How to Read a Story About Health and Science
Journalists are taught to put the most important aspects of the story they are writing into the first paragraph, called the “lede” (a deliberate misspelling of the word “lead”). Then, as they go along, more and more details and specifics are revealed. Many readers never get past that first paragraph and therefore miss all those details, a practice that can lead us astray when the article is about health and science.
We came across a good case in point of this problem in a story published online by a group called FingerLakes1.com. As we have noted, Critica is involved in a study of how people view the safety of their municipally supplied tap water, and so we were immediately drawn to the headline “Chlorine byproduct that contaminates local tap water linked to thousands of bladder cancers in Europe.”
The first paragraph of the story reads as follows:
The routine use of chlorine as a disinfectant in public drinking water across the Finger Lakes [a region in upstate New York] generates toxic chemical byproducts well above levels that recently triggered alarms in Europe over their links to bladder cancer.
There is absolutely nothing false about the above statement. Chlorine is added to water as a disinfectant to kill disease-causing microorganisms, like those that cause cholera and typhoid fever. One group of chlorine breakdown products that are found in drinking water are the trihalomethanes. Last January, a European study was published in the journal Environmental Health Perspectives that claimed that exposure to levels of THMs well below the maximum allowed in the U.S. is responsible for 5% of all bladder cancers, or about 6,561 cases per year in the European Union. The report in the Fingers Lakes online news picked up on this study, as did many other media outlets.
Reading that first paragraph will understandably terrify many of us. Could it be the case that by drinking the water from the faucets in our homes we are putting ourselves at risk for bladder cancer? Should we start purifying our tap water with filters or even switch to bottled water?
Or maybe first we should read a little further down in the Fingers Lakes article. In the eighth paragraph the European publication that triggered the article is heralded as a “major” study. That’s always a bell-ringer because what constitutes a “major” study is entirely in the eyes of the beholder. The journal Environmental Health Perspectives is a peer-reviewed journal, supported by the federal National Institute of Environmental Health Sciences, so what appears there can be seen as generally good science. But this particular study is only one of many that have examined health effects of THMs (also known as TTHMs) and not all have concluded that there is a substantial risk to human health. For example, a paper published in 2019 concluded that “Causal drinking water-related bladder cancer risks remain questionable and likely small compared to other factors…” So what makes the 2020 study “major?” Perhaps only the fact that its conclusion is alarming? Is the author of the Fingers Lakes story making an unwarranted value judgment here? After all, it is highly unlikely that studies showing that THMs don’t cause health problems will attract much attention.
The U.S. Environmental Protection Agency (EPA) places an enforceable maximum concentration level (MCL) on THMs in drinking water of 80 parts per billion (ppb). Animal studies suggest that that level is unlikely to cause the kind of cell damage associated with cancer. The Finger Lakes article spends considerable time noting instances in which the level of TCMs in drinking water in various municipalities in its area were found to be above 80 ppb. However, it is important to note that EPA mandates that water authorities monitor the levels of things like THMs on a regular basis and if they exceed the MCL they must both notify their customers immediately and take corrective action. Hence, it is unlikely that there is long-term exposure to elevated levels.
And if you read far enough down the Finger Lakes article you come across this statement: “Despite the fact that the Finger Lakes water systems produce TTHMs at rates significantly above the European and U.S. averages, the region has not been a particular hotbed for bladder cancer, according to the state’s highly detailed cancer registry.” A little further down you will read “…bladder cancer rates are influenced by a host of other factors besides disinfectant byproducts. Factors like smoking may be even more influential…bladder cancer rates and lung cancer have followed roughly similar trajectories, declining slightly in recent years as the prevalence of smoking has fallen off.” Now the risk of bladder cancer from drinking tap water perhaps seems a little less ominous than the headline and first paragraph would lead us to believe.
In fact, cigarette smoking is the leading risk factor for bladder cancer, causing about 50% of all cases. Every year there are approximately 81,400 new cases of bladder cancer in the U.S., so if we accepted the European study’s finding that 5% of those can be attributed to THMs in drinking water, that means slightly more than 4,000 cases. There are also many other risk factors for bladder cancer besides cigarette smoking and the American Cancer Society does not even list THMs as among them.
A Risk-Benefit Perspective
It is also important to consider a risk/benefit perspective. What if we did stop chlorinating our drinking water? Chlorination is a relatively simple and inexpensive way of disinfecting water and killing disease-causing bacteria and viruses. Without chlorination, we would be at risk for serious waterborne illnesses like cholera and typhoid fever, both of which are extremely uncommon today in the U.S. but not so in countries that do not have modern water purification systems. The EPA mandates a detectable level of chlorine be present in drinking water, up to a maximum of 4 parts per million (ppm).
So what are the risks and benefits of water chlorination? It is possible, although debated, that over a lifetime of drinking chlorinated water there is a small increased risk of bladder cancer. To put this in perspective, there are a little under 3 million deaths in the U.S. every year. There are slightly less than 18,000 deaths from bladder cancer annually in the U.S., so if 5% are attributed to THMs, that would be about 900 of the 3 million total deaths. And the risk of bladder cancer from drinking water is, again, unclear.
If we wanted to avert those possible 900 deaths, we could remove chlorine from the water. It is impossible to estimate at this point how many people would get sick or die from the resulting waterborne disease that would surely follow. The World Health Organization estimates that 120,000 people die from cholera worldwide every year.
We could institute an alternative method of disinfecting water. Ultraviolet (UV) light is an effective disinfectant. It was used in the U.S. in the early 1900’s, but abandoned due to high operating costs. Would we now be willing to install UV treatment equipment in municipalities throughout the U.S.? We were unable to find estimates about how much that would cost.
The story about chlorine safety is clearly far more complex than is captured in the headline and first paragraph of the Finger Lakes article. If one does take the time to read through the entire article, this begins to become clear, but unfortunately, most of us do not even read a newspaper article past the headline.
Even reading the whole article will not get you enough insight to really make an informed decision about whether water chlorination is safe. That can only come from doing further research and then doing the most difficult thing of all—making a risk/benefit analysis.
Risk/benefit analyses are particularly hard to stomach when the risk involves deaths. We are of course highly uncomfortable with the notion that a small number of potentially preventable deaths is acceptable if a larger number of deaths can be prevented. A headline linking chlorine byproducts to “thousands of bladder cancers” obscures the fact that many more people would develop potentially fatal illnesses if we stopped chlorinating our water supply, or that the alternative to chlorination requires a decision to pay for it with tax dollars that are also needed for healthcare, education, transportation, and public safety. Science journalists have a tough mission. On the one hand, like all journalists, they have to attract readers. They know that most people will not read much beyond the lede and therefore must cram in the most attention-getting material in a sentence or two at the very beginning. On the other hand, they are responsible for informing the public as accurately and clearly as possible about emerging science. Knowing that, it becomes critical that we media consumers always read past that first paragraph and give the journalist a chance to describe all the nuances and caveats that apply to that first paragraph. And if we don’t find them by the time we reach the end of the story, it’s time to consider doing some research on our own.