Since August 2014, coastal regions of the Caribbean and French Guiana have experienced successive waves of accumulated Sargassum seaweed on their coasts. Despite clean-up efforts, the seaweed continues to decompose on the shore. This decomposition produces hydrogen sulfide (H2S) gas, which can sometimes be detected in high concentrations. Reports by physicians in conjunction with health effects perceived by people exposed to H2S, as well as complaints from the general public regarding unpleasant odours, have increased sharply.
The Ministries of health, the environment and labour therefore asked ANSES to conduct an expert assessment of the gases produced by decaying Sargassum seaweed and emitted into the ambient air in the Caribbean and in French Guiana. An opinion published in March 2016 presented the initial findings and recommendations of the Agency. It emphasised the necessity of collecting the seaweed without delay and recommended that measures be taken to protect the workers in charge of collecting, transporting and processing the seaweed. It also recommended that the local population be informed that the seaweed should not be handled.
The Agency pursued its work by examining the ecology of Sargassum seaweed, as well as its chemistry, biodegradation profile and the kinetics of H2S emissions and that of other substances, especially during decay of the seaweed following its accumulation on the shore.
The Agency’s recommendations
The conclusions of the expert assessment published today have led the Agency to reiterate the recommendations to be implemented regarding preventive measures for the health risks of exposure to H2S:
- limit exposure by the general public, by regularly collecting the seaweed accumulated on the coast, by marking off collection sites, and by informing the population of the health risks of exposure to H2S;
- limit worker exposure through use of H2S detectors, mechanical means of collection whenever possible, personal protective equipment, training and informing workers about the risks of exposure to H2S and implementing a traceability system for work that exposes workers.
In addition, the expert assessment published today reveals that Sargassum seaweed has a high capacity for accumulating heavy metals - arsenic and cadmium in particular - which may pose a risk to human health and to the environment. Therefore, the Agency recommends prohibiting any possible food or feed uses of this seaweed until more in-depth studies can be conducted on the heavy metal contamination of seaweed.
The Agency also recommends pursuing research on:
- exposure linked to accumulated Sargassum seaweed and effects on human health;
- the toxicity of H2S, in particular the effects of chronic exposure to low doses of H2S;
- the indirect environmental and health impact of accumulated Sargassum seaweed (seaweed composition, presence of heavy metals);
- the proliferation of seaweed and its accumulation on dry land in the French départements in the Americas.