Chemicals identified as potential contaminants by governments and regulatory bodies were reviewed in some recent Murrang blog posts. These included chemicals such as phthalates, PBDEs, and arsenic, all of which are listed in the National Environmental Protection Measures. While conducting this research, I came across an article which stated that antibiotic resistant bacteria (ARB) should also be listed as a contaminant of concern.
Initially this seemed a bit weird – bacteria aren’t chemicals after all. But asbestos is not a chemical either (it is a physical rather than chemical contaminant), and other parameters such as turbidity, faecal coliforms, and even temperature are also monitored in the environment much like chemicals. So is there a case for adding ARB to the list of potential contaminants?
There are many similarities between ARB and other contaminants of potential concern. Bacterial resistance to antibiotics, for example, occurs naturally in the environment. This is not really all that surprising, with many antibioticsused by humans originally deriving from fungi and bacteria. There is, therefore, natural evolutionary pressure for bacteria to evolve antibiotic resistance to these fungi and bacteria and this pressure has existed since long before humans discovered antibiotics. This means that similar to other contaminants of potential concern like PAHs, lead, and arsenic, ARB has naturally occurring background concentrations in the environment.
Additional similarities between ARB and other formally identified contaminants of potential concern also exist. The natural occurrence of ARB in the environment implies that humans are also routinely exposed to them, just as humans are and have always been exposed to other potential contaminants like PAHs, lead, and arsenic. Humans, with their highly developed immune systems, are evolved to cope with these background concentrations; there are only a few examples of contaminants naturally occurring at concentrations toxic to humans.
Like many contaminants which are naturally occurring, anthropogenic development has led to the proliferation and spread of ARB in the environment. Since their discovery in 1928, for example, the quantity of ARB in the environment has grown exponentially. The incidence of Vancomycin-resistant enterococci increased in the United States from 0% to 25% in the first ten years of its use. A study conducted in Spanish wetlands showed that up to 100% of some bacteria were resistant to the antibiotic Erithromycin and an Australian studied found between 32 and 51% of Australian oysters were resistant to different types of antibiotics. Even seawater contains ARB, with up to 90% of bacteria collected from seawater resistant to more than one antibiotic and 20% resistant to at least five types of antibiotic.
Although much discussed, the misuse of antibiotics for treating non-bacterial illnesses is not the only factor contributing to the proliferation of ARB. More than half of the antibiotics used in the United States of America are fed to livestock, for example, with 90% of these used as growth or prophylactic agents rather than for infection control. Antibiotics are also applied to fruit trees as a means of controlling bacterial infections. This widespread use of antibiotics outside of medicine has also created pressure for ARB to evolve.
The continued evolution of antibacterial resistance in bacteria is also encouraged by the discharge of pharmaceuticals into the environment in volumes similar to pesticides. Even the widespread use of anti-bacterial agents in hand wash and soap has led to antibiotic resistance (but ironically not decreased the prevalence of bacteria on hands more than normal soap).
The use of antibiotics and chemicals with antibiotic properties is global and has created created much higher populations of ARB than would ever naturally occur. The same can be said of many other potential contaminants of concern like lead, arsenic, and PAHs, which have all increased in concentration within the human habitat as a result of industrialisation.
Again, similarly to lead, or arsenic, or PAHs, it is not simply exposure to these bacteria which is the problem. The frequency and concentration of exposure have major impacts on the likelihood of antibiotic resistant infection arising.
But perhaps more concerning than the existence of ARB is that advanced engineering processes used to treat water and sewage are not removing themduring treatment processes. Instead ARB are discharged into the environment by sewerage treatment plants. Some studies even found an increase in ARB occurred after tertiary sewerage treatment due to the high density of bacteriain sewage increasing the likelihood of successful antibiotic resistant gene transfer between bacteria. As a result, ARB are systematically discharged into the environment and are now found in sediments, in river water, and in the dust which blows from country to country and continent to continent.
So should ARB be listed as potential contaminants of concern, to be evaluated along with other potential contaminants such as lead, PAHs, and arsenic? The evidence presented within this blog suggests the answer is yes. Due process, however, must be followed if this is to occur, with the review of substances as potential contaminants usually undertaken on behalf of governments by expert scientists who are subject to systematic peer review. This blog post only utilised a limited number of sources and limited peer-review and therefore falls outside the required scientific process.