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Antibiotic pollution in rivers follows 65% increase in human consumption, study shows

Human consumption of antibiotics increased by 65% between 2000 and 2015. These drugs are not completely metabolized while passing through the body, nor completely destroyed or removed by most wastewater treatment facilities.

in PNAS Nexus, Heloisa Ehalt Macedo and colleagues calculate that worldwide humans consume around 29,200 tonnes of the 40 most used antibiotics. After metabolism and wastewater treatment, an estimated 8,500 tonnes (29% of consumption) may reach the world's river systems, and 3,300 tonnes (11%) may arrive at the world's oceans or inland sinks (such as lakes or reservoirs).

The authors calculate these figures using a model validated by data on measured concentrations of 21 antibiotics at 877 locations globally. While the total amounts of antibiotic residues translate into only very small concentrations in most rivers, which makes the drugs very difficult to detect, chronic environmental exposure to these substances can still pose a risk.

Antibiotics in rivers and lakes can reduce microbial diversity, increase the presence of antibiotic-resistant genes, and possibly impact the health of fish and algae. The authors calculate that levels of antibiotics are high enough to create a potential risk for aquatic ecosystems and antibiotic resistance during low-flow conditions (i.e., at times of less dilution) on 6 million kilometers of rivers.

Waterways with high concentrations are found across all continents, with the most impacted regions located in Southeast Asia. Amoxicillin is the antibiotic most often predicted to be found at high-risk concentrations and is the most-consumed antibiotic around the world.

The authors note that this version of their model does not include antibiotics given to livestock, which include many of the same drugs, or pharmaceutical manufacturing waste. However, the results show that antibiotic pollution in rivers arising from human consumption alone is a critical issue, which would likely be exacerbated by veterinary or industry sources of related compounds.

According to the authors, monitoring programs and strategies to manage antibiotic contamination of waterways, especially in areas at risk, are warranted.