Research and analysis

Determining selective concentrations for antibiotics and antifungals in natural environments: summary

Published 24 October 2024

Applies to England

1. Chief Scientist’s Group report summary

This project determined the concentrations of specified antimicrobials at which selection for resistance may occur. The findings will help the Environment Agency and others to assess the significance of environmental concentrations of these substances on the development of antimicrobial resistance (AMR) in the environment.

1.1 Background

Antimicrobial substances in the environment may drive selection for resistant microorganisms in soils and waters. Understanding the concentrations at which this selection occurs is vital to assessing the potential impact of environmental concentrations of antimicrobials on the development of AMR. To date, research in this area has focused on antibiotics and the water environment, with limited research on other antimicrobials, such as antifungals, or other environmental media, such as soil. This project aimed to determine selective concentrations for a range of clinical and agricultural antifungal compounds in water, and to explore possible concentration values for antibiotics and antifungals in soil based on extrapolation from water values.

1.2 Approach

The project applied a method originally used to determine selective concentrations for antibiotics in water based on extrapolation from existing data, known as Minimum Inhibitory Concentrations (MIC). The project used this method on a range of antifungal compounds chosen based either on the amount used in the UK or because of known detection in the environment. The project also explored the use of the Equilibrium Partitioning (EqP) approach to estimate selection concentrations for antibiotics and antifungals in soil. EqP is widely used in chemical assessment to predict thresholds in soil from thresholds in water.

1.3 Results

Selective concentrations in the water environment were derived for 17 of 53 antifungal compounds considered. For the remaining substances insufficient MIC data was available to apply the methodology. This was a particular problem with agricultural antifungal compounds, and we were unable to determine values for any of the specified substances. For the soil environment, the EqP approach was used to determine selection concentrations for 16 antibiotics and 10 antifungals.

1.4 Conclusions

The methods used require detailed data on the effects of antimicrobials to estimate the concentrations that may drive development of resistance. For many of the substances investigated there was insufficient information to calculate these threshold concentrations. Nevertheless, by considering antifungals this work is a step towards identifying thresholds for substances other than antibiotics. Alongside aqueous thresholds the project has also developed thresholds that can apply in soil, an area that to date has been relatively unexplored. The concentrations derived can be compared with detected concentrations in soil and water to consider whether they are high enough to drive the development of antimicrobial resistance.

1.5 Publication details

This summary relates to information from project SC220006/R, reported in detail in the following output:

• Report: SC220006/R
• Title: Determining selective concentrations for antibiotics and antifungals in natural environments
• Project manager: Helen Wilkinson, Chief Scientist’s Group
• Research contractor: Isobel C Stanton, UK Centre for Ecology and Hydrology

This work was carried out as part of the Environment Agency Chief Scientist’s Group research into AMR in the environment and has been funded by the PATH-SAFE programme which has been funded by HM Treasury through the Shared Outcomes Fund.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency