Salmon's Plastic Pollution: A Growing Concern

Plastic pollution is a pressing issue that has contaminated marine environments worldwide, including the Arctic and deep-sea sediments. This has led to the ingestion of microplastics by various marine species, including fish. Salmon, a commonly consumed fish, has been found to contain microplastics in its gut, and potentially in its flesh. With plastic production increasing globally, it is important to understand the extent and effects of plastic pollution on human and environmental health. Researchers are working on methods to quickly assess the amount and characteristics of plastic in complex samples to address this growing concern.

Microplastics in juvenile Chinook salmon

Plastic pollution is a substantial threat to marine ecosystems, including both macro (5 mm) and microplastics (5 mm). While we know more about other types of marine pollution, less is known about the threat of microplastics. Microplastics can be produced from primary or secondary sources. Primary sources include plastics produced at the micro-scale, such as those found in cosmetics and textiles. Secondary sources include macroplastics from litter and industry materials that can break down into smaller particles and eventually become microplastics. Both primary and secondary sources can be transported to the marine environment through wastewater outfall.

Microplastics have been found in most ecosystems globally, including remote areas such as Arctic ice and deep-sea sediments. The ingestion of microplastic particles has been documented in a variety of marine species, ranging from zooplankton to fish to marine mammals. The potential risks of ingesting microplastics include internal physical and/or chemical damage. Studies have shown that rainbow trout exposed to microplastics along with a virus died more often than rainbow trout exposed to the virus alone.

Microplastics have been detected in juvenile Chinook salmon on the east coast of Vancouver Island, British Columbia. The microplastics found in the juvenile Chinook salmon were predominantly fibrous plastics, with coloured microfibers making up about 85% of the total microplastics, and the rest being uncoloured fibers and irregularly shaped microplastics. The analysis showed that juvenile Chinook salmon contained 1.2 ± 1.4 (SD) microplastics per individual, while water and sediment samples had 659.9 ± 520.9 microplastics m−3 and 60.2 ± 63.4 microplastics kg−1 dry weight, respectively.

The concentration of microplastics in juvenile Chinook salmon was relatively low compared to literature values, and given the size and type of microplastics observed, they are unlikely to pose an immediate threat to fish in this area. However, microplastics less than 100 μm in size were not included in the study and may represent a greater threat due to their ability to translocate through tissues. More studies are needed to fully determine the risk to juvenile Chinook salmon from microplastic ingestion.

Plastic particles in salmon muscle tissue

Plastic particles, or microplastics, have been found in the edible muscle tissue of salmon and several other iconic Pacific Northwest fish and seafood species. These include Chinook salmon, Pacific lamprey, black rockfish, lingcod, Pacific herring, and pink shrimp. The presence of microplastics in salmon muscle tissue is a cause for concern, as it indicates that humans may be consuming these foreign particles when eating salmon, a popular seafood choice.

Microplastics are tiny pieces of plastic that result from the degradation of plastic in the environment. They are smaller than 5 millimeters in size and can be found in the air, soil, water, and food we consume. Marine species mistake these plastic particles for food or accidentally filter-feed them, leading to ingestion. Freshwater species can also absorb microplastics through their gills and possibly their skin. Once ingested, microplastics can cause physical harm to fish by blocking their intestines, puncturing their organs, or filling their stomachs with garbage. They can also enter the circulatory system, cells, and tissues, including the liver and brain, altering the animal's behavior and feeding patterns.

Research has shown that microplastics can transfer from the gut to other parts of the body, including the muscle tissue of fish. A study by Portland State University found microplastics in the edible tissue of Chinook salmon, indicating that humans are likely consuming these foreign particles when eating this type of salmon. While the concentration of microplastics in the edible tissue of Chinook salmon was reported to be low compared to other organisms sampled in the study, it still highlights the presence of plastic particles in salmon muscle tissue.

The potential health risks of consuming microplastics are not yet fully understood. However, it is known that chemicals added to plastics to enhance certain properties can have adverse health effects. These chemicals may remain on the microplastic particles and cause harm when consumed. Additionally, the size and shape of the microplastics may lead to different impacts or movements within the body. Further research is needed to fully understand the implications of microplastic consumption, both for the health of salmon and other affected species and for human health.

Sources of microplastics in the ocean

Plastic is the most prevalent type of marine debris found in our oceans and lakes. Plastics in the ocean break up into very small particles, known as "microplastics". These microplastics are small plastic pieces less than five millimetres long, which can be harmful to our ocean and aquatic life.

Microplastics in the ocean come from a variety of sources. They can be produced from primary or secondary sources. Primary sources include plastics produced at the micro scale, such as those found in cosmetics and personal care products (e.g. cleansers and toothpastes) and textiles. Secondary sources include macroplastics from litter and industry materials (e.g. derelict fishing gear) that can break down into smaller particles and eventually become microplastics. These primary and secondary sources can be transported to the marine environment through wastewater outfall.

In addition, microplastics can also come from larger plastic pieces that break apart, resin pellets used for plastic manufacturing, and tyre wear. The ingestion of microplastic particles has been documented in a variety of marine species, ranging from zooplankton to fish to marine mammals, with potential risks of internal physical and/or chemical damage.

Research has shown that microplastics are present in the flesh and gastrointestinal tracts of various fish species, including Chinook salmon and Atlantic salmon. The presence of microplastics in popular seafood such as salmon is a major concern, as it may pose risks to human health.

Health risks of consuming plastic-contaminated salmon

Salmon is a popular seafood choice, especially in the United States, where Americans eat more salmon than almost any other fish. However, the presence of plastic particles in salmon has become a growing concern for those who consume it. Plastic pollution has infiltrated every part of the world, including our oceans and, subsequently, the seafood we eat.

Sources of Plastic in Salmon

Plastic particles, known as microplastics, enter the marine environment through various sources, including primary and secondary sources. Primary sources include plastics produced on a micro-scale, such as those found in cosmetics and textiles, while secondary sources include larger macroplastics that break down into smaller particles, like litter and industrial materials. These microplastics are then ingested by various fish species, including salmon, as they feed on prey or directly consume the particles from the water and sediment.

Health Risks

The health risks associated with consuming plastic-contaminated salmon are not yet fully understood. However, researchers have identified several potential concerns:

• Internal Physical Damage: This can include abrasion or blockage in the gastrointestinal tract or even the migration of microplastics into the muscle tissue.
• Chemical Damage: Microplastics can contain toxic chemicals, and their ingestion may lead to an imbalance of antioxidants and free radicals in the body, known as oxidative stress. This imbalance can increase the risk of serious health issues such as cancer and heart disease.
• Viral Infections: Research has shown that exposure to microplastics can make fish more susceptible to viral infections, and this may also be a concern for humans who consume contaminated salmon.

It is important to note that the effects of consuming plastic-contaminated seafood may take decades to fully understand, and it is challenging to control studies due to potential microplastic exposure from sources other than seafood.

In conclusion, the consumption of plastic-contaminated salmon may pose a risk to human health, but further comprehensive research is needed to fully understand the extent and specific health risks associated with it.

Methods for detecting and measuring microplastics

Microplastics are a growing concern as a marine pollutant and contaminant, with evidence linking plastic ingestion to negative health consequences for humans and other organisms. The detection and measurement of microplastics in seafood, including salmon, is a complex and evolving field. Here are some methods currently used or proposed for detecting and measuring microplastics:

Sample Collection and Preparation

The first step in detecting and measuring microplastics is to collect relevant samples, such as fish tissue or digestive tracts, from specific habitats or seafood markets. This involves defining and delineating species distribution and habitat, which can be challenging in marine environments. For example, researchers studying microplastics in the Salish Sea used multibeam echosounder (MBES) bathymetric data and acoustic Doppler current profilers (ADCP) to map benthic habitats and measure current strength.

Spectroscopy Techniques

Spectroscopy techniques are commonly used to identify and quantify microplastics in seafood samples. Fourier-transform infrared spectroscopy (FTIR) is one such technique, employed to detect microplastics in canned tuna, salmon, and sardines. This method involves analysing tissue samples after digestion with a solution, and it can identify various polymers like nylon and ethylene vinyl alcohol. Another spectroscopy technique is pyrolysis-gas chromatography/mass spectrometry (GC/MS), which has been adapted from sewage sludge analysis to detect microplastics in seafood. This method helps report plastic mass concentrations and works by breaking down the edible parts of seafood with an alkaline solution, then filtering, extracting plastics, and identifying polymers.

Separation and Analysis

A traditional method for identifying microplastics involves manually separating particles from animal tissue, suspending them in a solvent, and then analysing them using spectroscopic techniques like infrared or Raman spectroscopy. This process can be time-consuming and challenging, especially when dealing with complex natural materials. However, newer sample preparation and extraction methods are making this process more efficient.

Biomonitoring

Biomonitoring studies are also crucial for understanding microplastic exposure in humans. These studies measure microplastic levels in human blood and urine, providing data to enforce regulations and protect public health.

While these methods offer insights into microplastic detection and measurement, there are still challenges. The lack of standardised analytical methods, especially for specific food groups, hinders our ability to assess public health risks accurately. Additionally, the potential for microplastics to "biomagnify" in animal flesh as they move up the food chain and the unknown health effects of consuming these particles are areas of ongoing research.

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