LOS ANGELES (AP) — Levels of wretched-smelling hydrogen sulfide gas that have plagued south Los Angeles County communities for weeks are declining as authorities use various mitigation methods in a flood control channel emitting the gross odors, authorities said Friday in an online news conference.
The problem was reported Oct. 7 and traced to the 15-mile-long (24-kilometer) Dominguez Channel, which flows into Los Angeles harbor. The smell has chiefly affected the city of Carson and several other Los Angeles suburbs.
The gas is being created by a natural phenomenon called anaerobic digestion which occurs when bacteria break down vegetation when there’s a lack of oxygen in the water, said Mark Pestrella, the county’s public works director and chief engineer of the flood control district.
In addition, the investigation revealed the presence of chemicals that are contributing to the problem. Pestrella did not identify those chemicals and he said he could not comment further because it may involve criminal or civil actions.
Public works is spraying the channel with a biodegradable odor neutralizer called Epoleon, which converts hydrogen sulfide to a salt. Daily tides are being relied on to spread the neutralizer, and Pestrella said drones are being considered to help that process.
A system of bubblers is being installed in the channel to oxygenate the water and convert the decay process into aerobic decomposition, eliminating production of hydrogen sulfide, Pestrella said.
Also, high intensity lighting is being placed along the channel for use at night because it’s believed the bacteria involved is photosensitive, he said.
Measurements by air-quality regulators “are showing drastic reductions in gas readings,” Pestrella said, but he could not estimate when the problem would be eliminated because people have individual levels of sensitivity.
Authorities have recommended that residents keep windows closed, buy special air filters or leave the area, if necessary.
The county has placed 26 households in hotels and so far has approved 857 of more than 2,000 reimbursement requests, Pestrella said.
Some area residents claim the problem originated Sept. 30 when a big commercial fire in the city of Carson erupted among pallets and boxes of ethanol-based hand sanitizer, and that debris and sanitizer then flowed into Dominguez Channel
Pestrella said he could not speculate on those materials.
Public health teams have visited more than 7,000 homes, nearly 200 business and all the schools in the area to share health recommendations, answer questions and provide technical assistance on how to reduce odors indoors.
“What we hear time and time again is that people are frustrated and they are worried, and that’s understandable,” said Dr. Muntu Davis, the county health officer.
Exposure to hydrogen sulfide can cause headaches, dizziness, irritation of the eyes, nose, throat and lungs, Davis said. Symptoms also may include nausea and abdominal discomfort that may lead to vomiting. The smell might also cause an asthma attack.
“Since the beginning of the incident, hydrogen sulfide readings in the air have been low enough that these symptoms are expected to be transient, short-term and reversible,” Davis said.
The symptoms are due to the smell of the odors and not due to hydrogen sulfide accumulating in the body, he said.
“Symptoms tend to go away when you leave the area or when the odors decrease or are no longer present, which is what we all hope will happen in the near future,” he said.
Davis said that people in Carson have expressed concern about exposure to hydrogen over days, weeks or months even though the levels are low.
“Based on what we are currently seeing, we generally do not expect people to develop long-term health issues after this odor event goes away,” Davis said. “Hydrogen sulfide is a gas that does not stay in your body for very long.”
Pestrella said there is no green vegetation left because it has been completely broken down into what looks like inky black soot.
The long-term plan is to dredge the channel and remove the vegetation but that can’t be done immediately to solve the problem because that could create additional health hazards by exposing legacy pollutants such as sulfur and metals trapped in 100 years of sediment, Pestrella said. That project will take two years.