Mercury speciation in seafood using non-chromatographic chemical vapor generation capacitively coupled plasma microtorch optical emission spectrometry method – Evaluation of methylmercury exposure

Advances in atmospheric pressure plasma-based optical emission spectrometry for the analysis of heavy metals

Over the past decade, miniaturized optical emission spectrometry (OES) systems utilizing atmospheric pressure plasmas (APPs) as radiation sources have exhibited impressive capabilities in trace heavy metal analysis. As the core of the analytical system, APPs sources possess unique properties such as compact size, light weight, low energy requirement, ease of fabrication, and relatively low manufacturing cost. This critical review focuses on recent progress of APP-based OES systems employed for the determination of heavy metals. Influences of technical details including the sample introduction manner, the sampling volume, the sample flow rate, the pH of the solutions on the plasma stability and the intensity of analytical signals are comprehensively discussed. Furthermore, the review emphasizes the analytical challenges faced by these techniques and highlights the opportunities for further development in the field of heavy metal detection.

One-Pot Pretreatment Coupled to Microplasma Optical Emission Spectrometry for Field and Sensitive Determination of Inorganic Mercury and Methylmercury in Fish

Field and sensitive analysis of mercury species in seafood is helpful to assess the risk of human exposure to mercury, but the cumbersome pretreatment process is time-consuming and laborious. Herein, a simple one-pot pretreatment system is designed for extraction, separation, and enrichment of inorganic mercury (Hg(II)) and methylmercury (MeHg) in fish, and coupled to dielectric barrier discharge (DBD) microplasma optical emission spectrometry (OES). Both Hg(II) and MeHg species in fish can be effectively extracted by tetramethylammonium hydroxide under ultrasound, then separated from the fish matrix by vapor generation and photochemical vapor generation, and finally enriched on the activated carbon electrode tips. Mercury trapped on the activated carbon electrode tips can be rapidly released to produce OES under the DBD microplasma excitation for quantitative analysis. The pretreatment and analysis of a batch of 12 samples are completed within 50 min, and the extraction efficiency of total mercury is up to 90% for 100 mg of freeze-dried fish or 86% for 1 g of fresh fish. Under the optimized conditions, the detection limits are 2 μg kg^-1 for Hg(II) and 1.2 μg kg^-1 for MeHg in freeze-dried fish, and precisions are 3.2% for Hg(II) and 3.9% for MeHg. The present method is applied to the analysis of the certified reference material and real marine fishes, giving rise to spiked recoveries of 95-103%. The present system hardly leads to MeHg and Hg(II) transforming into each other during extraction, providing a simple, convenient, and low-cost analytical tool to evaluate the risk of mercury species in fish.

Tissue dynamics of potential toxic elements in the Pacific hake (Merluccius productus): distribution and the public health risk assessment

This study aimed to establish the distribution of As, Cd, Pb, Cu, and Zn in the main tissues (muscle, liver, gonads, and gills) of the Pacific hake (Merluccius productus) from the northern Gulf of California to establish baseline bioavailability levels in the northern stock. The results for Pb and Cd were the lowest in the studied tissues (Pb < 0.005 mg kg^-1 in the liver and gonads and 1.43 mg kg^-1 for Cd in the liver), followed by levels of Cu and As (muscle > liver > gonads > gills) and Zn with the most abundant levels in all the tissues. The sex of the organisms was not a factor that influenced the bioaccumulation and distribution of the potential toxic elements (PTEs) nor total length, except for As in gills and Cd in muscle and the liver. Important interactions among Zn and non-essential elements were established. The Pacific hake intake of PTEs was probably through the diet via bioaccumulation of the elements in their prey and less by pollution of the water column. In the muscle, a major distribution and storage of As, Zn, and Pb were observed, but in the liver, higher loads were from Cd and Cu. The maximum tolerable weekly intake must be very high to be at health risk for the essential elements and Cd. However, the population might be at risk for Pb and As consumption if more than 124 g of M. productus in adults and 35 g in children are consumed per week. Further investigations are required to understand the dynamics of PTEs in M. productus as it could be proposed as a biomonitor species.

Bioaccumulation of mercury and selenium in tissues of the mesopelagic fish Pacific hake (Merluccius productus) from the northern Gulf of California and the risk assessment on human health

With the aim of evaluating health risk to hake consumers, mercury and selenium were measured in muscle, liver, gonads, kidney, and gills of 62 specimens of Merluccius productus from northern Gulf of California. Means ± confidence interval (95% confidence level) concentrations (mg kg^-1 wet weight) of Hg in tissues were: gonads (1.01 ± 0.25) > muscle (0.44 ± 0.06) > gills (0.29 ± 0.04) > kidneys (0.20 ± 0.07) > liver (0.02 ± 0.004). No significant differences between sexes were found for Hg. The distribution of mean concentrations of Se (mg kg^-1 wet weight) were: kidneys (4.61 ± 1.27) > liver (1.66 ± 0.22) > gonads (1.66 ± 0.75) > gills (0.86 ± 0.04) > muscle (0.40 ± 0.09). Se in gonads showed a significant difference between sex (females > males). Positive significant correlations with total length (p < 0.05) and total weight (p < 0.05) were found in the same tissue for both morphological variables: Hg in muscle, Se in muscle and Se in liver. An excess of Se over Hg (molar ratio Se:Hg > 1) was found in all tissues. The Hazard Quotient health risk index was evaluated for humans that consume muscle and gonads. The recommended Hg safe intake for adults and children were 110.0 and 33.0 g week^-1, respectively for muscle; for gonads weekly consumption portions of 35.0 and 14.0 g for adults and children represent no Hg risk. There was no risk of exposure to Se.

Development and Validation of a Spectrometric Method for Cd and Pb Determination in Zeolites and Safety Evaluation

An analytical method based on microwave-assisted acid digestion and atomic absorption spectrometry with graphite furnace as atomization source was developed and validated for determining trace elements (Cd and Pb) in zeolites used as dietary supplements, for their characterization and safety evaluation. The method was checked for the main performance parameters according to the legislation requirements in the field of dietary supplements. In all cases, the obtained performance parameters were satisfactory. The selectivity study showed no significant non-spectral matrix effect. The linearity study was conducted for the calibration curves in the range of 0–10 ng mL⁻¹ for Cd and 0–30 ng mL⁻¹ for Pb. The obtained limits of detection (LoDs) and the limits of quantification (LoQs) were sufficiently low in order to allow Pb and Cd determination in dietary supplements. For the internal quality control, certified reference materials were analysed and good recoveries were obtained. The precision study was performed in terms of repeatability and reproducibility, considering the requirements imposed by the Commission Decision (2007/333/EC) and the method fulfilled these performance parameters. Expanded measurement uncertainties were estimated to 11% for Cd and 10% for Pb. Cd and Pb content were measured in real zeolite samples and, using these data, a safety evaluation was carried out.

Interference-free, green microanalytical method for total mercury and methylmercury determination in biological and environmental samples using small-sized electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry

An analytical method for the quantification of total Hg and CH₃Hg⁺ in biological tissues (fish, mushroom) and water sediment was developed based on small-sized electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry using a low-resolution microspectrometer as detector. Sample preparation was carried out according to the procedure recommended by JRC Technical Report of European Commission for the determination of CH₃Hg⁺ in seafood and adapted by us for lower consumption of reagents. Amounts of 0.1 - 0.5 g sample were subjected to extraction in 5 ml of 47% HBr then CH₃Hg⁺ was extracted in 2 × 1 ml toluene and back-extracted in 2 ml aqueous solution of 1% l-cysteine. Total Hg/CH₃Hg⁺ were quantified in 10 μl of acidic extract/l-cysteine solution after electrothermal vaporization and measurement of 253.652 nm Hg signal in the episodic emission spectra. Under the optimal working conditions of system (70 °C sample drying, 1300 °C sample vaporization, 10 W plasma power and 150 ml min^-1 Ar flow) the limits of detection were 7.0 μg kg^-1 total Hg and 3.5 μg kg^-1 CH₃Hg⁺. Comparison of slopes in external calibration and standard addition procedure revealed the lack of non-spectral interferences of multimineral matrix, so that the calibration against Hg²⁺ standards was adopted. Pooled recovery of total mercury/methylmercury was 101 ± 7%/100 ± 7%, while precision assessed from measurements of real samples was in the range 1.6-9.6%/2.7-12.8%. The proposed method validated according to Eurachem Guide 2014 is selective and complies with demands in European legislation (Decisions 657/2002; 333/2007; 836/2011) and Association of Official Analytical Chemists Guide in terms of performances for food control. The method displays a high degree of greenness by circumventing cold vapor generation, use of small amounts of reagents and full-miniaturized instrumentation resulting in low analytical costs without reducing results quality. Besides, the method is simple and rapid, since it uses external calibration curves prepared from Hg²⁺standard solutions both for total Hg and CH₃Hg⁺ determination.

Mercury Determination in Natural Zeolites by Thermal Decomposition Atomic Absorption Spectrometry: Method Validation in Compliance with Requirements for Use as Dietary Supplements

Natural zeolites are hydrated aluminosilicate minerals that, due to their remarkable physical-chemical properties of being molecular sieves and cation exchangers, have applications in different areas such as environmental protection, catalysis, animal feed, and dietary supplements. Since natural zeolites may contain traces of undesirable compounds such as toxic metals, the accurate quantification of these elements is necessary. In this study, a direct method for Hg determination in zeolite samples based on the thermal desorption atomic absorption spectrometry (TD-AAS) technique is fully validated, taking into account the legislative requirements in the field. The chosen quantification limit was 0.9 µg kg⁻¹, which is satisfactory for intended use. Trueness was evaluated by recovery rate using certified reference materials containing mercury, with satisfactory results. Other figures of merit, such as repeatability and measurement uncertainty, also fulfill the legislative requirements related to the analysis of dietary supplements. This paper presents, for the first time, a fully validated method for mercury determination in zeolite samples, and the obtained results reveal that the method can be applied successfully for the intended purpose.

Determination of Hg in Farmed and Wild Atlantic Bluefin Tuna (Thunnus thynnus L.) Muscle

Mercury (Hg) is a well-known toxic element, diffused in the environment, especially in the Mediterranean Sea which is rich in cinnabar deposits. Mercury bioaccumulation in fish is of great concern, especially for top-level aquatic predators (e.g., shark, tuna, swordfish) and above all for species of large human consumption and high nutritional value. This work aimed to determine Hg concentrations in farmed and wild Atlantic Bluefin tuna (Thunnus thynnus) caught in the Mediterranean area in order to evaluate the level of Hg bioaccumulation. selenium (Se) content was also determined, since this element is an antagonist of mercury toxicity. Mercury and Se were analysed by atomic absorption spectrometry after microwave digestion of the samples. Hg content in farmed tuna was below the legal limit (1 mg/kg, wet weight, w.w.) for all specimens (0.6 ± 0.2 mg/kg), whereas the wild ones had a content over the limit (1.7 ± 0.6 mg/kg); Se concentration was higher in farmed specimens (1.1 ± 0.9 mg/kg) compared to wild ones (0.6 ± 0.3 mg/kg). A safe seafood could show a Se/Hg ratio >1 and a health benefit value (HBV_Se) > 0: farmed tuna had higher values than the wild specimens (Se/Hg 5.48 vs. 1.32; HBV_Se 11.16 vs. 0.29). These results demonstrate that for Hg, there is a better risk/benefit ratio in farmed T. thynnus. making it safer than wild tuna.

Investigation of Hg Content by a Rapid Analytical Technique in Mediterranean Pelagic Fishes

Mercury (Hg) fish and seafood contamination is a global concern and needs worldwide sea investigations in order to protect consumers. The aim of this study was to investigate the Hg concentration by means of a rapid and simple analytical technique with a direct Mercury Analyzer (DMA-80) in pelagic fish species, Tetrapturus belone (spearfish), Thunnus thynnus (tuna) and Xiphias gladius (swordfish) caught in the Mediterranean Sea. Hg contents were evaluated also in Salmo salar (salmon) as pelagic fish not belonging to the Mediterranean area. The results obtained were variable, ranging between 0.015–2.562 mg kg−1 for T. thynnus species, 0.477–3.182 mg kg−1 for X. gladius, 0.434–1.730 mg kg−1 for T. belone and 0.004–0.019 mg kg−1 for S. salar, respectively. The total Hg tolerable weekly intake (TWI) and tolerable weekly intake % (TWI%) values according to the European Food Safety Authority (EFSA) were calculated. The results highlighted that the pelagic species caught in the Mediterranean Sea should be constantly monitored due to their high Hg contents as well as their TWI and TWI% with respect to S. salar samples.