloride by iron metal

Carbon tetrachloride (CT) batch degradation experiments by four commercial irons at neutral pH indicated that iron metal (Fe0) purity affected both rates and products of CT transformation in anaerobic systems. Surface-area-normalized rate constants and elemental composition analysis of the untreated metals indicate that the highest-purity, least-oxidized Fe0 was the most reactive on a surface-area-normalized basis in transforming CT. There was also a trend of increasing yield of the hydrogenolysis product chloroform (CF) with increasing Fe0 purity. Impurities such as graphite in the lower purity irons could favor the alternate CT reaction pathway, dichloroelimination, which leads to completely dechlorinated products. High pH values slowed the rates of CT disappearance by Peerless Fe0 and led to a pattern of decreasing CF yields as the pH increased from 7 to 12.9. The Fe/O atomic ratio vs depth for Peerless Fe0 filings equilibrated at pH 7 and 9.3, obtained by depth profiling analysis with X-ray photoelectron spectroscopy, indicated differences in the average oxide layer composition as a function of pH, which may explain the pH dependence of rate constants and product yields. Groundwater constituents such as HS-, HCO3-, and Mn2+ had a slight effect on the rates of CT degradation by a high-purity Fe0 at pH 7, but did not strongly influence product distribution, except for the HS amended Fe0 where less CF was produced, possibly due to the formation of carbon disulfide (CS2).     

发酵条件对花生酸奶质地和酸度影响

以自制的花生分离蛋白为原料,不添加牛奶,经乳酸菌发酵制作花生酸奶。研究花生蛋白浓度、加糖量、灭菌条件、接种量和发酵时间对花生酸奶质地评分和酸度影响。结果表明:花生蛋白浓度、灭菌条件和发酵时间是影响花生酸奶质地的主要因素;加糖量、接种量和发酵时间对花生酸奶的酸度有明显影响。当花生蛋白浓度为4%,灭菌条件为115℃/15min,加糖量为8%,接种量为0.10%,发酵时间为7 h时,花生酸奶组织状态良好,质地评分较高。     

Some studies directed at increasing the potential use of palmyrah (Borassus flabellifer L) fruit pulp

Attempts have been made to predict the most feasible end‐use for palmyrah fruit pulp (PFP), which is still largely regarded as a waste product. Correlation of end‐use with flabelliferin profile is logical but practically difficult, as it has been found that the morphology of the fruit and the colour of the pulp (carotenoid content) do not correlate with each other, and that neither has predictive value for the flabelliferin profile. It appears that some varieties of palmyrah are sweet and can be used for products such as jams and cordials. A few very bitter PFPs can be de‐bittered with a cheap commercial enzyme for similar uses. The majority of available PFP appears to be best used as an alcoholic fermentation base, with the possibility of using the carotenoids (by‐product) as a food colorant. © 2001 Society of Chemical Industry     

Effects of metal ions (Cu,Fe and Fe) on HPLC analysis of catechins

Catechins [(−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG)] were analysed by HPLC using an ODS column, an electrochemical detector (0.75 V vs. Ag/AgCl) and an eluting solvent composed of water containing buffer (84% v/v), acetonitrile (12% v/v) and ethylacetate (4% v/v) in the presence of metal ions (Cu²⁺, Fe²⁺ and Fe³⁺). HPLC peaks were affected by metal ions: the peak intensities of ECG and EGCG decreased, but the peak intensities of EC and EGC were not affected seriously. Fe²⁺ most markedly decreased the peak intensities of EGCG. EDTA was added to mask metal ions and an optimum condition was proposed. The effects of the metal ions on HPLC analysis are discussed from the viewpoints of metal complex formation with catechins and oxidation of catechins on the basis of ultraviolet–visible (UV–vis) spectrophotometry, electrospray ionisation mass spectrometry (ESI-MS) and cyclic voltammetry (CV).     

Trace metal levels in uncontaminated groundwater of a coastal watershed: importance of colloidal forms

Groundwater and surface water were collected using trace metal clean techniques from the upper glacial aquifer of West Neck Bay (Shelter Island) in eastern Long Island, NY, during the late spring and summer of 1999. The collection sites on Shelter Island are located in an area that is primarily residential and believed to have uncontaminated groundwater. Ultrafiltration was used to size-fractionate the dissolved (<0.45 microm) fraction into colloidal (1 kDa - 0.45 microm) and low molecular weight (<1 kDa) size pools. These fractions were analyzed for trace metals (Al, Ag, Cd, Cu, Mn, Pb, and Zn), organic carbon, and inorganic nutrients (NH4, NO3, PO4). The levels of metals and organic carbon in the groundwater were as low as those found in the open ocean, far removed from anthropogenic inputs. These findings corroborate the need to apply trace metal clean techniques in the determination of metal levels in uncontaminated groundwater. A significant fraction of dissolved metals (22-96%) and organic carbon (approximately 40%) in the groundwater and in surface waters of the Bay was found to be associated with colloids. The significance of the metal association with the colloidal fraction decreased in the order of Al > Cu > Ag > Zn = Cd = Mn and appeared to be dependent on the affinities of these metals for humic substances. In contrast, NO3 and NH4 were found to be almost entirely (approximately 98-99%) in the low molecular weight size fraction. Metal/aluminum and metal/carbon ratios measured in the colloids were similar to those reported for humic substances and significantly different from those of soils. This suggests that colloidal particles might originate from humic materials as opposed to purely inorganic minerals. These results indicate the need to consider the colloidal fraction in the fate and mobility of metals in groundwater and that, despite the low levels of organic matter (<50 microM of DOC) measured in groundwater, some groundwater colloids appear to be organic in nature.     

Use of polymer mats in series for sequential reactive barrier remediation of ammonium-contaminated groundwater: laboratory column evaluation

Large-scale column experiments were undertaken to evaluate the potential of in situ polymer mats (installed in series) to be used as permeable reactive barriers for delivery of oxidants and reductants to induce sequential bioremediation of ammonium-contaminated groundwater (approximately 120mg L(-1) NH4+-N), without bioaugmentation. The strategy was for the first group of polymer mats to deliver oxygen to induce bacterial nitrification of the ammonium to nitrite/ nitrate as the groundwater moved past and for the second group of polymer mats to deliver hydrogen or ethanol, to induce bacterial denitrification of the nitrite/nitrate to produce nitrogen gas. Once purging of the first polymer mat commenced, ammonium concentrations decreased downgradient from the polymer mats. Nitrification rates increased and stabilized over the 6-month experiment, with stable nitrification half-lives in the range 0.07-0.25 days. Nitrification most likely occurred in a biologically active zone at the polymer wall/aqueous interface. With hydrogen delivery via the polymer mats, a denitrification half-life (nitrate plus nitrite removal) of 3.5 days was induced. Denitrification rates were significantly enhanced when ethanol was delivered via a polymer mat, with denitrification half-lives in the range of 0.12-0.34 days. Nitrification/ denitrification rates were maintained for groundwater flow rates up to 300 m yr(-1), suggesting oxygen and ethanol delivery rates via the polymer mats were sufficient not to limit nitrification or denitrification. In soil columns, the polymer mat delivery system provided an effective and reliable technique for delivery of oxygen and hydrogen or ethanol for sequential nitrification/denitrification of ammonium-contaminated groundwater. Scale-up of this concept to a field pilot-scale is currently underway.     

Effects of increasing dietary protein on nutrient utilization in heifers

Four prepubertal Holstein heifers, average age 146.0 +/- 3.6 d and 152.8 +/- 8.6 kg of body weight (BW), fitted with rumen cannulae were used to evaluate increasing levels of dietary protein with a constant metabolizable energy intake on rumen ammonia N concentrations, N balance, total tract apparent digestibility, and urinary excretion of purine derivatives in a 4 x 4 Latin square design with 20 d periods. Heifers were fed dietary crude protein levels (CP) of 11.9, 16.7, 18.1, and 20.1% CP with similar amounts of metabolizable energy (ME) (2.6 Mcal per kg of dry matter) at 2.0% BW as dry matter intake. Resulting protein to ME ratios (CP:ME) were 45.0, 63.3, 69.4, and 77.3 g of dietary CP per Mcal of ME. Rumen ammonia N and plasma urea nitrogen increased as CP level increased. Rumen pH, volatile fatty acids, and the acetate-to-propionate ratio were not affected with increasing CP levels. Greater urinary N excretion resulted in an increase in total N excretion with increasing CP levels. Apparent dry matter digestibility was similar for all diets, while apparent total tract N digestibility was lowest for the 11.9% CP level. Microbial N calculated from urinary excretion of purine derivatives increased with increasing CP levels. Holstein heifers between 153 and 196 kg consuming a diet at 2.0% BW as dry matter intake containing a CP level of 16.7% achieved a better synergistic relationship of dietary protein to energy (CP:ME of 63.3 g of CP per Mcal of ME) than the diets lower or higher in CP that were studied.     

Iron(II)-catalyzed oxidation of arsenic(III) in a sediment column

Arsenic contamination in aquatic systems is a worldwide concern. Understanding the redox cycling of arsenic in sediments is critical in evaluating the fate of arsenic in aquatic environments and in developing sediment quality guidelines. The direct oxidation of inorganic trivalent arsenic, As(III), by dissolved molecular oxygen has been studied and found to be quite slow. A chemical pathway for As(III) oxidation has been proposed recently in which a radical species, Fe(IV), produced during the oxidation of divalent iron, Fe(II), facilitates the oxidation of As(III). Rapid oxidation of As(III) was observed (on a time scale of hours) in batch systems at pH 7 and 7.5, but the extent of As(III) oxidation was limited. The Fe(II)-catalyzed oxidation of As(III) is examined in a sediment column using both computational and experimental studies. A reactive-transport model is constructed that incorporates the complex kinetics of radical species generation and Fe(II) and As(III) oxidation that have been developed previously. The model is applied to experimental column data. Results indicate that the proposed chemical pathway can explain As(III) oxidation in sediments and that transport in sediments plays a vital role in increasing the extent of As(III) oxidation and efficiency of the Fe(II) catalysis.     

Effects of the antimicrobial sulfamethoxazole on groundwater bacterial enrichment

The effects of "trace" (environmentally relevant) concentrations of the antimicrobial agent sulfamethoxazole (SMX) on the growth, nitrate reduction activity, and bacterial composition of an enrichment culture prepared with groundwater from a pristine zone of a sandy drinking-water aquifer on Cape Cod, MA, were assessed by laboratory incubations. When the enrichments were grown under heterotrophic denitrifying conditions and exposed to SMX, noticeable differences from the control (no SMX) were observed. Exposure to SMX in concentrations as low as 0.005 μM delayed the initiation of cell growth by up to 1 day and decreased nitrate reduction potential (total amount of nitrate reduced after 19 days) by 47% (p=0.02). Exposure to 1 μM SMX, a concentration below those prescribed for clinical applications but higher than concentrations typically detected in aqueous environments, resulted in additional inhibitions: reduced growth rates (p=5×10(-6)), lower nitrate reduction rate potentials (p=0.01), and decreased overall representation of 16S rRNA gene sequences belonging to the genus Pseudomonas. The reduced abundance of Pseudomonas sequences in the libraries was replaced by sequences representing the genus Variovorax. Results of these growth and nitrate reduction experiments collectively suggest that subtherapeutic concentrations of SMX altered the composition of the enriched nitrate-reducing microcosms and inhibited nitrate reduction capabilities.     

Comparative studies on trace metal levels in marine biota

Summary In whole krill, krill muscle tissue, krill products and in fillets of the antarctic fishNotothenia rossi marmorata, Dissostichus eleginoides, andNotothenia gibberifrons the levels of Cd, Pb, Cu, Ni, Hg and As have been determined. The methods applied were electrothermal AAS for Cd, Pb, Cu, and Ni, cold-vapour and hydride-generation AAS for Hg- and As, respectively, usually after HNO, pressure decomposition and for As followed by a HClO₄/H₂SO₄ treatment. Quality control was performed by analysis of appropriate Standard Reference Materials and working standards and by intercomparison with differential pulse anodicstripping voltammetry (DPASV) for Pb and Cd. The mean values obtained related to fresh weight for krill muscle meat (46 ng Cd/g, 50 ng Pb/g, 380 ng Cu/g, 130 ng Ni/g, 20 ng Hg/g, and 340 ng As/g) and fillets of antarctic fish ( ng Cd/g, 100 ng/Pb/g, 200 ng Cu/g, 150 ng Ni/g, 50 ng Hg/g, and 300-1500 ng As/g) confirm the absence of toxic risks for human food according to the present knowledge. Due to the somewhat higher, but not excessive, trace metal contents of krill products, these should be more suitable as a protein rich animal feed.

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Vergleichende Studien zum Spurenmetallgehalt in marinen BiotaII. Spurenmetalle in Krill, Krillprodukten und Fischen aus der antarktischen Scotia-See

Zusammenfassung In Rohkrill, Krillfleisch, Krillprodukten und in Filets der antarktischen FischeNotothenia Rossi Marmorata, Dissostichus Eleginoides undNotothenia Gibberifrons wurden die Gehalte an Cd, Pb, Cu, Ni, Hg und As bestimmt. Als Methoden wurden elektrothermale AAS für, Pb, Cu und Ni, Kaltdampf-bzw. Hydridtechniken für Hg und As nach HNO₃-Druckaufschluß, für gefolgt von einer Naßveraschung mit HCIO₄/H₂SO₄, eingesetzt. Die Qualitätskontrolle erfolgte durch die gleichzeitige Analyse geeigneter Standardreferenzmaterialien und Arbeitsstandards sowie durch Vergleich mit der differentiellen Pulsinversvoltammetrie (DPASV) füb und Cd. Die erhaltenen, auf Frischgewicht bezogenen, Mittelwerte für Krillfleisch (46 ng Cd/g; 50 ng Pb/g; 380 ng Cu/g; 130 ng Ni/g; 20 ng Hg/g und 340 ng As/g) und im Filet antarktischer Fische ( 3 ng Cd/g; 100 ng Pb/g; 200 ng Cu/g; 150 ng Ni/g; 50 ng Hg/g und 300-1500 ng As/g) bestätigen nach derzeitigem Kenntnisstand deren toxische Unbedenklichkeit für die menschliche Ernährung. Aufgrund höherer, aber nicht exzessiver Spurenmetallgehalte der Krillprodukte durften sich diese eher als proteinreiches Tierfutter eignen.

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Reference [37] constitutes part I of thin series, references [8] and [38] are parts III and IV, respectively     

Complexation studies of Eu(III) with alumina-bound polymaleic acid: effect of organic polymer loading and metal ion concentration

To contribute to the comprehension of the metal ion sorption properties in mixed mineral-organic matter systems, interaction studies between Eu(III) and polymaleic acid (PMA)-coated alumina colloids were carried out at pH 5 in 0.1 M NaClO4. The studied parameters were the metal ion concentration (1 x 10(-10) to 1 x 10(-4) M) and PMA loading on alumina (gamma = 10-70 mg/g). The data were described by a surface complexation model. The constant capacitance model was used to account for electrostatic interactions. The results showed thattwo sites were necessary to explain the sorption data. At high Eu loading, Eu is surrounded by one carboxylate group and one aluminol group. The existence of this ternary surface site was in agreement with time-resolved laser-induced fluorescence spectroscopy measurements. At low metal ion concentrations, a surface site corresponding to a 1:1 Eu/COO-stoichiometry was deduced from modeling. Spectroscopic data did not corroborate the existence of this latter site. This discrepancy was explained by postadsorption kinetic phenomenon: a migration of the metal ion within the adsorbed organic layer.     

Effects of different cleaning treatments on heavy metal removal of Panax notoginseng (Burk) F. H. Chen

The quality and safety of Panax notoginseng products has become a focus of concern in recent years. Contamination with heavy metals is one of the important factors as to P. notoginseng safety. Cleaning treatments can remove dust, soil, impurities or even heavy metals and pesticide residues on agricultural products. But effects of cleaning treatments on the heavy metal content of P. notoginseng roots have still not been studied. In order to elucidate this issue, the effects of five different cleaning treatments (CK, no treatment; T1, warm water (50°C) washing; T2, tap water (10°C) washing; T3, drying followed by polishing; and T4, drying followed by tap water (10°C) washing) on P. notoginseng roots’ heavy metal (Cu, Pb, Cd, As and Hg) contents were studied. The results showed that heavy metal (all five) content in the three parts all followed the order of hair root > rhizome > root tuber under the same treatment. Heavy metal removals were in the order of Hg > As > Pb > Cu > Cd. Removal efficiencies of the four treatments were in the order of T2 > T1 > T3 > T4. Treatments (T1–T4) could decrease the contents of heavy metal in P. notoginseng root significantly. Compared with the requirements of WM/T2-2004, P. notoginseng roots’ heavy metal contents of Cu, Pb, As and Hg were safe under treatments T1 and T2. In conclusion, the cleaning process after production was necessary and could reduce the content of heavy metals significantly. Fresh P. notoginseng root washed with warm water (T2) was the most efficient treatment to remove heavy metal and should be applied in production.     

Effects of metal cations on betanin stability in aqueous-organic solutions

An effect of metal cations on betanin stability was investigated in aqueous and organic-aqueous solutions. The presence of organic solvents (methanol, ethanol, and acetonitrile) affects substantially the pigments decomposition in acidic media induced by metal cations whose degrading action in such media is significantly higher than in aqueous solutions. The influence of Cu²⁺ on the stability was studied by spectrophotometry in more detailed manner, because of its ability to form complexes with betanin. The possibility of a complex formation between betanin and Ni²⁺ was also stated at pH 7–8; its relatively high stability in aqueous samples was observed. A presence of numerous products of betanin decomposition was detected in the wavelength range 380–500 nm in spectra obtained for most of metal cations investigated, especially for higher concentrations of the organic solvents.     

金属离子对蓝莓花色苷的影响

花色苷具有重要的生理功能,但其稳定性易受各种理化因素的影响而发生变化.本试验系统地研究金属离子对其稳定性的影响,为蓝莓花色苷的加工生产提供理论指导.通过测定蓝莓花色苷在不同浓度金属溶液中的吸光度的变化,确定金属离子对蓝莓花色苷稳定性的影响.结果表明:蓝莓花色苷在酸性水溶液中的吸收峰分别在279,520 nm处.K+不能使花色苷的吸光度增加,对花色苷的稳定性也无显著影响;Ca2+、Cu2+、Al3+具有增色作用,对花色苷的稳定性无显著影响;高浓度Na+、Zn2+、Mn2+具有增色作用,而且能够增强花色苷的稳定性;Fe2+、Fe3+、Pb2+对花色苷具有破坏作用,使花色苷的稳定性下降,含Fe3+、Pb2+的花色苷溶液中有白色沉淀生成.