Pesticide Impact on Bay Delta Fish Could Be Greater Than Realized

New monitoring in the Bay Delta shows that the water is a soup of urban and agricultural insecticides, herbicides and fungicides. When combined, pesticides at sublethal levels can have deadly synergistic effects on fish. “The Sacramento River and San Joaquin River have been monitored for years, but historically there has been little monitoring in the Delta itself,” says Michelle Hladik, an environmental chemist who leads the USGS Pesticide Fate Research Group. “We need more information on what is actually occurring in the Delta now.” As part of the recently launched Delta Regional Monitoring Program, the team is in its second year of checking agricultural and suburban runoff at five sites in the Delta. They’re testing for more than 150 pesticides that are in current use. “We’re monitoring a long list of pesticides including the new or understudied, such as those that have increased in use in the recent past but are not currently in other monitoring programs,” she says.

More than half of the pesticides applied in the Delta watershed are not routinely tracked. “It’s a moving target, there’s always something new coming along,” says the USGS’s Orlando, who is also a member of the Pesticide Fate Research Group. “The Delta watershed has had an average of nine new pesticide active ingredients introduced each year since 1995.”

In a series of recent studies, the team has detected a wide variety of insecticides, herbicides and fungicides in the Delta. Examples include pyrethroids, neurotoxicants that have grown more popular as organophosphate use has waned; fipronil, which is used to control fleas on pets; and neonicotinoids, which are implicated in the honeybee decline. “It’s a soup out there,” Hladik says.

Benchmarks for toxicity to aquatic life are based on the effects of individual compounds. But that doesn’t reflect the reality for fish and other creatures that live in Delta waterways. “You can see 30 different pesticides in a sample – how does that mixture affect living organisms?” Orlando says. “There’s not a lot of information on this because it’s so hard to test. Just testing one compound is hard enough.”

New research suggests that the impact of pesticides on the Delta’s fish could be greater than is recognized. In the December 2016 issue of San Francisco Estuary & Watershed Science, Stephanie Fong and colleagues reported that pyrethroid use correlates with declines in several species of fish in the Delta, including Delta smelt, longfin smelt, Sacramento splittail, American shad, threadfin shad and striped bass.

Source: Water Deeply, April 18, 2017…