Toxicity of human urine and its main nitrogen excretory and degradation products to Daphnia magna

• The discovery of nitrogen as a major cause of eutrophication, especially in the marine environment, has intensified the research on nitrogen removal from sewage water. About eighty percent of the nitrogen in domestic sewage water originates from human urine. One alternative for nitrogen reduction technology in sewage treatment, is to separate the urine from fecal matter, and use the urine as a fertilizer, either in agriculture or in aquaculture. In temperate regions urine has to be stored during the winter season. The objectives of this study were to determine the toxicity to Daphnia magna of human urine, its major nitrogen excretory products (urea, uric acid, ammonia and creatinine) and their degradation products (nitrite and nitrate) and to determine how storage affects the chemical composition of these nitrogen compounds in urine and the resulting effect on urine toxicity to D.magna. The 48-h EC50 for D.magna of fresh morning urine from ten persons ranged from 2.8 to 12.5 percent by volume (mean +/- SD: 5.4 +/- 2.9). The 48h EC50s (expressed as mM of nitrogen) for the nitrogen compounds were 679 for urea, 78 for nitrate, 49 for creatinine, 2.4 for uric acid, 1.5 for ammonia and 0.6 for nitrite, at pH between 8.2-8.5. The toxicity of urine increased approximately five rimes during storage in 32 days at 20 degrees C. The major cause of this increase was conversion of urea to ammonia, which was accompanied by an increase in pH from 5.7 to 9.7, making the ammonia even more toxic. Therefore, the use of human urine as a fertilizer in aquaculture and probably also in agriculture must consider the potential toxicity of ammonia.

Ämnesord

NATURVETENSKAP  -- Biologi -- Annan biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Other Biological Topics (hsv//eng)

Nyckelord

Daphnia magna

toxicity

human urine

ammonia

nitrate

nitrite

creatinine

uric acid

storage

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