Sargassum Poses Toxic Gas Risk to Harvesters, UNAM Warns

Quintana Roo, Mexico — The ongoing crisis of massive sargassum accumulation along the Mexican Caribbean coastline has taken a new and troubling turn. Beyond its known environmental and economic impacts, decomposing sargassum now poses a serious public health risk to beach workers, according to researchers from the Institute of Marine Sciences and Limnology at the National Autonomous University of Mexico (UNAM) in Puerto Morelos.

UNAM scientists have developed a series of real-time sensors to measure hydrogen sulfide (H₂S) concentrations in sargassum collected on beaches in Quintana Roo. This initiative is part of an international health project in collaboration with the University of Victoria (Canada) and the University of São Paulo (Brazil), aiming to document—scientifically and systematically—for the first time, the gas exposure risks faced by sargassum harvesters in Mexico.

A Collaborative Health Initiative

The low-cost sensors were designed by UNAM researcher Miguel Ángel Gómez Real and are currently in a pilot phase. The project’s lead investigator, Rosa Rodríguez Martínez, emphasized the significance of understanding this exposure. “What we are doing is measuring how much gas is released while working with sargassum. We want to know if workers are at risk, under what conditions, and at what concentration levels,” she explained.

Rodríguez Martínez also pointed to how other countries handle similar scenarios: “In the French Islands, if hydrogen sulfide concentrations exceed 5 parts per million, the military intervenes—they enter with masks and full protective gear because it is then considered a toxic gas due to its harmful levels.”

The research team is validating the sensors against certified equipment, with plans to eventually distribute at least one device per cleanup brigade, beginning in Playa del Carmen. These sensors will help identify high-risk areas and document the conditions under which gas concentrations rise to dangerous levels.

On June 10, Rodríguez Martínez visited El Recodo Beach, historically one of the worst sargassum accumulation points in Playa del Carmen. She described the conditions as “terrible,” noting the beach had essentially turned into a swamp. “It’s mud,” she said, referring to the dense, decomposing seaweed. She warned of “a severe decomposition problem” and a clear health hazard for cleanup workers exposed to high levels of hydrogen sulfide.

Understanding the Toxic Threat

Hydrogen sulfide is a colorless gas with a distinct rotten-egg smell. It is released when bacteria break down organic matter in oxygen-deprived conditions—such as the thick piles of rotting sargassum commonly seen on Caribbean beaches. While the gas can be detected by smell at concentrations as low as 0.7 parts per million (ppm), higher levels can cause the body to stop perceiving it—a phenomenon known as olfactory fatigue.

This loss of smell is dangerous. In industrial settings like wastewater treatment plants, it has been linked to fatal accidents, particularly when people unknowingly remain in confined spaces where concentrations are high. Exposure to levels above 10 ppm is considered unsafe even in short bursts, according to the U.S. National Institute for Occupational Safety and Health (NIOSH).

Rodríguez Martínez reported that in Puerto Morelos and Playa del Carmen, H₂S levels during sargassum removal often exceeded 100 ppm, with some readings peaking at 180 ppm. These are considered acutely hazardous exposures, particularly for workers without protective gear.

“When workers start digging with shovels or lifting the sargassum, pockets of trapped gas are released. So, even if the general environment doesn’t have high levels, there can be intense exposure at that moment,” she said. This “intermittent but recurring exposure,” she added, is difficult to monitor without portable, real-time sensors.

Studying Health Impacts and Building a Safety Database

In addition to measuring gas levels, the research team plans to create a comprehensive database linking sensor readings to self-reported health symptoms among cleanup workers. While anecdotal evidence already points to issues such as headaches, nausea, eye irritation, and breathing difficulties, no formal study has yet established a direct correlation between hydrogen sulfide exposure from sargassum and specific health outcomes.

By documenting both exposure and symptoms, UNAM hopes to lay the groundwork for improved safety protocols, including the use of protective gear and work-rest cycles based on gas concentration levels.

Rodríguez Martínez emphasized that this project is about more than academic research—it is a step toward safeguarding the health of hundreds of workers currently tasked with cleaning up tons of decomposing sargassum across the state.

As the region braces for what could be another record-breaking sargassum season, the findings from this study could prove critical not only in improving local working conditions, but also in shaping national and international policy responses to a worsening environmental and public health challenge.