Factors affecting the bioaccessibility of methylmercury in several marine fish species

Bioaccessibility refers to the maximum bioavailability of pollutant ingested with food, and its measurements can lead to a more accurate risk assessment as compared to the measurements of total concentrations of pollutant in food. This study examined the factors affecting the bioaccessibility of methylmercury (MeHg) in nine species of marine fish with an aim to identify ways of reducing MeHg bioaccessibility. MeHg bioaccessibility without any treatment in the nine species of marine fish ranged from 16.0 to 67.7%. Steaming, grilling, and frying reduced MeHg bioaccessibility by 29.4-77.4% for rabbitfish and 74.6-95.8% for grouper. Co-consumption of phytochemical-rich foods such as green tea decreased the bioaccessibility of MeHg by 72.2% for rabbitfish and 74.0% for grouper, whereas meso-2,3-dimercaptosuccinic acid increased it by 39.2-108% for rabbitfish and 45.3-75.7% for grouper. The bioaccessibilities of both MeHg and inorganic mercury were independent of the total Hg concentration and the exposure route (dietary vs dissolved). In eight of the nine species studied, bioaccessibility was negatively correlated with the extent to which MeHg was partitioned into the metal-rich granule fraction and the trophically available fraction. It was positively correlated with partitioning into the cellular debris fraction. This study demonstrated the important control of subcellular distribution in MeHg bioaccessibility.     

Improved gas chromatographic method for determination of daminozide by alkaline hydrolysis and 2-nitrobenzaldehyde derivatization and survey results of daminozide in agricultural products

An improved method was developed for the quantitative determination of daminozide. This new method combines the alkaline hydrolysis and distillation steps of the PAM II method for daminozide with the derivatization, cleanup, and gas chromatographic determination steps of the Wright method for unsymmetrical dimethyl hydrazine (UDMH). The minimum detectable level is 0.05 ppm. Recoveries range from 85 to 110% when daminozide is added at 0.1 to 1.0 ppm, and are generally 40% at the 0.05 ppm level. A variety of domestic and imported products were analyzed by this improved method and daminozide was detected in 33 of the 98 samples analyzed. Levels detected ranged from a trace amount to 0.80 ppm. The identity of UDMH hydrazone was confirmed by mass spectrometry in many samples, thus confirming the presence of daminozide. Two samples containing daminozide were analyzed independently by a second laboratory and the findings were closely duplicated.     

Linkages between atmospheric mercury deposition and the methylmercury content of marine fish

Enhanced Hg deposition to productive marine systems may result in concurrent increases in monomethyl Hg (MMHg) concentrations of marine fish. Consequently, it is important to understand what effects an increasing Hg supply may have on the marine food chain. A simple ocean model is employed to estimate the fraction of total Hg inputs which is required to sustain “average” marine fish MMHg concentrations annually. Calculations show that upwelling zones require 20% of total annual Hg inputs, coastal zones 5%, and open-ocean regions only 0.02%. The value for coastal areas is similar to that calculated for the acidified basin of Little Rock Lake, Wisconsin, a small fresh water seepage lake. These calculations point to Hg source strength and rates of particle scavenging as being key factors in controlling the rate of transport to sites of methylation (and subsequent entry into the marine food chain). If biological variables (scavenging rates, primary productivity) remain constant while anthropogenically-derived Hg deposition increases, it is likely that concentrations in marine biota (including fish) will rise in accord.     

Fluorometric determination of benzylideneacetone in fragrance products by liquid chromatography with post-column derivatization

A method is described for the liquid chromatographic (LC)-fluorometric determination of benzylideneacetone in fragrance products. Benzylideneacetone is first separated from other fragrance ingredients by LC and then reacted post-column with a methanolic solution of isonicotinic acid hydrazide and aluminum nitrate. The reactants are maintained at 65 degrees C for about 1.5 min to quantitatively form the fluorescent isonicotinoyl hydrazone derivative of benzylideneacetone. The aluminum ion forms a complex with the hydrazone to enhance the fluorescence of the derivative. The amount of benzylideneacetone is determined by measuring the intensity of the fluorescence emitted by the hydrazone derivative and comparing that value with those obtained for derivatized standards. Recovery studies were conducted by spiking commercial fragrances with benzylideneacetone at concentrations of 0.01, 0.05, and 0.1% (w/v). Recoveries ranged from 98 to 104% with a mean recovery of 100.2% and a standard deviation of 2.4%.     

Uptake of aqueous methylmercury by larvalChaoborus americanus

The uptake of monomethylmercury (mmHg) from water by larvalChaoborus americanus was studied. When exposed to aqueous mmHg for 6 days, the pattern of uptake was sigmoidal. The concentration of mmHg in the exposure water, however, was subject to demethylation and volatilization and therefore decreased over time. A model of passive diffusive uptake underestimated the uptake constant while a bioenergetics-based uptake model provided a reasonable estimate. The data suggest that uptake is not merely a passive diffusive process but may be coupled with oxygen uptake.     

Spectrofluorometric determination of histamine in fish and meat products

A method has been developed for spectrofluorometric determination of histamine in fish and meat products. After a perchloric extract is obtained from samples, histamine is extracted with n-butanol and transferred to hydrochloric acid. Finally, histamine is subjected to a condensation reaction with o-phthalaldehyde (OPT). The method was tested for lack of interference from other amines. Precision of the method in fish products was 6.60% CV; recovery was 96.50%. In meat products, precision was 5.42% CV; recovery was 96.20%. By analysis of variance (P = 0.05), no significant statistical differences were found for recovery values vs histamine content in both foods.     

Simultaneous derivatization and trapping of volatile products from aqueous photolysis of thiamethoxam insecticide

An aqueous photolysis study was conducted with radiolabeled thiamethoxam, 4H-1,3,5-oxadiazin-2-imine, 3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro, to establish the relevance of aqueous photolysis as a transformation process for (14)C-[thiazolyl]-thiamethoxam. (14)C-[thiazolyl]-thiamethoxam was applied to sterile sodium acetate pH 5 buffer solution at a dose rate of approximately 10 ppm. The resulting samples were incubated for up to 30 days at 25 degrees C under irradiated and nonirradiated conditions. The irradiated samples were exposed to a 12-hour-on and 12-hour-off light cycle. Volatile fractions accounted for up to an average of 56.76% of the total dose for the irradiated incubations and <0.08% for the nonirradiated incubations. These fractions were proposed to be a mixture of carbonyl sulfide (COS) and isocyanic acid (CONH). Verification of these components was accomplished by trapping with cyclohexylamine and formation of the thiocarbamate and the isocyanic acid derivatives. A similar method of trapping thiocarbamate metabolites was reported (Chen and Casida, 1978) where filter paper saturated with isobutylamine in methanol was arranged to trap (14)COS and (14)CO(2) under a positive flow of O(2) at 25 degrees C. Mass spectroscopy of the derivatized components confirmed the presence of carbonyl sulfide as the cyclohexylamine thiocarbamate and of isocyanic acid as its cyclohexylamine derivative. Evidence from this study indicates that thiamethoxam degrades significantly under photolytic conditions.     

Methods of sample preparation for detecting alkaline phosphatase in casein: collaborative study

A collaborative study was conducted in which 2 different sample preparation techniques were used to determine alkaline phosphatase in casein by the rapid colorimetric test. Seven collaborators tested 10 unknown casein products containing different amounts of residual phosphatase. Results indicated that the phosphatase contents of casein prepared by the 2 methods were not significantly different. The collaborators correctly analyzed 100% of the test samples that were ground and 98% of the test samples that were unground. The alternative rapid sample preparation method has been adopted official first action.     

Separation and determination of diesel contaminants in various fish products by capillary gas chromatography.

A semiquantitative capillary column gas chromatographic method is described for the determination of diesel fuel contamination in various canned seafood products. The diesel contaminants are separated from the fish sample by steam distillation, with little carry-over of interfering intrinsic materials such as fish oils. The diesel fuel is extracted from the condensate with n-hexane, and the extract is analyzed on an SPB-1 fused silica capillary column. The efficiency of recovery of diesel fuel added to canned seafood at levels of 40-400 ppt ranged from 72 to 102%. With the additional step of concentrating the hexane extract, the sensitivity of this procedure may be increased at least 10-fold. This procedure can detect the differences among diesel fuel grades No. 1, 2, and 5, and variations within diesel grade No. 2, and thus may be useful in determining the type of petroleum contaminants present in various canned fish products.     

Selective determination of melamine in aqueous medium by molecularly imprinted solid phase extraction

A molecularly imprinted polymer able to recognize melamine in partially aqueous medium was synthesized using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross-linking agent. The bound specificity and selectivity of the obtained material were verified by performing binding experiments with melamine and its structural analogue, 2,4,6-trimethoxy-1,3,5-triazine, respectively, using different aqueous binding media. Finally, the ability of MIP to selectively extract melamine from two real samples, a food supplement and a freeze-dried meat sample, was demonstrated.     

Determination of methylmercury in fish by headspace-gas chromatography with microwave-induced-plasma detection

Some additional experiments checking out the extraction method recently developed for the determination of MeHg in biological samples by Headspace Gas Chromatography with Microwave Induced Plasma atomic emission spectroscopy detection were performed. In this method, the MeHg is cleaved from the biological tissue by H₂SO₄ and by addition of iodoacetic acid converted to the iodide form. These reaction steps take place in a closed headspace vial. The H₂SO₄ concentration and the sample matrix have an important influence on the recovery of the MeHg from the sample and these effects are discussed. The method was then applied to the determination of MeHg in cod fish caught in the North Sea. Levels found ranged from 0.13 to 0.63 μg g⁻¹ dw with a mean of 0.33 μg g⁻¹ on the 25 samples analyzed. The total Hg content of these samples was also determined by Cold Vapour Atomic Absorption Spectrometry, and all data pooled ranged from 0.19 to 0.90 μg g⁻¹ with a mean of 0.40 μg g⁻¹. A study of the ratio MeHg/total Hg revealed that MeHg always constituted more than 60 % of the total Hg level, with a mean of 83 % on the 25 samples. The percentage MeHg did not increase or decrease markedly when the total Hg content increased. It could be concluded that these North Sea samples are not much contaminated by Hg and are surely suitable for consumption.     

Sample preparation and liquid chromatographic determination of vitamin D in food products

Vitamin D in different fortified foods is determined by using liquid chromatography (LC). Sample preparation is described for fortified skim milk, infant formulas, chocolate drink powder, and diet food. The procedure involves 2 main steps: saponification of the sample followed by extraction, and quantitation by LC analysis. Depending on the sample matrix, additional steps are necessary, i.e., enzymatic digestion for hydrolyzing the starch in the sample and cartridge purification before LC injection. An isocratic system consisting of 0.5% water in methanol (v/v) on two 5 microns ODS Hypersil, 12 X 0.4 cm id columns is used. Recovery of vitamin D added to unfortified skim milk is 98%. The results of vitamin D determination in homogenized skim milk, fortified milk powder, fortified milk powder with soybean, chocolate drink powder, and sports diet food are given.     

Toward fish and seafood traceability: anchovy species determination in fish products by molecular markers and support through a public domain database

Traceability in the fish food sector plays an increasingly important role for consumer protection and confidence building. This is reflected by the introduction of legislation and rules covering traceability on national and international levels. Although traceability through labeling is well established and supported by respective regulations, monitoring and enforcement of these rules are still hampered by the lack of efficient diagnostic tools. We describe protocols using a direct sequencing method based on 212-274-bp diagnostic sequences derived from species-specific mitochondria DNA cytochrome b, 16S rRNA, and cytochrome oxidase subunit I sequences which can efficiently be applied to unambiguously determine even closely related fish species in processed food products labeled "anchovy". Traceability of anchovy-labeled products is supported by the public online database AnchovyID ( http://anchovyid.jrc.ec.europa.eu), which provided data obtained during our study and tools for analytical purposes.     

Phosphite determination in fertilizers after online sequential sample preparation in a flow injection system

A flow injection spectrophotometric system is proposed for phosphite determination in fertilizers by the molybdenum blue method after the processing of each sample two times on-line without and with an oxidizing step. The flow system was designed to add sulfuric acid or permanganate solutions alternately into the system by simply displacing the injector-commutator from one resting position to another, allowing the determination of phosphate and total phosphate, respectively. The concentration of phosphite is obtained then by difference between the two measurents. The influence of flow rates, sample volume, and dimension of flow line connecting the injector-commutator to the main analytical channel was evaluated. The proposed method was applied to phosphite determination in commercial liquid fertilizers. Results obtained with the proposed FIA system were not statistically different from those obtained by titrimetry at the 95% confidence level. In addition, recoveries within 94 and 100% of spiked fertilizers were found. The relative standard deviation (n = 12) related to the phosphite-converted-phosphate peak alone was 相似文献   

Liquid chromatographic determination of aflatoxins, ochratoxin A, and zearalenone in grains, oilseeds, and animal feeds by post-column derivatization and on-line sample cleanup

A liquid chromatographic method using on-line sample cleanup, reverse flow analytical column loading, gradient elution, and postcolumn derivatization with iodine permits direct, rapid determination of aflatoxins B1, B2, G1, and G2, as well as ochratoxin A and zearalenone. Limits of quantitation are 5 ppb for the aflatoxins and ochratoxin A and 30 ppb for zearalenone. This procedure performs well as a multimycotoxin screen for cereal grains and oilseeds, with more limited success in complete animal feeds.     

Direct aqueous injection-liquid chromatography with post-column derivatization for determination of N-methylcarbamoyloximes and N-methylcarbamates in finished drinking water: collaborative study

An interlaboratory method validation study was conducted on EPA Method 531.1, Measurement of N-Methylcarbamoyloximes and N-Methylcarbamates in Water by Direct Aqueous Injection HPLC with Post Column Derivatization, to determine the precision and mean recovery for determination of 10 carbamate pesticide compounds in reagent water and in finished drinking waters. The study design was based on Youden's nonreplicate plan for collaborative tests of analytical methods. The waters were spiked with 10 carbamate pesticides at 6 concentration levels, as 3 Youden pairs. Eight laboratories analyzed the samples by direct aqueous injection, with separation by reverse-phase liquid chromatography and post-column hydrolysis of the carbamates and carbamoyloximes to methylamine, followed by reaction of the methylamine with o-phthalaldehyde and 2-mercaptoethanol using fluorescence detection. Results were analyzed using an EPA computer program, which measured precision and recovery for each of the 10 compounds and compared the performance of the method between water types. The method was acceptable for all analytes tested. After removal of a nonrepresentative data set for aldicarb sulfoxide, no matrix effects were observed; the statistics for the pooled drinking waters were not significantly different from the statistics for the reagent waters. The method has been adopted official first action by AOAC.     

Identification and quantification of polybrominated hexahydroxanthene derivatives and other halogenated natural products in commercial fish and other marine samples

During routine analysis of commercial fish on halogenated pollutants, an unknown tribromo component (TriBHD) was initially detected as an abundant peak in sample extracts from the Mediterranean Sea. The molecular formula was established to be C16H19Br3O by gas chromatography with electron ionization high-resolution mass spectrometry (GC/EI-HRMS). GC/EI-MS data were virtually identical with a polybrominated hexahydroxanthene derivative (PBHD) previously isolated from an Australian sponge species known to occur in the Mediterranean Sea as well. A tetrabromo isomer (TetraBHD) was also found in the fish samples. The concentrations of TriBHD and other halogenated compounds in commercial fish (sea bass, gilt head bream, anchovy, sardine, and salmon) were estimated with GC/electron capture detection (ECD). Using the ECD response of trans-nonachlor, the concentration of TriBHD reached up to 90 ng/g lipid weight and accounted for up to >90% of the concentration of p,p'-DDE, which was the most abundant peak in the most samples investigated. On the basis of the GC/ECD response, TetraBHD amounted for approximately 1/7 of TriBHD in all fish samples investigated. The sample with the highest content was a green-lipped mussel from New Zealand (236 ng/g lipid weight). The halogenated natural products TBA, Q1, and MHC-1 were also present in most of the samples. We assume that the bulk of the residues in fish from aquaculture may originate from algae and sponges living in proximity of the fish farms. Detection of TriBHD and TetraBHD in blubber of a monk seal (Monachus monachus) suggests that both HNPs may reach the top predators of food webs and thus also humans.     

Soil nitrogen fractions as influenced by sample preparation and extraction

Abstract

In order to evaluate the influence of extraction procedure on extractable nitrogen (N) fractions, fresh as well as dried soil samples were extracted with CaCl₂ at various temperatures (20,40,60, 80°C) for 30–120 minutes. Data obtained were compared with those from the electro‐ultra‐filtration (EUF) method. Increasing the drying temperature as well as the extraction temperature led to an increase in N_org content. The EUF and CaCl₂‐method produced comparable results for all N‐fractions (NO₃ ^‐, NH₄ ⁺, N_org) when an extraction temperature of 80°C was applied for two hours. Data presented suggested that the N_org fraction represented mainly the microbial biomass and may thus be considered as being easily available to plants.