Mona Webber | Sargassum seaweed: what to do and what not to do with it
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Published:Sunday | April 9, 2023 | 12:50 AM
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In this 2021 photo, sargassum is seen along the shoreline of the Hellshire Beach in St Catherine.
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In this 2021 photo, sargassum is seen along the shoreline of the Hellshire Beach in St Catherine.
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All predictions for the 2023 sargassum season are that it will be the worst on record! Scientists out of Florida have been ‘sounding the alarm’ for over a month and National Environment and Planning Agency (NEPA) has repeatedly put a ‘Sargassum Advisory’ in one of our daily newspapers.
Although the excessive blooming of pelagic (floating) sargassum seaweed (normally confined to the Sargasso Sea) started in 2011, Jamaica did not experience damaging amounts until 2018. In 2018 the term ‘Great Atlantic Sargassum Belt’ (GASB) was coined when 20 million metric tons (MT) of the seaweed stretched 8,000 km across the Atlantic from the coast of Ghana to e Gulf of Mexico and Florida. In 2021 the quantities in May reached a new record for that month and by 2022, the GASB increased to a new record of 24 million MT! January 2023 was another record month with 8.7 million MT and so was March with approximately 13 million MT of algal biomass. Biomass estimates are provided monthly by the University of South Florida – USF, Optical Oceanography Laboratory.
SARGASSUM – THE ‘NEW NORMAL’
Yearly sargassum inundation, said to be the ‘new normal’, is now regarded as the single greatest threat to the Caribbean. Some of us continue to suggest that the seaweed could also present a great opportunity to develop new industries around this ‘new crop’. Researchers at MIT working in Dominican Republic have developed relatively cheap and efficient technologies to ‘reap’ sargassum which they ship using 40-foot containers to ‘markets’ outside of the Caribbean. High-value substances like alginates and bioactive compounds are being extracted from the algal bioms.
Currently, companies like Carbonwave have conducted extensive research and product development, generating biomaterials from sargassum seaweed. Their products range from vegan plant-based leather and rubber, cosmetic emulsifiers and biostimulants to using sargassum to make biochar (a high-carbon fine-grained material that can be used to improve soil fertility).
In the absence of such manufacturing technologies throughout most of the areas affected by sargassum (spanning West Africa to Mexico), many have explored using sargassum in agriculture, and even feed it in measured amounts to livestock as it is reputed to increase efficiency of the ruminant’s digestive system and reduce the production of methane, a normal byproduct of their digestion. Some have explored simply collecting and adding it to crops as compost or mulch.
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Pelagic sargassum studies in Jamaica began at the UWI in 2019 with esarch at Department of Chemistry (Dr Winklet Gallimore and then student Doleasha Davis with collaborators at the University of York), assessing the composition of sargassum to inform “valorisation pathways”. NEPA further requested assistance from the UWI to do exploratory research into the range of potential uses of sargassum. The thinking was that high-value sargassum products could potentially help fund sargassum control and management, including removal of the seaweed from our beaches. These early experiments at the UWI indicated that sargassum (like many brown algae) contains plant nutrients, alginates, natural anti-bacterial compounds and bioactive compounds with anti-proliferative properties (acting against certain cancer cells).
ARSENIC DANGER!
However, there is great danger in using unprocessed sargassum as fertiliser. It naturally contains high levels of inorganic arsenic. The UWI Chemistry team found arsenic values ranging from 58-65 ppm in sargassum collected around Jamaia i 2019.
While the Agency for Toxic Substances and Disease Registry (ASTDR) in 1985 gave the limit of inorganic arsenic in agricultural soils as 20 ppm, in 2010 the Food and Agriculture Organization (FAO) and World Health Organization lowered the provisional tolerable weekly intake of inorganic arsenic from 15 ppm of body weight to 3 ppm, due to evidence that lower levels of exposure to inorganic arsenic than previously thought could cause cancer. Studies indicate that continuing exposure to arsenic affects the circulatory system, potentially triggering cardiovascular disease and it has been classified as a group one carcinogen by the International Agency for Research on Cancer.
Researchers at the UWI have over the last three years been involved in a sargassum project titled ‘Teleconnected Sargassum risks across the Atlantic: building capacity for Transformational Adaptation in the Caribbean and West Africa (SARTRAC)’. The team included the UWI (DLS – Centre for Marine Sciences andMonaGeoinformatics, Jamaica; CERMES at Cave Hill, Barbados), University of York, University of Ghana and the University of Southampton (project lead – Prof Emma Tompkins from Southampton).
The findings of the section of the SARTRAC project tasked with exploring “Use of sargassum to generate benefits for developing countries in the Caribbean and Western Africa”, could help inform how to use or NOT use sargassum seaweed. And as we continue to do research, analysis and publishing we believe it is best to take the ‘precautionary approach’ and exercise great care in the direct use of pelagic sargassum seaweed.
SEED GERMINATION AND SEEDLING PRODUCTION
Experiments done under the SARTRAC project on seed germination of corn, tomatoes and scotch bonnet pepper indicated that sargassum/sawdust cocompost significantly improved percentage germination of seeds. Similarly, sargassum co-compost (sargassum mixed with sawdust) contained much reduced levels of arsenic (
Mangrove seedlings grown in pur sargssum compost added to potting sand, at the appropriate ratio, showed enhanced growth in the nursery. The mangrove plants contained relatively little arsenic (0.44 in leaves and 24 ppm in the roots), despite the pure compost having 202 ppm of arsenic. The research, while positive, indicated such high arsenic levels in the pure sargassum compost that the material cannot be added directly to restoration sites. Therefore, sargassum has utility for enhancing nursery seedling production or in contained processes like seedling germination.
USE FOR ADOBE BLOCKS/RED BRICKS
One interesting sargassum application that has been explored in Mexico and West Africa is the use of sargassum to make Adobe blocks. Also called mud bricks or red bricks, Adobe blocks are usually made by adding plant material (e.g. straw) to mud or soil that has a high clay content. Sargassum is now being used as the plant material to make Adobe blocks. The small bricks which are brown/red brown can be used in landscapng, tomake walkways or in some countries like Mexico, to build houses. Sargablocks, as they are called, could potentially be made by coastal communities in Jamaica for specialised uses.
USE IN BIOGAS PRODUCTION
Under the SARTRAC project, the Scientific Research Council’s, Wastewater Research and Management Unit was contracted to conduct biomethane experiments. The SRC used sargassum mixed with animal waste and was able to produce burnable gas, showing that 250,000 kg of sargassum (mixed in a specific ratio with animal waste) can produce one cubic metre/h of burnable biogas. Biodigestion of sargassum alone produced gas but it was not burnable. Farming communities often use the sludge remaining after biogas production as a fertiliser or soil additive and so at the end of our experiments the sludge was analysed for arsenic. Unfortunately, the sludge produced using sargassum contained up to 76 ppm of arsenic making it unsuitable for use on crops or soil. So while sargassum has potential or use n biogas generation (also shown in Barbados), the sludge produced as a byproduct is not suitable for use as fertiliser and should NOT be added to soils.
Although not directly researched, the tendency for the plants in our experiments to accumulate sargassum at the roots is suggesting that sargassum MUST NOT be used to grow crops like yam, dasheen or sweet potato (which are root tubers). Crops where the root of the plant is what is eaten could be very harmful due to potential arsenic accumulation in the root area of plants. We should also NOT add fresh or composted sargassum collected from the beach to our agricultural soils as this will make the soil useless for especially ‘root’ crops.
SARGASSUM IS NOT IRISH MOSS!
Coastal communities should also be advised NOT to collect sargassum and boil it into a drink as is done with ‘Irish moss’. Irish moss is from a group of marine red algae mostly from the genus Gracillaria. Sargassum seaweed is brown (golden brown) algae from the gens sargasum. The types of seaweed are NOT the same.
The prospects for coastal communities collecting and directly using sargassum are therefore not good. However, coastal communities could gain from collecting, drying and shipping sargassum to potential global markets. Experiments showed that one MT (1,000 kg) of sun-dried sargassum can yield 51 kg of alginates! We need to explore new opportunities in the global sargassum market and there is still hope that local manufacturing could develop around the product after arsenic removal (as has happened in other countries). Until then it is important that we let persons know what they can and cannot do with unprocessed sargassum.