1. Strawberry growers rely on some of the riskiest and hardest-to-control pesticides used in agriculture.

The little red fruit is nutritious and delicious. It’s also fragile, valuable and often grown on coastal California real estate.

So strawberry growers use a class of pesticides known as fumigants, blasting the soil with gases before they plant each season’s crop. Fumigants are like an insurance policy – taking out possible pests, diseases and weeds before they can cause any problems.

Even when used correctly, fumigants turn into hard-to-control gases that float into the air, affecting workers and nearby residents. They’ve been linked to cancer, developmental problems and ozone depletion.

2. Growers use a lot of pesticides. And they often use them close to schools, homes and businesses.

Strawberries take up less than 1 percent of all farmland in California but account for at least 8 percent of the state's pesticide use.

The three ZIP codes in the state with the heaviest pesticide use all fall within two prime strawberry-growing counties, Ventura and Monterey.

Strawberries like to grow where people like to live, in the perpetual spring of coastal California.

The state Department of Public Health categorizes fumigants as among the pesticides of greatest health concern. No school in the state is as close to fields using such large amounts of these problematic pesticides as Rio Mesa High School in Oxnard. It is surrounded on all four sides by strawberry fields.

3. Farmers began using fumigants after researchers in Hawaii experimented with leftover stockpiles of a chemical weapon that soldiers called ‘vomiting gas.’

After World War I, the United States had vast leftover stocks of chloropicrin. The chemical had been added to tear gas to make enemy soldiers vomit and throw off their gas masks, exposing themselves to other harmful gases.

After the war, with the pineapple industry struggling with pests in the soil, researchers pumped chloropicrin into the ground. The results were dramatic. An acre treated with chloropicrin yielded 20 more tons of pineapple than the untreated acre.

By the 1950s, fumigants were being used in strawberry fields. With breakthroughs in breeding and technology, along with the new chemical cocktails, California strawberry farmers had by the 1970s doubled the amount of berries a single acre could produce.

4. Americans now eat four times as many fresh strawberries as they did in the 1970s.  

Strawberry production was booming by the 1970s. But growers needed demand to match the supply.

Strawberries started appearing on the cover of Cool Whip containers. The California strawberry growers’ association went looking for other products that paired well with strawberries – chocolate dips, pie shells and daiquiris. Soon, strawberries were on boxes of Corn Flakes and Cheerios. American strawberry consumption went from 2 to 8 pounds a year per capita.

5. Fumigants don’t end up on the fruit you eat. But these particular pesticides pose risks to farmworkers, nearby residents and the environment.

The strawberry industry’s most popular fumigant, methyl bromide, was banned by an international treaty in the 1990s for depleting the ozone layer.

There are few studies on the long-term health impacts of fumigants. Human health risks often are extrapolated from animal studies. Last year, a group of researchers at the University of California, Berkeley found a connection between living near places where methyl bromide is used and giving birth to babies who were lighter, shorter and had smaller heads.

The fumigants that growers have turned to in place of methyl bromide carry their own health risks. For example, the state considers 1,3-Dichloropropene, another popular fumigant called 1,3-D for short, a carcinogen.

6. California strawberry growers largely are the only ones still using methyl bromide.

The Montreal Protocol, the international treaty banning methyl bromide, called on developed countries to quit using the chemical by 2005. Since then, its use in California agriculture has dropped – decreasing 60 percent between 1991 and 2012. But it hasn’t gone away.

The authors of the Montreal Protocol created an escape hatch to ensure the treaty wouldn’t result in economic disaster. A country can get exemptions by proving that there are no viable alternatives and that a lack of methyl bromide would put the industry in a financial bind. They are known bureaucratically as “critical use exemptions.”

California’s strawberry industry got about 90 percent of the exemptions issued globally this year.

7. Despite scientists’ warnings, the state allowed growers to use significantly higher amounts of 1,3-D for more than a decade at the request of Dow AgroSciences.

With methyl bromide being phased out, strawberry growers have turned more to 1,3-D to replace it. From 2003 to 2012, their 1,3-D use increased by more than 200 percent. It’s now the third most heavily used pesticide in California.

State scientists calculate at what levels it’s safe for workers and residents to be exposed to pesticides like 1,3-D. After a scare in the 1990s, the state set strict regulations to cap the amount that could be used in each community. The goal was to limit the risk to one estimated extra cancer case per 100,000 people.

Dow, the pesticide’s manufacturer, then began chipping away at those regulations. In 2002, the state agreed to create a loophole to allow up to twice as much 1,3-D use in a year. State officials created the loophole and allowed it to persist for more than a decade, despite internal scientists’ warnings that it had no basis in science.

The decision increased cancer risk for residents and workers in more than 100 California communities, documents and interviews show.

For the full story, read our investigation. Want to see if you live near areas where these pesticides are used? Check out our app.

This story was edited Andrew Donohue and copy edited by Stephanie Rice.

Bernice Yeung can be reached at byeung@cironline.org, and Andrew Donohue can be reached at adonohue@cironline.org. Follow them on Twitter: @bmyeung and @add.