Manganese in Central Valley water threatens fetuses and children

Water in California’s Central Valley contains enough manganese to cause cognitive impairments and problems with motor control in children, and Parkinson’s disease-like symptoms in adults.

Manganese, a naturally occurring mineral, is found in water supplies around the world. It is regulated as an essential pollutant in many Southeast Asian countries as the climate causes it to seep into the groundwater. However, in the United States it is only regulated as a secondary pollutant, which means that no cap is imposed. A new study led by the University of California, Riverside, shows that the highest manganese concentrations among Central Valley communities are found in untreated private well water systems. However, researchers also found that in public water systems in concentrations higher than studies have shown it can have adverse health effects.

the study, published in the journal Environmental science and technologynot only measured manganese levels in the central valley water supply, but also identified areas of higher concentration according to annual income levels.

Overall, the research team estimates that nearly half of all domestic well water users in the Central Valley live in disadvantaged communities, as measured by annual income. Among these populations, approximately 89% have a high probability of accessing highly manganese-contaminated water.

“The number of people who have access to contaminated water is relatively small, compared to the total population of the state. But for them, the health risks are high,” said Samantha Ying, a UCSD soil scientist and lead researcher on the study. “These people are particularly concentrated in disadvantaged communities, so if they want to monitor and treat water, they will find it difficult to do so,” Ying said.

Point-of-use treatment options range from oxidation and sedimentation filters to water softeners, chlorinators, and reverse osmosis systems. But water quality monitors can cost up to $400 annually, and manganese-contaminated water treatments are very expensive.

“It is possible to buy manganese filters, but many people cannot afford them. We hope that people in these communities will have support to buy treatment options,” Ying said.

Previously, the research team found that groundwater contaminated with manganese tends to be found at relatively shallow depths, compared to arsenic. They wondered if drilling deeper wells would avoid manganese contamination. Unfortunately, this strategy is unlikely to be effective.

“Using existing groundwater model predictions of manganese concentrations at deeper depths did not change the number of potentially contaminated wells,” Ying said.

The conditions that cause arsenic and manganese to leach are similar, so they tend to appear in groundwater side by side. Arsenic has long been regulated as an essential pollutant in the U.S. “Wells are classified as unsafe if they contain arsenic, but not if they contain manganese,” Ying said. “Thus, the number of wells considered safe may be greatly exaggerated.”

Furthermore, the researchers used a standard of 300 parts per billion manganese to rate the water quality. This is the level of manganese contamination that some studies have linked to neurodevelopmental issues, especially for fetuses and infants during early developmental periods. It is possible though that adverse effects could occur at lower levels.

“New studies from Canada, where manganese is now a major pollutant, show there may be 100 parts per billion impacts,” Ying said. “We were conservative at 300.”

This study focused on the Central Valley in part because conditions that cause manganese to move from aquifer materials into water are common there. Drinking water from wells in other parts of the state is likely to be similarly contaminated. More than 1.3 million Californians depend on unmonitored private wells.

“The exposed population is much larger than we think. There are a lot of communities statewide drinking from private wells,” Ying said.