Factors Influencing Microplastic Levels in Fish
Microplastic contamination is a complex issue, with particle ingestion and accumulation in fish influenced by a variety of factors. Understanding these dynamics is key to making informed dietary choices.
Diet and Feeding Habits
An organism's feeding strategy is one of the most significant determinants of microplastic ingestion. Bottom-feeding organisms and filter-feeders, such as shrimp and mussels, often consume microplastics that accumulate in sediment or water, which they may mistake for plankton. Conversely, some predatory fish may consume contaminated prey, accumulating particles through a process known as trophic transfer. Research has shown that omnivorous fish often exhibit higher microplastic loads due to their varied diet sources, which increases their chances of exposure.
Size and Trophic Level
Contrary to assumptions that microplastics would accumulate higher up the food chain in a manner similar to heavy metals (bioaccumulation), recent research suggests a different pattern for microplastics. One study found that smaller fish might contain a higher concentration of microplastics per gram of tissue than larger fish, indicating that size alone is not a perfect indicator. Smaller organisms might feed in areas where microplastics are highly concentrated, leading to significant ingestion. However, larger, predatory fish are more susceptible to bioaccumulation of chemical toxins associated with plastics.
Wild-Caught vs. Farmed Fish
Both wild-caught and farmed fish have been found to contain microplastics, but studies show significant differences in contamination pathways. Farmed fish can be exposed to microplastics from their feed, which is often made from marine trash fish, and from the plastic infrastructure of their enclosures. Some studies have found higher concentrations of microplastics in farmed fish compared to their wild counterparts. However, the results can be inconsistent and depend heavily on farming practices, feed quality, and the specific environment.
Fish with Lower Microplastic Contamination
Based on various studies, certain species consistently show lower levels of microplastics in their edible tissue, making them potentially safer choices for consumers.
Chinook Salmon and Pacific Cod
An Oregon-based study published in early 2025 indicated that Chinook salmon contained some of the lowest microplastic concentrations among the tested species. Similarly, Pacific cod is often cited as a better choice, particularly when sourced from well-managed, cleaner waters like those in Alaska. The low levels in salmon may be attributed to feeding habits or life stages where they consume less, such as during spawning runs.
Silver Hake
Research conducted in Newfoundland found that silver hake showed very low microplastic ingestion rates, even while actively feeding. This makes it a potential low-risk option for consumers.
Bivalves and Crustaceans
While some smaller filter feeders like shrimp have shown high microplastic loads because they consume particles directly, shellfish like oysters, mussels, and clams also function as filter feeders, and microplastic levels can be highly variable depending on their harvest location. Additionally, shellfish are often eaten whole, increasing the likelihood of ingesting microplastics that are typically concentrated in the digestive tract. However, some studies indicate the microplastic burden in shellfish might be lower than contamination from other household sources.
Comparison of Microplastic Levels in Common Seafood
| Seafood Type | Contamination Level | Reason for Variation | Notes |
|---|---|---|---|
| Chinook Salmon | Low to Very Low | Life stage dependent; lower trophic level feeding | Alaskan-sourced wild salmon is often recommended. |
| Silver Hake | Low | Observed low ingestion rates even while feeding | A solid choice based on one specific study. |
| Tuna (Canned) | High-Tier Carnivore | High trophic level, bioaccumulation risk | Processing can also introduce plastics. |
| Shrimp (Pink) | High | Filter feeder, consumes particles mistaken for plankton | Contamination can be higher in processed products. |
| Sardines & Anchovies | Variable | Lower trophic level generally good, but can ingest plastics directly | Often consumed whole, so digestive tract contaminants are ingested. |
| Oysters & Mussels | Variable | Filter feeders; contamination depends on water source | Can accumulate significant microplastics depending on location. |
How to Reduce Your Microplastic Exposure from Seafood
While choosing fish with lower contamination is important, taking additional steps can further mitigate exposure.
- Buy Wild-Caught and Alaskan: As a general rule, many experts recommend choosing wild-caught fish, especially from regions with well-managed fisheries like Alaska, which may have healthier populations with less contaminant exposure. Some studies show higher microplastic rates in farmed fish, though this can vary.
- Select Larger Fish Fillets: Many microplastics reside in the digestive tracts of fish. When buying fish that are gutted, like larger fillets, you often consume less of the contaminated portion compared to eating whole, smaller fish.
- Rinse Seafood Thoroughly: Research has shown that rinsing fillets and shellfish before cooking can help remove microplastics present on the surface from handling and processing.
- Vary Your Protein Sources: Limiting overall seafood intake by incorporating other protein sources like plant-based options or ethically raised poultry and meat can help reduce total microplastic ingestion from a single food type.
- Support Regulation: The most effective long-term solution is to reduce plastic pollution at its source. Support organizations and legislation that push for better waste management and stricter regulations on plastic production.
Conclusion
Navigating the complex issue of microplastics in seafood requires a multi-faceted approach. While no fish is entirely free of these pervasive contaminants, certain species like Chinook salmon, silver hake, and some wild-caught whitefish appear to offer lower contamination risk based on recent studies. However, consumer choice is only part of the solution; broader systemic changes are needed to combat the global issue of plastic pollution at its source. By being a more mindful consumer and supporting environmental initiatives, you can play a role in protecting both your health and marine ecosystems.
For more information on the impact of plastic pollution and efforts to combat it, consider visiting the Ocean Conservancy blog.
