Microscopic silver particles that are added as an antimicrobial agent to athletic clothing, condoms and yoga mats, among many other products, have been shown to harm fish and freshwater ecosystems when released in quantities that are similar to what is thought to be emerging from wastewater plants across Canada.
Researchers who laced a Northern Ontario lake with the material, known as nanosilver, as part of a multiyear experiment, say the adverse effects they measured in two species of fish were significant enough, both individually and at the population level, to warrant including the unregulated substance as part of Canada’s water safety guidelines for the metal.
“We found effects right down to the cellular level,” said Lauren Hayhurst, a fisheries biologist at the Experimental Lakes Area, near Kenora, Ont., where the work was conducted.
Ms. Hayhurst said that soon after nanosilver was added to a small lake at the research facility in 2014 and 2015, the yellow perch she and her colleagues examined were found to be accumulating the tiny metallic particles, primarily in their gills. The fish were then shown to experience a chemical imbalance in their cells know as oxidative stress, which made them more lethargic and less able to feed. Their populations also shrank and shifted to deeper waters. Northern pike, which eat the perch, were also affected, showing accumulations of silver in their livers which persisted another four years after the experiment was completed.
In total, 15 kilograms of finely milled silver were used by the experiment, and suspended in a diluted solution that researchers repeatedly carried through the bush in 80-pound backpacks to pump into the 16-hectare lake used for the study.
While the amounts of nanosilver in the lake water were at the parts-per-billion level, the quantities that turned up in the fish were approximately one thousand times higher. The study did not look at the effects of nanosilver on human health.
Chris Metcalfe, director of the Institute for Watershed Science at Trent University in Peterborough, Ont., and a senior author on the study said that one of the key findings of the study includes the demonstration that nanosilver is mobile in the environment and does not simply sink to the lake bottom once it is released. The other is that entire fish populations can be influenced by its presence.
However, the findings do not point to an effect that is more severe or substantially different from that of silver in its natural, or ionic form. This suggests nanosilver does not need to be regulated as a separate material but should instead be considered as part of the total silver load on a freshwater ecosystem. The Canadian water quality guideline for silver in freshwater is set at 0.25 micrograms per litre (equivalent to 0.25 parts per billion) but the guideline does not currently include nanosilver.
“We should be keeping an eye on it and applying the regulatory limits that we have for silver," Dr. Metcalfe said.
The results of the study were published online on Friday and will appear in the October issue of the Archives of Environmental Contamination and Toxicology, a research journal. It is part of a long-running series of experiments, conceived nearly a decade ago, to explore the environmental impact of a substance whose invisible presence in daily life has grown dramatically in that same period of time.
The popularity of nanosilver is due, in large part, to the bacteria-killing properties of silver ions – something that has been known for over a century. Although the mechanisms are not well understood, silver is thought to disrupt bacterial cell walls and may also affect the ability of microbes to reproduce. This has led to the use of silver coatings in situations where bacterial infections pose a threat, such as medical devices and implants. More recently, the ability to deposit nanosilver – tiny manufactured particles of silver that range from one to 100 billionths of a metre across – on virtually any material has led to a proliferation of nanosilver-infused products, including socks and underwear, where it inhibits odour-causing bacteria.
Ms. Hayhurst said that she hoped the study would encourage better labelling and raise awareness that the use of nanosilver in hundreds of products is both non-essential and an unnecessary burden on the environment. Monitoring of wastewater plants for nanosilver could also lead to better practices that capture more of the material before it is released into the environment.
The long-running experiments, which began first by dosing small freshwater enclosures with nanosilver in 2012, were almost stopped in their tracks when the Harper government moved to shutter the Experimental Lakes Area that same year. The former federal facility, billed as the only place on Earth were many types of environmental contaminants are studied in a controlled fashion at the ecosystem level, was later rescued in a scaled-down form with a combination of provincial and not-for-profit funding.
Émilien Pelletier, an ecotoxicologist at the University of Quebec at Rimouski, who was not involved in the experiments but who has studied nanosilver in marine and river-estuary environments, said the material looked to be more of a potential threat in small enclosed, freshwater systems like the one selected by Ms. Hayhurst and her coauthors.
He said that a simple way to deal with detrimental effects from nanosilver would be to apply some common-sense principles to its use.
“If your socks smell bad, just wash them,” he said.
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