Antibiotics are flowing down the world’s rivers. Scientists warn of this silent threat

Antibiotics are one of the cornerstones of modern medicine. They save lives by inhibiting the development of bacterial infections. However, their indiscriminate use brings unexpected consequences. They do not just affect hospitals or farms, but also nature. A new study, the results of which were published in PNAS Nexus, highlights the scale of the problem – 6 million km of rivers around the world were found to exceed safe levels of antibiotic concentrations. That’s more than the length of all river networks in Europe and Africa combined.

As much as 29 percent of antibiotics end up in rivers

A team of researchers, led by Rim Jim of York University, has developed a global model of antibiotic transport in the aquatic environment. The researchers took into account demographics, drug consumption and their metabolism in human bodies. Based on the 40 most commonly used substances, they estimated that people around the world consume about 29,200 tons of antibiotics annually. Of this number, as many as 20.5 thousand tons (68 percent) are excreted, but are still biologically active. Some are degraded or retained in sludge and purification processes, but a significant amount ends up in the environment.

According to the global dispersion model used by the researchers (HydroFATE), each year 8,500 tons of antibiotics enter watercourses, which means that almost one in three grams of used drugs goes directly into the aquatic environment. As many as 3,300 tons reach the final recipients, namely lakes, seas and oceans.

Not only nature in danger

The threat of antibiotics in rivers goes beyond ecology. Although fish, invertebrates or algae are at risk of physiological disruption and changes in community structure, the greatest risk is to humans and comes in the form of increased antibiotic resistance. Contact of microorganisms with low concentrations of drugs in the environment can lead to the selection of resistant strains, which can then enter back into our bodies, such as through contact with water or food consumption.

According to the World Health Organization, antibiotic resistance is among the most serious public health threats. And while the fight against this phenomenon is mainly taking place in hospitals, the source of the problem we have created can be traced back to rivers.

Amoxicillin, ceftriaxone and cefixime under the magnifying glass

Not every antibiotic poses the same risk. A Risk Quotient (RQ) was calculated for each compound (21 antibiotics were considered), which compares the predicted concentration of a substance with a threshold value below which no environmental impact is observed. If RQ ≥ 1, the substance may have adverse effects on aquatic organisms or promote the development of antibiotic resistance in environmental bacteria.

Analyses showed that some 6 million river kilometers globally exceed RQ limits ≥ 1. The study clearly identified the leaders of this infamous list: amoxicillin, ceftriaxone and cefixime. These are popular antibiotics used to treat respiratory, urinary tract and middle ear infections, among others. Their ubiquity, combined with their low removal efficiency in standard wastewater treatment plants, results in significant accumulation in surface waters.

Asia at the top of the infamous ranking

Antibiotic contamination is not evenly distributed worldwide. Countries with high population density, high antibiotic use and low levels of wastewater treatment are most at risk. Topping the list are India, Pakistan and China. In these countries, many rural areas do not have access to sewage systems, and wastewater is often discharged directly into rivers.

However, the problem also affects developed countries. In the large metropolitan areas of Europe and North America, overburdened and outdated wastewater treatment systems also fail to remove pharmacological substances. Seemingly clean water can bear the marks of medical decisions.

New data, new scale of challenge

It is worth mentioning that the study focuses only on emissions resulting from human drug use. It does not take into account agents used in animal husbandry or the pharmaceutical industry. And yet we are talking about millions of kilometers of rivers at risk. What’s more, the model has been verified using actual data from 877 locations around the world – these are not theoretical estimates, but calculations based on specific measurements.

What’s next?

Scientists leave no doubt – the time has come for concrete action. At the top of their list of priorities, they mention improving wastewater treatment technology, reducing the unnecessary use of antibiotics, and introducing systemic monitoring of the presence of pharmaceuticals in the environment. Otherwise, rivers, will cease to be a source of life, and will become vectors of resistance, which can no longer be stopped.