There were reports of the strong odor from Pasadena, Deer Park, La Porte, Clear Lake and Seabrook. Some people all the way in Houston also reported the foul odor.
A shelter-in-place order issued for the city of La Porte late Sunday evening was lifted during the overnight hours.
Harris County Pollution Control originally reported that hydrogen sulfide was spilled at a Lubrizol Plant in Deer Park. It is a chemical compound that tends to smell like rotten eggs.
However, La Porte Emergency Management later reported that it was determined that hydrogen sulfide was not the primary chemical compound of interest in the "odor nuisance."
By mid-morning Monday, authorities with the Lubrizol plant clarified that the cause of the odor was an organic sulfur material widely used to odorize natural gas because of its distinctive unpleasant smell.
Officials say the odor does not pose a risk to neighboring communities or to on-site employees. They added that while the odors have largely dissipated, any lingering nuisance odors will continue to subside.
In a statement, authorities explained that "this vapor release happened while Lubrizol teams were preparing a railcar for unloading on-site. This included safely heating the rail car to prepare the stored materials for transfer. We are investigating why the stored material began to break down, resulting in an offsite odor release. Our response team immediately began treating the railcar to minimize the odor, notified local authorities and initiated air monitoring."
La Porte lifted its shelter-in-place order just before 11:30 p.m. Sunday.
Seabrook also issued a shelter-in-place order in regards to the leak, but lifted it around 11:50 p.m.
For updates to this story, follow TJ Parker on Facebook, Twitter and Instagram.