The biological cost of exposure to antimicrobial nanosilver

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In a study published in the journal Total Environmental Sciencethe number and development of an apex predator, the northern pike, was measured following exposure to nanosilver.

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​​​​​​​Study: Lakewide nanosilver additions reduce northern pike (Esox lucius) growth. Image Credit: bekirevren/Shutterstock.com

Nanosilver and its uses

Nanosilver (AgNP) is widely used in a variety of consumer items, most notably apparel such as sportswear, pants, and socks, for its antimicrobial, antiviral, and anti-odor characteristics. Therefore, when clothes are cleaned, nanosilver is discharged into urban wastewater.

The majority of nanosilver partitions to sewage sludge in wastewater treatment facilities, with approximately 2-3% escaping to runoff. Nanosilver can be sulfidated in waste water treatment plants (WWTP) due to lowering conditions, which slows down its decomposition into Ag ions. sewage can increase rapidly.

Disadvantages of silver nanoparticles

With observed and documented effluent levels ranging from 6 ng L-1 to 2.89 g L-1 and anticipated values ​​in natural rivers ranging from the low ng L-1 region to the low g L- 1, even this modest proportion of nanosilver releases poses a major hazard to aquatic species.

Once in the aquatic system, nanosilver can clump together into larger particles and sink into soils, or it can be captured by creatures. Dissolution of nanosilver can also cause Ag ions to be emitted into the liquid, which is very harmful to sea creatures.

Previous experimental investigations of the impacts of nanosilver on many species of fish have revealed negative effects. Yet these tests were often conducted at levels that were not ecologically applicable, i.e. higher than the amounts expected in nature.

Nanosilver has been shown to be harmful to fish at exceptionally high levels in tests using different fathead minnow life cycles, causing death and developmental defects in the eggs produced. Further research with mature Fathead Minnow subjected to lower amounts of nanosilver revealed altered gene expression in the lungs and fluctuating mucosal secretion, first increasing and then decreasing compared to controls.

Harmful effects of silver nanoparticles on fish

Many fish species subjected to nanosilver at g/L levels, including young Atlantic salmon, have shown a variety of toxic reactions involving respiratory problems. Rainbow trout treated with nanosilver at a dose expected to be achieved in the ecosystem deposited Ag in organs and demonstrated a stress response due to higher circulating serum levels.

Concerns about the possibility of a release of nanosilver into the atmosphere and effects on marine microbes prompted a lake-wide trial of nanosilver addition in Lake 222. Here, a combined amount of nanosilver of 15 kilograms was given to the lake over two field periods.

Prior to the lake-wide inclusion survey, IISD-ELA performed mesocosm experiments on the trajectory and impacts of nanosilver. The introduction of nanosilver did not affect many bacteria or algae in the microhabitats. Yet plankton biodiversity declined, while the amount of surviving species increased fourfold compared to the treated group.

Assessments of northern pike ages calculated by fin rays revealed that the precise consistency between readers was reasonable and that the consistency between all authors within a single year was extremely high. An exaggeration of age was observed in age categories two and three of the fish of the ages originally provided by DFO. Nevertheless, this bias should limit the ability to detect significant reductions in height at age.

Despite this possible bias, substantial reductions in height-at-age for these age groups were found. Additionally, the strongest patterns of reduced development in age categories 4 and 5 were observed. The strong consensus between the dates assigned to novices and those assigned by DFO was higher, indicating that the results were not likely to vary between readers.

Main results of the study

The results of the present study showed the possibility of indirect impacts on northern fish leading to variations in different trophic levels, in particular the quantity of yellow perch. Nevertheless, the direct effects of nanosilver contamination may also have played a role in the reduced yield of Northern Hook.

Sustained inhibition of development in northern fish for up to two years after the end of nanosilver injections suggested that the effects lasted well beyond the duration of nanosilver consumption. Similarly, other lake-wide surveys have shown considerable delays in the longevity of consequences, years to centuries beyond the response phase.

This may be particularly true in the case of nanosilver pollution since the substance that settles in sands may be a continuing cause of “in situ” groundwater pollution. Nanosilver’s ability to gradually emit Ag+, the same property that made it useful as an antibacterial agent, underscored the possibility of long-term effects in aquatic environments.

Reference

Slongo, BD, Hayhurst, LD, Drombolis, PC, Metcalfe, CD and Rennie, MD (2022). Additions of nanosilver throughout the lake reduce the growth of northern pike. Total Environmental Science. Available at: https://www.sciencedirect.com/science/article/pii/S0048969722033162?via%3Dihub

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