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Risk assessment of antimicrobial resistance (AMR) in wastewater treatment processes

Ordered: 18.02.2019

Report no: 2020:08

Published: 01.10.2020

Key message:

We have too little knowledge about how residues of antimicrobials and resistant microorganisms affect animals, humans and the environment. To get more representative and longitudinal data, VKM suggests establishing a new monitoring program for resistant bacteria in the environment, NORM-ECO.

This proposal from the Norwegian Scientific Committee for Food and Environment (VKM) is made in a scientific assessment of the effect of treatment methods for wastewater and sludge, and the development of antimicrobial resistance. The assessment was commissioned by the Norwegian Food Safety Authority and the Norwegian Environment Agency and is an extension of an assessment from 2009.

Development of resistance

Antimicrobial resistance is one of the greatest public health threats of our time. Exposure to antimicrobials is regarded as the main driver of resistance development and dissemination.

Resistant bacteria and residues of antimicrobials (antibiotics, antifungal agents, potentially toxic metals, and disinfectant agents) are excreted to sewage that goes to a treatment plant. The treatment plants produce purified wastewater and sludge. Antimicrobial agents and resistant bacteria that survive the treatment processes can be found in both products.

When sludge is used as a soil improver and fertiliser, resistant bacteria can be spread in arable soil, and thus recycled to the food production chains. Resistant bacteria are also released into rivers, lakes or fjords with the effluent wastewater, and can be recycled for food production from here.

Missing data

"There is no doubt that ecological systems are affected by residues of antimicrobial agents and resistant bacteria, but we lack understanding of how this affects animals, humans and the environment, " says Yngvild Wasteson, Scientific Leader of the project group.

She points out that there are different views on the importance of the release of residues of antimicrobial agents and resistant bacteria from treatment plants for the development of antimicrobial resistance.

"Single studies indicate that treated wastewater contributes relatively little to the total exposure to which organisms in aquatic and marine environments are exposed. On the other hand, freshwater environments may be an important reservoir for new determinants of resistance. It seems that a certain amount of antimicrobial resistance in wastewater-exposed rivers and lakes is inevitable, as compared to pristine water sources," says Wasteson.

A new and comprehensive study from Sweden shows that the use of sewage sludge on agricultural land over several years only resulted in minor changes in soil bacteria. No evidence was found that the use of treated sewage sludge increased the amount of resistant bacteria or resistance genes in the soil.

New monitoring program?

To provide more data, VKM proposes to establish a new monitoring program for resistant bacteria in the environment in Norway, which may be parallel to NORM (Norwegian monitoring programme for AMR in human pathogens) and NORM-VET (Norwegian monitoring programme for AMR in animal pathogens).

"Today's monitoring program lacks detection of resistance in the environment so that we can cover the entirety of people, animals, food and environment. We propose a “NORM-ECO” that can fill this knowledge gap. However, a new monitoring program means that we need research efforts to clarify a number of questions about assessing resistance in non-clinical environments, " says Wasteson.

The assessment is approved by VKM’s Panel on Microbial Ecology.

The Norwegian Scientific Committee for Food and Environment

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