Sargassum seaweed washed up on beaches: immediate measures to be taken to limit the exposure of workers and residents

Since August 2014, successive waves of Sargassum seaweed have been washing up on the coastlines of the French départements in the Americas (the French West Indies and French Guiana). Despite the successive efforts to clean it up, this seaweed decomposes in situ. This leads to the production of hydrogen sulphide (H₂S), a toxic strong-smelling gas that may be detected at high concentrations.

Monitoring of complaints and health disorders, measuring of exposure in the affected populations, and prevention and information measures were established in 2014. The monitoring unit of the Martinique Regional Health Agency (ARS) has observed a significant increase in the number of medical consultations relating to the health effects suffered by the population chronically exposed to H₂S. It also records doctors' reports, and complaints from residents, individuals or establishments open to the public, in areas downwind from the washed-up seaweed.

In this context, ANSES received a formal request from the Ministries of Health, the Environment and Labour to conduct an expert appraisal on the issue of emanations from decomposing Sargassum seaweed in the French West Indies and French Guiana. The Opinion published today presents the initial findings of the Agency's expert appraisal: a review of current knowledge on the health effects of H₂S, as well as short-term recommendations on the preventive measures to be implemented to protect workers involved in collecting, transporting and processing the seaweed.

For this work, the Agency drew in particular on the knowledge acquired during earlier studies relating to green algae washing up on the French coastline, which is broadly transposable.

Agency conclusions and recommendations

Individuals are mainly exposed to H₂S via the respiratory route. Absorption via the oral and dermal routes is possible, but this only makes a small contribution to overall exposure.

While the effects in humans related to acute exposure (i.e. for a short period of time) are well documented (neurological and respiratory effects whose severity increases with the concentration of exposure), less is known about the effects associated with H₂S exposure over longer periods. The first effects observed are irritation of the upper airways and eyes. Neurobehavioural effects and neurological symptoms (headache, loss of balance and memory) are suspected. Moreover, on the basis of current knowledge and in light of the few studies available, no conclusions can be drawn as to the carcinogenic potential of H₂S. The strong unpleasant odours associated with this gas should also be noted.

In light of the data currently available, the Agency believes that its recommendations on prevention, made during an earlier expert appraisal concerning workers in contact with decomposing green algae on the coasts of Brittany (lien vers l’avis ou l’article relatif),should be considered for workers in contact with Sargassum seaweed.

The Agency thus recommends:

• immediately implementing the regular, systematic collection of seaweed washed up on the coast;
• clearly defining the seaweed collection zones and limiting access to operators alone;
• informing the population of the health risks associated with exposure to H₂S, especially near  beaches where seaweed is decomposing. In addition, the population needs to be informed that they must not handle the seaweed.

During seaweed collection, transport and processing operations, ANSES recommends:

• equipping each worker, including those inside machinery cabs, with a portable H₂S detector, sited near the respiratory tract;
• getting workers to wear personal protective equipment, including gloves, boots and anti-gas filtering half-masks, or hoods with forced ventilation when the H₂S concentration exceeds 10 ppm;
• prioritising mechanical collection, while considering the environmental constraints;
• providing regular worker training and information;
• setting up traceability for work involving exposure.

The Agency also believes that it would be useful to establish a prospective epidemiological study focusing particularly on population exposure situations at the local level, as this would increase knowledge of the health effects associated with chronic exposure to H₂S at low doses.

Lastly, the Agency is continuing its expert appraisal work on this topic by investigating the ecology of Sargassum seaweed, its chemistry and biodegradation as well as the emission kinetics of H₂S and other substances, especially when this seaweed decomposes after washing up on the shore.