Farmers use 50 percent more untreated wastewater from cities to irrigate crops than previously thought, exposing nearly one-eighth of the world’s population to serious health risks, according to a new study.
The situation could become more grave as climate change worsens.
“One of the key adaptation strategies to climate change is using water very carefully and reusing it as much as possible,” Pay Drechsel, a researcher at the International Water Management Institute, told HuffPost over Skype from his home in Sri Lanka. “Wastewater is the only water source that is actually increasing in the future. The more people that consume it, the more wastewater will be generated.”
The research, published last week in the journal Environmental Research Letters, analyzed data from previous studies that looked at land-use maps and satellite images, then added new official figures from city treatment agencies in major cities around the world. That gave researchers a sense of how much diluted sewage had made it into water systems.
The findings were staggering. Researchers had previously estimated that between 6 million and 20 million hectares were being irrigated with wastewater. The results of the new research, which included diluted wastewater, put that figure at about 29.3 million hectares.
That leaves the farmers and food vendors, as well as the 885 million urban consumers who depend on their crops, susceptible to ailments like diarrhea, typhoid and, in particularly bad cases, cholera.
“These waterborne disease become foodborne diseases,” Drechsel said. “We enter a second highway where it can affect people, and that makes it very, very tricky.”
Most of the affected cropland is in China, India, Pakistan, Mexico and Iran, according to the study, which was conducted by the nonprofit International Water Management Institute, Stanford University and the University of California, Berkeley.
But such irrigation problems can also have a major impact on smaller countries where cities are growing rapidly.
In Ghana, a West African nation where the urban population has more than tripled over the last three decades, greens such as lettuce, cabbage and spring onion are increasingly grown on patches of undeveloped land using contaminated city water.
“Farmers can make a lot of money if they find an open space in the cities or close to the cities, where people don’t build houses because it’s too wet or there are power lines,” Drechsel said, who lived in Ghana for 11 years.
Unlike other vegetables, those items are often served uncooked at street food vendors.
“As long as you can boil something you can kill a lot of the pathogens,” Drechsel said.
Improving sewage treatment is the obvious best solution. But countries can take other steps to decrease the amount of wastewater used for irrigation.
A chloride solution for washing vegetables is popular in some countries, including Burkina Faso and Benin, and Drechsel said it’s becoming more widely used in places like Ghana. In other countries, such as Sri Lanka, the International Water Management Institute is working to emphasize the potential benefits of human waste by creating a market for composted feces, although some experts have raised serious concerns about excrement-based fertilizers.
“We are trying to get the shit out of the system by transforming it into fertilizer,” Drechsel said. “With this, we can bring incentives into the sanitation chain.”