Drowning (Signs Of) (World of Forensic Science)
A forensic examiner must consider that a body recovered from water may or may not have been dead when the water was entered. If the person died in the water, there are several possible causes of death, including drowning. It is actually difficult to prove drowning as a cause of death with 100% accuracy. The forensic pathologist cannot rely on autopsy or laboratory findings alone. Instead, the pathologist may focus on elimination of other causes for the death and on the circumstances surrounding the event.
Immersion of a body in water causes certain characteristic changes that are not necessarily signs of drowning. The skin on the palms and soles becomes white and wrinkled. A similar effect is seen on the tips of the fingers in someone who has their hands in water for extended periods of time. After a few days in water, this macerated skin will begin to separate, and after about a week, it will peel off from the body.
There may also be some evidence of decomposition when a body is pulled from water, although this occurs more slowly than it would on land. After about two weeks in water, the rest of the skin and the hair are sloughed, and the face, abdomen, and genitals become bloated with the gases of decomposition. This results in most bodies eventually floating to the surface, unless they have been weighted down to avoid discovery. Predators, such as fish and reptiles, will tend to prey on a corpse in water and this will accelerate decomposition. The body may also knock against objects in the water such as boats, piers, and rocks, and this may cause postmortem injury.
Drowning occurs when water enters the airways and blocks off the supply of oxygen to the body. When this happens, the person will struggle to breathe and will cough, which unfortunately sets off a reflex action that only draws more water into the lungs. The person will generally lose consciousness within a minute or two and then the heart will stop. The brain is the most vulnerable part of the body to oxygen deprivation and it can usually survive for less than four minutes before irreversible damage occurs, along with cardiac arrest. In some cases, however, hypothermia, or the chilling of the body that occurs in cold water, has protected the brain by slowing metabolic demands for oxygen, and allowed the person to survive.
The mechanism of drowning differs depending on whether the person was found in fresh water or salt water. Fresh water enters the circulation through the lungs rapidly and dramatically increases the blood volume, creating great strain on the heart. The massive dilution of the blood also causes substantial disruption to its normal chemistry and starts to break down red blood cells. Sea water has an opposite effect. It draws fluid from the blood plasma into the lungs. This does not have the effect of increasing the workload on the heart, so people tend to survive for longer before drowning in salt water.
Postmortem, there may be few obvious signs of drowning on external examination. There may be a copious (visible amount of) froth, perhaps bloodstained, that has come from the lungs and surrounds the nose and mouth. This is a mixture of water and protein from the blood plasma, which froths up as the person struggles to breathe. However, the froth is not always present in cases of drowning and should not be relied on as an indicator.
Internal examination may reveal froth in the windpipe and lungs. Although the lungs are usually swollen, spongy, and full of water on drowning, this can also be seen with other causes of death, such as drug overdose or cardiac arrest upon hitting the water. The struggle to breathe causes great pressure to the sinuses, which often bleed and sometimes leave evidence of hemorrhage.
Laboratory tests may reveal the presence of diatoms in the body. Diatoms are microscopic algae found in both seawater and fresh water. Their silica-based skeletons do not readily decay and they can sometimes be detected even in heavily decomposed bodies. If the person is still alive when entering the water, diatoms will enter the lungs if the person inhales water and drowns. The diatoms are then carried to distant parts of the body such as the brain, kidneys, and bone marrow by circulation. If the person is dead when entering the water, then there is no circulation and diatoms cannot enter the body. Diatoms do not occur naturally in the body. If laboratory tests show diatoms in the corpse that are of the same species found in the water where the body was recovered, then it may be good evidence of drowning as the cause of death. However, the diatom test is now considered very unreliable and would never be used, on its own, as evidence of drowning. The forensic pathologist has to rely on many other sources of evidence to determine cause of death when a body is found in water.
SEE ALSO Death, cause of; Death, mechanism of.