‘Stay out of seaweed-infested water!’ – Dr Cassander Titley-O’Neal PhD
It has been confirmed that over the last few days fishes have been turning up dead in the water in places off Virgin Gorda and on Tortola to a lesser extent.
While we have seen photographs taken on Virgin Gorda recently depicting dead fishes and lobsters, our roving cameras also found dead fishes in the water near Village Cay yesterday October 3, 2015.
“As it relates to swimming, in areas where the seaweed is stagnant and is decomposing, it is advised that no swimming should take place because of the release of hydrogen sulphide in the water and potential for swallowing it by accident,” said Dr O’Neal to this news site yesterday.
Low oxygen/low pH levels likely causing fish kills
“Let me first say that, although I have not done any recent water quality testing of the water samples. However, based on previous water quality data from areas around Road Town analysed earlier in the summer, it almost certain that the vast quantities of Sargassum seaweed that are washed up along the shoreline is changing the water chemistry of bays around the BVI. I was at Village Cay today, and there are several dead fish floating on the surface, including barracudas, mullets, gobbies, and baby lobsters,” said Dr Titley-O’Neal in an email to this news site.
She said that while the organisms living within the seaweed provide food for several species of birds, the sargassum in the large quantities is posing some environmental problems that are quite evident, such as the pungent odour of the shoreline and the recent fish kills.
"I suspect that it is the low oxygen levels coupled with the low pH levels that are more than likely contributing to the fish kills," said Dr Titley-O'Neal.
Strong enough to kill
According to her, oral ingestion of some sulphides has been reported to cause nausea, vomiting and epigastric pain, as well as an irritant to the mucous membranes; it has been estimated that an oral dose of 10 to 15 grams of sodium sulphide would be fatal to humans.
“To date, studies on human health consequences associated with prolonged low-level exposure to hydrogen sulphide, from air pollution, have not yet been carried out,” she said.
Discolouration due to compounds in the water
Dr Titley-O’Neal gave an explanation for the possible discolouration of faucets that persons have been reporting in the territory.
“A few residents in the Handsome Bay area on Virgin Gorda have reported that their faucets are becoming discoloured or blackened. This is likely due to a combination of different things. Firstly, the presence of hydrogen sulphide in the seawater, acts as a weak acid contributing to corrosion. Secondly, if there is hydrogen sulphide and soluble iron in the water, the combination of both compounds can cause black deposits on fixtures,” Dr Titley-O’Neal explained.
Prolonged inhalation not advisable
She noted that according to the United States Occupational Safety and Health Administration, the smell of the seaweed is offensive with an estimated concentration of 3 to 5 parts per million.
“Exposure of hydrogen sulphide at this concentration for a prolonged period of time can cause effects such as nausea, tearing of the eyes, headaches and loss of sleep, while persons affected by asthma, may experience airway problems.”
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