Waves of stinky sargassum, a floating brown seaweed, have been washing up on Caribbean beaches for over a decade. In hopes of turning this natural trash into a treasure, sargassum has found use in agriculture to improve crop production organically. However, a June released report of a joint study between the World Wildlife Fund-Mexico and STINAPA Bonaire, showed vegetables grown in soil fertilized with sargassum had higher levels of arsenic and cadmium. These heavy metals can be toxic to humans and animals.
“Arsenic is already present in a lot of food sources and often in drinking water: long-term exposure can cause cancer. Our study only showed the presence of total arsenic: organic and inorganic. We did this study as all research mentioned heavy metals in sargassum and we were worried that using sargassum as compost or animal fodder without knowing whether the arsenic would be transferred to plants and/or animals. This is a call for the scientific world to do more in-depth studies,” says Bonaire-based marine biologist, Sabine Engel, who with Jessica Johnson, are both researchers for STINAPA and authored the report, Sargassum Fertilizer Transfers Heavy Metals to Vegetables.
To conduct their experiment, the researchers filled one planter box with 50/50 dried sargassum and potting soil and another with only potting soil. There were no significant physical differences between the plants. However, samples of vegetables grown in the sargassum-soil mix showed bok choy had 37 times, zucchini 21 times, and spinach 4 times more arsenic than their counterparts grown in plain potting soil. Cadmium levels were also higher in plants grown in sargassum-enriched soil. dcnanature.org/sargassum-fertilizer/