Today we will explain the science behind a whole new technology for measuring water quality. San Diego is the first in the world to use it and it has already generated controversy.
The most sensitive test shows that there is more poop on the southernmost beaches of San Diego than we could ever say before, especially in the summer, when coastal cities like Coronado virtually never failed water quality testing using the old evidence. In the case of South Bay, there is an obvious source of human wastewater that has affected the coast for decades: Tijuana.
But instead of closing the beaches that failed these sensitive water quality tests, the county backtracked, replacing the closure signs with new ones that warned of possible sewage contamination and leaving the public the decision of whether or not to enter the water.
Richard Bailey, the mayor of Coronado, understood this as meaning that the county does not believe what their new test is telling them. He asked for data from the county during a series of closures on Coronado Beach starting May 5 to compare the results with both the old and the new way of testing the water. He pointed to examples where the new test showed that the water was dirty, but at the same time the old test showed that the water was safe.
“If the test thresholds for the new test are exceeded … but they are well below the thresholds of the old test, Coronado’s position is that the beaches should be open,” Bailey said.
Scientists say: this is lost.
How the County’s New Water Quality Test Works
San Diego County worked with the U. See the article : Reconnecting with Old Friends can improve your mental health, and they.S. Environmental Protection Agency, the California Department of Public Health and the Southern California Coastal Water Research Project worked for years with the test technology.
The test, called the polymerase chain reaction in digital droplets or ddPCR, counts the presence of bacteria in the water by their DNA. The old method, called culture, counted bacteria organism by organism with a much less accurate method.
To count bacteria with the culture method, scientists must encourage intestinal bacteria to grow so that collections of organisms are visible enough to be counted. This process can take up to three days, which doesn’t really help bathers, as it tells them today what the water was like yesterday. Some of these bacteria may die or may not be willing to grow enough to be counted, leading to an inaccurate representation of water quality.
Both tests, old and new, use the same disease risk threshold set by the EPA on water quality. If water quality is so poor that about 30 out of every 1,000 swimmers will get sick, governments should notify the public of this risk, according to these guidelines.
Scientists have to measure something in the water to determine if it makes people sick. In this case, it is Enterococcus, which is found in the intestines of warm-blooded mammals, including humans, meaning it comes off when mammals poop. Find Enterococcus and there are many chances that there is poop in the water as well. You find poop in the water and this indicates that there are harmful viruses and pathogens in the water as well. That’s why scientists call Enterococcus an “indicator bacterium.”
The crop-based test, which San Diego had been using for decades, tells us that more than 104 enterococcal organisms in a 100-milliliter water sample means the water is too dirty for human contact.
Once the scientists developed the new DNA counting water quality test, they had to figure out how much Enterococcus DNA also means the water is too dirty for humans. Enter Marva Seifert, an assistant professor at the University of California-San Diego who worked in the study behind the new test.
After running hundreds of water samples under both tests, the team of researchers concluded that 1,413 copies of this organism’s DNA equate to the risk posed by 104 enterococcal bacteria. So now, San Diego County knows it needs to post its new beach signs warning of possible wastewater contamination when water tests show bacterial DNA above that 1,413 number. “This is the first step in identifying what the correlation is between the number of DNA copies and the culture results,” Seifert said. “I don’t think it’s a hard and fast number, but it’s a very good indicator that there are potentially harmful bacterial viruses in the water.”
What this means is that this is the best figure considering the data the researchers had at the time of the study.
The problem remains that once the new technology is applied to South Bay waters, it shows much higher levels of bacteria than the public expected. Therefore, if the beaches were closed only on the basis of water quality tests, which the county maintains is not the case, the coasts from Tijuana to Coronado could be closed much more frequently, even in the summer.
There are some things that no test can do, such as distinguishing between human or animal feces in water samples. It is more dangerous for humans to come in contact with human waste, as they can transmit viruses more easily.
And San Diego County may be careful when deciding whether to close a beach or not.
“(The test) is not an indicator of human wastewater. It could be any type of animal or human bacterium,” Elise Rothschild, an environmental health specialist at the county’s Department of Environmental Health, told me.
However, this is why South Bay’s coastal water quality is now considered unsafe for human health more often than we have ever seen before.
Today we will explain the science behind a whole new technology for measuring water quality. San Diego is already the first in the world to use it and has already generated controversy.
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