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This article was originally featured on Hakai Magazine, an online publication about science and society in coastal ecosystems. Read more stories like this at hakaimagazine.com.

They had no idea the shipping container was full of toxic gas. But mere moments after opening it, the two workers began to feel the effects. One man fell unconscious, convulsing with epileptic seizures. The other felt an irritation in his throat and began salivating uncontrollably.

The cargo papers for the container stated it contained glassware and ceramics. The workers had no reason to suspect they were in danger. But they were. And so was the ambulance crew that came to their aid. Arriving on the scene, they saw the man having seizure after seizure, so they quickly anesthetized and intubated both workers. In the ambulance on the way to the hospital, the medics also began to feel ill: sore throats, irritated eyes, and hypersalivation.

This frightening and little-known incident occurred in 2006 at the port in Rotterdam, Netherlands. Thankfully, all involved survived their initial exposure, though it was undoubtedly a close call. The toxic gas that had assailed them was the odorless and colorless methyl bromide. Acute doses of methyl bromide can be fatal; chronic and acute exposure increases the risk of prostate cancer.

In the years since that distressing day, researchers have investigated the many poisonous chemicals sometimes lurking inside sealed shipping containers.

Ruth Hinz, a doctoral candidate at Massey University in New Zealand, led a recent study cataloging the harmful airborne chemicals in a sample of containers shipped to New Zealand. Hinz’s work is in line with similar recent research conducted in Sweden, which suggests that around one in eight containers arriving in that country harbors significant levels of dangerous airborne chemicals. When workers crack a container open, they may have little way of knowing what awaits them.

“It can be such a cocktail of chemicals in the container,” says Hinz. “You don’t know in advance which ones will be in there.”

Some toxic chemicals are pumped into cargo containers on purpose as fumigants. Methyl bromide is one example, though its use is now banned in many countries. But the additional challenge for dockworkers is that the presence of other dangerous gases could be entirely unintentional and unexpected. As in Rotterdam, a lack of cautionary labeling could also mask the danger.

Before sending containers on their way, workers at the port of departure sometimes fumigate cargo boxes with pesticides, especially if the container is loaded with food, animal feed, or timber. These chemicals, such as methyl bromide, ethylene oxide, and phosphine, can cause myriad symptoms, ranging from nausea and skin irritation to seizures and even death.

Some cargo may off-gas harmful chemicals. For instance, product packaging could contain toluene, while plastics might emit benzene. The latter can damage bone marrow and cause anemia.

And there could be substances from previous cargo left inside, lining the interior of the container, too. Dockworkers might not realize such toxicants are awaiting them in a newly arrived container.

For their study, Hinz and her colleagues enlisted the help of the New Zealand customs authority. Staff used probes, which they pushed through the rubber seals of the container doors, to collect gas samples from 490 sealed containers. Hinz also gathered air samples from dozens of other containers herself, tracking how the concentrations of compounds changed in real time as the containers were opened and the air inside allowed to mix with fresh outside air.

The investigation revealed plenty of nasty substances. The customs authority staff found methyl bromide, the compound that overwhelmed the Rotterdam dockworkers, in 3.5 percent of the sealed containers. They found formaldehyde in 81 percent of the containers, and ethylene oxide in 4.7 percent, to name a few of the chemicals. Exposure to ethylene oxide can cause various unpleasant symptoms, including nausea, vomiting, and diarrhea. Formaldehyde, a preservative, is carcinogenic and can also cause internal irritation when inhaled, among other symptoms.

In their study, Hinz and her colleagues found that some of the measured concentrations appeared high enough to cause an acute reaction that triggers immediate symptoms. However, Hinz says that, in practice, it’s unusual for a worker to come into direct contact with toxic gases at such elevated levels. Instead, there is a more common but still notable risk from repeat exposure to low concentrations. Chronic contact with these chemicals can potentially increase the risk of cancer or cause psychiatric problems, for example. And yet, relatively little research exists on the risks of the chemicals inside cargo containers.

“I definitely think it needs attention, far more attention than it’s got,” says Hinz.

Gunnar Johanson, a toxicologist at the Karolinska Institute in Sweden who acted as a peer reviewer for Hinz’s study, agrees with her assessment.

“We don’t know exactly how big the risk is, but it’s an unnecessary risk because you can easily address it,” he says. All it takes is better ventilation.

A few years ago, Johanson and his colleagues were called to examine a suspect container in Sweden. It was loaded with rice, but inside the container was also a strange blue bag filled with white powder. When Johanson analyzed the air, he found phosphine, a fumigant, at a concentration high enough to be fatal.

To protect dockworkers, Johanson and his colleagues have designed a device that connects to an extraction fan and attaches to the existing—but tiny—ventilation holes on the sides of most containers. Experiments suggest that once the device is switched on, the concentration of harmful gases falls within minutes.

“We can reduce roughly 90 percent of the volatile contaminants in one hour,” says Johanson. The contraption is currently used by the Swedish customs authority, he adds.

There should be higher awareness in the shipping and logistics industries of the dangers associated with exposure to harmful gases in shipping containers, says Martin Cobbald, managing director of Dealey Environmental, an environmental services firm in the United Kingdom.

His firm is frequently contracted to open and ventilate containers, but, he adds, “We don’t do it nearly as much and for the range of people that we should do.”

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