Green algae, risks to surrounding populations, walkers and workers

Assessment of the risks associated with gaseous emissions from green algae for the health of surrounding populations, walkers and workers

Every summer for more than 30 years, massive quantities of green algae have been washing up on parts of the French coastline. Once washed up on beaches, these algae deposits decompose and produce large quantities of gases, especially hydrogen sulfide (H2S), potentially exposing walkers, local residents and workers required to collect these algae,to risks. Following a formal request made by the French authorities as part of the National Green Algae Control Plan, the Agency assessed the risks associated with gaseous emissions from green algae for the health of surrounding populations, walkers and workers. This work resulted in two opinions and one report.

Episodes of massive proliferation of macro-algae on the coasts and beaches of Europe have been reported in the scientific literature as early as 1905 on the Irish coast. This phenomenon seems to have increased over the past forty years. The proliferation of these algae is mainly linked to the presence of nitrates in the water generated by human activities (particularly agriculture), and the shape of the coastline (bays).

Once washed up on the beaches, these massive deposits of algae decompose. During the decomposition process, large quantities of gases are released, including hydrogen sulfide (H2S) which may cause disagreeable smells and health problems for walkers and local residents. To remedy this situation, the algae are removed from some beaches, and are then processed on the land. These various steps expose workers to these gases.

The work of the Agency

Following an urgent formal request by the health authorities in February 2010 under the National Green Algae Control Plan, the Agency initially providedrecommendations for professionals involved throughout the algae elimination chain.

In order to limit emissions due to their decay, the Agency stated that these algae should be collected while still "fresh", i.e. within 24 hours, or at most 36 hours, of their washing up on the beaches, and should then be processed within 48 hours. Beyond these time limits, the emissions may be such that collecting, transporting and treating the algae would require highly restrictive means of protection. Regardless of the state of decomposition of the algae masses, workers should be equipped with hydrogen sulfide (H2S) detectors and should mark the collection and storage sites in order to keep walkers away.

Following this first Opinion, and to better characterise exposures, during the summer of 2010 ANSES carried out measurements of the gas emitted by the green algae during decay. On this basis a Report and Opinion supplementing the Agency’s first recommendations were produced in spring 2011. This work reinforced many of the recommendations made in 2010. Firstly, ANSES recalled that by preventing the proliferation of green algae, risk situations due to masses of beached rotting green algae wouldde factobe limited.

To avoid decaying algae and the associated gas emissions, ANSES pointed out that, in accordance with its earlier recommendations, the collection, transportation and management of algae in treatment centres should take place as soon as possible. The available observations provide insufficient information on the exact interval after which fermentation gas emissions become significant, especially given the considerable number of parameters influencing this decomposition. The data, however, indicate that beyond 48 hours, it may be impossible to avoid risk situations.

The Agency also recommends favouring mechanical removal and indicates that this should be carried out under conditions that minimise exposure of the public. Marking collection sites is thus advocated by the Agency.

For some beaching sites where access for the purpose of collection is impossible, and which thereby constitute areas at risk, the Agency recommends that information be made available to users, walkers and local residents.

For the professionals involved in the process of collection, transportation, and processing of green algae, regardless of their status and including seasonal staff, ANSES recommends in particular the wearing of individual portable detectors for hydrogen sulfide (H2S). The Agency also recommends that these personnel receive appropriate information and training, and their exposure be noted in their medical records.

Finally, because the expert appraisal conducted by ANSES was constrained by incomplete knowledge in some areas, the Agency has recommended the acquisition of further knowledge to enable better characterisation of such gas emissions by green algae and their changes over time, so as to better understand exposure and the toxicity of the various substances emitted, and to make further advances in assessment of the risks associated with green algae.