Silver is a potent antimicrobial agent and has been used throughout history for its useful properties. Evidence suggests that civilizations have been using silver since at least 3000 BCE, where ancient Persians and Egyptians used it to keep their water clean and safe; during the 19th century, silver was medically applied in treatments for eyes and skin ulcers. As a nanomaterial, silver is even more potent at killing microorganisms – but how beneficial are these properties in clinical settings and what are the risks involved?
Weighing the benefits and risks
Antimicrobial agents are commonly used to prevent the growth of bacteria on surfaces and within materials. In healthcare, nanosilver can be incorporated into medical devices or fabrics suitable for wound care management; silver-containing preparations are also used to prevent infections in burns, traumatic wounds, and diabetic ulcers. Urinary and vascular catheters and other invasive devices such as bone prostheses, cardiac implants, and needles used in ocular surgery can be impregnated with silver compounds to reduce the risk of infection. A recently published review presents a compilation of patented antimicrobial silver in medicinal and consumer applications between 2007–2017.
Whilst incorporating nanosilver into medical devices and textiles can be beneficial, we should not forget that silver, due its biocidal properties, can be regarded as a toxin. What are the benefits of adding silver to other products such as medical staff clothing, curtains, hospital furnishings, or building materials?
Currently, there is no sufficient evidence that the presence of antimicrobial agents in such products adds value to routine cleaning and disinfection. Maillard and Hartemann concluded in 2012 that the wide use of silver and silver nanoparticles (at a low concentration) in applications such as fabrics, textiles and other surfaces will remain controversial as long as the benefits have not been addressed, measured and justified appropriately.
In 2016, Health Care Without Harm’s report Antimicrobials in Hospital Furnishings: Do They Help Reduce Healthcare-Associated Infections? found very little evidence that adding antimicrobials to furnishings helped to reduce healthcare-associated infections (HAI).
The widespread and ever-increasing application of nanosilver in consumer products threatens both consumers and the environment by exposing them to new sources of this metal. The potential unintended consequences of increased use of nanosilver have simply not been explored fully.
Human skin is exposed to nanosilver via various medical applications containing nanosilver – other medical applications, especially coated catheters and orthopaedic implants, represent more invasive routes of exposure. Most of the time these exposures are local, but catheters for example can lead to intravenous, and thus systemic exposure. A high probability and/or possibility of high exposure via skin and inhalation has been recorded for wound dressings and breathing masks, respectively.
In general, more information is required on the possible contribution of nanosilver to human toxicity; in vivo and in vitro studies so far have indicated that nanosilver exposure can lead to changes in activity of the immune system, and an accumulation of silver in the spleen, liver, and testes.
Silver embedded into textiles and other products can be worn away through washing, cleaning, and abrasion - eventually it is released into the environment, where it will affect life in surface waters.
Several years ago, the Swedish Environmental Protection Agency published a compilation of all the screenings made by the Agency in their search for biocides in the environment, and silver came on top of the list (76% of so called ”rate of discovery”). According to REACH registrations provided by companies to ECHA, silver is classified as very toxic to aquatic life with long lasting effects.
A recent review concluded that repeated exposure to even safe doses of nanosilver through consumer products could lead to health complications. Despite the fact that nanosilver has proven to be an effective agent in exterminating microbes, it can potentially do the same damage to healthy cells, animals, humans, and the wider ecosystem if not used under safe thresholds without a thorough risk assessment.
Bacterial resistance to ionic silver and nanosilver has been observed; further evidence suggests that the indiscriminate use of silver in numerous products may contribute to the increasing development of antimicrobial resistance (AMR). Such a risk remains to be evaluated - researchers emphasise that without effective, regulated use and monitoring of nanosilver and its role in AMR, the antimicrobial capacity of nanomaterials will be significantly diminished.
What needs to be done?
Currently, tracking products that contain nanosilver is difficult because the products are packaged under numerous brand names, and, with a few exceptions, current labelling regulations do not require listing the nanomaterial specifically as an ingredient, unless the nanomaterial has hazardous properties which are distinguishable from those of the bulk material of the same substance.
Life cycle safety concerns associated with the manufacture, use, and disposal of nanosilver require careful consideration. Releasing nanosilver into indoor and outdoor environments can result in unwanted exposures for humans, wildlife, and ecosystems with adverse and sometimes unanticipated consequences. In HCWH Europe’s 2009 report, we recommended that the release of nanosilver in the environment should be avoided and a precautionary approach to nanosilver technology is essential. Both the UK and Germany have also recommended the application of the precautionary principle, i.e. that manufacturers should refrain from using nanosilver in consumer products until all its potential health risks are ruled out.
A 2012 paper published in Nature Nanotechnology raised deep concerns over nanosilver health hazards and pointed out that the European Commission should be regulating nanosilver, not asking for yet another report on its impact on health and the environment. Little progress has been made, however, in implementing any of these recommendations - in contrast, nanosilver and other nanomaterials are now even more widespread on the EU market despite the fact that additional effects caused by their widespread and long-term use cannot be ruled out.
One of the key points in assessing the toxicity of nanosilver is to adopt toxicological standardised assessment methods that are suitable for nanomaterials. Also, there are still significant uncertainties regarding required environmental risk assessment for nanomaterials.
As silver nanoparticles show antiviral activity against a range of viruses in laboratory tests, there is rapidly growing interest in applying nanotechnology to combat SARS-CoV-2 transmission (the strain of Coronavirus that causes COVID-19). During the current COVID-19 pandemic, antimicrobial impregnated products are increasingly being offered up as an added tool to reduce the burden of Coronaviruses – companies are not only offering these products to hospitals, but direct to consumers as well. Again, the purported specific advantage of a biocide treatment is frequently questionable.
HCWH Europe member, Region Västra Götaland in Sweden, oversees the region’s delivery of healthcare across 17 hospitals, 200 primary-care centres and 170 dental clinics. Their procurement teams mostly avoid purchasing any products containing nanosilver with a small number of exceptions for wound/burn dressings.
We advise healthcare providers to demand detailed evidence from suppliers on the effectiveness of antimicrobial products before making any purchasing decisions. Providers should consider whether products carry associated risks that should also inform their decision-making. The nanotechnologies used in healthcare products need to be evaluated not only for their initial antiviral activity but also for their durability under conditions of use and how well they stand up to repeated cleaning and disinfection (i.e. assessed for leaching potential).
While nanosilver holds promise in the medical sector in the fight against unwanted microbes, the rapidly increasing application and commercialisation of silver related products and technologies must be critically reassessed for both safety and necessity.
Historically, failure to examine risks of seemingly beneficial chemical agents has resulted in large-scale exposures that have led to adverse human health and environmental effects discovered years or decades later, long after damage is done. We have an opportunity to avoid repeating the same mistakes with nanosilver.
Dr Dorota Napierska
I hold PhD degrees in Biology (Biochemistry) and in Biomedical Sciences (Nanotoxicology), obtained from the University of Gdansk and Katholieke Universiteit Leuven, respectively. Prior to joining HCWH Europe, I worked at the European Commission (DG Joint Research Center) and at the Department of Public Health of KU Leuven (Belgium). At HCWH Europe, I am leading the Safer Chemicals programme.
Health Care Without Harm (HCWH) Europe brings the voice of healthcare professionals to the European policy debate about key environmental issues. HCWH Europe educates the healthcare sector to understand the importance of the environment and presses healthcare leaders and professionals to advocate for broader societal policies and changes.