In this study, 33 different dried seaweed products were purchased in local markets in Madrid and analyzed. Arsenic, cadmium, mercury, nickel, lead and iodine were determined by inductively coupled plasma–mass spectrometry (ICP-MS) in samples previously digested in a microwave oven. In addition, inorganic arsenic (iAs) was determined by high performance liquid chromatography (HPLC) combined with microwave-assisted extraction followed by ICP-MS. Results indicate that the levels of Cd, Ni, and Pb were relevant in some of the samples, and may pose a risk to consumers. The concentrations of Hg were overall the lowest found in the samples. Hijiki seaweed (

) contained a considerable iAs fraction, whereas all the other seaweed species contained minimal fractions. Lastly, iodine content in most of the seaweeds surpassed the tolerable daily intakes recommended by the European Food Safety Authority (EFSA), which may pose a risk to consumers.

Seaweed has been a part of Asian diets since ancient times, but only more recently has it become a popular ingredient in Western diets because of its potential as an alternative and healthy source of food. Other applications of seaweed are also being explored, such as in food additives, feeds, fertilizers, biofuels, cosmetics, and medicines (1).

Current research on the health benefits of seaweed reveals that it contains various important vitamins (A, B1, B12, C, D, and E), minerals (potassium, sodium, phosphorus, iodine), and compounds with remarkable antioxidant capacities (2–5). Seaweed also has a low-calorie content (between 1% and 5% dry weight) (5).

However, some studies highlight that there are adverse effects to consuming large quantities of seaweed because it contains an excessive amount of heavy metals, arsenic, and iodine. As a result, there are possible risks associated with consuming too much seaweed (6).

Heavy metals not only have no beneficial function in the human body, but they are also considered toxic for humans even at low concentrations. Exposure to heavy metals usually leads to negative gastrointestinal, neurotoxic, and carcinogenic effects (7).

It is widely known that marine organisms, especially seaweed, accumulate relevant amounts of arsenic. The chemical similarities between arsenate (H

-) is the reason why both are absorbed equally through membrane transport systems. Thus, inorganic arsenic (As

) is introduced in these organisms and metabolized to organic arsenic species, such as arsenobetaine, monomethylarsonic acid, dimethylarsinic acid, arsenosugars, and arsenolipids (8,9). It is reported that inorganic forms of arsenic are more dangerous and toxic than organic forms of arsenic (10). For that reason, a suitable speciation analysis must be carried out to determine the levels of inorganic arsenic in seaweed.

Iodine is a diet-essential mineral because of its importance in the thyroid gland. It serves important biological and physiological functions in the human body, especially during early growth and organ development (11). Although iodine is necessary in the diet, either an excess or a deficiency in iodine may cause disorders related to the thyroid functions. The consequences of these pathologies can be very serious in children and pregnant women (12,13).

Regulation (EU) 2017/2470 established and updated the list known as the “Novel Food Catalogue” that contains all European Union’s authorized novel foods. This list included 22 different types of edible seaweed by the end of 2020, but does not specify the maximum limits of heavy metals, iodine, and arsenic (14).

Food supplements that are seaweed-based are regulated by Commission Regulation (EC) N

 629/2008, which indicates the maximum amount of cadmium that food products can contain (15). However, there is currently no specific legislation about maximum limits related to seaweed as food yet. Therefore, the Europe Union published 

 on the monitoring of different elements, such as arsenic, cadmium, lead, mercury, and iodine, in edible seaweed. 

 also mentions the importance of quantifying different species of arsenic (As

, and total arsenic) and, if possible, other relevant arsenic species. The aim for this recommendation is to gather results from different studies, which will allow us to assess the risks associated with the consumption of seaweed, and consequently set maximum levels in the future (16).

Inductively coupled plasma–mass spectrometry (ICP-MS) is a fitting technique to quantify several elements in foodstuffs at low concentrations simultaneously. However, it is important to notice several issues in using ICP-MS when analyzing inorganic arsenic and iodine.

Total arsenic and heavy metals analysis are commonly the same; the process for both first undergoes an acid digestion followed by quantification using an elemental analysis instrument. Nevertheless, inorganic arsenic analysis has significant differences that need to be considered. A regular acid digestion is not suitable because organic arsenic species would deteriorate into As

. Thus, it is mandatory to utilize a previous extraction followed by a separation technique. High performance liquid chromatography (HPLC) is the most common methodology for arsenic speciation because it allows for the separation of individual arsenic species so they can be quantified accurately afterwards (17).

The literature highlights the problematic sample preparation of iodine because of memory effects and its complex redox chemistry. Equation 1 reveals that at low pH (typical digestion mixture where H

) is oxidized to volatile molecular iodine (I

 > 0 V), thus a regular acid digestion would lead to iodine loss and an incorrect approach to sample pretreatment, which why methods involving alkaline digestion are widely used (18,19). An alternative method being proposed in this study is performing a suitable acid digestion followed by a dilution using an alkaline solution, which is an unique and simultaneous sample pretreatment. Performing a suitable acid digestion followed by a dilution using an alkaline solution saves time and resources while taking advantage of ICP-MS multielemental analysis (20).

The cadmium, mercury, lead, nickel, total arsenic, and iodine totals were determined using an ICP-MS instrument (Agilent Technologies model 7900). An Integrated Sample Introduction System (ISIS 3) and a SPS 4 autosampler, both from Agilent Technologies, were used alongside the ICP-MS instrument, in determining the quantities of the elements mentioned above. The ICP-MS analysis operating parameters are shown in Table I.

Inorganic arsenic was determined using a HPLC instrument (Agilent Technologies model 1200 Infinity) equipped with a model 1260 Quat Pump VL quaternary pump; a model 1260 ALS injector; and a model 1260 column compartment. The HPLC system was used in conjunction with the ICP-MS instrument mentioned earlier. For the inorganic arsenic determination, the operating parameters are listed in Table I.

Samples were treated in a Milestone model Ethos One microwave oven with a capacity of 10 polytetrafluoroethylene (PTFE) vessels at 100 mL each. One of the PTFE vessels is always used for a blank process.

The volumetric materials used were calibrated with polypropylene single-use tubes (DigiTubes from SCP Science), 15 mL single-use centrifuge tubes (Superclear Labcon), and a 1 L volumetric flask to prepare the mobile phases.

To centrifuge the samples, a refrigerated Lisa centrifuge from AFI groups was used.

All solutions, cleaning procedures, digestion, and extraction methods were prepared with deionized water (H

O) class type I (according to UNE-EN-ISO 3696), and purified using a Milli-Q system from Merck. Nitric acid (HNO

 65%) pro analysis (p.a.) quality was used, supplied by Fluka and previously distilled by a Savillex distiller model DST-1000. Hydrocloric acid (HCl 37%) was ultratrace ppb-trace analysis grade from Scharlau, and hydrogen peroxide (H

, 30%) was suprapur grade and supplied by Merck.

Regarding the ICP-MS instrument, the tuning solution contained 10 μg/L cerium, cobalt, lithium, magnesium, thallium, and yttrium. The argon and helium used in plasma generation and interference elimination (KED mode) were both 99.999% accurate.

The alkaline solution used in the iodine determination was prepared with 40 g of NH

OH (Fluka p.a. quality), 10 g of 1-buthanol (Merck), and 1 g of ethylenediaminetetraacetic acid (EDTA) (Panreac pharma grade) mixed with 1 L of deionized water.

The extraction solution used in the inorganic arsenic determination was 0.2% HNO

. In arsenic and heavy metals analysis, standards of 1000 mg/L arsenic, cadmium, mercury, nickel, and lead (all supplied by LGC Standards) were used. Intermediate solutions and the calibration curve were prepared in 2% HNO

 and 1% HCl (v/v). Regarding the iodine determination, a 1000 mg/L iodine standard was provided by Scharlau. Suitable intermediate solution and calibration curve were prepared in a 1:2 diluted alkaline solution. For the inorganic arsenic determination, 100 mg/L As

 (LGC Standards) were utilized. Moreover, monomethylarsonic acid from High Purity Standards, dimethylarsinic acid from AccuStandard, and arsenobetaine from the National Metrology Institute of Japan (NMIJ) standards, were also used to check the chromatographic separation. The intermediate solutions and the calibration curve were prepared in 0.2% HNO

The internal standards used for each element in the ICP-MS analysis were germanium and rhodium from LGC Standards and iridium and tellurium from Sigma-Aldrich. A 0.4 mg/L mixture of these elements was prepared as the internal standard solution with 2% HNO

, 1% HCl, and 5% acetic acid. To stabilize the mercury signal, 0.4 mg/L of gold from SCP Science were also added.

The seaweed samples were purchased in several markets in Madrid, Spain. To obtain representative results, numerous species of seaweed were collected.

A total of 33 samples were analyzed in this study, including two dulse (

.) was also included in this study because of its use in foods and cuisine. Note that the conclusions related to species with fewer than three samples should be carefully considered.

All seaweed were homogenized first using a coffee grinder. The different methods are detailed in Figure 1.

Determination of Iodine, Arsenic, and Heavy Metals

First, the homogenized samples were weighed into polytetrafluoroethylene (PTFE) vessels, and the digestion mixture of acids was added. Next, the samples were placed in the microwave oven. Once the digestion was complete and the samples cooled down to room temperature, they were transferred to DigiTubes and the tubes were filled with deionized water. An aliquot was taken and diluted with the alkaline solution (the ratio for the sample–alkaline solution was 1:2) for the parallel iodine analysis. These solutions were ready to be measured if no more dilutions were needed.

Inorganic arsenic is determined as the sum of arsenate (As

). The homogenized sample was weighed, mixed with the extraction solution, and introduced to the microwave oven. Validation proved that all As

 determined is equal to the complete inorganic fraction. After the microwave-assisted extraction, samples were centrifuged, diluted (if necessary), and filtered through a 0.45 μm polyvinylidene fluoride (PVDF) filters.

The determination methods of this work meet the criteria established in Commission Regulation (EC) N

Moreover, the laboratory is accredited according to ISO/IEC-17025 requirements. The studied heavy metals, total, and inorganic arsenic in foodstuffs are included in the schedule of accreditation.

Regarding the iodine determination, the analysis was not included in the schedule of accreditation then. Therefore, the laboratory participated in a proficiency test (FAPAS-Food Chemistry Proficiency Test 07380) to evaluate method accuracy and obtained a satisfactory result (

This work aims to provide information about the potential risks involved in seaweed consumption. For that purpose, the percentage contribution (%) by a daily portion of seaweed to a reference daily intake is estimated.

First, it is necessary to describe the typical portion of seaweed consumed in a day. Normally, labels on seaweed products give some instructions about how to cook them (an amount between 2 and 5 g is usually recommended). The literature also mentions a general daily intake of seaweed depending on the region. For example, the literature recommends estimating daily intake at 8 g/day in Asian cultures (4), 4–7 g/day in Japan (21), and <5.2 g/day in Western diets (22).

Second, a reference intake based on health impact is needed. European Food Security Authority (EFSA) scientific reports establish recommended intake values of the studied elements in foods considering their potential health risks. These values are often expressed in μg/kg bodyweight (b.w.) per day or per week, which means an average human bodyweight must be established to make the assessment.

Finally, once the results are obtained, the daily intake contribution for each element can be estimated using equation 2:

 is the highest result found of the corresponding element in seaweed (mg/kg), and the maximum value obtained allow to assess the worst-case scenario when discussing the results; 

 is the daily portion consumed of seaweed (kg/day); and TDI is the tolerable daily intake according to scientific reports published by EFSA (in mg/day). To estimate this contribution, a reasonable daily portion of 5 g and an average 60 kg (~132 lbs.) body weight are set.

The overall results are summarized in Table II. Concentrations, averages, and ranges obtained are shown as well as the number of samples quantified. The percentage of inorganic arsenic related to total arsenic is shown as well, and it is also displayed in the reference intakes from EFSA and its corresponding contributions (23–27). Moreover, individual results of each sample are shown in Figure 2.

Heavy metals results show that mercury and nickel are not a threat in seaweed consumption because their contribution to the TDI was minimal (<1% and <6% for mercury and nickel, respectively). Regarding cadmium and lead, their contribution may be significant in some specific seaweeds. In some nori and wakame samples, a portion of 5 g could provide up to 70% of the allowed daily intake of cadmium. On the other hand, some kelp, wakame, and dulse samples presented a sizable contribution of lead, between 15–23%.

Concerning total arsenic, values obtained ranged from 0.4 mg/kg to 100 mg/kg. However, inorganic arsenic results were much lower in most of the samples. In nori, kelp, and sea spaghetti samples, inorganic arsenic could not be determined (< 0.10 mg/kg). The rest of the species other than hijiki had inorganic arsenic values close to the quantification limit, and their contribution to the TDI was not significant (<16%). Regarding hijiki, it must be highlighted the average of inorganic arsenic found was 62 mg/kg, much higher than the rest of species. This amount exceeds the corresponding TDI in up to 1780%, which means hijiki’s inorganic arsenic content may pose to a risk to consumers if ingested regularly.

Because both total arsenic and inorganic arsenic were quantified, it is possible to estimate the contribution of the inorganic fraction to the total. For hijiki seaweed, 70% of the total arsenic is in inorganic form, an overwhelming percentage compared to other species. This could lead to the conclusion that this species does not metabolize arsenic the same way than other types of seaweed. Moreover, for agar-agar, the inorganic arsenic fraction is also important (45%), but the amount of total arsenic is low compared to the rest of the species examined (only 0.4 mg/kg).

Finally, iodine contributions were extraordinarily high in most cases. Only sea lettuce, agar-agar, and nori sample contributions were lower than 100% (up to 57%, 61%, and 72%, respectively). On the other hand, a 5 g portion of kelp or kombu exceeded the tolerable daily intake by approximately 3000 and 4000%, respectively, which could mean that an important potential risk exists in consuming kelp and kombu. In addition, EFSA published afterwards that an adequate intake for adults was 150 μg/day, lower than the upper TDI used in this study, which suggests a worse picture for the risk assessment.

The method has proved to be suitable in analyzing heavy metals, arsenic, and iodine in dried seaweed simultaneously in a unique sample pretreatment, over- coming iodine determination issues using ICP-MS.

A 5 g daily portion of seaweeds like agar-agar, dulse, nori, sea spaghetti and wakame does not present a critical risk to consumers. However, a decent amount of cadmium, lead, and iodine may be found in some of them.

Sea lettuce contain the lowest values of metals, arsenic, and iodine. However, only one sample was included in this study, so clear conclusions cannot be reached.

Inorganic arsenic content in hijiki seaweed were extraordinarily high in contrast to other seaweeds. According to the results of this study, it is recommended that humans only consume 2.5 g per week of hijiki seaweed.

Kelp and kombu species were found to contain extremely high concentrations of iodine. Considering the results obtained, an intake of no more than 1 g per week of these seaweeds is suggested; regular consumption of higher amounts may lead to iodine excess disorders in consumers.

(1) A.H. Buschmann, C. Camus, J. Infante, A. Neori, A. Israel, M..C. Hernández-González, S.V. Pereda, J.L. Gómez-Pinchetti, A. Golberg, N. Tadmor-Shalev, and A.T. Critchley, 

(2) E.M. Brown, P.J. Allsopp, P.J. Magee, C.I. Gill, S. Nitecki, C.R. Strain, and E.M. Mcsorley, 

(4) P. MacArtain, C.I. R. Gill, M. Brooks, R. Campbell, and I.R. Rowland, 

(5) V. Quitral, C. Morales, M. Sepúlveda, and M. Schwartz, 

(6) J.L. Banach, E.F. Hoek-van den Hil, and H.J. van der Fels-Klerx, 

(8) Z. Ma, L. Lin, M. Wu, H. Yu, T. Shang, T. Zhang, and M. Zhao, 

(10) M. Leermarkers, W. Baeyens, M. De Gieter, B. Smedts, C. Meert, H.C. De Bisschop, R. Morabito, and P.H. Quevauviller, 

(11) Scientific Committee on Food (SCF), 

Scientific Panel on Dietetic Products, Nutrition and Allergies. Tolerable Upper Intake Levels for Vitamins and Minerals 

(2006). https://www.efsa.europa.eu/sites/default/files/efsa_rep/blobserver_assets/ndatolerableuil.pdf.

(12) M.B. Zimmerman, Y. Ito, S.Y. Hess, K. Fujieda and L. Molinari, 

(14) A. Lähteenmäki-Uutela, M. Rahikainen, M.T. Camarena-Gómez, J. Piiparinen, K. Spilling, and B. Yang, 

(15) Commission Regulation (EC) No 629/2008 of 2 July 2008 amending Regulation (EC) No 1881/2006 setting maximum levels for certain contaminants in foodstuffs. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32008R0629.

Commission Recommendation (EU) 2018/464 of 19 of March 2018 on the monitoring of metals and iodine in seaweed, halophytes and products based on seaweed.

 https://eur-lex.europa.eu/legal-content/EN/TXT/uri=uriserv%3AOJ.L_.2018.078.01.0016.01.ENG.

(17) M.S. Reid, K.S. Hoy, J.R.M. Schofield, J.S. Uppal, Y. Lin, X. Lu, H. Peng, X.C. Le, 

(18) H.J. Reid, A.A. Bashammakh, P.S. Goodall, M.R. Landon, C. O ́Connor, and B.L. Sharp, 

(19) E.M.M. Flores, P.A. Mello, S.R. Krzyaniak, V.H. Cauduro, and R.S. Picoloto, 

(S3), e8727 (2020). DOI: 10.1002/rcm.8727.

(20) K. Fujisaki, H. Matsumoto, Y. Shimokawa, and K. Kiyotaki, 

(22) M.Y. Roleda, H. Marfaing, N. Desnica, R. Jóns-dóttir, J. Skjermo, G. Rebours, and U. Nitschke, 

(23) EFSA (European Food Safety Authority), 

 is with the Head División at the Laboratorio de Salud Pública de Madrid Salud in Madrid, Spain. 

 is with the Technical Laboratory at the Laboratorio de Salud Pública de Madrid Salud in Madrid, Spain. 

 is an Assistant to the Department at the Laboratorio de Salud Pública de Madrid Salud in Madrid, Spain. Direct correspondence to: 

Articles

Seaweed has become a popular ingredient in Western diets. Concerns for heavy metals and inorganic arsenic have been raised as potential risks to consumers. Methods for analysis are described, including microwave digestion, HPLC,
and ICP-MS for quantitation and speciation.

Studying Inorganic Arsenic, Heavy Metals, and Iodine in Dried Seaweed

Although the public uses a wide range of face masks for the prevention of Covid-19 transmission, the most common is the 3-layer hygienic mask, which is manufactured and used globally. Since the rigorous quality standards required for certified medical masks, such as N-95 face masks, are not applicable to hygienic masks, it is important to assess the quality and safety of this mask category. Although consistent global standards do not exist for the determination of metal content in hygienic facemasks, 

 “Biocompatibility Evaluation of Breathing Gas Pathways in Healthcare Applications–Part 4: Leachables in Condensate” provides guidance for the analysis of metals in facemasks. This work describes the determination of metals in hygienic facemasks using ICP-OES, following the guidelines of 

, including sample preparation, analysis, and validation of the methodology.

The use of face masks for preventing the spread of Covid-19 is a required safety precaution in many public indoor areas across the globe. Face masks fall into two broad categories: surgical/medical and hygienic/disposable. The most common surgical/medical face mask is the N-95 respirator. Because these face masks are designed to minimize the spread of particles to protect both patients and medical staff, regulations have been established to ensure product quality and protect human health. Since regulations must be met, production cannot meet the demand of the general population, which therefore wears hygienic/disposable face masks to reduce the spread of airborne diseases. Even though these types of face masks do not have required standards that must be met in Europe and the United States, they have been recommended for limiting transmission of the Covid-19 virus and protecting people.

There are many types of hygienic face masks being used by the general public, with the most common being the three-layer disposable hygienic face mask, consisting of an innermost layer (closest to the wearer’s face), a middle layer, and an outer light blue layer, as shown in Figure 1. These types of face masks are being manufactured and worn globally.

As with any consumer product, it is important to validate that hygienic face masks do not pose any additional risk to their users. Two categories of analytes which must be evaluated are volatile organic compounds (VOCs) and metals. This work will discuss the determination of metals in hygienic face masks.

Globally, there are no consistent regulations or agreed-upon levels of metals in hygienic face masks, with different regions having different classifications, metals, and limits. However, 

 “Biocompatibility of Breathing Gas Pathways in Healthcare Applications–Part 4: Leachables in Condensate” (1) provides guidance that is relevant and may be applied, since it discusses the sample preparation, analytes, and methodologies used to evaluate data quality. This method states that the analytes and limits are defined by 

 (3). Because face masks cover the nose and mouth, 

states that the route of exposure is inhalation, assuming a maximum daily condensate intake of 1 mL. Analytes and their maximum daily exposure through inhalation (as defined in 

 defines the relevant concentrations as the 

with PDE equaling maximum permissible daily exposure (μg/g); Maximum Daily Dose equaling maximum amount of the medication consumed; and Dilution Factor equaling dilution used in sample preparation and the mass of sample or sample preparation volume. 

Disposable, non-medical face masks are challenging to analyze, due to the light weight of the inner layer, which results in lower analyte concentrations for method validation, a direct result of the 

To simulate exposure, sample preparation is vital, as 

 discusses in detail. It is important that analytes be leached at 37 °C (normal human body temperature) from the part of the face mask which the wearer is exposed to for a time representative of the duration the face mask is worn.

This work describes the sample preparation and analysis of metals in disposable, non-medical face masks with ICP-OES to meet the criteria defined in 

A variety of disposable, three-ply, non-medical-grade face masks were purchased, and the inner layer removed. Depending on the brand, the inner layers ranged in mass from 0.50–0.58 g, with most being ≈ 0.55 g. To minimize the creation of additional surface area and to better simulate a user’s exposure, the inner layer of each mask was not cut into smaller pieces, but rather leached whole.

For the leaching procedure, each inner layer was added to a 50 mL autosampler tube and pushed to the bottom, followed by the addition of 10 mL of 10% HCl + 1% HNO

 (v/v). Nitric acid was used to stabilize most elements, while the hydrochloric acid was required to stabilize the platinum group elements; 10% HCl was required to stabilize gold (Au) in solution over the leaching time. The tubes were capped and shaken before being heated in a sample preparation block at 37 °C for 4 h to simulate a common time a person may wear a face mask during a typical day. After 4 h, the acid was decanted into 15 mL autosampler tubes for analysis.

 requires several pre-sample preparation spikes to ensure that no analyte is lost during the sample preparation procedure. Sample spikes of 0.5

 were added to empty 50 mL autosampler tubes, followed by the mask inner layers. The inner layers were pushed to the bottom of the autosampler tubes to maximize contact with the spike solutions and allowed to sit for 30 min to absorb as much of the spike solutions as possible.

The acid mixture was then added so that the final volume of liquid added to each tube was 10 mL. The sample preparation is then continued as for the unspiked mask inner layers.

Calibrations were made against external calibration curves at 0.5

), and yttrium (Y) was added to all blanks, calibration standards, and samples as an internal standard.

All analyses were performed on a PerkinElmer Avio 550 Max ICP-OES using the analytes and wavelengths in Table I, along with the conditions and parameters in Table II. For maximum sensitivity, all analytes were measured with an axial plasma view, while high resolution was used to separate analytes from potential interferences. Multicomponent spectral fitting (MSF) was applied to Ir 208.882 nm to more easily resolve the peak from the baseline noise.

To assess the presence of analytes in the mask inner layers, samples were measured after 4 h of leaching. The concentrations of all analytes in all samples were less than 0.3

, a level more than three times lower than the inhalation PDE. These results indicate that the acids used for leaching do not extract excess analytes over time, as compared to normal respiration.

 states that methodology must be validated following 

1. Accuracy: Pre-preparation spike recoveries of 0.5

2. Repeatability: Relative standard deviations (RSDs) of six independent samples spiked at 

3. Ruggedness: Six solutions must be analyzed on different days, with different instruments, or with different analysts. The RSDs over the 12 measurements must be less than 25%.

4. System Suitability: The difference in the results of the high calibration standard (1.5

) measured at the beginning and end of a batch must be <20%.

Figure 2 shows that all the above criteria are met for all elements, with the exception of gold (Au) and palladium (Pd) in the accuracy study: both of these elements recovered just at or below the 70% minimum threshold.

To investigate Au and Pd, another accuracy study was performed, but without the mask inner layers. The leach procedure was followed and spikes added, except the mask inner layers were not added to the sample tubes; only the acid mixture and spike solutions were added to the tubes. The recoveries from this accuracy study show that all elements recover within 10%, including Au and Pd, suggesting that Au and Pd stick to the mask inner layers and are not extracted during the leach process. The implication is that wearers will not inhale Au and Pd if they are present in face mask inner layers.

This work has demonstrated the ability of ICP-OES to effectively measure metals in non-medical, disposable mask inner layers, following 

, which references the analytes and validation procedures from 

. A four-hour leach simulates how long a person may wear a mask during a typical day. The results indicate that the methodology easily meets the criteria for 

 for all analytes, except Au and Pd, which stick to the mask inner layers and would not be inhaled. Although ICP-MS could also be used for this analysis, ICP-OES has proven to be a cost-effective alternative to ICP-MS capable of meeting the criteria in 

 “Biocompatibility Evaluation of Breathing Gas Pathways in Healthcare Applications – Part 4: Leachables in Condensate,' ISO 2017.

(2) General Chapter <232> “Elemental Impurities–Limits,” in 

2nd Supplement in United States Pharmacopeia 35-National Formulary 30

 (United States Pharmacopeial Convention, Rockville, Maryland, 2018).

(3) General Chapter <233> “Elemental Impurities–Procedures,” in 

 is a Principal Application Scientist at PerkinElmer, Inc. in Shelton, Connecticut. Direct correspondence to: 

The determination of metals in hygienic face masks is important for global heath
at this time. Following the guidelines of ISO 18562-4, an ICP-OES method is described including sample preparation, analysis, and validation of the methodology.

The Determination of Metals in Disposable, Non-Medical Face Masks by ICP-OES

Particulate matter (PM) contributes significantly to environmental pollution globally. Fine particulate matter with an aerodynamic diameter of 2.5 μm or smaller, classified as PM2.5, is of great concern on a global level. In contrast to exposure to bigger particles, exposure to PM2.5 is more dangerous because its small diameter makes it invisible to the human eye, and it has the potential to penetrate deep into the respiratory system when inhaled. The chemical composition of these particles may comprise both organic and inorganic components. Depending on the geographical location, PM2.5 can be contaminated with toxic elements such as arsenic, cadmium, or lead. Because of its high mobility, the presence of PM2.5 can be influenced by local environmental conditions. This study describes how interference-free, low-level analysis of toxic elements as well as major elements in PM 2.5 can be accomplished. Results of two different sample locations at Kanagawa prefecture in Japan are presented and compared against each other.

Inductively coupled plasma–mass spectrometry (ICP-MS) is the most widely employed technique for analyzing trace elements in environmental samples because it produces rapid multielement analysis and enables unmatched detection limits to be achieved. The high detection power of ICP-MS is a way to overcome the limitations of other analytical techniques (1). For example, ICP-MS can detect the potential presence of silicon in the PM2.5 fraction, which is something other techniques are insufficient in handling. The composition of PM2.5 is commonly analyzed using X-ray diffraction (XRD) or fluorescence (XRF), however, for some lighter elements, the low concentrations in samples can be problematic. The ICP-MS technique having the ability to detect the presence of silicon in the PM2.5 fraction is important because the consequences of inhaling fine dust containing silicon particles are that the particles can result in serious health risks after both short- and long-term exposure. As an example, significant exposure to silicon particles has been linked to the development of lung cancer in the human body (2). As a response to this research, the United States Environmental Protection Agency (EPA) has set a maximum allowance, a maximum allowance up to 12 μg/m

Even if the sampling period is extended, the absolute amount of analyzed material may still not result in a significantly higher signal of the analyte because of the ultralow concentration. Therefore, it is important to analyze critical contaminants, such as silicon, at ultratrace levels with high accuracy using a more sensitive technique such as ICP-MS.

In this study, the ambient air samples were collected using a high-volume air collector system at two different locations. The PM2.5 fraction was collected on polytetrafluoroethylene (PTFE) filters, which were analyzed using triple quadrupole (TQ) ICP-MS following microwave digestion. The resulting concentrations in the measured solutions were typically below 1 μg/L, so the high detection power of ICP-MS was needed for accurate quantitation of the elemental composition.

A Thermo Scientific iCAP TQ ICP-MS instrument was used for all measurements. Table I gives an overview of the full configuration of the system. The instrument used in this study was equipped with a novel torch made from high-purity ceramic, replacing the standard torch (typically made from high purity quartz). This special torch, in conjunction with superior interference removal based on the use of TQ technology, enabled the detection of silicon at concentration levels well below the regulatory requirement.

Each air sample was collected from two different locations in the Kanagawa prefecture in Japan over a 24 h period. The air samples were collected onto a 47 mm diameter PTFE filter (Pall Corporation) with a 2 μm pore size, using a sequential ambient particulate sampler (Partisol 2025i, Thermo Fisher Scientific) at 16.7 L/min (or 1 m

/hr). Both sampling locations were in the Kanagawa prefecture, one within a municipal area, whereas the second location was close to a motorway.

To monitor and quantify changes in the elemental composition of PM2.5, air samples were collected over a period of 14 days at one of the sampling sites. In a second study, the influence from Asian dust was evaluated at the second sampling location. Asian dust is defined as a seasonal metrological phenomenon, where large amounts of yellow sand are transported from the deserts of western Asia (mostly originating from Kazakhstan, Mongolia, and northern China) eastward towards China, the Korean Peninsula, and Japan. Because of industrial pollution, this phenomenon is becoming an increasing concern. The summary of the details about Asian dust is shown in Table II.

The filters with collected air were digested by a microwave using a mixture of 5 mL HNO

 (68% Optima grade, Fisher Chemicals), 2 mL HF (48% Optima grade, Fisher Chemicals) and 1 mL H

 (31% Optima grade, Fisher Chemicals) in a vessel microwave digestion system (Milestone Ethos 1). After digestion, the samples size was increased to 50 mL using ultrapure water. In all digestions, an unused filter was digested using the same procedure as a control to assess potential contamination in the process of sample preparation.

All blanks and calibration standards were prepared from 2% (v/v) HNO

) with multielement standards (XSTC-1667 and XSTC-1668, Spex CertiPrep). An internal standard solution containing 5 μg/L lithium, yttrium, indium, and thallium was added to all samples.

Silicon is an analyte of special importance for the evaluating the elemental composition of fine dust because of its potential to cause severe respiratory diseases (such as silicosis) when it penetrates the human body deeply. Based on current legislation by the Ministry of the Environment in Japan, a minimum required detection limit (MRDL) of 10 ng/mL is set for this element, which is often one of the main components of PM2.5. Therefore, it is required to detect this element with high sensitivity and low background. The regulatory limit corresponds to a final concentration in a sample collected over 24 h and following the above sample preparation procedure. The result is that the final concentration of the sample is less than 5 μg/L. Often, the filter sample may be split in half to allow for additional measurements to be taken, further reducing the concentration in the analyzed solution for this critical contaminant.

Silicon is known as a challenging analyte in ICP-MS, mostly because of the polyatomic interferences arising from nitrogen in the ambient atmosphere (creating 

 on the most abundant isotope 28Si), but also contamination from the ubiquitous presence of the element in the laboratory and the glassware used in the ICP-MS source.

The resulting calibration curve for silicon using a mass shift reaction with oxygen is shown in Figure 1. The calibrated concentration range was between 0–100 μg/L (with calibration points at 5, 10, 25, 50, and 100 μg/L) and returned an instrumental detection limit (IDL) of 0.081 μg/L and a blank equivalent concentration (BEC) of 1.9 μg/L. The IDL was calculated using three times the standard deviation of 10 replicate measurements of the calibration blank.

Table III summarizes the obtained analytical figures of merit (IDL, BEC, and R2) for all 31 elements analyzed in this study. The typically achieved IDLs were well below 0.1 μg/L, even for often challenging analytes, such as arsenic, selenium, or cadmium.

To comply with applicable legislation, all analysis results (obtained as μg/L) were converted into mass per volume in the PM2.5 fraction (in ng/m

 represents the mass of the analyte in fine particulate matter PM2.5 in 1 m

 is the result of the analysis of the sample (ng/mL); 

 represents the result of the analysis of the preparation blank (ng/mL); 

 is the volume of the test solution (mL); 

 is the PM2.5 filter area where the sample was collected (cm

 is the filter area used for analysis (1/4 of S (cm

 is the collected volume of ambient air (m

Table IV shows the results for all elements that were studied across both sampling locations. The obtained results for the analysis of the elemental composition of the PM2.5 fraction clearly provides meaningful evidence to evaluate the pollution level because of the possibility to determine a wide range of elements in a single analysis.

The composition of PM2.5 at sample location two shows a higher presence of typical wear metals, such as iron, nickel, copper, or zinc. Other metals, such as molybdenum, antimony, and lead were significantly increased in this size fraction. This is likely related to the higher urbanization and the specific sampling location near by a motorway. Although these concentrations cannot readily be compared to another location, an increase of other elements, including silicon or sodium, could be expected in more rural locations, such as the adjacent Yamanashi prefecture. Agricultural activities usually lead to a higher erosion of soils, which may specifically liberate small particles containing these elements.

Although measurements were only accomplished during a single day, the presence of Asian dust as a temporary weather phenomenon has an observable influence on the elemental composition of the collected PM2.5 fraction. Whereas PM2.5 seems to generally contain a certain level of silicon in sampling location (2), this element is significantly increased under the influence of Asian dust. A similar tendency is also observed for other elements commonly found in sand, such as aluminum, potassium, and calcium. The influence of Asian dust also seems to have an impact on the observed levels of wear metals present in the PM2.5 fraction, with elements such as iron and zinc, but also antimony and lead being increased. Whether this is because of transportation from other locations or within the area around the sampling location could not be confirmed in this study.

A highly sensitive method for the analysis of the elemental composition of PM2.5 was developed and applied to the analysis of samples derived from two sampling locations in Japan. Using a combination of reactive gases (O

) and Helium (He) kinetic energy discrimination (KED) mode, respectively, common interferences on important contaminants were eliminated and excellent signal-to-noise (S/N) ratios were obtained across all elements under study. As an analyte of concern, silicon could be detected at levels well below the minimum required detection limit because of superior interference removal and reduced backgrounds using a novel ceramic torch. The new method allowed the simultaneous assessment of 31 elements in one analysis, helping to get a better understanding of the natural and anthropogenic processing contributing to the composition of PM2.5.

The authors would like to thank the Taiki Kankyou Innovation Center Group at Seikan Kensa for supporting sample preparation and this research.

(1) R. Seibert, I. Nikolova, V. Volná, B. Krejci, D. Hladký, 

(3) United States Environmental Protection Agency, 

National Ambient Air Quality Standards for Particulate Matter, Final Rule

 are with Thermo Fisher Scientific in Bremen, Germany. 

 is with the Seikan Kensa Center in Japan. 

 is with Thermo Fisher Scientific in Yokohama, Japan. Direct correspondence to: 

This study describes how interference-free, low-level analysis of toxic elements as well as major elements in particulate matter (PM), with an aerodynamic diameter of 2.5 μm or smaller, can be accomplished. Comparison study examples are given for two locations.

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