A recent study paints an alarming picture of the levels of antibiotics in the river basins of China, the world's largest producer and user of antibiotics.
The study, started in 2006 by the Guangzhou Institute of Geochemistry under the Chinese Academy of Sciences, studied the discharge of 36 frequently detected antibiotics and built a model predicting levels of antibiotics in all 58 river basins across the country.
The study found that the average antibiotics levels in river basins of the densely populated, economically developed eastern and southern China were more than six times higher than in less developed western China.
Northern China's Haihe River basin, mainly covering Beijing, Tianjin and Hebei province, and southern China's Pearl River basin were the most worrying, according to the study.
The high antibiotic concentration in the Haihe River basin is due to the river's slow flow and low rainfall, which make it difficult to dilute the large antibiotics emissions from Beijing, Tianjin and densely populated Hebei province.
The Pearl River basin had the highest level, because of its large population and prosperous livestock breeding industry.
"Antibiotics in water and soil can enter the human body if people drink contaminated water or eat food grown with contaminated water. But the amount ingested in this way is small compared with that from medical treatment," Ying Guangguo, leader of the research team at the Guangzhou Institute of Geochemistry, said on Thursday.
"The biggest danger from antibiotics abuse and poorly treated antibiotics emissions into the environment is increased bacterial resistance, which will make it harder for medicine to work effectively and eventually harm public health," Ying said.
"Antibiotics will inevitably increase bacterial resistance, but we need to slow the process so later generations will still have effective medicines to kill bacteria," he said.
"The most appalling finding of the survey is that some rural pig farms directly discharge faeces and urine into the river," he said.
"On average, the wastewater produced by one pig is equal to that of 10 people, and one farm might have up to 10,000 pigs."
Ying urged the government to increase the supervision of hospitals and farms as well as sewage plants, and start monitoring the concentrations of antibiotics in the most affected river basins as soon as possible.