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. 2023 Oct 17;13(1):17644.
doi: 10.1038/s41598-023-44685-4.

Evidence of elevated heavy metals concentrations in wild and farmed sugar kelp (Saccharina latissima) in New England

Brianna K Shaughnessy  1 , Brian P Jackson  2 , Jarrett E K Byrnes  3   4
Affiliations

Evidence of elevated heavy metals concentrations in wild and farmed sugar kelp (Saccharina latissima) in New England

Brianna K Shaughnessy et al. Sci Rep. .

Abstract

Seaweed farming in the United States is gaining significant financial and political support due to prospects to sustainably expand domestic economies with environmentally friendly products. Several networks are seeking appropriate synthesis of available science to both inform policy and substantiate the sector's sustainability claims. Significant knowledge gaps remain regarding seaweed-specific food hazards and their mitigation; a resource-intensive challenge that can inhibit sustainable policies. This is particularly concerning for rapidly expanding Saccharina latissima (sugar kelp) crops, a brown seaweed that is known to accumulate heavy metals linked to food hazards. Here, we present baseline information about concentrations of arsenic, cadmium, lead, and mercury, in both wild and farmed sugar kelp from the New England region. We interpret our findings based on proximity to potential sources of contamination, location on blade, and available heavy metals standards. Contrary to our expectations, high concentrations were widespread in both wild and farmed populations, regardless of proximity to contamination. We find, like others, that cadmium and arsenic consistently reach levels of regulatory concern, and that dried seaweeds could harbor higher concentrations compared to raw products. We also share unique findings that suggest some toxins concentrate at the base of kelp blades. Our results are one step towards aggregating vital data for the region to expand its seaweed farming footprint.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Geography of study area and potential contamination sources. Potential contamination sources are marked with red triangles and sample sites are marked with green circles. Numbers within the green circles coincide with Table 1, which contains more details regarding site locations and specification about contamination sources. The inset map shows the entire US east coast, with a red square highlighting our region of study. Anonymized sugar kelp farm sites fall within the southern and northern bounds of the red square. The map was created using the ‘tmap’ package in R Statistical Software v.4.0.4 http://www.R-project.org/.
Figure 2
Figure 2
Average total arsenic concentrations in wild sugar kelp. Average total arsenic concentrations (ppm) at the base (left panel) and distal tip (right panel) of sugar kelp blades at each of the ten wild kelp sample sites. Potential contamination sources are marked with red triangles. See Table 1 for more details regarding each site. Maps were created using the ‘tmap’ package in R Statistical Software v.4.0.4 http://www.R-project.org/.
Figure 3
Figure 3
Observed percent over MCL. Each sugar kelp sample’s observed percent (%) of the maximum contaminant level (MCL; vertical axis) set for each heavy metal in feed (see Table 2). A red dashed line represents 100% of the MCL. Results are grouped by site (horizontal axis) and blade location (purple = base of blade; green = mid blade; yellow = distal tip). Grey shaded boxes highlight farmed kelp samples, all other sites are ordered from South-to-North (left to right).
Figure 4
Figure 4
Average inorganic arsenic concentrations in wild sugar kelp. Average inorganic arsenic concentrations (ppm) at the base (left panel) and distal tip (right panel) of sugar kelp blades at each of the ten wild kelp sample sites. Potential contamination sources are marked with red triangles. See Table 1 for more details regarding each site. Maps were created using the ‘tmap’ package in R Statistical Software v.4.0.4 http://www.R-project.org/.
Figure 5
Figure 5
Average cadmium concentrations in wild sugar kelp. Average cadmium concentrations (ppm) at the base (left panel) and distal tip (right panel) of sugar kelp blades at each of the ten wild kelp sample sites. Potential contamination sources are marked with red triangles. See Table 1 for more details regarding each site. Maps were created using the ‘tmap’ package in R Statistical Software v.4.0.4 http://www.R-project.org/.
Figure 6
Figure 6
Pearson’s correlation coefficients. Observed Pearson’s correlation coefficients (horizontal axis) for heavy metals of interest, as well as phosphorus (vertical axis). All kelp samples were used for calculating coefficients (n = 117).
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