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. 2022 Nov 7;56(23):16996–17006. doi: 10.1021/acs.est.2c03241

Assessing Analytical Methods for the Rapid Detection of Lead Adulteration in the Global Spice Market

Alandra M Lopez †, Carla M Nicolini †, Meret Aeppli †, Stephen P Luby ‡, Scott Fendorf †,‡, Jenna E Forsyth ‡,*
PMCID: PMC9730856  PMID: 36343212

Abstract

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Lead adulteration of spices, primarily via Pb chromate compounds, has been documented globally as a growing public health concern. Currently, Pb detection in spices relies primarily on expensive and time-consuming laboratory analyses. Advancing rapid Pb detection methods, inclusive of their accuracy and precision, would improve field assessments by food safety inspectors, stakeholders, and the public in the hope of reducing Pb exposure risks at its source. Here, we present two field procedures for Pb detection: portable X-ray fluorescence analysis (pXRF) and a simple colorimetric test. We assess their efficacy to detect Pb and its chemical form in seven spice types, including powders, spice–salt mixtures, and dried roots, compared to the proven laboratory technique, inductively coupled plasma mass spectrometry (ICP-MS). Lead concentrations measured using pXRF and ICP-MS were within 5% of each other for spice powders and 24% for dried roots. By pXRF, spice samples were analyzed within collection plastic bags without preparation, resulting in a detection limit of 2 mg Pb/kg for spice powders, which is comparable to national food standards. The colorimetric test utilized here targets hexavalent chromium, making the method selective to Pb chromate adulteration assuming that this is its dominant source in spices. Color development, and thus detection, was observed when Pb concentrations exceeded approximately 5–70 mg/kg in dried turmeric roots and 1000 mg/kg in spice powders; however, it was ineffective for the spice–salt mixture. We show that pXRF analysis and a colorimetric assay provide information that may improve field decisions about Pb adulteration in a range of spice types, helping to minimize Pb exposure.

Keywords: Pb, lead chromate, spices, adulteration, rapid detection, pXRF, colorimetry, ICP-MS

Short abstract

This study proposes and compares multiple rapid detection tests for Pb in spices with field application that can be employed to lessen human exposure.

Introduction

Lead adulteration of spices is widespread globally and a growing public health concern,1 particularly in Bangladesh, Pakistan, Nepal, Morocco, and the Republic of Georgia, with concentrations reaching up to 48,000 mg/kg.2−5 There are no international standards for maximum levels of heavy metals, such as Pb, in spices; however, in consumable salts, the World Health Organization (WHO) and United Nation’s Food and Agriculture Organization (FAO) regulate a maximum limit of 1 mg Pb/kg.6 Furthermore, only a few national Pb food standards currently exist, which range between 2.5 and 10 mg Pb/kg in turmeric powder by the Bangladesh Standards and Testing Institution,7 Bureau of Indian Standards,8 and the Indian Agricultural Produce Grading and Marking Act.9 In the United States, the Food and Drug Administration (FDA) does not recommend a maximum Pb limit in spices, but previous work has evaluated spice Pb concentrations with respect to the regulated allowable Pb limit of 0.1 mg/kg in candy products.10,11 Likewise, the New York City Department of Health and Mental Hygiene uses a reference Pb limit of 2 mg/kg because it is a permissible limit in certain food additives.2

Recent studies in rural Bangladesh and the United States have cited Pb-contaminated spices, including turmeric, swanuri marili, kharchos suneli, and kozhambu (an Indian spice mixture), as contributors to elevated blood lead levels (BLLs) and Pb poisoning in children and adults.12−15 A bioaccessibility experiment estimated that approximately 50% of Pb in various spices was extractable using an in vitro gastric fluid solution.16 As a neurotoxin, even low-level exposure to Pb (below permissible limits established for food products) impacts cognitive development and behavior and can lower IQ in children.17,18 Furthermore, adults are at increased risk of hypertension, peripheral neuropathy, and renal disfunction, and pregnant women are vulnerable to adverse birth outcomes.19,20 Although governmental regulatory limits exist for BLLs in adults and children,21 no level of Pb is considered safe.18

Lead can be deliberately added to spices, known as adulteration, or unintentionally added during production, known as contamination. Turmeric adulteration has been well-documented, whereby Pb chromate (PbCrO4) is intentionally added to turmeric roots during polishing to enhance the spice’s yellow color.12,13,22 Red Pb (Pb3O4)-based pigments have also been detected in paprika and other spices, presumably to enhance their red color.16,23 Lead adulterants increase the weight of spices;3,24,25 however, this is likely minimal based on the absolute quantity of Pb in adulterated spices.5 Geogenic Pb may be derived from air, dust, or soil and can inadvertently mix with spices to result in Pb contamination. Molar Pb/Cr ratios are used to distinguish anthropogenic PbCrO4 pigment from geogenic Pb sources in spices and environmental samples.13,22 For example, average Pb/Cr molar ratios were 1.1 in adulterated turmeric and 1.3 in PbCrO4-based pigment samples from Bangladesh,13 both consistent with the chemical formula of PbCrO4 (Pb/Cr = 1). Slight differences in Pb/Cr molar ratios of adulterated spices, typically greater than 1, may be explained by the presence of minor Pb and Cr phases within added pigments.13 Lead chromate adulteration of spices was further confirmed by visual observations during the polishing process and during stakeholder interviews.22,26 Spices contaminated by geogenic Pb sources commonly have Pb/Cr molar ratios less than 1.13

Lead adulteration of spices, especially from PbCrO4 additives, represents an appreciable route of human Pb exposure27 and highlights the need to increase food safety, including monitoring efforts and regulatory enforcement. Lead concentrations and Pb/Cr molar ratios are commonly determined by dissolution and concomitant inductively coupled plasma mass spectrometry (ICP-MS), which possesses desirably low detection limits (0.001 mg/kg) but requires expensive laboratory instrumentation and time-consuming sample preparation by acid digestion.5,13 Moreover, low-resource countries rely on additional shipment of spice samples to high-income countries where analytical instrumentation for ICP-MS is more readily available, further delaying the identification and removal of adulterated food products. Recent studies have focused on developing rapid detection tests for PbCrO4 in turmeric powder using Fourier transform Raman spectroscopy (FT-Raman)28 and X-ray powder diffraction (XRD).29 Under optimal conditions, these approaches have a limit of detection of 5000 mg PbCrO4/kg or approximately 3200 mg Pb/kg. From a global database with 252 turmeric samples,2 the median Pb concentration was 0.7 mg/kg and the maximum concentration was 2700 mg/kg. Moreover, red Pb (at levels greater than 2 wt %) was screened in adulterated paprika using photoacoustic spectroscopy.23 Although these methods are nondestructive and require minimal sample preparation, their detection limits and instrumental costs make them impractical for routine analysis of spices. Alternatively, portable X-ray fluorescence (pXRF) techniques allow for the rapid detection of Pb in the field (e.g., markets, homes, bazaars, and ports) using portable instrumentation5,15 and have improved detection limits (1–8 mg/kg) that typically are near regulatory limits. In soil and sediment applications, pXRF results correlated well with laboratory-based spectrometric measurements of Pb concentrations;30−34 however, the comparison between pXRF and ICP-MS has not been rigorously documented for Pb-containing spices.5

In this study, we aimed to (a) investigate multiple qualitative and quantitative methods to detect adulteration with Pb-containing compounds in spices (n = 69 samples), (b) compare their relative performances to detect Pb and Cr, and (c) assess advantages and limitations of each method based on the spice type. Rather than focusing on a single spice type or origin country, we present results from colorimetric and instrumental (XRF and ICP-MS) analyses of seven spice types, including powders, salt mixtures, and dried roots, purchased in four countries and containing a range of Pb concentrations. Lead chromate-based pigment was hypothesized as the common adulterant. We thus applied a colorimetric test using a diphenylcarbazide (DPC) reagent as an indicator for the presence of hexavalent chromium [Cr(VI)], which we propose to be an effective proxy for Pb by PbCrO4 adulteration. Our qualitative approach is modified from a protocol by the Bureau of Indian Standards to determine PbCrO4 adulteration in turmeric powder by ashing and sequential addition of dilute acid and DPC.8 Unlike established techniques that determine Cr(VI) in food matrices and require additional analytical instrumentation,35 we focus on proposing a method that identifies one form of Pb adulteration (PbCrO4), is low resource-intensive, and intended for field use. A previous attempt to use color-changing test strips with sodium rhodizonate was unsuccessful in differentiating Pb-adulterated and Pb-free turmeric samples.22 Effective methods to rapidly detect Pb-adulterated spices (not only turmeric powder) will help remove potential sources from the global supply chain and shift consumer behaviors to reduce Pb exposure risks.

Materials and Methods

Spice Sample Selection

Seven types of spice samples were selected for analysis: turmeric powder, dried turmeric roots, coriander powder, red chili powder, blue fenugreek powder, as well as khmeli suneli and svaneti salt (spice mixes typically containing marigold, blue fenugreek, coriander, red chili, and other spices). Spices selected for this study were from a larger library of spices collected from the field (e.g., markets and homes) and were characterized by a broad, representative range of genuine Pb concentrations (0 to 11,531 mg/kg), natural colors, and compositions. Samples were obtained from India, Pakistan, Bangladesh, and the Republic of Georgia, including a subset of samples previously described.5,22 In the Republic of Georgia, 70% of spice samples purchased contained greater than 2 mg Pb/kg.2 Within South Asia, Pb concentrations exceeded 2 mg/kg in 13% of spices from India, 25% from Pakistan, and 54% from Bangladesh.2

A total of 69 spice samples were analyzed in this study. Turmeric powder (n = 11), red chili powder (n = 10), and coriander powder (n = 12) were collected from Patna, India, in 2020. Dried turmeric roots (n = 11), including bulbs and roots, were acquired from Pakistan in 2019 and Bangladesh13 in 2017. Khmeli suneli powder (n = 10), blue fenugreek powder (n = 6), and svaneti salt mixture (n = 9) samples were collected in the Republic of Georgia during 2019.5 Samples were stored individually in plastic bags under dry conditions and at room temperature since acquisition. The plastic composition varied based on the sampling location.

Method Investigation

Lead and Cr concentrations in each spice sample were assessed via three methods:

Portable X-ray Fluorescence Analysis

Lead and Cr concentrations in each spice sample were measured in triplicate by energy-dispersive X-ray fluorescence spectrometry using a portable X-ray fluorescence (pXRF) analyzer (Olympus Vanta C Series). The pXRF excitation source is a Rh anode X-ray tube that operates at 10–40 keV with a silicon drift detector. The full scan time was 60 s and consisted of a sequence of two beams using the proprietary Geochem mode. Samples were first measured for 45 s (dwell time) with a 40 keV beam (aluminum filter) followed by 15 s with a 10 keV beam for a total analysis time of 1 min. Powder and root samples were analyzed in their plastic collection bags, and replicate handheld measurements were taken from different parts of the sample. The exterior of bags was lightly cleaned to remove external dust using ethanol and Kimwipes. Because Pb is a heavy element, the varying plastic materials do not significantly interfere with pXRF measurements.36,37 Based on Pb and Cr concentrations, we calculated Pb/Cr molar ratios for each sample. Portable XRF measurements of Pb collected for this study by the Olympus Vanta C Series analyzer were compared to previous pXRF measurements made by field personnel using different handheld instruments (ThermoFisher Scientific Niton XL3T 700S GOLDD and Olympus Delta DCC-4000) and sample preparation (Figure S1).5

Acid Digestion—Inductively Coupled Plasma Mass Spectrometry

We analyzed spice powder and root samples for Pb and Cr concentrations using inductively coupled plasma mass spectrometry (ICP-MS, Thermo Scientific XSERIES 2). Prior to analysis, powder samples (0.3–0.5 g) were dissolved in 69% nitric acid (trace-metal grade) using a microwave digester (MarsXpress, CEM). Dried turmeric root samples (1–3 roots, approximately 2–7 g) were soaked in 35% nitric acid (trace-metal grade) for 30 min to remove external powder coatings, and the solution was further digested by microwave digestion.13 Actual weights of sample aliquots were recorded to the nearest 0.001 g. The microwave digestion program settings were twofold: the first stage ramped up and held at 175 °C and 80% of 1,600 W for 20 min, while the second stage cooled the samples for 20 min at zero temperature and power. Thereafter, samples remained in the instrument for approximately 1 h to ensure sufficient cooling before processing for ICP-MS analysis. Triplicate digestions were completed for each sample, and at least three blank digestions were processed with every 30 samples. All samples were diluted to 2% nitric acid and stored at 4 °C prior to ICP-MS analysis. Based on Pb and Cr concentrations, we calculated Pb/Cr molar ratios.

Colorimetric Assay—Diphenylcarbazide Method for Chromium(VI)

Lead is sometimes added to spices as a PbCrO4-based pigment to enhance the color of powders and roots. As a result, Cr(VI) (as CrO42–) is added to spices, and its presence (as a proxy for Pb adulteration) can be determined using a diphenylcarbazide (DPC) colorimetric assay, a method regularly used in soil and water analyses.38 Portable XRF and ICP-MS do not distinguish Cr speciation and instead measure total Cr, which may consist of Cr(III) and Cr(VI). In the presence of DPC, Cr(VI) is reduced and forms a violet-red complex, Cr(III)-diphenylcarbazone, which can be a qualitative indicator of spice adulteration or be further quantified using UV–vis spectrophotometry.38

The DPC reagent was prepared in two ways to test the efficiency of ethanol- versus methanol-containing solutions, which have differing chemical hazards. To prepare the DPC reagent (per 100 mL), 0.05 g of 1,5-diphenylcarbazide was dissolved in 10 mL of ethyl alcohol (95%, HPLC grade) or methanol (≥99.9%, HPLC grade) and added to approximately 87.2 mL of double-deionized water and 2.8 mL of sulfuric acid (98%). The color reagent was stable for at least one month when stored in the dark at 4 °C to minimize photo-oxidation of DPC. Additionally, a blank reagent of similar composition without DPC was prepared to evaluate the background color of the sample solution.

Approximately 0.05 g of the powder spice sample was added to duplicate microcentrifuge tubes to assess solution color change after the addition of DPC and blank reagents (Figure S2). One milliliter of DPC and blank reagents were added to separate sample tubes and agitated for 30–60 s. For turmeric roots, one root was placed in duplicate centrifuge tubes, and 2 mL of DPC and blank reagents were added after which tubes were agitated for 30 s. For all spice types, relative color change between the DPC and blank tubes were immediately compared by visual inspection against a white background and documented with a phone camera. Final observations of color development were made after 45 min of the tube resting. Timing was determined to be sufficient for both color development and settlement of solids after the initial agitation. Multiple people independently evaluated color visibility; however, sample IDs were not masked during final color observations. Although this method is qualitative, we approximated a limit of detection by visual inspection by comparing color changes with Pb concentrations measured by ICP-MS in all spices and based on spice types. We observed no significant differences in final color development when the DPC reagent was prepared using ethanol versus methanol, which lessens the chemical hazards associated with the method (Figure S3); therefore, we strongly recommend preparing the DPC reagent using ethanol.

While sample preparation was not required before testing with the DPC method described above, the Bureau of Indian Standards (2010) recommended ashing powder samples to improve color development.8 To test this, we heated a subset of turmeric powder samples (described below) at 500 °C in a muffle furnace for approximately 3 h. Afterward, approximately 0.02 g of ashed turmeric powder was added to microcentrifuge tubes and analyzed as described above.

To extend the lower limit of detection of the DPC method for spices, we analyzed a subset of spice powder samples by UV–Vis spectrophotometry (Shimadzu UV-1601). Lead-free turmeric powder (TP-01) was spiked with various amounts of PbCrO4-based yellow pigment for final Pb concentrations of 6, 14, 39, 43, 88, 643, and 1275 mg/kg (determined by ICP-MS). The pigment–turmeric mixtures were analyzed by the DPC method described above with and without ashing in a muffle furnace. After qualitative color observations, the blank and DPC samples were syringe-filtered with a 0.22 μm nylon filter membrane into polystyrene cuvettes. Absorbances of DPC-spiked samples were measured at 540 nm.38 Additionally, four turmeric powder samples (TP-03, TP-05, TP-07, and TP-08) from the study data set were similarly analyzed in triplicate and compared to the concentration curve based on the pigment–turmeric mixtures.

Statistical Analyses

We calculated descriptive statistics for Pb concentrations based on the spice type using ICP-MS measurements by Microsoft Excel 2016. The mean and standard error were calculated for spice Pb and Cr concentrations measured by pXRF and ICP-MS using triplicate measurements. Linear regression is a primary statistical tool for method comparison.33,39 We compared Pb and Cr concentrations by the pXRF and ICP-MS using ordinary least squares (OLS) linear regression and Deming regression.40 Deming regression assumes that both pXRF and ICP-MS data have random error.33 Deming and OLS regression analyses were executed using the statistical programming language R’s mcr and stats packages, respectively. We assessed regression slopes, intercepts, goodness of fit (r2; Deming), and coefficient of determination (R2; OLS). According to US Environmental Protection Agency guidelines,39 data quality levels for pXRF analyses were approximated (with respect to reference values from the ICP-MS in lieu of CRMs) using R2 values, relative standard deviations, regression slope, and intercept from OLS linear regression.

Results and Discussion

Lead Concentrations by the Spice Type

Lead concentrations are presented by the spice type in Table 1. Sixty-nine spice samples were analyzed and consisted of seven spice types, including powders and dried roots (Table S1). Spice samples within each type were subselected from a larger spice collection based on their Pb concentration (field pXRF measurements) to be representative of the range in global markets. The mean Pb concentration across all study samples was 1075 mg/kg, and the median Pb concentration was 137 mg/kg. As described in the following sections, the multiple analyses utilized in this study suggested that all spice samples with Pb concentrations greater than 1 mg/kg were adulterated with PbCrO4, composing 87% of samples (Table S1). The highest Pb concentration (11,531 mg/kg) was measured in a khmeli suneli powder from the Republic of Georgia. Consistent with previous work, turmeric powder and roots from multiple countries (India and Pakistan) and spice types from Georgia, including khmeli suneli and svaneti salt, contained the highest Pb concentrations.2,5

Table 1. Spice Types Selected for This Study and Their Pb Concentrations in mg/kg (Measured by ICP-MS).

spice type country origin sample size average [Pb] St. Dev. [Pb] minimum [Pb] Q1 [Pb] median [Pb] Q3 [Pb] maximum [Pb]
all samples   69 1075 2174 0.00 35 137 506 11,531
Powders
turmeric India 11 1118 1736 0.00 94 221 1135 5279
red chili India 10 114 75 12 57 130 148 240
coriander India 12 97 76 0.05 44 86 149 250
Khmeli Suneli Georgia 10 4398 3641 0.33 1104 4904 5804 11,531
blue fenugreek Georgia 6 86 73 0.43 23 93 142 169
svaneti salt Georgia 9 631 860 0.04 0.44 213 742 2496
Roots
turmeric Bangladesh, Pakistan 11 857 1632 1.04 38 134 313 4221
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Spice Pb Quantification: Portable XRF and ICP-MS

Spice powders and unpowdered dried turmeric roots were analyzed by both pXRF and ICP-MS. Approximately 73% of spice samples had detectable Pb concentrations above the pXRF detection limit (2 mg/kg) when analyzed in plastic collection bags (Table S1). Besides one turmeric powder sample, all spice samples had detectable Pb levels by ICP-MS, with a detection limit of 0.001 mg/kg. The two analytical methods were consistent for the various spice powders with Pb concentrations up to nearly 12,000 mg/kg (Figures 1A,B and S4A,B and Table S2). All nondetectable samples by pXRF contained Pb concentrations less than 2 mg/kg as measured by ICP-MS (Table S1). The pXRF slightly underestimated Pb concentrations in powder samples (4.8%) (Figure 1A), but its overall consistency with the ICP-MS, the current “gold standard” analysis for Pb, underscores its major advantages as a rapid screening tool that is nondestructive, requires minimal sample preparation (e.g., analysis in plastic collection bags), and can be used at ports or within markets. For spice powders with Pb concentrations less than 300 mg/kg, the regression slope was 1.10 with a 95% confidence interval of 0.89 to 1.4 (Figure 1B and Table S3). It is possible that deviations in concentrations by pXRF compared to ICP-MS were partly due to measuring samples in their plastic collection bags; however, these differences were minimal at Pb concentrations less than 100 mg/kg (Figure 1B). Data quality levels of the pXRF analysis were classified as “definitive” or “quantitative” for all spice powder types based on respective R2 values, relative standard deviations, slope, and intercepts from linear regression analysis (Table S2 and Figures S5 and S6).33,39 “Definitive” pXRF data are described as equivalent to ICP-MS measurements (reference method), while “quantitative” data confirm the presence or absence of Pb and quantification, but it is recommended that at least 10% of screened samples be further analyzed by ICP-MS to confirm field Pb concentrations.39

Figure 1.

Figure 1

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Average pXRF versus ICP-MS measurements of total Pb concentrations (mg/kg) and Deming regression line (dashed) for (A) all powder samples of various spice types, (B) powder spices with Pb concentrations less than 300 mg/kg, and (C) turmeric root samples. Note that the axis bounds differ by panel. Sample measurements below the limit of detection (2 mg/kg) on pXRF were plotted as 0. Error bars represent the standard error of the mean of three measurements. Regression details are reported in Table S3.

There were significant differences in measurement types for dried turmeric roots (Figures 1C and S4C). The pXRF overestimated Pb concentrations by approximately 24% relative to ICP-MS based on Deming regression. Sample precision (replication error) for pXRF and ICP-MS was higher for root samples compared to powder samples, especially at high Pb concentrations (Figure 1C). Due to the high demand for artificially colored turmeric roots, polishers add yellow pigments (often containing PbCrO4) to root exteriors.22 This results in a coating of Pb-rich pigmented powder on turmeric roots that unevenly distributes Pb because there is no contamination within roots. Previous work has suggested that total root digestion was not necessary to quantify Pb concentrations by ICP-MS.22 The pXRF algorithm used in this study assumed a homogenous powder sample, which worked well for well-mixed spice powders but inaccurately described dried turmeric roots. Furthermore, the data quality level of the pXRF measurements for dried turmeric roots was defined as “qualitative,” meaning that the instrument can detect Pb presence or absence but does not provide reliable Pb concentrations (Table S2 and Figure S4). The instrument detection limit for Pb ranged from approximately 2 to 6 mg/kg. Our study supports that a pXRF should be considered semi-quantitative (particularly using common “soil” or “geochem” methods) for unpowdered, dried turmeric roots and be used to rapidly detect the presence of Pb (for follow-up investigation) instead of approximating an absolute Pb concentration for reporting.

Energy-dispersive X-ray fluorescence spectroscopy, including a pXRF analyzer, does not effectively measure Cr in spice samples, and the instrument detection limit is typically 5–10 times greater than other laboratory methods, such as ICP-MS.39 The pXRF overestimates detectable Cr concentrations in spice powders by 43% relative to the ICP-MS (Figure S7A), and the detection limit for Cr in spice powders was approximately 50 mg/kg (Figure S7B). This resulted in near or undetectable Cr concentrations in PbCrO4-contaminated spices with Pb levels less than approximately 200–300 mg/kg (Table S1). Moreover, pXRF measurements of Cr are affected by the spice type; Cr concentrations are overestimated in svaneti salts compared to spice powders. For dried turmeric roots, Cr concentrations measured by pXRF were nearly fivefold greater than measurements using ICP-MS (Figure S7C,D). For a solid SiO2 matrix, Ravansari et al.36 estimated that approximately 55 pXRF measurements were needed to compare Cr concentrations from pXRF and an acid digestion method.

By ICP-MS, we observed that when Pb concentrations exceeded 1 mg/kg, the molar Pb/Cr ratio was near or above 1 (Figure 2A), indicating adulteration with a PbCrO4 compound for all spice types.13 Here, the average Pb/Cr ratio was 1.32 and median Pb/Cr ratio was 1.26 (Table S1). Similarly, Forsyth et al. (2019) reported that the average molar Pb/Cr ratio for pigments was 1.3.13 Seven spice samples (svaneti salt, khmeli suneli, blue fenugreek, and coriander powder) had detectable Pb concentrations less than 1 mg/kg and associated Pb/Cr ratios less than 0.5 (Table S1), suggesting that these samples were likely contaminated with geogenic Pb and Cr (e.g., soil) rather than adulterated with anthropogenic PbCrO4-based products.13

Figure 2.

Figure 2

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Average molar Pb/Cr ratio versus Pb concentrations (mg/kg) measured by (A) ICP-MS and (B) pXRF. Symbols and colors are based on the spice type, and error bars represent the standard error of three sample measurements. Chromium concentrations were below the instrumental limit of detection for all red chili, coriander, and blue fenugreek powder samples, and therefore, molar Pb/Cr ratios could not be calculated by pXRF. Turmeric powder (n = 6), svaneti salts (n = 4), khmeli suneli (n = 3), and dried turmeric roots (n = 3) with undetectable Cr by pXRF are shown with molar Pb/Cr ratios of 0 (could not be calculated) (Table S1).

Molar Pb/Cr ratios significantly differed between analytical methods (Figure 2). Importantly, acid digestion paired with ICP-MS remains the reliable technique to determine molar Pb/Cr ratios.13 Molar Pb/Cr ratios could not be calculated by pXRF for all red chili, coriander, and blue fenugreek powder samples, in addition to some turmeric (powder and roots), svaneti salt, and khmeli suneli powder samples that contained nondetectable Cr concentrations (when Pb concentrations were less than 200–300 mg/kg) (Figure 2B). Because Cr concentrations were overestimated by pXRF, molar Pb/Cr ratios were typically lower compared to calculations using ICP-MS measurements (Figure 2). We observed notable discrepancies in molar Pb/Cr ratios for turmeric roots and Pb-rich svaneti salts, where pXRF-derived Pb/Cr values were less than 1 unlike ICP-MS equivalents. Without ICP-MS analysis, it is possible that molar Pb/Cr ratios calculated using a pXRF may falsely overlook Pb chromate as a source of Pb adulteration in certain spice types.

Lead quantification by pXRF was consistent with ICP-MS, especially for spice powders and salts. With rapid analytical times (1 min) and no required sample preparation or consumption, pXRF can expedite the assessment of Pb concentrations in spices and complement ICP-MS analyses that confirm elemental concentrations and identify Pb-containing compounds using molar ratios. To ensure high-quality pXRF measurements during field screening, certified reference materials (CRM) having a similar matrix and preparation need to be frequently measured during analysis.33,36 Within this study, CRMs for spices containing reference Pb and Cr concentrations were not commercially available. Instead, we prioritized measuring all spice samples in triplicate by pXRF and ICP-MS, using the ICP-MS results to assess the precision and accuracy of the pXRF. If pXRF analyzers become a common detection tool for food safety inspectors and other stakeholders in multiple countries, we recommend the development of a suite of CRMs based on the spice type due to their matrix heterogeneity. These CRMs should be regularly analyzed within collection plastic bags consistent with spice sample analysis and similarly measured by ICP-MS for quality assurance. Importantly, CRMs may allow users to determine a correction factor for Pb and Cr measurements by pXRF based on the difference between the measured and true value.39

The DPC Method: Rapidly Detecting Lead Chromate

Hexavalent chromium, a proxy for Pb adulteration by PbCrO4, was detected in turmeric (powder and dried roots), khmeli suneli, blue fenugreek, and coriander powder using DPC in a colorimetric assay. In PbCrO4, Cr is present in its oxidized state as Cr(VI). Portable XRF and ICP-MS measure total Cr, which can include multiple oxidation states, including Cr(III) and Cr(VI). Total Cr concentrations (up to 1.4 mg/kg) in unadulterated spices depend on background levels in agricultural soils, and Cr(III) is the dominant oxidation state.41 Like Pb, we deduce that PbCrO4-containing pigments are the dominant Cr(VI) source, which is shown by the spice molar Pb/Cr ratios. Without Pb quantification, the DPC assay of spices serves as an indicator for possible PbCrO4 adulteration. Paired with pXRF analysis of Pb, the colorimetric method can potentially act as a substitute for calculating Pb/Cr ratios by ICP-MS to determine Pb phases in spices. Based on previous studies, we attempted two additional tests to detect Pb adulteration in the spice samples using sodium rhodizonate and water as indicators,42−44 which are described in the Supporting Information. Ultimately, these methods were unsuccessful at detecting Pb-adulterated spices and were not rigorously tested in this study.

The colorimetric method had the greatest applicability and visible detection range on dried turmeric roots (Figure 3). A strong violet color (Figure 3C) was observed from roots with Pb concentrations that range from 71 to 4221 mg/kg (13–1040 mg Cr/kg) (Figure 3A), and a slight color change was noted on a root sample with 5 mg Pb/kg and 0.91 mg Cr/kg (Figure 3B). The DPC reagent contains dilute sulfuric acid that effectively washes pigment coatings and external dust from roots (Figure S8). In contrast to powders, the Cr(VI) signal from turmeric roots was not diluted by natural spices mixing with the reagent because roots were not fully digested.

Figure 3.

Figure 3

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(A) Color rankings of the DPC method for turmeric roots (n = 11) by total Pb concentration (mg/kg; ICP-MS). Each bar represents a spice sample. (B,C) Photographs of turmeric root samples (bars with asterisks) with DPC (left) and blank (right) reagents after 45 min of color development showing (B) slight (medium) and (C) strong (high) color change. Light yellow, light violet, and dark violet bar colors represent no (low), slight (medium), and strong (high) color change after 45 min of color development using the DPC method, respectively.

Despite the background color from spices, we observed strong violet color development after DPC addition at Pb concentrations greater than 1000 mg/kg (223 mg Cr/kg) in powder turmeric and 4000 mg/kg (791 mg Cr/kg) in khmeli suneli samples (Figure 4). Color change was observed in 7 out of the 10 khmeli suneli samples, all containing Pb levels greater than 4000 mg/kg (Figure 4B). No color change was detected in one khmeli suneli sample with 2 mg Pb/kg (0.45 mg Cr/kg) nor in two samples containing less than 1 mg Pb/kg. Slight color change was detected in turmeric samples with Pb concentrations of 215, 506, and 1182 mg/kg, most notable immediately after DPC was added and before mixing the sample (Figure S9); a sample containing 221 mg Pb/kg had no distinguishable color change compared to the blank equivalent (Figure 4C and Table S1). Turmeric and red chili powder samples exhibited the most vivid background solution color, which may obscure visible color change from the colorimetric assay compared to other spice types (Figure S9). For example, blue fenugreek and coriander powders had a less natural background color (Figure S10). Blue fenugreek samples showed slight color changes between 88 and 169 mg Pb/kg (15–29 mg Cr/kg) (Figure 4D). Likewise, for coriander powder, we observed color development in samples with as low as 87 mg Pb/kg (13 mg Cr/kg); however, one coriander powder that contained nearly twice the Pb concentration (167 mg/kg) did not change color. Lead concentrations in blue fenugreek and coriander powders were below 1000 mg/kg (the approximate visible detection limit for turmeric), but slight differences were distinguishable by eye due to the reduced background color (Figure 4E and Table S1). The highest Pb concentrations were 169 mg/kg in blue fenugreek and 250 mg/kg in coriander powder samples. Chromium(VI) levels may be too low to visually distinguish color development compared to control (blank) samples. We recommend assessing sample replicates when slight color changes are observed, further supporting colorimetric results with ICP-MS analysis (e.g., molar Pb/Cr ratio).

Figure 4.

Figure 4

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DPC color rankings by total Pb concentration (mg/kg; ICP-MS) for (A) all powder spice types (except red chili powder and svaneti salt), (B) khmeli suneli, (C) turmeric, (D) blue fenugreek, (E) coriander, (F) svaneti salt mixture, and (G) red chili powder samples. Each bar represents a spice sample. Light yellow, light violet, and dark violet bar colors represent no (low), slight (medium), and strong (high) color change after 45 min of color development using the DPC method, respectively. Striped light violet bars correspond to turmeric powder with mixed color results (see Figure S9). Note that the y-axis bounds differ by panel.

The DPC method was unsuccessful at detecting adulteration in the svaneti salt (Figure 4F) and red chili powder (Figure 4G) samples despite high Pb concentrations and molar Pb/Cr ratios suggesting PbCrO4 adulteration and thus Cr(VI) presence. Red chili powder exhibited a strong red background color after reaction with the blank reagent, which interfered with slight DPC-driven color differences. Like for coriander and blue fenugreek, it is possible that all red chili powder samples were below the visible detection limit of the method because Pb concentrations ranged from 12 to 240 mg/kg (Table 1). Up to 2400 mg Pb/kg has been previously documented in chili powder, hot pepper, and paprika, but typical Pb contamination in this spice grouping was lower compared to other spices.2 For example, the 90th percentile of Pb concentrations was 27 mg/kg in chili powder, while it was 6,340 mg/kg in khmeli suneli.2 Despite the broad Pb concentration range (0.04 to 2496 mg/kg) and molar Pb/Cr ratios of svaneti salts, no color changes were observed using the DPC method (Figure S10). Aside from natural spice colors, sample matrices appear to interfere with the DPC reaction. Color development was still not visible after Pb-rich svaneti salts were pre-rinsed multiple times with water to dissolve salts.

By visual inspection, we detected color change in spice powders (except svaneti salt mixtures) with greater than 250 mg Cr/kg, equating to approximately 1000 mg Pb/kg. The colorimetric assay may have lower levels of detection depending on the spice type and associated natural background color. We investigated whether color differences could be detected at lower Pb concentrations by UV–vis spectrophotometry after the colorimetric assay. The limit of detection decreased to approximately 50 mg Pb/kg in natural turmeric samples spiked with PbCrO4-based pigment (Figure 5A), even though these color differences were not apparent by the eye relative to the blank control (Figure 5C). For select unspiked turmeric powders (TP-03, TP-05, TP-07, and TP-08), absorbances generally increased with Pb concentration but values deviated from turmeric–pigment mixtures with similar Pb concentrations (Figure S11). It is possible that the sample matrix, including different spice types, spice vendors, and resulting molar Pb/Cr ratios, may influence UV–vis measurements.

Figure 5.

Figure 5

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UV–vis absorbance values at 540 nm using the DPC method versus ICP-MS measurements of total Pb concentration (mg/kg) of pigment–turmeric mixtures. The powder samples were analyzed by DPC (A) before (slope p-value = 4.4 × 10–7, 95% CI: 0.00021–0.00024; intercept p-value = 0.65) and (B) after ashing in a muffle furnace (slope p-value = 0.0009, 95% CI: 0.009–0.017; intercept p-value = 0.53). Photographs of DPC-spiked (C) unashed and (D) ashed samples.

Ashing spices in a muffle furnace removes the organic material that contributes to the background color and concentrates present metals; however, this preparation step requires laboratory access and diminishes the method’s applicability for rapid detection in the field. We observed detectable adulteration by UV–vis in ashed pigment–turmeric mixtures with Pb concentrations as low as 6 mg/kg pre-ashing (Figure 5B). Consistent with UV–vis absorbances, violet color was distinctly visible in solution from ashed samples (Figure 5D) and highlighted that color change correlated with total Pb concentrations.

Rapid Detection of Pb-Spice Adulteration in the Field

The pXRF and the color changing DPC test advance our ability to assess Pb pigment adulteration in the field. Table 2 summarizes the advantages and limitations of each method presented in this study. An additional study limitation was that people were not blinded to sample Pb concentrations during final DPC color assessments because sample IDs were visible.

Table 2. Summary of Investigated Methods for Pb Detection in Spices and Methodological Considerations (* = Low/Minimal, ** = Moderate, and *** = High).

rapid test analysis spice type estimated Pb LOD (mg/kg) laboratory required preparation results complexity capital waste considerations potential applications
DPC qualitative powder 1000 no 5 min 60 min * * * chromate-specific (Pb adulteration proxy), high LOD for powder spices (unashed), spice-dependent color interferences, unable to determine the Pb/Cr ratio, and ineffective for svaneti salts dried turmeric roots with visible powder coatings; pXRF follow-up if spice powder has [Pb] > 1000 mg/kg to determine if adulterant is Pb chromate; potential to be used by more people/public (e.g., at-home test), particularly for highly adulterated spice powders/roots to supplement quantitative methods
    roots ∼5–70              
  quantitativeb powder <1000a yes 10 min 1–2 h ** ** *  
portable XRF quantitative powder 2 no N/A 1 min ** ** N/A nondestructive, multi-element quantitative analysis, similar results between pXRF makes/models, X-ray trained personnel needed, high Cr LOD, unreliable Pb/Cr ratio, semi-quantitative analysis of roots, and high as LOD in Pb-rich samples initial spice screenings for Pb in the field/laboratory. Follow-up analytical needs can be determined depending on [Pb], spice type, and resource access
  qualitative roots 2–6                
ICP-MS quantitative powder, roots 0.001 yes 24–48 h days–months *** *** *** lowest Pb and Cr LOD (below regulatory thresholds), multi-element quantitative analysis, molar Pb/Cr ratio, resource intensive, usually requires sample shipping, and high potential error during sample preparation portable XRF follow-up if: (a) spice powders < 1000 mg Pb/kg to determine if adulterant is Pb chromate (molar Pb/Cr ratio) and (b) for quantitative Pb results and molar Pb/Cr ratios for dried turmeric roots and other spices with Pb < 2 mg/kg
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a

Quantitative approach and detection limit by UV–vis analysis require further work; triplicate tests needed per sample.

The ideal application for pXRF and the DPC colorimetric assay is to be used by food safety inspectors and NGO stakeholders to expose and interpret Pb adulteration in spices. When Pb concentrations exceeded 2 mg/kg in powders of various spice types, the pXRF and ICP-MS results were within 5% of each other. For dried turmeric roots, we were able to distinguish Pb-contaminated roots from unpolished (unadulterated) roots and approximate Pb concentrations within 24% of ICP-MS results. Importantly, pXRF analyses do not require sample preparation and spices are investigated nondestructively through sample collection bags in 1 min. Portable XRF analyzers cost more than 20,000 USD, which presents a barrier for implementation (Table S4); however, the ability to analyze thousands of samples with minimal resources and maintenance compensates for this fixed cost across the instrument lifetime. Independent of laboratory analyses, food safety inspectors and stakeholders can use pXRF analyzers to monitor for and detect Pb in spices, in order to initiate prompt removal of adulterated goods along the supply-and-demand chain. An initial screening of Pb concentrations by pXRF will improve sample selection for detailed laboratory analyses and reduce associated costs (Tables 2 and S4). Due to higher detection limits, pXRF is not advised for Cr analysis (and molar Pb/Cr ratios) of spices.

To increase consumer and stakeholder visibility around spice adulteration, we proposed a cost-effective and simple color changing test to rapidly detect the presence of PbCrO4-containing pigment in spices (Table S4). In water applications, a recent study presented a rapid Cr(VI) detection method combining DPC colorimetry and smartphone technology.45 The proposed DPC test in our study is optimal for dried turmeric roots with greater than 5 mg Pb/kg and spice powders containing greater than 1000 mg Pb/kg; however, increasing the number of samples, spice types, and users will continue to improve the robustness of the qualitative data and approximations of detection limits. Here, we were able to distinguish Pb-rich and Pb-free spices to varying degrees depending on the spice type. Unlike laboratory analyses, the color changing test was qualitative and exposed spice adulteration by the eye, which has the potential to empower individuals (if packaged into a kit) to reduce personal health threats. By pairing the pXRF with DPC, we can measure Pb concentrations and decipher Pb speciation (PbCrO4) without necessitating ICP-MS for quantification or molar Pb/Cr ratios (Table 2). We recommend DPC for Pb detection on turmeric roots. Further studies could address modifications to the DPC method to quantify Cr(VI) concentrations in spices by UV–vis spectrophotometry or possibly using smartphone-based image analysis software,45 which would obviate the need for laboratory instruments and improve feasibility for public use. Some anticipated challenges may be (1) the complex spice-dependent matrices, which may influence Cr(VI) reduction, interfere with DPC reaction, or confound color measurements and (2) the presence of minor Pb phases, particularly for approximating Pb concentrations.

Acknowledgments

This research was funded by the King Center on Global Development at Stanford University. We thank Emily Nash, Dinsha Mistree, and Bret Ericson for sharing spice samples used in this study. We appreciate discussions with Prof. Alexander van Geen while developing a sodium rhodizonate method to detect Pb in spices. We are grateful to our colleagues Alexis Wilson, Ethan Li, Anesta Kothari, Manu Prakash, Karrie Weaver, Katie Dunn, Eric Sperling, Juan Lezama Pacheco, and Guangchao Li for their laboratory and analytical support.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.2c03241.

  • Alternative Pb detection methods; spice sample descriptions, chemical concentrations, and calculated molar Pb/Cr ratios; simple linear regression data for Pb concentrations measured by pXRF and ICP-MS; Deming regression data for method comparison (pXRF and ICP-MS) to measure Pb concentrations; cost analysis of study methods; Pb concentrations measured using different pXRF analyzers; schematic of DPC colorimetric assay; photograph examples of color change using the DPC method with ethanol versus methanol in the colorimetric reagent; fitted OLS linear regression lines for Pb concentrations in spice powders and dried roots using pXRF and ICP-MS; OLS regression analyses based on the spice powder type; Deming regression analyses based on spice powder types; Cr concentrations in spice powders and dried roots measured by pXRF and ICP-MS; photograph examples of color changes using the DPC method on dried turmeric roots; photograph examples of slight color changes observed upon DPC addition in turmeric powder samples; photograph examples of final color observations for low, medium, and high color rankings for each spice powder type; and UV–Vis measurements of select DPC-spiked turmeric powders compared to turmeric–pigment mixtures (PDF)

Author Present Address

# School of Architecture, Civil, and Environmental Engineering, EPFL, 1015 Lausanne, Switzerland

The authors declare no competing financial interest.

Supplementary Material

es2c03241_si_001.pdf (1.7MB, pdf)

References

  1. Ishida M. L.; Greene V.; King T.; Sheridan R.; Luker J.; Oglesby D. V.; Trodden J.; Greenberg J.. Regulatory Policies for Heavy Metals in Spices – a New York Approach. J. Regul. Sci. 2022, 10, 1–12. 10.21423/jrs-v10i1ishida [DOI] [Google Scholar]
  2. Hore P.; Alex-Oni K.; Sedlar S.; Nagin D. A Spoonful of Lead: A 10-Year Look at Spices as a Potential Source of Lead Exposure. J. Publ. Health Manag. Pract. 2019, 25, S63–S70. 10.1097/PHH.0000000000000876. [DOI] [PubMed] [Google Scholar]
  3. Cowell W.; Ireland T.; Vorhees D.; Heiger-Bernays W. Ground Turmeric as a Source of Lead Exposure in the United States. Public Health Rep. 2017, 132, 289–293. 10.1177/0033354917700109. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Kákosy T.; Hudák A.; Náray M. Lead Intoxication Epidemic Caused by Ingestion of Contaminated Ground Paprika. J. Toxicol. Clin. Toxicol. 2008, 34, 507–511. 10.3109/15563659609028008. [DOI] [PubMed] [Google Scholar]
  5. Ericson B.; Gabelaia L.; Keith J.; Kashibadze T.; Beraia N.; Sturua L.; Kazzi Z. Elevated Levels of Lead (Pb) Identified in Georgian Spices. Ann. Global Health 2020, 86, 1–6. 10.5334/AOGH.3044. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Codex Alimentarius Commission . General Standard for Contaminants and Toxins in Food and Feed, 1995. CXS 193-1995.
  7. List of 155 Products Brought under Mandatory Certification Marks Scheme. Turmeric Powder BDS 991: 2001, 2012.
  8. Spices and Condiments—Turmeric, Whole and Ground—Specification: New Delhi, India, 2010.
  9. Plotto A.Turmeric; Post-Production Management, 2004. [Google Scholar]
  10. Cowell W.; Ireland T.; Vorhees D.; Heiger-Bernays W. Ground Turmeric as a Source of Lead Exposure in the United States. Public Health Rep. 2017, 132, 289. 10.1177/0033354917700109. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Guidance for Industry: Lead in Candy Likely to Be Consumed Frequently by Small Children. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/guidance-industry-lead-candy-likely-be-consumed-frequently-small-children. FDA-2005-D-0084, 2018.
  12. Gleason K.; Shine J. P.; Shobnam N.; Rokoff L. B.; Suchanda H. S.; Ibne Hasan M. O. S.; Mostofa G.; Amarasiriwardena C.; Quamruzzaman Q.; Rahman M.; Kile M. L.; Bellinger D. C.; Christiani D. C.; Wright R. O.; Mazumdar M. Contaminated Turmeric Is a Potential Source of Lead Exposure for Children in Rural Bangladesh. J. Environ. Public Health 2014, 2014, 730636. 10.1155/2014/730636. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Forsyth J. E.; Weaver K. L.; Maher K.; Islam M. S.; Raqib R.; Rahman M.; Fendorf S.; Luby S. P. Sources of Blood Lead Exposure in Rural Bangladesh. Environ. Sci. Technol. 2019, 53, 11429. 10.1021/ACS.EST.9B00744. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Kappel M.; Kraushaar V.; Mehretu A.; Slater W.; Marquez E. Notes from the Field: Childhood Lead Poisoning Associated with Turmeric Spices — Las Vegas, 2019. MMWR Morb. Mortal. Wkly. Rep. 2021, 70, 1584–1585. 10.15585/mmwr.mm7045a4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Woolf A. D.; Woolf N. T. Childhood Lead Poisoning in 2 Families Associated with Spices Used in Food Preparation. Pediatrics 2005, 116, e314 10.1542/PEDS.2004-2884. [DOI] [PubMed] [Google Scholar]
  16. Lin C. G.; Schaider L. A.; Brabander D. J.; Woolf A. D. Pediatric Lead Exposure From Imported Indian Spices and Cultural Powders. Pediatrics 2010, 125, e828–e835. 10.1542/PEDS.2009-1396. [DOI] [PubMed] [Google Scholar]
  17. Budtz-Jørgensen E.; Bellinger D. C.; Lanphear B. P.; Grandjean P.; Hornung R.; Khoury J.; Yolton K.; Baghurst P.; Canfield R. L.; Dietrich K. N.; Bornschein R.; Greene T.; Rothenberg S. J.; Needleman H. L.; Schnaas L.; Wasserman G.; Graziano J.; Roberts R. An International Pooled Analysis for Obtaining a Benchmark Dose for Environmental Lead Exposure in Children. Risk Anal. 2013, 33, 450–461. 10.1111/J.1539-6924.2012.01882.X. [DOI] [PubMed] [Google Scholar]
  18. Lanphear B. P.; Hornung R.; Khoury J.; Yolton K.; Baghurst P.; Bellinger D. C.; Canfield R. L.; Dietrich K. N.; Bornschein R.; Greene T.; Rothenberg S. J.; Needleman H. L.; Schnaas L.; Wasserman G.; Graziano J.; Roberts R. Low-Level Environmental Lead Exposure and Children’s Intellectual Function: An International Pooled Analysis. Environ. Health Perspect. 2005, 113, 894–899. 10.1289/EHP.7688. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Tong S.; von Schirnding Y. E.; Prapamontol T. Environmental Lead Exposure: A Public Health Problem of Global Dimensions. Bull. W. H. O. 2000, 78, 1068. 10.1590/S0042-96862000000900003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Röllin H. B.; Rudge C. V. C.; Thomassen Y.; Mathee A.; Odland J. Levels of Toxic and Essential Metals in Maternal and Umbilical Cord Blood from Selected Areas of South Africa—Results of a Pilot Study. J. Environ. Monit. 2009, 11, 618–627. 10.1039/B816236K. [DOI] [PubMed] [Google Scholar]
  21. CDC Updates Blood Lead Reference Value for Children | CDC Online Newsroom | CDC. https://www.cdc.gov/media/releases/2021/p1028-blood-lead.html (accessed Jan 12, 2022).
  22. Forsyth J. E.; Nurunnahar S.; Islam S. S.; Baker M.; Yeasmin D.; Islam M. S.; Rahman M.; Fendorf S.; Ardoin N. M.; Winch P. J.; Luby S. P. Turmeric Means “Yellow” in Bengali: Lead Chromate Pigments Added to Turmeric Threaten Public Health across Bangladesh. Environ. Res. 2019, 179, 108722. 10.1016/J.ENVRES.2019.108722. [DOI] [PubMed] [Google Scholar]
  23. Döka O.; Bicanic D.; Szöllösy L. Rapid and Gross Screening for Pb3O4 Adulterant in Ground Sweet Red Paprika by Means of Photoacoustic Spectroscopy. Instrum. Sci. Technol. 1998, 26, 203–208. 10.1080/10739149808002693. [DOI] [Google Scholar]
  24. Angelon-Gaetz K. A.; Klaus C.; Chaudhry E. A.; Bean D. K. Lead in Spices, Herbal Remedies, and Ceremonial Powders Sampled from Home Investigations for Children with Elevated Blood Lead Levels — North Carolina, 2011–2018. MMWR Morb. Mortal. Wkly. Rep. 2019, 67, 1290–1294. 10.15585/MMWR.MM6746A2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Galvin-King P.; Haughey S. A.; Elliott C. T. Herb and Spice Fraud; the Drivers, Challenges and Detection. Food Control 2018, 88, 85–97. 10.1016/J.FOODCONT.2017.12.031. [DOI] [Google Scholar]
  26. Govindarajan V. S.; Stahl W. H. Turmeric - Chemistry, Technology, and Quality. Crit. Rev. Food Sci. Nutr. 1980, 12, 199–301. 10.1080/10408398009527278. [DOI] [PubMed] [Google Scholar]
  27. Rees N.; Fuller R.. The Toxic Truth: Children’s Exposure to Lead Pollution Undermines a Generation of Future Potential, 2020.
  28. Erasmus S. W.; van Hasselt L.; Ebbinge L. M.; van Ruth S. M. Real or Fake Yellow in the Vibrant Colour Craze: Rapid Detection of Lead Chromate in Turmeric. Food Control 2021, 121, 107714. 10.1016/J.FOODCONT.2020.107714. [DOI] [Google Scholar]
  29. Paranthaman R.; Moses J. A.; Anandharamakrishnan C. Development of a Method for Qualitative Detection of Lead Chromate Adulteration in Turmeric Powder Using X-Ray Powder Diffraction. Food Control 2021, 126, 107992. 10.1016/J.FOODCONT.2021.107992. [DOI] [Google Scholar]
  30. Markey A. M.; Clark C. S.; Succop P. A.; Roda S. Determination of the Feasibility of Using a Portable X-Ray Fluorescence (XRF) Analyzer in the Field for Measurement of Lead Content of Sieved Soil. J. Environ. Health 2008, 70, 24. [PubMed] [Google Scholar]
  31. Radu T.; Diamond D. Comparison of Soil Pollution Concentrations Determined Using AAS and Portable XRF Techniques. J. Hazard. Mater. 2009, 171, 1168–1171. 10.1016/J.JHAZMAT.2009.06.062. [DOI] [PubMed] [Google Scholar]
  32. Landes F. C.; Paltseva A.; Sobolewski J. M.; Cheng Z.; Ellis T. K.; Mailloux B. J.; van Geen A. A Field Procedure to Screen Soil for Hazardous Lead. Anal. Chem. 2019, 91, 8192–8198. 10.1021/ACS.ANALCHEM.9B00681. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Rouillon M.; Taylor M. P. Can Field Portable X-Ray Fluorescence (PXRF) Produce High Quality Data for Application in Environmental Contamination Research?. Environ. Pollut. 2016, 214, 255–264. 10.1016/J.ENVPOL.2016.03.055. [DOI] [PubMed] [Google Scholar]
  34. Rouillon M.; Taylor M. P.; Dong C. Reducing Risk and Increasing Confidence of Decision Making at a Lower Cost: In-Situ PXRF Assessment of Metal-Contaminated Sites. Environ. Pollut. 2017, 229, 780–789. 10.1016/J.ENVPOL.2017.06.020. [DOI] [PubMed] [Google Scholar]
  35. Tiwari S.; Deb M. K.; Sen B. K. Cloud Point Extraction and Diffuse Reflectance-Fourier Transform Infrared Spectroscopic Determination of Chromium(VI): A Probe to Adulteration in Food Stuffs. Food Chem. 2017, 221, 47–53. 10.1016/J.FOODCHEM.2016.10.034. [DOI] [PubMed] [Google Scholar]
  36. Ravansari R.; Wilson S. C.; Tighe M. Portable X-Ray Fluorescence for Environmental Assessment of Soils: Not Just a Point and Shoot Method. Environ. Int. 2020, 134, 105250. 10.1016/J.ENVINT.2019.105250. [DOI] [PubMed] [Google Scholar]
  37. Kalnicky D. J.; Singhvi R. Field Portable XRF Analysis of Environmental Samples. J. Hazard. Mater. 2001, 83, 93–122. 10.1016/S0304-3894(00)00330-7. [DOI] [PubMed] [Google Scholar]
  38. Bartlett R. J.; James B. R.. Chromium. In Methods of Soil Analysis. Part 3. Chemical Methods; Soil Science Society of America and American Society of Agronomy: Madison, WI 53711, USA, 1996; pp 683–701. [Google Scholar]
  39. Hess E.; Splichal P.. Environmental Technology Verification Report: Field Portable X-Ray Fluorescense Analyzer - SCITEC, MAP Spectrum Analyzer; Washington, DC, 1998. EPA/600/R-97/147 (NTIS PB2001-101792).
  40. Martin R. F. General Deming Regression for Estimating Systematic Bias and Its Confidence Interval in Method-Comparison Studies. Clin. Chem. 2000, 46, 100–104. 10.1093/CLINCHEM/46.1.100. [DOI] [PubMed] [Google Scholar]
  41. Garcia E.; Cabrera C.; Lorenzo M. L.; López M. C. Chromium Levels in Spices and Aromatic Herbs. Sci. Total Environ. 2000, 247, 51–56. 10.1016/S0048-9697(99)00467-2. [DOI] [PubMed] [Google Scholar]
  42. Feigl F.; Suter H. A. Analytical Use of Sodium Rhodizonate. Ind. Eng. Chem. 1942, 14, 840–842. 10.1021/i560110a034. [DOI] [Google Scholar]
  43. Sudhabindu K.; Samal L. C. Common Adulteration in Spices and Do-at-Home Tests to Ensure the Purity of Spices. Food Sci. Rep. 2020, 1, 66–68. [Google Scholar]
  44. FSSAI . Quick Test for Some Adulterants in Food: Instruction Manual—Part II (Methods for Detection of Adulterants), 2012.
  45. Bamane S. D.; Bhojwani V.; Balkunde P. L.; Bhattacharya M.; Gupta I.; Mohapatra A. K.; Shekhar A.; Singh A. Smartphone-Enabled Field Monitoring Tool for Rapid Hexavalent Chromium Detection in Water. Anal. Bioanal. Chem. 2021, 413, 3455–3469. 10.1007/s00216-021-03291-x. [DOI] [PubMed] [Google Scholar]

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Supplementary Materials

es2c03241_si_001.pdf (1.7MB, pdf)

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