Inorganic Arsenic in holopelagic Sargassum spp. Stranded in the Mexican Caribbean: Seasonal Variations and Comparison With International Regulations and Guidelines

Overview

Ortega-Flores et al. measured inorganic arsenic in stranded holopelagic Sargassum biomass from the Mexican Caribbean over a full seasonal cycle. The same sample set had total arsenic reported previously, and this paper adds inorganic arsenic (iAs) by morphotype and season. The values are raw stranded biomass on a dry-weight basis, not washed or processed seaweed food.

Key numbers

The abstract and conclusion summarize the full dataset as iAs 12.7 to 62.9 mg kg-1 dw, representing 14.1% to 81.7% of TotAs. The introduction states that the same samples had previously reported TotAs 9.5 to 255 mg kg-1 dw.

Section 3.1 reports iAs by morphotype in mg kg-1 dw:

Section 3.1 also reports seasonal iAs summaries in mg kg-1 dw:

Section 3.2 reports annual mean TotAs of 91.8 mg kg-1 dw for S. natans VIII, 90.7 mg kg-1 dw for S. fluitans, and 68.2 mg kg-1 dw for S. natans I. The highest TotAs concentrations occurred during the rainy season, with August values above 200 mg kg-1 dw for S. natans VIII and S. fluitans.

The iAs proportion increased over the study period. Section 3.2 reports iAs:TotAs ranges of 14-32% for June-September and 56-80% for March-May. It also states that iAs proportions remained below 40% in samples with TotAs above 100 mg kg-1 dw, whereas iAs proportions over 50% occurred in samples with TotAs below 50 mg kg-1 dw.

Table 1 summarizes the present study row as stranded Mexican Caribbean S. fluitans, S. natans I, and S. natans VIII with iAs 12.7-62.9 mg kg-1, TotAs 21.7-255 mg kg-1, and iAs:TotAs 14-82%.

Methods (brief)

Samples were collected monthly from June 2018 to May 2019 at Puerto Morelos, Quintana Roo, Mexico. Raw stranded biomass was collected from ten 0.5 x 0.5 m² quadrats along a 50 m transect, classified into the three morphotypes, visually cleaned of sand by hand, oven-dried at 60°C for 24 h, crushed with an agate mortar, and stored for analysis. TotAs was measured by HG-AAS in the earlier Ortega-Flores et al. 2022 work, with IAEA-392 algae reference-material recovery greater than 90% and arsenic (As) LoD 0.5 mg kg-1. For iAs, dried ground biomass was extracted in ultrapure water under sonication for 30 min at a 1:100 sample/water mass ratio, centrifuged, and analyzed by anodic stripping voltammetry using standard additions of As(V). The iAs method LoD was 0.2 µg L-1, precision was ~6%, NMIJ CRM 7405-b Sargassum fusiforme was used for accuracy control, and each extract was analyzed in triplicate.

Implications

This source is high-value inorganic-arsenic evidence for raw stranded Sargassum biomass that may enter seaweed valorisation streams. It should not be treated as a ready-to-eat seaweed food result without preserving the raw stranded-biomass matrix and dry-weight basis. Downstream extraction should keep TotAs and iAs distinct, and should preserve the morphotype and seasonal stratification where row fit permits.

Related evidence

• Seaweed/kelp foods (nori, wakame, kombu, dulse — as food products)
• Ingredient class — algae/seaweed-based
• Seaweed
• Arsenic, Total
• Arsenic, Inorganic

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