ANNA ROTHSCHILD: This is Science Friday. I’m Anna Rothschild filling in for Ira Flatow this week. Later in the hour, a new book explores how Earth bursts into life. Plus the science of grilling, just in time for your holiday cookout. But first, the Paris Summer Olympics are fast approaching. Opening ceremonies for the Games kick off in less than a month, and all eyes are on the River Seine. It’s a notoriously polluted river. Due to aging infrastructure, sewage has sometimes flowed directly into it.

For the past hundred years, swimming in the river was banned, but the French government has spent roughly $1.5 billion to upgrade sewage treatment in Paris in time for athletes to be able to swim in the Seine. Earlier this week, Paris Mayor Anne Hidalgo was set to take a dip in the river to prove its cleanliness. In protest, some Parisians threatened to poop in the Seine to show their dislike of the disruptions and high price tag of the Games. The dip was postponed until after upcoming elections, but recent water-quality tests indicate that the river is not yet safe to swim in.

Joining me now to talk about the current state of the river is my guest Dan Angelescu, the founder and CEO of Fluidion, a water-testing company based in Paris, France. Dan, thank you so much for being here.

DAN ANGELESCU: Thank you very much, Anna. It’s a pleasure.

ANNA ROTHSCHILD: Let’s dive right in. What pollutants are you screening for in the Seine?

DAN ANGELESCU: Well, we’re particularly looking at any kind of fecal-indicator bacteria. These are bacteria such as E. coli, Escherichia coli, and Enterococci, which are found whenever there is sewage contamination to a waterway. So we look for those, and, generally, when there are large concentrations of these fecal indicators, it means that there are a lot of other pathogens associated with it.

ANNA ROTHSCHILD: So you’re testing the Seine every day. What’s the latest testing of the river showing?

DAN ANGELESCU: If we look at the results from the past few days here, we had better results in the past couple of days than we had previously. We have levels between 1,300, 1,700 E. coli per 100 mil. But this is still above the threshold that the European regulations and also the World Triathlon regulations allow for in terms of swimming.

ANNA ROTHSCHILD: Can you put that into context for us? Like, just how dangerous would it be to swim in the Seine in its current state with that much E. coli?

DAN ANGELESCU: You can swim in it, and nothing may happen. It’s not a given that you may get sick. It’s just that based on epidemiological studies that have been done decades ago, the risk goes above a certain threshold that you might get sick. And it really depends on you a lot. If you have a very strong immune system, you’re in really good shape, nothing may happen to you. But if you have a weaker immune system or if you’re a kid and you get diarrhea and you can dehydrate, that can be really dangerous. So you can even die from exposure to some of the pathogens in the water.

It’s not that E. coli or the Enterococci generally that will get you but everything else. Most often it’s norovirus. But we screened for E. coli and Enterococcus because these are relatively standard to measure and can provide a pretty good indication of the risk.

ANNA ROTHSCHILD: Just to make sure I’m understanding, basically it means that the E. coli is like a proxy for how much poo is in the water, and the fecal matter will contain other pathogens that might be bad for you.

DAN ANGELESCU: Exactly. And E. coli also comes from poo that’s not necessarily human. It can come from dogs, from birds. It can come from cow manure and other sources. So in order to understand that, we also trace other human markers, as we call, which are certain organisms that are only found in the human intestinal tract. So that allows us to also have confidence that the E. coli we measure actually comes from human poop, and that is associated with the highest risk.

ANNA ROTHSCHILD: That’s really interesting. So I’ve read that the high levels of E. coli from your recent tests may be related to heavy rainfall. How does that happen?

DAN ANGELESCU: Yes, so, indeed, high rain has been traditionally associated with the important pollution from sewage. And the way that works is that in Paris we have a combined sewer system, which means that rainwater and sewage, they go through the same pipes. And normally in dry weather or with very little rain, it all goes to a wastewater plant. It’s treated and then released back into the river.

But when you get a lot of water, a lot of rain, well, the sewage system is unable to transport all that, right? So whatever is over, the capacity of the sewage system and of the treatment plants is released back in the river. And when it is released in the river, that’s essentially raw sewage that’s released, and that is really dangerous.

What the city has been trying to do is to stop the overflow from happening, and the way they tried to do that is by retaining it before it goes into the river. So they built underground storage tanks, which can store a few Olympic-sized pools of water mixed with sewage. And if the rain event is relatively small, then that should not overflow. And we’re not sure exactly if and when these will be operational. So this is one of the things we’ve been monitoring for to try to see in the data, what are the results of that?

ANNA ROTHSCHILD: Interesting So I know that the city built this giant water basin, the Austerlitz water basin, and it holds 20 Olympic pools full of water, something like that. Is that not operational yet?

DAN ANGELESCU: We don’t know. It was inaugurated officially, but by looking at the data, we cannot tell that it’s operational. We still see levels of pollution that are similar to what we saw earlier in the season.

ANNA ROTHSCHILD: Now, to be clear, you don’t have a contract with the city, right? How did you decide to start collecting water samples in the Seine?

DAN ANGELESCU: Well, first, we are on the borders of the Seine River, and we are developing water-quality instrumentation. So the Seine River has been our playground for many years, in a way. That’s where we do all our research. So we sample for our own research. That’s how we develop our instruments, and we use Seine samples every single day. This is a pretty big event, so we decided to start an independent sampling campaign.

But then in previous years, we have worked with the city, and the city decided for the Olympic Games to only stay with laboratory data, which is a decision on their side. And we continued monitoring on our own and developing the densest independent data set of water quality in the Seine River.

ANNA ROTHSCHILD: Has there been an improvement in the water quality since you began sampling?

DAN ANGELESCU: Well, a little bit. We can see that water quality has slightly improved. We had a dry period at about the beginning of the month of June until the 15th of June, and we saw that water quality has improved during that period. Then we had rain events again, and then water quality has degraded again. So it goes up and down.

Just yesterday, we measured some of the best water quality we’ve recorded since the beginning of April when we started monitoring, but it’s one data point so far. We’ll see if that trend continues and if the water quality will improve significantly after that.

ANNA ROTHSCHILD: The Olympic Committee remains committed to doing the triathlon and marathon swimming in the Seine. Do you think it will be clean enough to swim in by then?

DAN ANGELESCU: Well, that is the million-dollar question, and it is a little bit difficult for me to respond to that. I don’t know. I don’t know. The data will tell. This is where having systems that can provide you with water-quality results very quickly is essential because we see the water-quality results changing significantly from day to day, and if you don’t have timely data, it’s going to be very difficult to say whether the river is safe or not. So the data will tell. That’s all I can say.

ANNA ROTHSCHILD: Great. The ultimate plan is for people to swim in the river again recreationally next summer, so 2025. Is that realistic?

DAN ANGELESCU: Well, if this infrastructure project is effective and it does reduce the combined sewer overflows in Paris, then there could be portions of the river where water quality might be, for certain weeks of the year, acceptable for swimming. In past monitoring, we have seen several weeks on end where water quality was acceptable for swimming day after day. This usually happens during the driest part of the summer when there is a lot of sunlight and there is little river flow. So the water is not very perturbed. There is a lot of UV light that can kill the bacteria in the water, so the water flow is slow. So there is no sediment resuspended, and there are no rain events which would create combined-sewer overflows.

This is generally when we see the water quality improving significantly. So far this year, we haven’t been so lucky with the weather. It’s been raining a lot during the month of May, and now it’s raining again beginning of June until the middle of June.

ANNA ROTHSCHILD: Is the fact that there’s E. coli in the water a sign that the improvements haven’t worked, or is water contamination just bound to happen sometimes in a big, old city like this?

DAN ANGELESCU: Well, no. I mean, what we see is not necessarily a sign that the infrastructure projects are not working. They might be working, and the river is also polluted from upstream of where this capture project is. This one captures, really, the sewage releases within Paris, but you have plenty of cities upstream which have combined sewers, and then you have other sources of pollution. You have wastewater plants that release their effluent in the river.

Now the city now is implementing disinfection of the effluent, so that shouldn’t be a big contribution. But you have many houses that have illicit connections to the storm drainage rather than to the sewage. So they release their poop, if you’d like, directly in the river. And historically, there have been errors done by plumbers maybe a hundred years ago which now result in this having a big effect on water quality.

But looking for all of these sources of pollution house after house, it does require a lot of expertise. It does require time, and it’s not an easy project. So the city has done a very decent and honest effort to try to look for all those sources of pollution, but I think the river comes already polluted at the entrance of Paris. And if that is the case, you can not clean it. All that this big infrastructure project does is that it stops new pollution to be added to whatever comes in into Paris. So if it’s polluted when it comes in, you won’t clean it by the time it gets to the Olympic side.

ANNA ROTHSCHILD: Yeah, it’s a huge infrastructure project. Dan, thank you so much for taking the time to speak with me. I really appreciate it.

DAN ANGELESCU: Thank you so much as well. And I hope that this will raise interest about water quality, which is a global issue. It’s not only in Paris. It happens everywhere.

ANNA ROTHSCHILD: Dan Angelescu is founder and CEO of Fluidion, a water-testing company based in Paris, France.

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