Lots of foods and drinks contain trace levels of arsenic. As chemists explain it, arsenic is a natural element which is abundant in the Earth's crust, so it ends up in our soil and water.
And, as plants — including grapes — grow in the soil, they can take up, or absorb, the arsenic there. So, it's no surprise to chemists, or the wine industry, that there are trace levels detectable in wines.
"Wines from throughout the world contain trace amounts of arsenic as do juices, vegetables, grains and other alcohol beverages," according to a statement from the Wine Institute. And research, such as this analysis from the European Food Safety Authority, confirms this is true.
Were there dangerous levels of arsenic in some of the California wines tested by BeverageGrades?
The U.S. government does not set an allowable limit for arsenic in wine. But Canada's government does.
The upper threshold, set by Health Canada, is 100 parts per billion, or ppb. And the limit set by OIV, a European intergovernmental wine organization, is even higher at 200 ppb.
None of the California wines that were tested by BeverageGrades tested higher than 50 ppb, according to news reports. (Neither the company nor the lawyers have released the lab results.)
And three-quarters of the bottles of the roughly 1,300 bottles of wine reportedly tested below 10 ppb, which is the EPA's allowable limit for arsenic in drinking water.
So, by Canadian standards, the levels of arsenic in the California wines that were tested are acceptable.
In addition, the Liquor Control Board of Ontario, a government enterprise in Canada, has performed its own testing on arsenic in wines. The LCBO's spokesperson tells The Salt by email that last year, its laboratory tested 2,247 wines from California.
All of them tested below the maximum allowable limit for arsenic. In fact, 90 percent of the California wines tested below 10 parts per billion, and 99 percent had levels of 25 ppb or lower.
There are experts who've raised a red flag about the concentrations of arsenic detected in some California wines. "Arsenic is highly toxic," Allan Smith, director of the Arsenic Health Effects research program at the University of California, Berkeley, told CBS News. And, over time, that can be be deadly.
But, as many scientists point out, it's the overall exposure that determines the potential health effects.
"Whenever you're talking about toxicity, it's the dose that makes the poison," Susan Ebeler, a professor and chemist in the Foods For Health Institute at the University of California, Davis, says.
As Health Canada notes, "Studies of populations in Asia have associated the development of skin lesions, various cancers and neurotoxicity ... with chronic ingestion of drinking water containing elevated concentrations of arsenic ranging from 10 to 100 times greater than the current Canadian Drinking Water Quality Guideline for arsenic," or 10 ppb.
These exposures are also typically much higher than what Americans are exposed to through water, food or wine.
And, some experts say a drinking water standard shouldn't be used to determine how much trace arsenic should be tolerable in wine in part because people drink much less wine than water.
Also, the safety thresholds in drinking water must take into consideration the toxicity to young children, who are more vulnerable.
What about adults who drink wine or consume foods with trace levels of arsenic in the U.S.?
"There's no reason to believe that exposure to arsenic in food and wine is above levels that are considered to be safe," Ebeler says.
But, there are differences of opinion. The lawsuit filed in Los Angeles County Superior Court alleges that some California wineries produce and market wines that are "dangerously high levels" of arsenic.
Is there anything wine makers or food producers can do to lower the amount of arsenic in their products?
One strategy is to be aware of the geographic hot spots where concentrations of arsenic in surface soil are highest.
This map by the U.S. Geological Survey shows that some areas of the country have much higher levels than others — states like Nevada, Montana and Pennsylvania, among others.
The higher concentrations of arsenic can be explained by a number of factors. For instance, bedrock or glacial deposits that contain high levels of arsenic can influence the ground soil above them. In addition, mining and coal-burning activities release arsenic.
In other cases, there are residues from arsenic-based pesticides used decades ago to grow apples, rice and other crops.
And another possibility: As we've reported, traces of arsenic in some alcoholic beverages may come from a filtering process.
Some brewers or winemakers use natural materials such as diatomaceous earth or, in the case of wine, bentonite clay to filter out small bits of plant matter or anything that might make the liquid cloudy. So it's possible that the arsenic in these natural materials can leach into the beverage.
The lead attorney in the lawsuit against the winemakers told the AP that arsenic in wines might have been introduced in the wine-making process.
Ebeler has published a study that assesses how soils and processing and storage techniques can influence trace metal concentrations in wines.
But it's not clear whether a filtering process — or another processing or storage technique — influenced the levels of trace arsenic found in the California wines that were tested by BeverageGrades.