https://www.thenorthernecho.co.uk/news/22858596.pyridine-caused-mass-north-east-sea-life-deaths
The information on Pyridine states:
“Pyridine appears as a clear colorless to light yellow liquid with a penetrating nauseating odor. Density 0.978 g / cm3. Flash point 68 °F. Vapors are heavier than air. Toxic by ingestion and inhalation. Combustion produces toxic oxides of nitrogen.CAMEO Chemicals
Pyridine is a colorless liquid with an unpleasant smell. It can be made from crude coal tar or from other chemicals. Pyridine is used to dissolve other substances. It is also used to make many different products such as medicines, vitamins, food flavorings, paints, dyes, rubber products, adhesives, insecticides, and herbicides. Pyridine can also be formed from the breakdown of many natural materials in the environment.CDC-ATSDR Toxic Substances Portal
Pyridine is an azaarene comprising a benzene core in which one -CH group is replaced by a nitrogen atom. It is the parent compound of the class pyridines. It has a role as an environmental contaminant. It is a mancude organic heteromonocyclic parent, a monocyclic heteroarene, an azaarene and a member of pyridines.ChEBI”
https://pubchem.ncbi.nlm.nih.gov/compound/pyridine
The region is experiencing a push just now as aBrexit inspired ‘Freeport’ and dredging is part of the preparation:
https://www.teessidefreeport.com/
Consider the facts around dredging:
“Dredging is the act of removing silt and other material from the bottom of bodies of water”
https://oceanservice.noaa.gov/facts/dredging.html
In the case of the river Tees, a site of centuries of toxic waste allowed to pollute the river when there was no regulation, and so all life in the river died.
To clear out the silt, dredging began in 2014:
https://www.gazettelive.co.uk/business/business-news/major-dredging-work-able-uk-7536063
The work of dredging has to be maintained to keep the port clear:
https://www.dredgingtoday.com/2020/03/04/tshd-heortnesse-arrives-at-ap-tees
According to noaa.gov:
“Dredging is also performed to reduce the exposure of fish, wildlife, and people to contaminants and to prevent the spread of contaminants to other areas of the water body. This environmental dredging is often necessary because sediments in and around cities and industrial areas are frequently contaminated with a variety of pollutants. These pollutants are introduced to waterways from point sources such as sewer overflows, municipal and industrial discharges, and spills; or may be introduced from nonpoint sources such as surface runoff and atmospheric deposition”
In which case, if this was environmental dredging, the contaminants should not have entered the North Sea, but should have been safely disposed of where toxins could not even enter groundwater.
https://www.thenorthernecho.co.uk/news/21121371.arguments-continue-dredging-tests-river-tees
Teesside was famous for steelmaking, plus many other industries which made the air above a yellow smog for decades:
https://discovery.nationalarchives.gov.uk/details/a?_ref=20
https://revisionworld.com/gcse-revision/geography/industry/heavy-industry-example-teeside-uk
The answer to this poisoning of marine life must be found and action taken to protect sea life in future from whatever mistaken error was made in this instance.
https://www.gazettelive.co.uk/news/teesside-news/thorough-crab-deaths-report-dubbed-26030691
If the cause was not dredging, then it might have been a virus:
https://www.msn.com/en-au/news/other/unknown-virus-is-likely-cause-of-crab-deaths/ar-AA16BTgW
And then, as Teesside is one of the new Freeports, we must ensure strict biosecurity:
https://emcsindustries.com/helping-you-to-reduce-pollution-and-guard-aquatic-biosecurity/
How did a new pathogen arrive in these waters?:
borderslynn 
Pingback: Free ports, organic compounds of the aromatic heterocyclic series and polution – Some View on the World