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According to statistics from the World Health Organization, death by drowning is the third leading cause of accidental or unintentional death worldwide. 7% of all injury-related deaths are the result of drowning, adding up to approximately 236,000 people a year, according to statistics through 2019.
Interestingly, the vast majority of these deaths occur in freshwater, rather than saltwater. In this sense, a study determined that approximately 90% of deaths related to drowning occurred in fresh water, whether in swimming pools, bathtubs or rivers. In fact, according to statistics from the United States Center for Disease Control (CDC), most drownings occur among children between the ages of 1 and 4, they occurred in swimming pools and bathtubs, mainly due to parental carelessness.
This leads us to ask the following questions:
Is the difference in the frequency of drowning in freshwater due to more people being exposed to freshwater than saltwater? Or is there some real difference between drowning in salt water and fresh water that makes the latter more dangerous?
To answer these questions, let’s start by understanding what happens when a person drowns.
What does it mean to drown?
A person drowns when water or any other liquid enters the lungs, blocking the passage of air that allows gas exchange between it and the blood. Simply put, drowning is not the same as drowning and only about 1/3 of drownings are usually fatal.
How does death by drowning occur?
When drowning, death can come from several mechanisms:
The most obvious of all is suffocation, that is, the lack of oxygen, which is vital for the functioning of all the cells in our body. When we drown, access to oxygen from the air is blocked, since our lungs are not equipped to extract the oxygen dissolved in the water. When this happens, after only a few minutes, the cells of our body will have completely consumed all the oxygen present in our blood and will not be able to keep going the cellular respiration mechanism that produces ATP, which, in turn, drives the metabolism. most cellular processes and that makes life possible.
However, this is not the only reason why people drown. In fact, many die even after removing the water from the lungs and reestablishing gas exchange with air. In these and other cases, people do not die from hypoxia, but from heart attacks or other complications related to ingesting and breathing large volumes of water. However, this depends to a large extent on the characteristics of the ingested water, in particular, on the osmotic concentration of the water, as we will see below.
What happens when drowning in fresh water?
Let’s start with the case that statistics indicate is the more dangerous of the two, drowning in fresh water. It might seem counter-intuitive to think that it’s worse to breathe fresh water than salt water, especially knowing how unpleasant and heartbreaking the latter can feel (as any child swimming at the beach for the first time will confirm). However, the danger of fresh water lies precisely in its purity.
Contrary to salt water, fresh water is practically pure water. This means that it has a very low concentration of solutes and therefore a very low osmolarity. As a consequence, fresh water is hypotonic in relation to our blood. For this reason, when we expose the cells of our body to fresh water, the water tends to enter the cells through the membrane through the process of osmosis.
When this happens, two things can happen:
- When water enters the cell, it becomes hypotonic with respect to our blood plasma and, therefore, the cell discharges excess water into the bloodstream.
- That the cell does not discharge excess water and swell until it bursts, a process known as osmotic lysis.
Either of these two processes is very dangerous when we drown in fresh water.
Consequences of excessive absorption of water by the body
To begin with, fresh water does not break our skin cells since we have several layers of dead cells and keratin that do not allow water to pass freely. However, as we breathe in water and it enters our lungs, it comes into direct contact with lung cells that are not protected by layers of skin. On the contrary, they are fully optimized to facilitate the passage of gases from the air into the bloodstream.
As a consequence, fresh water easily enters our blood, increasing its volume and therefore diluting it at the same time.
The same is true when we ingest large amounts of fresh water (ie when we swallow it and it goes into our stomach, then intestines). Both pathways cause the body as a whole to absorb large amounts of water when we drown in fresh water.
Now come the secondary consequences of this excessive absorption of water. Excess water dilutes the blood, reducing its osmolarity. The decrease in osmolarity causes red blood cells (already more dilute due to excess water) to swell and burst (osmotic lysis of blood cells, or hemolysis). This reduces the blood’s ability to carry oxygen to our body’s tissues, even if we manage to remove all the water and re-establish breathing.
On the other hand, dilution severely alters the ionic balance of the blood and this can cause ventricular fibrillation in the heart followed by cardiac arrest in a matter of as little as three minutes.
Osmotic lysis of other tissues
Blood cells like red blood cells are not the only ones that can suffer the effects of osmotic lysis. Lung cells can also burst from osmosis absorption of pure water. This can cause severe damage to lung tissue, further limiting oxygen uptake after respiration is restored.
The main consequence of these side effects of contact with freshwater is that many people who drown in freshwater and are rescued in time do not die instantly from hypoxia but die hours later from heart failure and other complications.
hypothermic shock
Lastly, when the water in which we drown is very cold, there is an additional risk that can be even more dangerous than the previous ones. The entry of a large volume of cold water into the blood can suddenly reduce core body temperature, having in just a few minutes the same effect as being exposed to cold temperatures for hours. This hypothermic shock can also quickly lead to cardiac arrest.
What changes when drowning in salt water?
Unlike fresh water, salt water contains a high concentration of salts and other solutes. This gives salt water a much higher osmolarity than fresh water. That being said, the consequences of drowning in salt water strongly depend on the particular concentration of salt in the water, since different bodies of salt water such as seas and oceans do not always contain the same osmolarity.
The case of isotonic saltwater
On average, seawater has an osmolarity very similar to that of our blood. This means that it is isotonic with blood plasma. As a consequence, since there is no difference in osmolarity that drives osmosis, when the cells of our body come into contact with seawater, they neither absorb nor release considerable amounts of water.
This means that most of the freshwater-related consequences listed above do not occur when we drown in these saltwater bodies. Generally, if a person swallows and/or breathes large amounts of salt water, removing as much water as possible is sufficient to restore breathing and save his life.
Of course, this depends on the person not having been in hypoxic conditions for too long, in which case brain damage or death may occur, whatever we do to get rid of the water.
The case of concentrated or hypertonic salt water
Some bodies of salty water such as the Dead Sea contain a much higher concentration of salts than the average oceans and seas and are therefore hypertonic solutions compared to our blood plasma.
Exposure of our lungs to hypertonic salt water has the opposite effect to that of fresh water. In this case, the tendency is for the water to leave the cells towards the salt water, trying to dilute it. As a consequence, blood plasma becomes increasingly concentrated and viscous, making it more difficult to pump through our circulatory system. This demands a greater effort from the heart, which can eventually fail under stress, causing cardiac arrest and death.
Concentrated blood also puts a greater strain on our kidneys, which now have to filter thicker blood. This can also lead to kidney failure and eventually death.
References
Center for Disease Control and Prevention (CDC). (2022, March 10). Drowning Facts | Drowning Prevention | CDC . CDC. https://www.cdc.gov/drowning/facts/index.html
González, RP (2015, June 16). Drowning by fresh and salt water . SlideShare. https://www.slideshare.net/leafartj1/drowning-by-fresh-and-saltwater-50607559
Juya, M., Ramezani, N., & Peyravi, G. (2019, July). Study of drowning in fresh and salt water . Journal of Injury & Violence Research. 11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7036150/
Ramos Aguilar, J. (1999, April 17). DROWNING AND NEAR DROWNING SYNDROME . medynet. http://www.medynet.com/users/jraguilar/ahoga.htm
Rocío, M. (2019, May 20). 8 Little-Known Facts About Drownings Around the World . Rolloid. https://rolloid.net/8-things-you-surely-didn’t-know-about-drowning-and-what-happens-around-the-world-2/
World Health Organization (WHO). (2021, April 27). Drowning . QUIEN. https://www.who.int/news-room/fact-sheets/detail/drowning
