Low mercury, cadmium and lead concentrations in tuna products from the eastern Pacific

Total mercury exposure through canned tuna in water sold in Quito, Ecuador

Mercury is a toxic trace metal found in seafood products owing to its bioaccumulative and ubiquitous nature. Seafood and fish are frequently consumed, being necessary to assess its human health risk. Accordingly, this study quantified total mercury in samples of canned tuna in water from supermarkets in the Metropolitan District of Quito in Ecuador, in order to ensure that Hg content is within the maximum limits stablished in national and international regulations. Total mercury levels were measured through cold vapor atomic fluorescence spectrophotometry. Three of the most consumed tuna brands in Ecuador were analyzed, coded as A, B, and C, according to the price at which they are sold in the market (A < B < C). Results indicated that mean total mercury in different tuna brands were within the permissible limits. Total mercury concentrations were 0.14 ± 0.11 mg kg-1; 0.41 ± 0.42 mg kg-1; and 0.25 ± 0.22 mg kg-1 for brands A, B, and C, respectively. However, for brand B the potential non-carcinogenic risk of mercury for consumers exceeded the threshold limit (> 1). When considering the highest total mercury content to which Ecuadorian population is exposed through the consumption of brand A, B, and C, the recommended weekly intake for children and adults were: A: 63 g and 306 g; B: 12 g and 57 g; C: 30 g and 144 g, respectively.

Validation of a New Liquid Asymmetric-Electrode Plasma Optical Emission Spectroscopy (LAEP-OES) Method for Measurement of Total Mercury in Tuna

BACKGROUND

Mercury intake is caused by eating seafood, such as tuna and other predatory fish species. To reduce the health risks of mercury intake, it is necessary to continuously measure and monitor mercury concentrations at fish farms and markets. We have developed a compact system that can detect multiple heavy metals by liquid asymmetric-electrode plasma optical emission spectroscopy (LAEP-OES).

OBJECTIVE

The validity of the LAEP-OES method for total mercury levels was evaluated using standard solutions, certified substances, and specimens of bluefin tuna and other fish species.

METHODS

All specimens were dissolved in 4 M lithium hydroxide solution and then dispensed into a sample reservoir well of the single-use measurement reagent pack. Total mercury levels were automatically measured within 15 min of placement into the dedicated equipment. A total of 102 fish specimens, classified into 10 fish species, were evaluated using the new method and the results were compared to those obtained from validated analytical methods.

RESULTS

LOD (0.02 mg/kg), LOQ (0.07 mg/kg), repeatability (4.0%), intermediate precision (9.8%), and trueness (recoveries 107%) of the proposed method were within satisfactory limits for total mercury levels in fish. Additionally, when using various fish species, the method had a strong positive correlation with the results of cold-vapor atomic absorption spectrometry (CV-AAS, the official method) with Spearman rs = 0.984.

CONCLUSION

The LAEP-OES method can be used for measuring total mercury levels in bluefin tuna. Total mercury measurement using this new method has the potential to be applied to other fish species.

HIGHLIGHTS

Total mercury levels in fish were measured using our unique analysis system. Pacific bluefin tuna, southern bluefin tuna, and Atlantic bluefin tuna distributed in the Japanese market were analyzed for total mercury in their wild and farmed fish varieties.

Effects of dietary and/or parental supplementation with selenium and mercury on their localisation in rainbow trout fry tissues (Oncorhynchus mykiss) by quantitative LA-ICP MS imaging

The increasing use of alternative feeds for sustainable aquaculture leads to a reduced selenium content requiring the use of supplements to maintain the antioxidant status of farmed fish. The introduction of tuna by-products in fish feed is attractive for their selenium content, but the presence of mercury limits their use as it may negatively impact fish health. Indeed, selenium and mercury metabolism, in relation to their interaction and biological effects in fish, is far from being fully understood. This study aims to assess the impact of parental and dietary supplementation with selenomethionine and methylmercury on selenium and mercury localisation and concentrations in tissues of 3-week rainbow trout fry. Six diets were used. Broodstock were fed a plant-based diet Bpc (with 0.2 μg g-1 selenium and 0 μg g-1 mercury) or a tuna by-product-based diet Bt (with 4 μg g-1 selenium and basal mercury at 0.2 μg g-1) during 6 months, supplemented or not with 4 μg g-1 of selenomethionine for the plant-based diet Bpo and/or with 2 μg g-1 of methylmercury for diets Bph, Bpho and Bth. Their offspring were fed the plant-based diet Fpc, supplemented or not with the same levels of selenomethionine and methylmercury, until their third week. Mercury and selenium concentrations were determined in fry whole-body by ICP MS and quantitative images of selenium and mercury were produced by LA-ICP MS from fry whole-body thin sections. Dietary supplementation of fry with selenium and/or mercury increased their concentration in all tissues, especially in liver, kidney, muscle and intestine. Parental selenomethionine supplementation had a more pronounced effect on fry selenium levels than tuna by-products diet. Mercury transfer from broodstock to their offspring was weak. Mercury concentrations decreased in the kidney of fry supplemented with both selenium and mercury, which could be related to the presence of selenium.

Concentration of potential toxic elements in canned tuna fish: systematic review and health risk assessment

The health risks (non-carcinogenic and carcinogenic risk) were calculated in both adults and children, using target hazard quotient (THQ) and carcinogenic risk (CR). The concentrations of Cd, Pb, and Ni were higher than the standard limits but they did not pose any non-carcinogenic health risks in adult and children's consumers (THQ <1). Meanwhile, the risk assessment of iAs indicates THQ > 1 for children in Egypt. Moreover, the THQ value due to Me Hg for adult in Tunisia and for children in Tunisia, Malta, Portugal, Latvia, Cambogia, Peru, South Korea, Romania, Hong Kong, United Arab Emirates, Morocco, and Egypt was higher than 1 value. In addition, the calculated CR values of iAs for the adults and children were within the threshold risk of developing cancer (Between 1.00E-4 to 1.00E-6). Therefore, it is recommended to continuously monitor the concentration of PTEs in canned tuna.

Detection of Salt Content in Canned Tuna by Impedance Spectroscopy: A Feasibility Study for Distinguishing Salt Levels

The electrical impedance of dilute aqueous solutions containing extracts from five brands of canned tuna is analyzed using impedance spectroscopy in order to analyze their salt content and detect the potential presence of other salts beyond the well-stated NaCl. A complex electrical impedance is modeled with an equivalent electrical circuit, demonstrating good agreement with experimental data. This circuit accounts for the contribution of ions in the bulk solution, as well as those contributing to electrode polarization. The parameters describing the equivalent circuits, obtained through fitting data to the electrical impedance, are discussed in terms of the various ion contributions to both the electrical double layer at the electrode interface and the electrical conductivity of each solution. The ionic contribution to the electrical impedance is compared with that of a pure NaCl solution at the same concentration range. This comparison, when extended to real samples, allows for the development of a model to estimate the electrical conductivity of canned tuna samples, thereby determining the salt concentration in tuna. The model enables differentiation among the various samples of tuna studied. Subsequently, the potential presence of other ions besides Na+ and Cl- and their contribution to the electrical properties of each canned tuna extract is considered, especially for samples with a higher ratio of the sum of K+ and phosphates to Na+ concentration. This analysis shows the potential of impedance spectroscopy for on-site and rapid analysis of salt content and/or detection of additives in canned tuna fish.

Baseline study for the total mercury determination in Yemeni fish

The high levels of mercury toxicity in humans make it necessary to monitor mercury levels in food, pharmaceuticals, and the environment to minimize human exposure. Between June 2020 and October 2021, researchers collected 240 fish samples from different locations along the Yemeni coast to evaluate mercury contamination. The Direct Mercury Analyzer was used to determine the concentration of mercury in each sample. To ensure method accuracy, a series of triplicate mercury concentration analyses were conducted. The samples ranged from 2 to 100 ng to determine linearity and repeatability i.e., within-day variation. The results showed a high level of precision, with a correlation coefficient of 0.9990 and a repeatability of 1.34 %-5.62 % RSD range. The method was also highly accurate, as the mercury recovery results from the contaminated fish samples ranged from 96.77 % to 105.14 %. The limits of detection and quantitation of mercury were 0.0015 ppm and 0.0049 ppm, respectively. This allowed the method to detect trace amounts of mercury in fish meat. Mercury concentration in the 240 fish samples did not exceed the FDA, but below the 0.5 ppm specified limit of YSMO.

Evaluation of a gold-nanoparticle-modified carbon-fiber microelectrode to quantify mercury in canned tuna sold in Ecuador

Seafood consumption is the primary exposure route for trace metals like mercury. Accordingly, canned tuna meat has been focused on by researchers because of the potential bioaccumulation of high amounts of mercury. This study aimed to test a novel and reliable electroanalytical method employing a working electrode consisting of gold-nanoparticle-modified carbon microfibers to quantify total mercury in canned tuna samples. Determination was achieved via differential pulse anodic stripping voltammetry. The proposed method had a limit of detection of 3.9781 ± 0.0001 μg L-1 and a limit of quantification of 33.6634 ± 0.0001 μg L-1, with a sensitivity of 0.3275 nA μg L-1. The modified electrode was evaluated in samples taken from three canned tuna brands sold in the Sangolquí parish in Rumiñahui, Ecuador. These brands, coded A, B, and C, represent 47.92%, 27.08%, and 11.98% of all canned tuna sold in the Ecuadorian market, respectively. The resulting respective total mercury concentrations were 0.5999 ± 0.0001 mg kg-1; 0.9387 ± 0.0001 mg kg-1; and 0.3442 ± 0.0001 mg kg-1 for A, B, and C. Method accuracy was determined through the recovery percentages of ≥98%, which indicated acceptable accuracy for the final optimized method. Mean mercury concentrations for all samples did not represent a carcinogenic risk for consumers. However, the values obtained for potential no-carcinogenic risk and daily consumption rate suggest that consumers of tuna canned in water, particularly brand C, may be at risk.

Metal Load of Potentially Toxic Elements in Tuna (Thunnus albacares)-Food Safety Aspects

The consumption of marine fishes has a positive effect on a consumer's health; however, it poses a potential risk due to their level of heavy metals in their body. Heavy metals can be naturally found in the environment, but their concentration can be increased with anthropogenic activities. Samples of tuna (Thunnus albacares) were collected at a fishery market. The potentially toxic elements (arsenic, cadmium, lead, and mercury) were determined with a validated method in the flesh of fish using inductively plasma optical emission spectrometry after microwave digestion. Generally, the average concentration of them was below the official limit values regulated by the European Union, except for lead. Based on the concentrations of arsenic (inorganic derivates: 0.05 ± 0.02 mg/kg) and cadmium (0.03 ± 0.01 mg/kg) in the tuna fish samples, and their calculated EDI values (As: 0.03-0.09 µg/kg/day; Cd: 0.05-0.07 µg/kg/day), the investigated food could be declared safe for human consumption. Generally, mercury content was below the official regulated limit, and the calculated EDI value was below the dietary reference value (0.3 μg/kg/day) in most of the samples (90%), exceeding it only in two samples (0.69 and 0.82 μg/kg/day); thus, they may not be harmful to the consumer. The concentration of lead above the official maximum limit (0.30 mg/kg) in 40% of tuna samples (0.30-1.59 mg/kg), as well as the exceeding of the dietary reference value for lead (adult: 0.16 μg/kg/day; children: 0.26 μg/kg/day) based on the calculated EDI values (0.28-1.49 μg/kg/day), draw attention to the importance of environmental pollution and the protection of consumers' health.

Heavy metals content in fresh tuna and swordfish caught from Hindian and Pacific Oceans: Health risk assessment of dietary exposure

Background and Aim

Yellowfin tuna and swordfish are seafood commodities commonly caught from deep oceans worldwide. Therefore, this study aimed to assess the levels of three heavy metals, namely, cadmium (Cd), lead (Pb), and mercury (Hg) in yellowfin tuna and swordfish. The results are expected to provide consumers with information on the safety of consuming or exporting these fishes caught in the Hindian and Pacific Oceans.

Materials and Methods

Fresh yellowfin and swordfish were obtained from fishermen's catches in FAO Fishing Zone 57 (Indian Ocean) and 71 (Pacific Ocean) and then collected at Benoa Harbor, Bali Province. The comparative method was to evaluate the levels of heavy metals in each fish. Furthermore, heavy metal concentrations, including Pb, Cd, and Hg, were determined using atomic absorption spectroscopy analysis. These results were then used to assess the safety of these fishes by calculating the estimated daily intake (EDI) and target hazard quotients-total target hazard quotients (THQs-TTHQs).

Results

The analysis showed that none of the samples exceeded the threshold levels for the three heavy metals, which was specified by the Indonesian National Standard (SNI) and European Commission Regulation (CR) No. 1881/2006. The EDI and provisional tolerable weekly index (PTWI) obtained in this study were still in the safe range. However, the PTWI values for Pb in yellowfin tuna product from the Indian Ocean were higher (0.0038 mg/kg) compared to the recommended standard for the adult population. The THQ-TTHQ values of fish caught from these oceans were also within the acceptable range specified by the two agencies, indicating that they are safe for consumption by people with various age groups and for export purposes.

Conclusion

The average levels of three heavy metals (Cd, Pb, and Hg) in muscle samples of yellowfin tuna and swordfish caught from the Pacific and Hindian Oceans were within the acceptable range as specified by the SNI and CR No. 1881/2006. Furthermore, the EDI and THQs values indicated that fishes caught from the Pacific and Hindian Oceans were safe for consumption. This research is still limited to assessing two capture fisheries commodities. Further research is needed on the assessment of heavy metal levels in other capture fisheries commodities in this capture zone.

A facile room temperature method to recycle Cd from CdS

Cadmium-based semiconductors have a wide range of applications in light-emitting, energy conversion, photodetection and artificial photosynthesis. With the concern about the potential toxicity of Cd, it is necessary to recycle the element from the Cd based semiconductors. Commonly, the precipitation of Cd cations with S^2- is deemed as the end point of recycling. However, actually, CdS is easy to be oxidized and released into the environment and accumulate in the food chain. It still remains challenges on how to refine the Cd element and convert it to the raw material. Herein, we demonstrate a facile room temperature method for recycling Cd from CdS. Cd can be produced from CdS within 3 h with the help of the lithium-ethylenediamine solution. DFT calculations further confirm that the high surface energy of (100) and (101) planes are selectively attacked by the solvated electrons in the solution, which is in good accordance with the XRD, STEM-HAADF and XPS characterizations. With a total recovery efficiency of 88%, Cd is successfully recovered from the CdS powder. This method provides a new perspective on the treatment of Cd-based semiconductor waste, which is of great significance for the recycling of cadmium metal.

Cadmium and lead levels in muscle tissue of blue shark (Prionace glauca) in the Southeastern Pacific Waters

Prionace glauca is a top predator, prone to bioaccumulate trace elements, representing the most captured elasmobranch species for human consumption in Peru. Concentrations of cadmium and lead in the edible muscle tissue of the blue shark captured in the south Peruvian coastal waters and offshore north-central Chile were determined. The Cd and Pb levels varied between 0.004 and 0.014 and 0.004 and 0.03 mg kg^-1, respectively. We found direct correlation of Cd concentration with the total length, nevertheless there was no clear relationship regarding sex, seasons, and capture areas. Both metals were below the safety limits for human consumption. The target hazard quotient (THQ) values suggest that its consumption does not represent a risk to the human health. In Peru, this is only the second paper that reports Cd and Pb in sharks. We recommend increasing the sampling by including larger sharks and in other regions of the Peruvian coastline.

How brand attitude, brand quality, and brand value affect Thai canned tuna consumer brand loyalty

As one of the world's most valuable fish, Tuna can either be found in inexpensive tins on grocery store shelves or on high-end auction blocks destined for Japanese sashimi and sushi restaurants. Moreover, Thailand is reported to be the world's largest exporter of prepared or preserved tuna, which in 2019 contributed an estimated $2.5 billion to Thailand's exports. However, brand research is very limited for canned tuna, especially when it comes to product packaging cues, and how packaging affects a consumer's decision-making process. Therefore, this study set out to investigate which factors play the greatest role in a Thai consumer's brand loyalty (BL) for tuna fish canned products. Research teams using systematic random sampling were dispatched to five supermarkets within the Bangkok metropolitan area and collected 400 questionnaires answering items related to brand attitudes (BA), brand quality (BQ), and brand value (BV) as they related to canned tuna brand loyalty (BL). Thereafter, data analysis of the four constructs and 13 observed variables was conducted with use of LISREL 9.1, which included a confirmatory factor analysis (CFA), a goodness-of-fit (GOF) analysis along with the study's structural equation modeling (SEM). Results determined that there was a positive effect (73% R²) between all the causal factors on Thai canned tuna BL. Furthermore, the factors affecting BL ranked from the greatest to the lowest were BA, BQ, and BV with total effect (TE) values of 0.85, 0.33, and 0.19, respectively. Key takeaways from the study's research seem to indicate that canned tuna is viewed by most consumers as a ‘commodity’, with product availability and convenience being of the utmost importance in product brand selection. Global fishing stocks sustainability, labor costs/practices, and dolphin free catches within the tuna industry were also determined to be important aspects within the international consumer community. Also, due to the demand for high-quality and safe tuna products, adding value has become increasingly important in satisfying consumer demands and represents an opportunity for marketplace expansion.