Metal contaminants in rice from Cuba analyzed by ICP-MS, ICP-AES and CVAAS

Label-free electrochemical aptasensor for ultrasensitive lead ion detection based on flower-like AuNPs@MoS2 and core-shell Pt@Pd bimetallic nanoparticles

A signal-amplified platform was designed to construct a label-free electrochemical aptasensor for lead ions (Pb2+) assay. First, flower-like molybdenum disulfide-supported AuNPs (AuNPs@MoS2) nanocomposites were synthesized and used as substrates for modifying the electrode. The AuNPs@MoS2 material possessed large surface area and superior biocompatibility, which was beneficial to improve the loading amount of the complementary DNA (cDNA) and amplified the response signal. Importantly, the prepared core-shell Pt@Pd bimetallic nanoparticles (Pt@PdNPs) were used to conjugate with redox marker thionine (Thi) and aptamer (Apt) for further signal amplification; the obtained signal probes (Thi-Pt@PdNPs-Apt) were connected by the cDNA assembled on the electrode through DNA hybridization. Differential pulse voltammetry was performed to monitor the signal of Thi. After incubating of aptasensor with Pb2+, the specific recognition of Pb2+ and Apt resulted in the dissociation of aptamer-cDNA complex, thereby the Thi-Pt@PdNPs-Apt separated from the electrode surface and decreased current response was obtained. The prepared electrochemical sensor exhibited linear response to Pb2+ in the range 5.0 × 10-4-100 nM and a detection limit of 1.0 × 10-4 nM was achieved. The sensor was applied to the determination of Pb2+ in actual sample with high sensitivity and accuracy, demonstrating potential applications in heavy metal monitoring.

ICP-OES analysis of total As and Cd in Columbian Oryza sativa L. rice

Arsenic (As) and cadmium (Cd) are considered toxic elements, even at trace levels. Their accurate quantification in crops can be complex at low levels and due to interference with other elements. The aim of this work was to develop and validate an analytical method for As and Cd quantification in rice stem and grains from the production systems "Irrigated Rice Ecosystems" (IRE) and "Rainfed Rice Ecosystems" (RRE) in Colombia. Mineralisation was carried out by acid digestion using an open system with a heating plate. Metal detection was performed by inductively coupled plasma optical emission spectrometry (ICP-OES). Method adjustment, calibration, and validation were performed in accordance with AOAC standards, considering sensitivity, precision, accuracy, and selectivity parameters. The obtained method was applied to quantify levels in 259 rice stem and 443 grain samples from IRE and RRE.

Arsenic, lead and cadmium concentration in food and estimated daily intake in the Cuban population and the health risks using a Total Diet Study

This study estimates the intake of arsenic, lead and cadmium by the adult population (aged 18-91) of Cuba. The food consumption indices were obtained through 24-h dietary recall surveys applied to 450 people between October 2020 and March 2021. The Estimated Dietary Intake (EDI) of t-As (54.6 μg/day), Pb (118.5 μg/day) and Cd (35.1 μg/day) complied with Cuban legislation but was higher than the EDI for Cd established by the CONTAM Panel. The Target Hazard Quotients for the three contaminants were: iAs (0.220), Pb (0.409) and Cd (0.424), making the value of the Total Target Hazard Quotient 1.05, which indicates potential health risks for the population. Additionally, associated carcinogenic risks were: iAs (1.0·10-4), Pb (7.2·10-4) and Cd (25.9·10-4). Therefore, 10, 72 and 259 persons per 100,000 inhabitants are likely prone to developing cancer due to the ingestion of iAs, Pb and Cd, respectively.

Label-free competitive time-resolved fluorescent aptasensor for the detection of Pb2+ using ssDNA-sensitized fluorescence of Tb3+ ions

Lead (Pb2+) is one of the most toxic heavy metals, and its environmental pollution and serious damages is a global concern. Therefore, it is necessary to develop effective sensing methods. This study describes a new strategy for the design of label-free competitive time-resolved fluorescent (TRF) aptasensor for detecting Pb2+ ions. The sensing principle of this aptasensor is the competition between Pb2+ and Tb3+ ions to bind to the guanine/thymine-rich sequence (lead aptamer) and the sensitized luminescence of Tb3+ by this sequence. The developed TRF aptasensor demonstrated a good linear detection range from 2.5 nM to 150 nM and a limit of detection (LOD) of 645 pM. In addition, the proposed TRF aptasensor has a high selectivity towards Pb2+, and it has also been successfully utilized to detect this ion in milk and human serum samples. This TRF aptasensor offers advantages such as short analysis time, simple operation, low cost, being label-free, and surpassing the interference of background fluorescence of biological samples due to its TRF characteristic. In this paper, we propose a Tb3+/guanine/thymine-rich sequence system for designing different aptasensors against diverse targets by applying a proper guanine-rich sequence.

Evaluation of heavy metals contamination in cereals, vegetables and fruits with probabilistic health hazard in a highly polluted megacity

Heavy metals (HMs) contamination in foodstuffs could pose serious health issues for public health and humans are continually exposed to HMs through the consumption of cereals, fruits, and vegetables. The present study was conducted to assess 11 HMs in foodstuffs to investigate pollution levels and health risks to children and adults. The mean contents of Cd, Cr, Cu, Ni, Zn, Fe, Pb, Co, As, Mn and Ba in foodstuffs were 0.69, 2.73, 10.56, 6.60, 14.50, 9.63, 2.75, 0.50, 0.94, 15.39 and 0.43 mg/kg, respectively and the concentration of Cd, Cr, Cu, Ni and Pb were higher than maximum permissible concentrations (MPCs) showing that these foods may be contaminated with metals and constitute a danger to consumers. Vegetables had relatively higher metal contents followed by cereals and fruits. The average value of the Nemerrow composite pollution index (NCPI) for cereals, fruits, and vegetables were 3.99, 6.53, and 11.34, respectively indicating cereal and fruits were moderately contaminated whereas vegetables were heavily contaminated by the studied metals. The total estimated daily and weekly intakes for all studied metals were higher than the maximum tolerable daily intake (MTDI) and provisional tolerance weekly intake (PTWI) recommended by FAO/WHO. The target hazard quotients and hazard index of all studied metals exceeded the standard limit for adults and children suggesting significant non-carcinogenic health hazards. The total cancer risk value of Cd, Cr, Ni, Pb, and As from food intake exceeded the threshold range (1.0E-04), suggesting potential carcinogenic risks. Based on practical and sensible evaluation techniques, the current work will assist policymakers in controlling metal contamination in foodstuffs.

Synthesis of a quinoxaline-hydrazinobenzothiazole based probe-single point detection of Cu2+, Co2+, Ni2+ and Hg2+ ions in real water samples

A novel quinoxaline-hydrazinobenzothiazole based sensor was synthesized and characterized using NMR, FTIR, and Mass spectroscopy techniques. The sensor achieves the distinct "single-point" colorimetric and fluorescent detection of Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions with distinguishable color changes from yellow to red, pale red, pale brown and orange, respectively. The UV-visible and fluorescence emission spectral investigation revealed the excellent single-point sensing ability of the probe towards four different heavy metal ions with a ratiometric response. Nanomolar levels of detection of about 1.16 × 10^-7 M, 9.92 × 10^-8 M, 8.21 × 10^-8 M, and 1.14 × 10^-7 M for Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions, respectively, were achieved using our sensor, which are below the US-EPA permissible limits. Additionally, the sensor was utilized for naked eye detection under normal daylight. Quantitative determination of the metal ions in real water samples was also demonstrated.

Recent advances in instrumental techniques for heavy metal quantification

Heavy metals (HMs) are ubiquitous; they are found in soil, water, air, and all biological matrices. The toxicity, bioaccumulation potential, and deleterious effects of most of these metals on humans and the environment have been widely documented. Consequently, the detection and quantification of HMs in various environmental samples have become a pressing issue. The analysis of the concentrations of HMs is a vital component of environmental monitoring; hence, the selection of the most suitable analytical technique for their determination has become a topic of great interest in food, environment, and human health safety. Analytical techniques for the quantification of these metals have evolved. Presently, a broad range of HM analytical techniques are available with each having its outstanding merits as well as limitations. Most analytical scientists, therefore, adopt complementation of more than one method, with the choice influenced by the specific metal of interest, desired limits of detection and quantification, nature of the interference, level of sensitivity, and precision among others. Sequel to the above, this work comprehensively reviews the most recent advances in instrumental techniques for the determination of HMs. It gives a general overview of the concept of HMs, their sources, and why their accurate quantification is pertinent. It highlights various conventional and more advanced techniques for HM determination, and as one of its kind, it also gives special attention to the specific merits and demerits of the analytical techniques. Finally, it presents the most recent studies in this regard.

A Simple and Rapid “Signal On” Fluorescent Sensor for Detecting Mercury (II) Based on the Molecular Beacon Aptamer

Biosensors for mercury (II) (Hg2+) with high sensitivity are urgently required for food safety, ecosystem protection and disease prevention. In this study, a simple and fast detection method of Hg2+ based on the molecular beacon aptamer was established, according to the principle that Hg2+ could change the structure of the molecular beacon aptamer, resulting in the changed fluorescence intensity. All of the detection conditions were optimized. It was found that an optimal molecular beacon aptamer MB3 showed the optimal response signal in the optimized reaction environment, which was 0.08 μmol/L MB3, 50 mmol/L tris buffer (40 mmol/L NaCl, 10 mmol/L MgCl2, pH 8.1), and a 10 min reaction. Under the optimal detection conditions, the molecular beacon aptamer sensor showed a linear response to Hg2+ concentration within a range from 0.4 to 10 μmol/L and with a detection limit of 0.2254 μmol/L and a precision of 4.9%. The recovery rates of Hg2+ in water samples ranged from 95.00% to 99.25%. The method was convenient and rapid, which could realize the rapid detection of mercury ions in water samples.

Nutritional Quality of the Most Consumed Varieties of Raw and Cooked Rice in Spain Submitted to an In Vitro Digestion Model

Rice is one of the most consumed staple foods around the world and its trade is highly globalized. Increased environmental pollution generates a large amount of waste that, in many cases, is discarded close to culture fields. Some species are able to bioaccumulate toxic substances, such as metals, that could be transferred to the food chain. The main goal of this study was to evaluate the content of metallic (Al, Cd, Pb, and Cr) and metalloid elements (As) in 14 of the most consumed varieties of rice in Spain and their effects on human health. The samples were cooked, and human digestion was simulated by using a standard in vitro digestion method. Metallic and metalloid element levels were analysed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), previous called microwave digestion. Both the human health risk index, Hazard Quotient, and Lifetime Cancer Risk did not show toxic values in any case. Rice with a higher non-digestible fraction showed a higher liberation of proteins and a lower glycemic index. There were no significant differences in the concentrations of metallic and metalloid elements in cooked rice or in the digestible fraction in all varieties analysed. However, Al concentrations were higher than other metals in all varieties studied due to its global distribution. No relationship has been observed between the digestibility of rice and the bioaccessibility of each metallic and metalloid element. All of the studied rice varieties are healthy food products and its daily consumption is safe. The regular monitoring of metals and As in rice consumed in Spain may contribute to improvements in the human health risk evaluation.