Survey of total mercury in some edible fish and shellfish species collected in Canada in 2002

Total mercury was measured in the edible portions of 244 selected fish and shellfish purchased in Canada at the retail level. By species, average mercury concentrations ranged from 0.011 μg g^-1 for oysters to 1.82 μg g^-1 for swordfish. The predatory fish contained the highest concentrations of mercury: swordfish (mean 1.82 μg g^-1, range 0.40-3.85 μg g^-1), marlin (1.43, 0.34-3.19 μg g^-1), shark (1.26, 0.087-2.73 μg g^-1), and canned, fresh and frozen tuna (0.35, 0.020-2.12 μg g^-1). Levels of mercury in the fresh and frozen tuna contained a mean of 0.93 μg g^-1 (range 0.077-2.12 μg g^-1) and were substantially higher than in the canned tuna (0.15, 0.02-0.59 μg g^-1). In the canned tuna, mercury concentrations varied with subspecies, with the highest average concentrations being found in Albacore tuna (mean 0.26 μg g^-1, range 0.19-0.38 μg g^-1) and the lowest (0.047, 0.025-0.069 μg g^-1) in five samples for which the subspecies of tuna were not identified. Mean concentrations of mercury in swordfish and fresh and frozen tuna were up to three times higher than reported for the USA. Dietary intake estimations found that provided fresh and frozen tuna, marlin, swordfish or shark are consumed once a month or less, the dietary intakes of total mercury by women of child-bearing age, averaged over 1 month, would fall below the Joint FAO/WHO Expert Committee on Food Additives provisional tolerable weekly intake for total mercury. The current Canadian advisory to children and women of child-bearing age is to limit their consumption of fresh and frozen tuna, swordfish and shark to no more than one meal per month.     

Cholesterol content of Indian fish and shellfish

Ninety-seven samples of fish and 17 samples of shellfish from tropical waters were analysed for fat, nonsaponifiable matter (NSM) and cholesterol contents. Significant differences were noted in the cholesterol contents of the various families of fish analysed. However, the variation in the content of cholesterol was found to be not significant within the families. Higher contents of cholesterol were observed in shellfish than in fish. No correlation existed between the fat content of the fish/shellfish and the levels of cholesterol or NSM. ©     

Biogenic amines in fish, fish products and shellfish: a review

Fish, cephalopods and shellfish provide a healthy source of high-quality proteins, essential vitamins, minerals and polyunsaturated fatty acids. The beneficial effects of fish consumption on human health such as protection against coronary heart disease and certain cancer may be offset by fish decomposition and the formation of chemical contaminants such as biogenic amines. There are several toxicological effects of biogenic amines on humans, especially histamine. It is the causative agent of histamine or scombroid fish poisoning which is a significant public health problem. In individuals with diminished histamine detoxification, ingestion of even a low or moderate histamine- or tyramine-containing fish may lead to food intolerance. Biogenic amines such as putrescine, tyramine and cadaverine can potentiate histamine toxicity. Furthermore, dietary polyamine intake should be minimised in some cancer patients. Besides their potential toxicity, biogenic amines are used for the evaluation of hygienic quality of different marine and freshwater species. Spoilage pattern and biogenic amine formation are species specific. Histamine has been traditionally used as an indicator of the quality of histidine-rich fish (dark-muscle fish). On the other hand, putrescine and cadaverine are the most objective indicators of quality of histidine-poor fish (white-muscle fish), shellfish and fermented seafood products.     

Biogenic amines in fish,fish products and shellfish: a review

Fish, cephalopods and shellfish provide a healthy source of high-quality proteins, essential vitamins, minerals and polyunsaturated fatty acids. The beneficial effects of fish consumption on human health such as protection against coronary heart disease and certain cancer may be offset by fish decomposition and the formation of chemical contaminants such as biogenic amines. There are several toxicological effects of biogenic amines on humans, especially histamine. It is the causative agent of histamine or scombroid fish poisoning which is a significant public health problem. In individuals with diminished histamine detoxification, ingestion of even a low or moderate histamine- or tyramine-containing fish may lead to food intolerance. Biogenic amines such as putrescine, tyramine and cadaverine can potentiate histamine toxicity. Furthermore, dietary polyamine intake should be minimised in some cancer patients. Besides their potential toxicity, biogenic amines are used for the evaluation of hygienic quality of different marine and freshwater species. Spoilage pattern and biogenic amine formation are species specific. Histamine has been traditionally used as an indicator of the quality of histidine-rich fish (dark-muscle fish). On the other hand, putrescine and cadaverine are the most objective indicators of quality of histidine-poor fish (white-muscle fish), shellfish and fermented seafood products.     

Mercury in UK imported fish and shellfish and UK-farmed fish and their products

Total mercury concentrations were measured in fish and shellfish and their products imported into the UK and also in UK-produced farmed salmon and trout. Three hundred and thirty-six samples were collected using a two-stage sampling plan. The sample plan was weighted to reflect consumption, but with some bias towards fish that might accumulate higher levels of mercury, such as large predatory fish at the top of the food chain. The highest levels of total mercury were found in billfish (swordfish and marlin) and shark. Mercury concentrations in the five samples of fresh/frozen shark ranged from 1.006 to 2.200 mg kg -1 , all above the European Commission limit for the species, and concentrations in 20 samples of fresh/frozen billfish ranged from 0.153 to 2.706 mg kg -1 with 13 samples above the 1.0 mg kg -1 limit for the species. One sample of Antarctic ice fish was collected and had a mercury concentration of 0.664 mg kg -1 . The limit for this species was 0.5 mg kg -1 . One sample of fresh/frozen tuna out of the 20 collected had a mercury concentration above the limit of 1.0 mg kg -1 (1.5 mg kg -1 ), but all other fresh tuna samples were well within the regulatory limit (average 0.4 mg kg -1 ). Mercury concentrations in canned tuna were lower with concentrations on average half that measured in fresh/frozen tuna. Mercury concentrations in UK-farmed salmon and trout were relatively low. The maximum concentration found in 46 samples of fresh/frozen or smoked trout and salmon was 0.103 mg kg -1 .     

鲜活贝类中单核细胞增生李斯特菌的分离鉴定及毒力基因与耐药性分析

目的研究采自产地的鲜活贝类中单核细胞增生李斯特菌(单增李斯特菌)的污染状况、毒力基因分布与耐药性。方法对采自产地的200份鲜活贝类,按照GB/T 4789.30—2010《食品安全国家标准食品卫生微生物学检验单核细胞增生李斯特氏菌检验》进行单增李斯特菌的分离与鉴定;采用Kirby-Bauer纸片扩散法测定分离株的耐药性;通过PCR法分析分离株9个毒力基因(包括prfA、plcB、hly、actA、iap、inlA、plcA、mpl、inlB)。结果在200份鲜活贝类中,共检出阳性样品4份(2.0%);有1株缺失inlB基因,1株缺失mpl基因;分离株对氨苄青霉素、庆大霉素等一线临床治疗药物敏感,但有2株对四环素和复方新诺明同时耐药,1株对复方新诺明和氧氟沙星耐药。结论采自产地的鲜活贝类存在单增李斯特菌的污染,分离株毒力基因有一定程度缺失,提示初级水产品中的单增李斯特菌污染需引起关注,并且需要继续加强食品中该菌的耐药性监测。     

Occurrence of an organochlorine synergist S-421 in fish and shellfish

S-421 is a synergist for pyrethroid and organophosphorus pesticides, and is widely used in termiticides or commercial household insecticides. S-421 is mutagenic, stable and ubiquitous in the environment, and has been detected in household dust, surface water, sediments and rain-water. Here we describe the concentration of S-421 residues in domestic and imported fish collected in Osaka. S-421 was extracted with acetone/hexane, purified through silica gel 40 and quantified by ECD-GC. S-421 was detected in 36 out of 44 samples of domestic fish and shellfish analyzed, at a level of < 0.2 to 2.3 ng/g (mean: 0.6 ng/g), and in 27 out of 43 imported samples at a level of < 0.2 to 1.0 ng/g (mean: 0.2 ng/g). The levels of S-421 detected in fish were lower than those of DDTs and almost the same as those of HCHs. More attention should be paid to the behavior in the environment of S-421, as well as other persistent organochlorine pollutants, such as HCHs, DDTs and chlordane.     

Biogenic amine formation and bacterial contribution in fish,squid and shellfish

Forty-one species of fish, squid and shellfish were analyzed for biogenic amine (BA) contents. Most of the fish samples showed lower BA contents, whereas some samples showed higher contents than the allowable levels. Shellfish and squid samples had negligible BA levels. Four fish species containing high BA levels were analyzed for changes in histamine contents during storage. In the most samples, the histamine contents remarkably increased up to 36.6–2123.9 mg/kg after 24 h of storage at 25 °C, while the contents began to gradually increase after 2–3 days of storage at 4–10 °C. The dominant microbial group was enterobacteria throughout the storage period. Meanwhile, out of total 119 strains isolated from different fish species showing high BA levels, 23 strains identified as Enterobacter aerogenes produced large amounts of histamine, putrescine and cadaverine, and 33 strains identified as two different Enterobacter spp. produced less histamine but large amounts of putrescine and cadaverine.     

Spoilage and shelf‐life extension of fresh fish and shellfish

Fresh fish and shellfish are highly perishable products due to their biological composition. Under normal refrigerated storage conditions, the shelf life of these products is limited by enzymatic and microbiological spoilage. However, with increasing consumer demands for fresh products with extended shelf life and increasing energy costs associated with freezing and frozen storage, the fish‐processing industry is actively seeking alternative methods of shelf life preservation and marketability of fresh, refrigerated fish and at the same time economizing on energy costs. Additional methods that could fulfill these objectives include chemical decontamination, low‐dose irradiation, ultra‐high pressure, and modified atmosphere packaging (MAP). This review focuses on the biochemical and microbiological composition of fresh fish/shellfish, the spoilage patterns in these products, factors influencing spoilage, and the combination treatments that can be used in conjunction with refrigeration to extend the shelf life and keeping quality of fresh fish/shellfish. The safety concerns of minimally processed/MAP fish, specifically with respect to the growth of Clostridium botulinum type E, is also addressed.     

Occurrence of Vibrio vulnificus in fish and shellfish available from markets in China

Vibrio vulnificus is a naturally occurring estuarine bacterium often associated with disease such as septicemia in humans following consumption of raw and lightly cooked seafood. In China and neighboring countries, rapid economic growth has encouraged increased consumption of seafood, and dietary habits are changing, with more people eating raw fish. In this study, the prevalence of V. vulnificus was investigated in 48 samples from 11 species of live seafood available from markets in coastal cities of China. The bacterium was detected in four of four razor clam samples, in seven of seven giant tiger prawn samples, and in five of nine mantis shrimp samples. The bacterium was also found in water samples of the prawn aquaria at the markets. The maximum level of V. vulnificus was 3.4 log CFU/g in the razor clam samples and 4.9 log CFU/g in the prawn samples by a direct spreading method. Differential bacterial counts on the prawn body revealed that most of the bacteria were found on the shells (exoskeletons), with very few in the edible muscle. However, dense populations can be found in the intestines. Biochemical tests indicated that the isolates of V. vulnificus were biotype 1 strain, which is pathogenic to humans. These isolates were susceptible to ampicillin, penicillin, kanamycin, streptomycin, and erythromycin. These results suggest that V. vulnificus is a potential health hazard to humans in cities consuming and handling live shellfish, especially giant tiger prawns.     

Heavy metal concentrations in fish,shellfish and fish products from internal markets of India vis-a-vis international standards

Heavy metals are an important group of chemical contaminants and food is the major vehicle for entry into the system. Fish constitute a major source of heavy metals in food. Concentration of heavy metals in commercially important species of fish, shellfish and fish products from fish markets in and around the Cochin area was evaluated using an atomic absorption spectrometer. The concentration ranges of Cd, Pb, Hg, Cr, As, Zn, Cu, Co, Mn, Ni, and Se in the samples were <0.07–1, <0.07–1.32, <0.05–2.31, <0.05 to 3.65, <0.1–4.14, 0.6 to 165, 0.15 to 24, <0.02 to 0.85, <0.08 to 9.2, <0.032–1.38 and; <0.03–1.35 mg/kg, respectively. The present study showed that different metals were present in the samples at different levels but within the maximum residual levels prescribed by the EU and USFDA and the fish and shellfish from these areas, in general, are safe for human consumption.     

Toxicity of puffer fish cultured in netcages

During 1990 to 2003, the toxicity of the liver in 4,515 specimens of the puffer fish Takifugu rubripes (torafugu) cultured in netcages or on land were investigated by means of mouse bioassay and liquid chromatography-mass spectrometry (LC/MS). Other tissues (skin, muscles, gonads, etc.) were also investigated in some of them. All the livers and other parts examined were found to be non-toxic. The peak corresponding to tetrodotoxin (TTX) was not detected in the samples by LC/MS analysis for TTX (< 0.1 MU/g). These results show that puffer fish fed on a non-toxic diet in netcages do not become intoxicated.     

Occurrence of Vibrio spp. in fish and shellfish collected from the Swiss market

The genus Vibrio includes gram-negative bacteria that inhabit estuarine ecosystems. V. cholerae, V. parahaemolyticus, and V. vulnificus pose a considerable public health threat as agents of sporadic and epidemic foodborne infections associated with the consumption of raw or undercooked contaminated fish or shellfish. In this study, we analyzed 138 fish and shellfish samples collected from the Swiss market (fish fillets [n = 102], bivalves [n = 34], and squid [n = 2]). Microbiological analysis was done according to International Organization for Standardization method 21872-1/21872-2:2007, using thiosulfate citrate bile sucrose agar and chromID Vibrio agar as selective agar. Presumptive-positive colonies on thiosulfate citrate bile sucrose agar or chromID Vibrio agar were picked and were identified by the API 20E and species-specific PCR systems. V. cholerae isolates were tested further by PCR for the presence of the cholera toxin A subunit gene (ctxA). V. parahaemolyticus isolates were tested by PCR for genes encoding for thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). V. cholerae was isolated from three samples and V. parahaemolyticus from eight samples. None of these strains harbored species-specific virulence factors. Further, V. alginolyticus was isolated from 40 samples, and V. fluvialis was isolated from 1 sample. Our study provides, for the first time, data for the assessment of exposure to Vibrio spp. in raw fish and bivalves consumed in Switzerland.     

辽宁沿海城市海鱼和贝类中重金属含量的测定及评价

经微波消解处理样品,采用石墨炉原子吸收光谱法(GFAAS)测定辽宁沿海城市常见海鱼和贝类中镉、铬、铜、铅、铁、锌六种元素的含量。其相对标准偏差(RSD)0.53%～4.01%,加标回收率90.0%～110.0%。结果表明:不同地区、不同鱼贝种类中重金属的分布存在差异,所检测鱼贝类中铬、铜、锌含量低于国家限量标准,部分样品中镉、铅含量超标,但低于暂定每周可耐受摄入量(PTWI)。因此辽宁沿海城市市售所检测的鱼贝类可食用,但仍有必要降低摄入量。     

Mercury, arsenic, lead and cadmium in fish and shellfish from the Adriatic Sea

The aim was to measure concentrations of total mercury, total arsenic, lead and cadmium in common edible fresh fish and shellfish from various areas of the Adriatic Sea. Estimates of intake of these elements were made through seafood consumption by the general population. Samples were either wet digested for mercury and arsenic, or dry ashed for lead and cadmium analysis. Mercury was measured by cold vapour atomic absorption spectrometry (CV AAS) and arsenic, lead and cadmium by electrothermal atomic absorption spectrometry (ET AAS). Quality control procedures of analytical methods, which included analyses of dogfish muscle-certified reference material DORM-2, confirmed the acceptability of methods. The highest mercury and arsenic concentrations were found in hake ( Merluccius merluccius ) and the lowest in mackerel ( Scomber scombrus ). The respective values in hake were 0.373 ±0.075 and 23.3 ±3.6, and in mackerel 0.153 ±0.028 and 1.06 ±0.29 mg kg -1 fresh weight (mean ±SD). Lead and cadmium concentrations were about 10 times higher in shellfish than in analysed fish. The highest lead and cadmium concentrations were found in mussel ( Mytilus galloprovincialis ) and the lowest in hake. Respective lead and cadmium values in mussel were 0.150 ±0.009 and 0.142 ±0.017, and in hake were 0.007 ±0.004 and 0.002 ±0.001 mg kg -1 fresh weight. The concentrations of analysed elements were below acceptable levels for human consumption set by the Croatian Ministry of Health, except for total arsenic. The estimated intake of those trace elements included in this study through seafood consumption by the general population did not exceed the provisional tolerable weekly intake recommended by the Joint FAO/WHO Expert Committee on Food Additives.     

Brominated flame retardants in fish and shellfish - levels and contribution of fish consumption to dietary exposure of Dutch citizens to HBCD

In order to determine the contamination with brominated flame retardants (BFR) in fish regularly consumed by Dutch citizens, 44 samples of freshwater fish, marine fish, and shellfish were analyzed for polybrominated diphenyl ethers (PBDE), tetrabromobisphenol-A (TBBP-A) and its methylated derivative (me-TBBP-A), and hexabromocyclododecane (HBCD), including its alpha-, beta- and gamma-diastereomers. The highest BFR concentrations were found in pike-perch and eel from the highly industrialized and urbanized rivers Rhine and Meuse. The sum concentrations of BDE 28, 47, 99, 100, 153, 154, 183, 209, and brominated biphenyl (BB) 153 and HBCD (selection based on The European Food Safety Authority monitoring recommendation) ranged from below quantification limits to 17 ng/g wet weight (ww) in marine fish and in freshwater fish from 0.6 ng/g ww in pike-perch to 380 ng/g ww in eel. The BDE congener profile in all fish and shellfish samples is dominated by BDE 47, followed by BDE 99, except for eel in which BDE 100 is higher than BDE 99. BDE 209 was detected in two mussel samples, most likely due to BDE 209 contaminated particulate matter in their intestines. Total-HBCD (as determined by GC/electron capture negative ion (ECNI)-MS) was detected in 22 out of the 44 samples in concentrations between 0.20 ng/g in marine fish and 230 ng/g ww in eel. Three HBCD diastereomers were determined by HPLC/ESI-MS/MS. alpha-HBCD was the prevalent congener in most fish samples, followed by gamma-HBCD. beta-HBCD, TBBP-A and me-TBBP-A were only detected in a few samples and at low concentrations. A considerable difference was found between HBCD results obtained from GC/ECNI-MS and HPLC/ESI-MS/MS: the GC/ECNI-MS results were 4.4 times higher, according to regression analysis. There is hardly any data on human dietary exposure to HBCD available. We have estimated the fish-related dietary exposure of HBCD for the average Dutch population. The medium bound intake was estimated at 8.3 ng/day for a 70-kg person (0.12 ng/kg bodyweight/day). For this estimation, we relied mostly on HPLC/ESI-MS/MS data as we argue that these results are more accurate than those obtained by GC/ECNI-MS.