Urine

Urine is a liquid produced by animals and humans through the kidney, and is collected in the bladder and excreted through the urethra. Urine formation helps to maintain the balance of minerals and other substances in the body. For example, excess of calcium is normally eliminated through the urine. Urine also excretes ammonia, the build-up of which is harmful to the body. In addition, urine is the result of a mechanism that maintains the appropriate amount of water in the body. A range of substances, including ethanol and artificial sweeteners, are also eliminated from the body through the urine.

Chemical Properties

pH

When it leaves the body, urine is usually at around pH 6, though it may be as low as 4.5, or as high as 8.2. As urea, the compound which accounts for 75-90% of the nitrogen in urine begins to decay, however, hydroxide ions form, raising the pH as high as 9-9.3.

The decay of urea into carbon dioxide is catalyzed by urease:

(NH₂)₂CO + H₂O → CO₂ + 2NH₃

Dissolved Heavy Metals

Because urine is a liquid collection of metabolic byproducts (whereas feces contains both metabolized and unmetabolized compounds), and because the concentration of heavy metals is low in metabolized compounds, this translates into a low concentration in urine.^[1] Studies of urine in organic cattle farms in Sweden in 1999 and 2002 yielded the following concentrations of heavy metals (all in μg/kg wet weight):^[2]

• Copper: 67
• Zinc: 30
• Chromium: 5
• Lead: 1
• Cadmium: 0

Urine Composition: Demographics

The presence of macronutrients in urine varies significantly from one region of the world to another. However, the amount of nutrients which is lost in the urine, in proportion to the amount of nutrients one consumes, remains relatively constant, as research by the Stockholm Environment Institute shows with the following data (it should be noted that no samples were taken in developed nations, where urine is not commonly used as a fertilizer):

Energy consumed per capita per day in each country:

Nutrients excreted in urine, in grams per capita per day.

Special uses

Taking advantage of the scents of male animals' urine, some companies sell animal urine, usually coyote or fox, to cities and other organizations to prevent their trees from being stolen for use as Christmas trees. The scents of carnivore urine (bobcat, mountain lion, and wolf, in addition to coyote and fox) are also sold to the public in pelletized form to repel garden browsing by herbivores such as squirrels and rabbits, as well as deterring domestic or feral cats from marking territory, or catching birds, in gardens. When the pellets are sprinkled on a target area, the intruding animal will instinctively recognize the territorial urinary scent of its predators and avoid the area. Additionally, in some cultures urine is used as an aphrodosiac during mating ceremonies.

Many drug tests and other clinical chemical analyses are done on urine. These test are used to find whether individuals are pregnant, drug users, or other hormone and substance usage questions.

In more rural times, urine was collected and used in the manufacture of gunpowder. Stale urine was filtered through a barrel full of straw and allowed to continue to sour for a year or more. After this period of time, water was used to wash the resulting chemical salts from the straw. This slurry was filtered through wood ashes and allowed to dry in the sun. Saltpeter crystals were then collected and added to brimstone and charcoal to create black powder.

Urine has often been used as a mordant to help prepare textiles, especially wool, for dyeing. Urine was used for dyes such as indigo where the urea in the urine reacted with the insoluble dye to form a soluble solution.

Urine is generally considered to be at least fairly sterile. When it leaves the body, however, the urine can pick up bacteria from the surrounding skin, which would contaminate it. However, it is not generally advisable to use urine to clean open wounds. Urine production and excretion is the body's primary method for removal of urea, a protein metabolic byproduct. Aquatic organisms such as fish, alternatively excrete ammonia. Birds and reptiles excrete uric acid, as a protein metabolic byproduct, instead of urea or ammonia. There are some exceptions to these excretion patterns.

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