Skip to main content

Overcoming barriers in estimating toxicity of arsenic species in seaweed

Periodic Reporting for period 1 - SilhouetteOfSeaweed (Overcoming barriers in estimating toxicity of arsenic species in seaweed)

Reporting period: 2015-04-01 to 2017-03-31

SilhouetteOfSeaweed contributes to consumer’s safety by overcoming barriers in estimating toxicity of arsenic in seaweed. The ocean covers 71% of the planet and for future sustainability and long term food security for a growing global population the need for using the ocean for food, e.g. seaweed, is increasing. Seaweed contains high amounts of arsenic, which can be found in different chemical forms (often called arsenic species) in the seaweed and one of these forms/species are arsenolipids. Arsenic can be toxic to humans and animals and is known to be carcinogenic, however, the toxicity depends on the arsenic species. The majority of the arsenic in seaweed is in the chemical form of arsenosugars, which are not acutely toxic, while other arsenic species are generally present in much lower concentrations. Recently the first data regarding the toxicity of arsenolipids has shown that they are as toxic as the most toxic chemical form of arsenic, the inorganic arsenic.
The production of arsenosugars most likely takes place within the seaweed itself, however, it is unclear where and how the arsenolipids are produced. There is a considerable lack of data on arsenolipids in seaweed products for human consumption. More research and information on arsenolipids are urgently needed to address and ensure the safety of seaweed used in food products. Currently, only few research groups worldwide work on arsenolipids partly due to difficulties associated with the measurements of these compounds.
The MCSA project SilhouetteOfSeaweed had two main scientific objectives. Firstly, to produce arsenolipid seaweed profiles in 4 different species of brown algae in 3 locations during 3 seasons in Iceland. Secondly, to use statistical evaluation and comparison of environmental conditions to e.g. make it possible to identify whether the seaweed could be harvested at specific conditions where the amount of toxic arsenic is at its lowest and thus minimises the risk of seaweed for human consumption.
SilhouetteOfSeaweed did fulfil its goal of producing valuable information on arsenolipids in seaweed.
a) Samples of four types of edible brown algae went through detailed arsenic speciation (speciation: An analytical technique to distinguish between the different arsenic compounds/species). The seaweed species investigated were all relevant for food production and included Alaria esculenta (AE), Saccharina latissima (SL), Ascophyllum nodosum (AN) and Fucus vesiculosus (FV). The arsenolipids accounted for 2-16% of the total arsenic. In comparison the toxic inorganic arsenic accounted for less than 1% of arsenic in the seaweed samples. Hence when considering the toxicity of arsenic in seaweed the arsenolipids may be a significant contributor. The arsenolipid speciation showed that the arsenolipid profile differed between the brown algae species where the majority of arsenolipids was in the form of arsenosugarphospholipids (AsPLs) for the AN and SL seaweed species with the remainder present as arsenohydrocarbons (AsHCs). On the other hand, the AE and FV seaweed species contained equal proportions of these two arsenolipid groups. Research indicates that AsHCs show high toxicity but currently no data exists on the toxicity of the AsPLs. This information is urgently needed for further toxicological assessment of the seaweed.
All the information on total arsenic, inorganic arsenic and the different arsenic species and fractions was compiled and statistical analysis carried out. Statistical analysis showed that the total arsenic was observed to be lowest during the summer months, however, such a trend was not consistent between species for the inorganic arsenic. Detailed statistical analysis showed that the arsenosugar composition differed by seaweed species but not by location. Further, it indicated that a specific arsenosugars seemed to be correlated with the total amount of polar arsenolipids.

b) Samples of seaweed were collected from the northern coast of the southern peninsula region of Iceland (January 2017). Approximately 30-40 individuals of Saccharina latissima and 15-20 individuals of Alaria esculenta were collected. SL grows such that the oldest section of the frond is at the end and the youngest is closest to the stipe, the old frond is constantly eroded by wave action and other environmental factors and this is particularly pronounced during summer when the growth is slowest, therefore it was important to sample in winter at a time where there was new growth. Saccharina latissima was divided into holdfast, stipe, young frond, old frond and sori (cluster of plant reproductive bodies; spores). The AE was divided into the following sections: Holdfast, stipe, midrib, frond and sporophyll (spore-bearing leaf).
These different sections of the seaweed were analysed for arsenolipid speciation, total arsenic and arsenosugar speciation. The seaweeds were rich in arsenolipids with the vast majority on the form of diverse AsPLs. Very little was found as AsHCs which differed from a certified seaweed reference material Hijiki which had approximately equal amounts of AsHCs and AsPLs. Additionally, the data showed an unequal distribution of the quantity of arsenolipids within the brown algae which is hypothesised to be dependent on the activity of the seaweed (e.g. growing) with higher AsPLs at high activity sections – a trend not seen e.g. for arsenosugars. This could prove to be a piece in the puzzle to understanding how and where arsenolipids are formed.

Main dissemination of the work to date:
• “What’s up with arsenic?” Video:
• ”Overcoming barriers in estimating toxicity of arsenic species in seaweed” Oral presentation, Chemistry departmental talk, University of Iceland.
• “Arsenic containing lipids in brown algae”, Oral presentations, Presented at ISAP Conference & COST action workshop
• “Arsenolipids are not evenly distributed within brown macro-algae Saccharina latissima“ Poster presentations, presented at MCAA conference & at RSC Twitter conference
SilhouetteOfSeaweed contributes important information and data to the necessary risk assessment needed for algae used for human consumption. The need for this information was underlined in the European Food Safety Authorities’ (EFSAs) Scientific Opinion on Arsenic in Food (2009). SilhouetteOfSeaweed contributes to Europe’s knowledge on arsenolipids. The data can be submitted to appropriate authorities, e.g. EFSA in case of a follow up Scientific Opinion on arsenic. The data and results may help shape future legislation on these toxic species. Furthermore, the innovation potential related to seaweed-based ingredients in food are huge as seaweed is considered an important untapped resource for new sustainable raw materials for food and food ingredients. Hence, this work will provide vital reference data to underpin the safety requirements for the marketing of these innovative seaweed-based food products in Europe.