A chemical ‘haze’ which mysteriously descended on the Sussex coast on Sunday has left authorities scratching their heads.
Some 150 people required treatment for stinging eyes, sore throats and vomiting, but the effects of the unknown substance were “mostly minor”, Sussex police said.
Long queues were reported at local hospitals near to Eastbourne, as medics donned hazardous material suits to help those affected.
Police quickly ruled out the possibility that the substance could have drifted over from northern France, but chemical experts have suggested some other ideas:
1. Floating toxic algal bloom
Weather conditions on Sunday were favourable to the development of a floating toxic algal bloom, experts said.
Temperatures peaked across the UK, with highs of 25C and clear sunshine recorded in Eastbourne.
Prof. Andrea Sella, at UCL, told HuffPost UK: “Algal blooms can provoke a light-induced reaction we might see on a sunny day.”
And Dr. Simon Boxall, at the University of Southampton, National Oceanography Centre agreed.
He said: “There are some published studies in the US which show that in [some] cases the toxins from algal blooms can form aerosols which enter the atmosphere and drift ashore. These cause respiratory problems and irritation, particularly in those with asthma.
“A long shot but the evidence points in that direction.”
2. Discharge from a ship
An illegal discharge from a passing ship in the English Channel could explain the cloud, which appeared to move towards land from the sea.
“An alternative could be that a ship may have dispersed something. This is illegal but possible,” Prof Sella told HuffPost.
“Such a discharge could react again with sunlight, explaining the unpleasant and highly disagreeable symptoms.”
Substances onboard may have spilled into the open water, causing a chemical reaction.
“The only possibility I can think of is that it might be a container of chemicals washed off a ship and ruptured,” another scientist was quoted by Science Media Centre as saying.
“It might not necessarily be chlorine as there are other chemicals which produce a similar smell and reaction when mixed with water.”
The Maritime and Coastguard Agency said it could take a long time to establish which ships were in the right location to be linked to the cloud.
3. Foreign source
Fears the toxic cloud came from France seemed at odds with weather conditions on Sunday.
Winds were very light, and blowing in the wrong direction, and the air remained relatively still all day.
“This means it is highly likely that any effect will have come from the UK side or, possibly, a vessel running close to shore with the tide bringing the material towards the beach,” Dr. Boxall said.
4. Local source
One expert said a local source was most likely to be the cause of Sunday’s event.
Hon. Prof. David Slater, at Cardiff University’s School of Engineering, said: “For what it’s worth, it seems a pretty localised phenomenon and I’d look for a local source.
“On Google there seems to be a discharge into the sea at that point and just inland is a [Southern Water] treatment works.
“From my experience in regulating water companies, unplanned discharges are not uncommon.”
But Southern Water strongly denied its site was involved. A spokesperson said: “Our sites are constantly monitored and everything is working normally. There have been no emergency releases recently from our Eastbourne Wastewater Treatment Works in the area and the site does not use chlorine gas.”
5. Old munitions
An unnamed expert said a remote possibility could be “old munitions”.
Relics from wars fought in the last century continue to pose difficulties, as toxic chemicals within them require painstaking treatment when found.
Operations in Belgium, for example, require stringent testing of air quality after planned detonations of old bombs.
No such operations were reported in Sussex this weekend, however.
Sussex Police said in a statement on Tuesday that a multi-agency task force continues to investigate the cloud.
“Neither the gas nor its source have been established but the cloud has now dissipated and advice to keep windows and doors closed has now been withdrawn,” the force said.
“Anyone still suffering the effects are advised by Public Health England to irrigate their eyes if they are irritated and to wash any other irritated areas with plenty of soap and water.
“If you were affected and after taking the precautions recommended you still feel ill, contact 111 for advice and only visit your local A&E if you are still suffering significant effects.”