Antibiotic1 medicines have been an important development for human health, and they’re credited with improving the average human lifespan. While important for human and animal health, there are issues from the overuse of these medicines, including antimicrobial resistance and possible environmental harms.
The Parliamentary Commissioner for the Environment's report Knowing what’s out there: Regulating the environmental fate of chemicals is an analysis of how New Zealand regulates chemicals2, including antibiotics, and how these chemical compounds enter and affect our environment. The report has case studies of a selection of chemicals that look at the life cycle of the substance, which includes its manufacturing, import, use, transport, disposal environmental fate3. The case studies are intended as examples of the different ways the environmental fate of chemicals are managed by New Zealand’s regulatory system.
Four chemicals were selected for this purpose, one of which was the antibiotic group, tetracyclines4.
Tetracyclines
Antibiotics are a set of drugs used to treat infection5 caused by bacteria6 and some other microorganisms7. An antibiotic will either kill bacteria or impede the growth or reproduction of the bacteria to stop the spread of the infection. This is referred to as their mechanism (or mode) of action. For example penicillin8 kills bacteria by destroying the bacterial cell wall9.
Tetracyclines are a class of broad-spectrum antibiotics including doxycycline and oxytetracycline. Tetracyclines are designed to inhibit10 protein synthesis11 in bacterial cells – this means they kill bacteria by preventing them from producing essential proteins, impairing cell12 growth and reproduction.
Tetracyclines are some of the most frequently used antibiotics because they act against a wide range of bacteria and are not very expensive. They’re used to treat human and animal infections13 in the skin, chest, urinary tract, genitals and lymph nodes14. They are used in combination with other medications to treat stomach15 ulcers and as a preventative for malaria16. In New Zealand, tetracyclines are mainly used in farmed animals (pigs, chickens, sheep and cows) with smaller amounts used for companion animals like cats and dogs and aviary birds.
The chemistry of tetracyclines
Tetracyclines can readily dissolve in water and are often not fully metabolised by the body. On average, more than 75% of tetracyclines consumed by humans and livestock are released into the environment in an active form (either as the main compound17 or as a metabolite18) via:
- faeces19 and urine
- the spread of manure and biosolids
- treatment plant effluents.
Tetracyclines have an affinity for sticking to the surface of soil (especially to acidic and clay20 soils), sludge, manure and sediments21. When they are bound to these types of soils, it means they are less likely to leach22 into surface water23 or groundwater24 or be taken up by non-target organisms. The stronger the bonds between soils and tetracyclines, the lower the uptake by organisms and the slower the degradation. This suggests that strong bonds may increase the time the antibiotic is active in the environment.
Once in the environment, ultraviolet light and microbial activity25 break down tetracyclines. In soils, the breakdown of tetracyclines is further influenced by the presence of specific metal26 ions27, type of soil and pH28. Fo example, the presence of magnesium and manganese oxides slow down the degradation process, while calcium or ferric (Fe³+) ions speeds it up.
Tetracyclines in the environment
Worldwide, tetracyclines are the second most frequently detected subclass of antibiotics in the environment. Tetracyclines and their metabolites29 have been found in low concentrations in above 80% of samples from environments surveyed overseas. Likely reasons for this high detection rate include repeated use of manure from livestock (who have been given tetracyclines) as a fertiliser30 and the long time it takes for tetracyclines to break down in soil. The strong adsorption31 and the slow degradation of tetracycline32 results in its persistence in topsoil, leading to potentially higher environmental risks to microorganisms..
Usually when faced with a lack of New Zealand-specific data33, scientists will look to overseas research. However, there is no systematic reporting for the amount of tetracycline antibiotics imported into New Zealand, so we can’t compare it to international levels.
Environmental concentrations of tetracyclines below the detection limits of analytical tools have been found to trigger antimicrobial34 resistance35 in some regions of Europe, Asia and North America.
Toxicity
Tetracyclines can have negative effects on non-target species36 (i.e. not the bacteria they are intended to kill) such as algae37 and invertebrates38. When compared to other antibiotics, tetracyclines are most toxic39 to beneficial to bacteria in the to soil, freshwater fleas and aquatic40 algae. While the toxicity41 of tetracycline compounds may be higher than that of other antibiotics, their availability and mobility to different systems is limited because of their affinity to soils, sediments and sludge.
Key environmental concerns
The toxicity of breakdown products (or metabolites) of tetracycline has yet to be fully assessed. While recent research has focused on the impact of tetracyclines on different organisms, there is a need to focus on the environmental risks associated with low exposure concentrations of both the antibiotic and it’s breakdown products.
To date, there are no accepted international guidelines, environmental limits or antibiotic reference standards for antibiotic pollution. This affects the way they are monitored and addressed in receiving environments.
The lack of monitoring of tetracyclines and tetracycline-resistant genes42 in the environment hinders our ability to assess their transport pathways, their interactions with other chemicals, and the potential risk for antimicrobial resistance development.
Knowing what’s out there: Regulating the environmental fate of chemicals
Report case study findings
These are some of the findings of the report case study on tetracyclines:
- There is some concern over the use of tetracyclines (and other antibiotics) in both humans and animals may trigger antimicrobial resistance in bacteria. There is a lack of regulation to monitor and treat tetracyclines at wastewater treatment plants or in manure as fertiliser in farmlands.
- Guidance is lacking for the disposal of antibiotic-containing vials that may contain residuals of the antibiotics. Currently, unused and empty containers are generally sent to landfill.
- The absence of monitoring programmes for antibiotics in different environments limits our ability to determine the risks they may pose to receiving environments.
How would you find solutions/solve some of the issues from the report findings? How might your approach differ if you were a scientist, a politician, a farmer, or a student at secondary school?
New Zealand’s current surveillance and the national antibiotic strategy
Some data on human and animal antibiotic consumption is collected via the Ministry of Health and through the Ministry of Primary Industry’s survey of use for animals. This valuable dataset helps identify volumes dispensed, general use patterns and the effectiveness of treatment.
The report Knowing what’s out there: Regulating the environmental fate of chemicals, stated that information collected through surveillance is fundamental for progressing the 2017 New Zealand Antimicrobial Resistance Action Plan – a strategy focused on addressing antimicrobial resistance.
In late 2021, the Office of the Prime Minister’s Chief Science Advisor (OPMCSA) produced the report Kotahitanga: Uniting Aotearoa against infectious disease and antimicrobial resistance, which notes “almost none of the recommendations made in the 2017 action plan have been put into place”. This report echoes the Parliamentary Commissioner for the Environment, stating, “We lack an understanding of the amount and distribution of antimicrobials in the environment in Aotearoa43 New Zealand, and we don't know what impact they have on the development of AMR [antimicrobial resistance], nor the potential flow-on impacts for human, animal, and plant health.”
Related content
The environmental fate of chemicals – a context for learning for learning uses this case study and two others to explore the socio-scientific44 issue of chemical use and environmental risks. The PLD article provides pedagogical information, curriculum links and inquiry questions.
Any use of antibiotics automatically creates resistance. Antibiotics are designed to either kill or inhibit the growth of bacteria. Bacteria react to this threat – as to any threat from their environment – by evolving. Learn more in Antimicrobial resistance explained, Global report on antibiotic resistance and Is the post-antibiotic era now here?
Understand threats to non-target species and the dilemmas involved in 1080 and the risk to non-target species.
Tetracyclines end up in soil – learn about Soil properties and What is in soil?
How could the contamination45 of tetracyclines impact organisms that live in soil? How could such contamination impact other plants and organisms?
Take a look at the condition46 of soils in Aotearoa New Zealand in the article Tupuānuku – land and soil, produced from the Ministry for the Environment and Stats NZ Environment Aotearoa 2022.
Useful links
The New Zealand Antimicrobial Resistance Action Plan can be downloaded from MPI.
The diagram of different classes of antibiotics and a brief overview can be found here.
Acknowledgement
This resource has been created from the case study of tetracycline antibiotics within the report Knowing what’s out there: Regulating the environmental fate of chemicals, with support from the office of the Parliamentary Commissioner for the Environment.
- antibiotic: A substance produced by an organism that kills bacteria.
- chemicals: Everything is made up of chemicals. All matter (anything made of atoms) can be called chemicals. They can be in any form – liquid, solid or gas. Chemicals can be a pure substance or a mixture.
- environmental fate: What happens to a chemical after it has been released, intentionally or unintentionally, into the environment. This can include the chemical’s movement from its original location, physical, biological or chemical transformations and/or its accumulation in the land, water or air.
- tetracyclines: A group of broad-spectrum antibiotic compounds. They are among the cheapest classes of antibiotics available and have been used extensively in treating human and animal infections and in animal feed as a growth promoter.
- infection: Invasion of the body or a species by something that could be harmful or cause a disease.
- bacteria: (Singular: bacterium) Single-celled microorganisms that have no nucleus.
- microorganism: A living organism which is too small to be seen with the naked eye and can only be observed using a microscope. Includes bacteria and most protists.
- penicillin: A type of antibiotic produced by the fungus Penicillium.
- cell wall: A tough, usually flexible but sometimes fairly rigid layer, that surrounds some types of cells.
- inhibit: Reduce or prevent.
- protein synthesis: When individual amino acids are joined together in a specific sequence to form a protein.
- cell: 1. Building block of the body. A human is made of millions of cells, which are adapted for different functions and can reproduce themselves exactly. 2. A simple electrolytic device that enables chemical energy to be transformed into electrical energy.
- infection: Invasion of the body or a species by something that could be harmful or cause a disease.
- lymph node: A group of small organs found throughout the body that form part of the lymphatic and immune systems. They filter the lymph to remove bacteria and toxins.
- stomach: An organ of digestion with a sac-like shape located between the oesophagus and the small intestine. It temporarily stores food, mixes and churns it with gastric juice and allows digestion of some of the protein content of food to take place.
- malaria: An infectious disease caused by protozoa that are transmitted through the bite of an infected Anopheles mosquito.
- compound: A pure substance made up of two or more different elements chemically combined.
- metabolite: A cellular chemical produced as part of metabolism.
- faeces: The excreted waste product of digestion in animals – poo.
- clay: A naturally occurring fine-grained material formed from the chemical weathering of feldspar minerals found in rocks.
- sediments: Material that settles to the bottom of a liquid. In geology, it describes the solid fragments of inorganic or organic material that come from the weathering of rock and are carried and deposited by wind, water or ice.
- leaching: When a compound becomes dissolved in water and moves from one place to another, for example, a fertiliser in the soil dissolves in rain water and ends up in a stream.
- surface water: A body of water above the substrate or soil surface – for example, streams, rivers, lakes and oceans.
- groundwater: Water located beneath the Earth’s surface in soil spaces and in fractures of rocks.
- microbial activity or processes: The metabolic activities of microorganisms resulting in chemical or physical changes.
- metal: Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity and can be melted or fused, hammered into thin sheets or drawn into wires (for example, copper).
- ion: An atom or group of atoms that has gained or lost electrons and has an electrical charge.
- pH: A measure of the acidity or alkalinity of a substance, based on a scale of 0 to 14. Acidic solutions have pH values less than 7, whereas alkaline solutions have pH values greater than 7.
- metabolite: A cellular chemical produced as part of metabolism.
- fertiliser: Compounds that are given to plants to promote growth.
- adsorption: The binding of molecules or particles to a surface. This is different from absorption – the filling of pores in a solid. Adsorption is usually weak and reversible.
- tetracyclines: A group of broad-spectrum antibiotic compounds. They are among the cheapest classes of antibiotics available and have been used extensively in treating human and animal infections and in animal feed as a growth promoter.
- data: The unprocessed information we analyse to gain knowledge.
- antimicrobial: A substance that stops the growth of microorganisms including bacteria, viruses, and fungi.
- resistance: 1. The opposition to the flow of electric current through a circuit. 2. The ability to withstand harmful or unfavourable conditions, such as an infectious disease.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- algae: A large, diverse group of photosynthetic eukaryotic organisms. Algae have no stems or leaves and grow in water or on damp surfaces.
- invertebrates: An animal without a backbone, for example butterflies, worms, snails, insects, spiders and aquatic species such as crabs and jellyfish.
- toxic: Poisonous and harmful.
- aquatic: Growing or living in or near water (either freshwater or marine).
- toxicity: The level of harm a toxin can cause.
- genes: A segment of a DNA molecule that carries the information needed to make a specific protein. Genes determine the traits (phenotype) of the individual.
- Aotearoa: The Māori name for New Zealand, meaning Land of the Long White Cloud.
- socio-scientific: Combining social and scientific factors.
- contamination: The introduction of contaminants into a substance.
- condition: An existing state or situation; a mode or state of being.
