Date: Mon 15 Jul 2019
Source: Daily Mail [edited]
Holidaymakers heading to France have been warned about a green tide of potentially toxic sea lettuce possibly having killed 2 men in under a week. An 18 year old oyster farmer died in Morlaix Bay last Saturday [6 Jul 2019], and a 70 year old retiree passed away in Douarnenez Bay on Tuesday [9 Jul 2019].
The Brittany beauty spots where the unidentified men apparently succumbed to heart attacks "in minutes" are hugely popular with tourists, including thousands who arrive from the UK at this time of year.
Jean-Philippe Recappe, the Brest prosecutor, confirmed fears had been raised about possible hydrogen sulphide poisoning caused by decomposing sea lettuce, or _Ulva lactuca_. Six beaches in the area are currently closed because of the green algae producing a smell like rotting eggs. [_U. lactuca_ is actually an algae grown in large sheet or leaflike formations resembling lettuce and has, at times, been referred to as seaweed. - ProMED Mod.TG] The colourless gas can attack nervous and respiratory systems inside the human body, paralysing breathing and then causing death.
Commenting on the death of the apparently healthy teenager at Morlaix, Mr Recappe said: "The cause of death has not yet been determined since the results of toxicological and pathological analysis is not yet known." Mr Recappe said all visitors to the beaches needed to be aware of the potential dangers caused by the algae.
Fears about sea lettuce were 1st raised as early as the 1970s, after wild animals, including boars, appeared to succumb to the fumes, along with horses and pet dogs.
_U. lactuca_, or sea lettuce, is found all over the world. It is usually found on sheltered rocks and shores, and in other pools of shallow water. This sea lettuce is light green and translucent, and can grow up to 7.1 inches (18 cm) in length. [Some sources indicate it may grow larger than mentioned here. The size may be dependent upon location, nutrients, temperatures, etc. - ProMED Mod.TG]
Large amounts of the algae are found in Brittany, France, which thrives in brackish waters. The area in Brittany is perfect for the sea lettuce because nitrates used in farming get washed out to sea. Sea lettuce becomes dangerous when it washes up on beaches because its decay produces hydrogen sulphide and other gases. Prolonged exposure to the gases can cause nausea, altered breathing, and eventually death.
Accusations about a public health scandal intensified in 1989 when an emergency doctor in Lannion, Brittany, questioned the cause of death of a jogger. His body was found tangled up in a mass of seaweed on the beach at Saint-Michel-en-Greve, with the whistleblower complaining the autopsy results were never made public.
The problem is now thought to be getting far worse because of compounds full of nitrogen caused by industrial farming. They build up in excrement from the animals on pig and poultry farms, and then wash out to sea where algae builds up before ending up back on beaches as a green tide. Workmen tasked with cleaning up the algae are also known to have become extremely ill. [Perhaps these individuals should be provided with protective equipment. - ProMED Mod.TG]
A runner collapsed and died in Jersey in 2017 after training on a Brittany beach covered in rotting seaweed where some 36 boars had also suddenly died. Nine experts, including 4 toxicologists, said seaweed was to blame, and now environmentalists are calling for all such suspicious deaths to be investigated. Ines Leraud, a French author who has carried out extensive work on the subject, said: "There should be systematic tests, just as there are tests for alcohol when there is a road accident." [byline: Peter Allen]
[Sea lettuce (_Ulva lactuca_)
- Appearance: green seaweed, sheetlike in appearance. Can be white or black when dry. Ranges in size from 6 inches to 2 feet.
- Habitat: high and low intertidal zones; water to 75 feet deep.
- Seasonal appearance: all year, with large blooms in the summer.
- Description: sea lettuce is a bright green algae composed of lobed, ruffle-edged leaves that are coarse and sheetlike and resemble a leaf of lettuce. The leaves may appear flat, thin, broad, and often rounded or oval. Its leaves are often perforated with holes of various sizes. Almost no stalk exists at the point of attachment, and no true roots are present. When dried by the sun, its color can range from white to black.
Sea lettuce may be found attached to rocks and shells by a holdfast, but it is also commonly found free floating. Among the most familiar of the shallow water seaweeds, sea lettuce is often found in areas of exposed rocks and in stagnant tide pools. Sea lettuce has also been recorded at depths of 75 feet [25 metres] or more. Sea lettuce grows in both high and low intertidal zones and marshes throughout the year.
Tolerant of nutrient loading that would suffocate many other aquatic plants, it can actually thrive in moderate levels of nutrient pollution. Large volumes of sea lettuce often indicate high levels of pollution. Growth is also stimulated by the presence of other pollutants. It is often found in areas where sewage runoff is heavy. As a result, sea lettuce is used as an indicator species to monitor pollution trends. The density and location of this alga can often indicate the presence of high amounts of nutrients.
- In areas where there is a high concentration or "bloom" of sea lettuce, sunlight is unable to reach submerged vegetation such as eelgrass, preventing photosynthesis and often killing the vegetation below.
- When sea lettuce dies, bacteria feeding on the decomposing sea lettuce use up a tremendous amount of oxygen in the water. This, in turn, depletes the oxygen available to other species, suffocating or driving them away.
- Masses of sea lettuce can hamper swimmers and foul lines and fishing nets, but it does provide a home to some small invertebrates such as amphipods.
- Like lettuce grown on land, it can be used in salads and soups. Sea lettuce is also used to make ice cream, other food products, and medicine.
Decomposing piles of sea lettuce could easily produce hydrogen sulfide, with a characteristic smell of rotten eggs. Rotting organic material, under the correct conditions, can produce this lethal gas. Often times, victims are believed to die of heart attack unless a thorough investigation/autopsy is performed.
Hydrogen sulfide has many synonyms including dihydrogen sulphide, sulphur hydride, sulphurated hydrogen, hydrosulphuric acid, "sewer gas", "swamp gas", hepatic acid, sour gas, and "stink damp".
Hydrogen sulphide (H2S) is a colourless, highly flammable and explosive gas produced naturally by decaying organic matter and by certain industrial processes. Hydrogen sulfide has a characteristic rotten-egg odor. (Source: <https://www.atsdr.cdc.gov/mmg/mmg.asp?id=385&tid=67
Persistent exposure to air concentrations above 100 ppm produces olfactory fatigue, which impairs the ability to detect the characteristic odor of rotten eggs (12).
H2S is responsible for many incidents of occupational toxic exposure, especially in the petroleum industry. The clinical effects of H2S depend on its concentration and the duration of exposure. H2S is immediately fatal when concentrations are over 500-1000 ppm, but exposure to lower concentrations, such as 10-500 ppm, can cause various respiratory symptoms that range from rhinitis to acute respiratory failure. H2S may also affect multiple organs, causing temporary or permanent derangements in the nervous, cardiovascular, renal, hepatic, and hematological systems.
Injury due to H2S exposure occurs primarily by inhalation. Once absorbed, the compound is distributed in the blood and taken up by the brain, liver, kidney, pancreas, and small intestines. Sulfur compounds are severely irritating to the respiratory tract, leading to rhinorrhea, sneezing, sore throat, wheezing, shortness of breath, chest tightness, hemoptysis, and a feeling of suffocation (1). Sulphur compounds can cause leucopenia and neutropenia (9,13), as well as cardiac injury with elevation of troponin I and creatine kinase (9,10). The mechanism of H2S toxicity is related to inhibition of oxidative phosphorylation, which causes a decrease in the available cellular energy. A phenomenon referred to as "knockdown" was reported in oil field workers to describe a sudden, brief loss of consciousness associated with amnesia, followed by immediate full recovery. This phenomenon usually occurs after short-term exposure to very high concentrations of H2S (17). (Source: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2850187/
>; see URL for complete list of references, including those cited here.) - ProMED Mod.TG]
[HealthMap/ProMED-mail map of Bretagne [Brittany], France: