Effects of Antibiotics on Environment

Pollution in the environment due to regular pollutants is quite heard of, but what is scarcely heard is an unconventional factor causing environmental pollution viz. antibiotics. It was only in the late 1990s that the understanding of the environmental dissemination of antibiotic resistant bacteria and antibiotic residues from agricultural and human sources become an important area of research. Though less popular, but it is quite an established fact now, that the environment is contaminated with antibiotics with the result being development of antibiotic resistance in bacteria, which in turn is posing a big threat to the treatment of human species.

Antibiotics are a type of medication that destroys or slows down the growth of bacteria. Discovery of antibiotics has been one of the most influential events of 20th century as it has increased the global life expectancy by decreasing mortality due to bacterial disease. Hundreds of antibiotics have appeared in the market and are being used after the discovery of 1st antibiotic penicillin. But there is a serious concern worldwide that antibiotics are being overused. Antibiotics are one of the most frequently prescribed medications of modern times. In humans, irrational use of antibiotic is the most potent driver for causing antibiotic resistance. Common situations in which antibiotics are inappropriately prescribed are diarrhoea and common cold. These illnesses are generally self limiting and caused by viruses, against which antibiotics do not work. Since most of the antibiotics are water soluble, as much as 90% of a single dose can be excreted in urine and up to 75% with the faecal matter (Halling-Sørensen, 2001) which then resides in the surroundings.

Antibiotics are generally disseminated into the environment from both human and agricultural sources, including excretion, flushing of old and out-of-date prescriptions, medical waste, discharge from wastewater treatment facilities, leakage from septic systems and agricultural wastestorage structures. Other pathways for dissemination are via land application of human and agricultural waste, surface runoff and unsaturated zone transport. Once in the environment, like any other organic chemicals, their efficacy depends on their physio-chemical properties, prevailing climatic conditions, soil types and variety of other environmental factors. During the past decade, concern has grown about the adverse effects the use and disposal of these antibiotics might potentially have on human health and environment, as sometimes the bacteria change their genetic makeup to protect themselves against these antibiotics and thus become resistant to them.

Apart from humans, antibiotics are abundantly used in veterinary medicine and poultry. In poultry farming, antibiotics are extensively used as a growth promoter. Traces of antibiotic additives added in feed, cause animals to grow faster and also enhance the feed efficiency of healthy livestock. Many antibiotics used in the animal food-producing industry are scarcely adsorbed in the gut of the animal, resulting in as much as 30–90% of the parent compound being excreted. According to a recent study, sheep excrete nearly 21% of an oral dose of oxytetracycline, and young bulls excrete about 17–75% of chlortetracycline as the parent compound (Montforts, 1999). The excreted compounds can be adsorbed, leached, biaccumulated, degraded through biotic or abiotic processes, and in some cases may revert back to the parent compound. In addition, antibiotic metabolites can also be bioactive and can be transformed back to the parent compound after excretion. Thus, a significant percentage of the administered antibiotics may be excreted into the environment in active forms (Warman and Thomas, 1981; Berger et al., 1986). For example, the excreted sulfamethazine metabolite, glucoronide of N-4-acetylated sulfamethazine, is converted back to the parent form in liquid manure (Berger et al., 1986). After the antibiotic is administered, sulfamethazine undergoes conjugation with sugars present in the liver and thus inactivates the compound. After excretion, microbes can rapidly degrade the sugars, thereby allowing the compounds back to their bioactive forms (Renner, 2002)

Hence when animal wastes are used as supplement to fertilizer in a cyclic pattern, they find their way into the receiving environment as a metabolite or as the parent compound and may result in the continuous exposure of soil microbes to antibiotic residues and develop antibiotic resistant populations of bacteria. This can potentially have deleterious effects in the environment, especially if the residues are transported by surface runoff or leaching through soil and reach nearby rivers or lakes. In a similar pattern, direct use of antibiotics which is a common practice in modern agriculture poses threat of antibiotic resistance among the soil microbes. Many of them are used in fruits and vegetables (e.g., use of gentamicin as a pesticide in apple orchards)

Antibiotics are also being increasingly used in aquaculture these days which has resulted in the emergence of antibiotic-resistant bacteria in aquaculture environments and increase of resistance in fish pathogens. Though they can be degraded in water through abiotic processes such as photodegradation and/or hydrolysis, but these processes are very slow. Sometimes there is transfer of these resistance determinants to bacteria of land animals and to human pathogens

Besides human, veterinary and agricultural activities another major source of accumulation of antibiotics in the environment is biomedical waste discharge from health care facilities and hospitals. Though the waste is treated in waste water treatment plants before being discharged into the environment, but researches show that even after passing through the plant, pharmaceuticals amongst other compounds, are released directly into the environment. This biomedical waste contributes extensively to environmental spread of resistant bacteria. However, as antibiotics are not considered pollutants, there are no limits to the extent to which they can exist in the environment. Even small traces of antibiotics present in the environment leads to the exposure of antimicrobial ecosystem to antibiotics, which induces the development of resistance in these microbes.

The risks posed by these compounds have led many countries to regulate their usage in a way that minimizes their effects. We can take examples from some of the developed nation which have acted on policy level to combat antibiotic resistance. Sweden, was the first country to ban the use of antimicrobial growth promoters in 1986, and claimes that their antibiotic resistance bacteria remained lower than its neighbouring countries during the period 1986–1995. Following this, Denmark and Germany banned the use of avoparcin as growth promoter in 1995 and 1996 respectively. In 1999 there was a total ban on the use of antibiotics as growth promoters in Denmark. In the following years, virginiamycin, tylosin, bacitracin, spiramycin, carbadox and olaquindox were banned as growth promoters in the EU (as they belonged to a class of antimicrobial drugs used in human medicine). After this, the Danish food-animal industries decided to voluntarily discontinue all further use of antimicrobial growth promoters in broilers, slaughter pigs and cattle in February and March 1998. According to the report published by Danish Integrated Antimicrobial Resistance Monitoring and Research Program there was a drastic decrease in antibiotic use and by 2000, the use of growth promoters in Danish food animals was nil. Even the Australian Government accepted recommendations of the Joint Expert Technical Advisory Committee on Antibiotic Resistance (JETACAR, 1999), to review the use of growth promoters on animals. Also, the use of antibiotics as growth promoters is prohibited in Japan. Their use as component of feed additives is permitted only after ministerial approval. In China and Russia only non-medicated antibiotics are permitted as feed additives. However in many developing countries such as India, Thailand, Indonesia there is a complete lack of control with antimicrobial use of antibiotics in animals intended for food and therefore there is no data available on the types of veterinary antibiotics and their amounts used in various food-producing animals.

According to WHO, the three main areas that need to be addressed in order to make the life saving antibiotics continuously available are, rational antibiotic use, control of infections through better hygiene practices and preventing contamination of environment with antibiotic residues. Besides, there should be adequate differentiated antibiotic consumption data which will help in the formulation of more effective and targeted interventions to reduce unnecessary antibiotic usage and resistance infections.

No unique strategy can solve the antibiotic resistance menace instead a multi-sectoral approach is required to fight this issue. Hospitals and medical practitioners should follow a proper treatment guideline prioritizing on antibiotics to treat serious and life threatening diseases. There should be research into new vaccines and diagnostics and emphasis should be on effective infection prevention and control initiatives. There should be proper guidelines on administration of antibiotics in agriculture, aquaculture and livestock. Any new policy on antibiotic use in animal agriculture should be mandatory, retroactive to already-approved drugs, and enforceable.