Elevated Concentrations of Metal(loids) in Seaweed and the Concomitant Exposure to Humans

Overview

Khandaker and colleagues measured 17 elements in cultivated Malaysian Eucheuma cottoni seaweed from Langkawi, Semporna, and Kota Belud. The study reports dry-weight concentrations in microgram per gram and estimates dietary intake, noncarcinogenic hazard, and carcinogenic risk for an assumed East Asian adult seaweed consumer. The paper labels chromium as Cr-VI and arsenic as As (III), but the analytical method was ICP-OES rather than a chromatographic speciation method.

Key numbers

Fresh seaweed samples were collected from Kota Belud and Semporna in March 2018 and from Pulau Dangli, Langkawi in September 2018. The authors collected 4 kg of fresh whole seaweed from each location, with samples obtained from at least four sublocations at each farming site. Table 3 reports location group sizes of LKW n = 3, SPN n = 3, and KBL n = 2.

Table 3 reports metal concentrations in microgram per gram as mean ± relative standard deviation (RSD), with range in parentheses:

Table 2 reports LoD values in µg/kg: Pb 11.31, Cd 2.15, Al 3.08, Mn 1.20, Cu 1.89, Zn 0.89, Fe 1.01, As 14.51, Ni 1.97, Cr 4.66, Ag 0.35, and Si 37.94.

Table 1 reports CRM 7405-a recovery checks for HMT-relevant analytes: Pb certified 0.43 ± 0.03 mg/kg, recovered 0.45 ± 0.04, recovery 104.7%; Cd certified 0.79 ± 0.02, recovered 0.75 ± 0.03, recovery 94.9%; Al certified 147 ± 7, recovered 141 ± 6, recovery 95.9%; As certified 35.8 ± 0.9, recovered 35.26 ± 0.88, recovery 98.5%; Ni certified 2.2 ± 0.1, recovered 2.3 ± 0.08, recovery 104.6%; Cr certified 3.4 ± 0.1, recovered 3.29 ± 0.09, recovery 96.8%.

Table 4 estimates daily intake in Microgram Per Kilogram/kg/Day for an assumed East Asian adult consuming Malaysian seaweed at 10 g/adult/day. The paper’s equation 2 cites a default adult body weight of 70 kg, but the East Asian risk assessment uses 65 kg as the nominal body weight; back-calculating Table 4 values from Table 3 concentrations confirms the published intakes were computed with 65 kg. Mean daily intakes were Pb 1.2, Cd 0.3, As 0.7, Ni 1.5, Cr-VI 4.0, Al 6.3, and Ag 0.03.

Table 5 reports noncarcinogenic and carcinogenic risk estimates for the same assumed intake scenario: Pb HQ 0.203 and LTCR 6.08 × 10−4; Cd HQ 0.171 and LTCR 4.89 × 10−3; As HQ 1.547 and LTCR 5.22 × 10−2; Ni HQ 0.053 and LTCR 1.34 × 10−1; Cr-VI HQ 0.912 and LTCR 1.03 × 10−1. The summed hazard index is 4.38, and the summed lifetime carcinogenic risk is 2.94 × 10−1.

Methods (brief)

Fresh Eucheuma cottoni seaweed was collected from three Malaysian farming locations, washed, cut, dried at 70 °C to constant dry weight, blended, and sieved through a 25 µm mesh. For each analysis, 0.5 g dw was digested with 10 mL HNO3 and 3 mL HCl on a hot plate at 100 °C for 2 h, filtered through Whatman No. 41 paper, diluted with 10 mL deionized water, and analyzed by ICP-OES (Optima 5300DV, PerkinElmer). Calibration used Agilent multi-element standard solution 2A in 5% HNO3; validation used NIST SRM 1400 and NMIJ CRM 7405-a. The authors state each sample was analyzed in duplicate.

Implications

This source provides dry-weight occurrence data for cultivated Malaysian seaweed in the seaweed-kelp-foods product row. It is directly relevant for Pb, Cd, Al, and Ni; arsenic and chromium values are reported elementally by ICP-OES and routed as tAs and Cr rather than the source’s claimed As (III) and Cr-VI species labels (see Verification notes). The paper’s risk calculations are source-reported scenario estimates, not HMTc threshold calculations.

Verification notes

• PDF text extracted with pdftotext -layout; title page, sample preparation, Tables 1-5, arsenic-speciation discussion, and conclusions were readable.
• DOI 10.3390/foods10020381, raw handle MFK_khandaker2021, and cite-key checks found no existing source page before creation.
• Table 3 concentration values, Table 2 LoDs, Table 1 recovery checks, Table 4 intake estimates, and Table 5 risk estimates were checked against extracted text. Units are preserved as microgram per gram, µg/kg, mg/kg, and Microgram Per Kilogram/kg/Day; no conversion was performed.
• Speciation: the source labels the arsenic row As (III) and chromium row Cr-VI in Table 3. The analytical method, however, was ICP-OES with no chromatographic step. The arsenic-speciation discussion on page 11 acknowledges that ICP-OES provides elemental 75As rather than a particular species and infers inorganic As(III) only by analogy to Zhao et al. [45], who used HPLC-ICP-MS on different seaweed samples. The chromium discussion on page 10 provides no chromatographic speciation evidence at all; Cr-VI is asserted on toxicological grounds. The metals: frontmatter therefore routes this paper as tAs and Cr (the species the method actually measured), while the body preserves the source’s own As (III) and Cr-VI labels in Table 3 transcription.
• Source-internal anomalies preserved without correction: (a) Table 3’s overall mean for Cr-VI is reported as 26.0 µg/g, which is not consistent with the LKW/SPN/KBL location means of 40.57, 30.3, and 40.15; an n-weighted mean of the three locations is approximately 36.6, not 26.0. (b) The arsenic-speciation paragraph on page 11 states “SPN (1.6 ± 5.86 µg/g)” while Table 3 reports SPN As (III) as 6.3 ± 2.86. Table 3 was used as the authoritative source for both values in this page.
• Brand firewall: no sampled product brands are attached to contamination values. Instrument and standard vendors appear only in Methods.
• Frontmatter slugs were checked against docs/gpt-collaboration/taxonomy-snapshot.md; no new slug was invented.

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